Lactose intolerance
Encyclopedia
Lactose intolerance, also called lactase deficiency or hypolactasia, is the inability to digest
and metabolize
lactose
, a sugar
found in milk. It is caused by a lack of lactase
, the enzyme
required to break down lactose in the digestive system, and results in symptoms including abdominal pain
, bloating
, flatulence
, diarrhea
, nausea
and acid reflux.
Most mammal
s normally become lactose intolerant when they are young but some human populations have developed lactase persistence
, in which lactase production continues into adulthood. It is estimated that 75% of adults worldwide show some decrease in lactase activity during adulthood. The frequency of decreased lactase activity ranges from 5% in northern Europe through 71% for Sicily to more than 90% in some African and Asian countries.
having one or more symptoms upon the consumption of food substances containing lactose. Individuals may be lactose intolerant to varying degrees, depending on the severity of these symptoms. "Lactose malabsorption" refers to the physiological concomitant of lactase deficiency (i.e. the body does not have sufficient lactase capacity to digest the amount of lactose ingested). A medical condition with similar symptoms is fructose malabsorption
.
Lactase deficiency has a number of causes, and is therefore classified as one of three types:
Lactose intolerance is not an allergy
because it is not an immune response
but caused by lactase deficiency. Milk allergy
is a separate condition with distinct symptoms.
and cramps, flatulence
, diarrhoea, nausea
, borborygmi (rumbling stomach) and vomiting
(particularly in adolescents).
. Some countries require by law that milk be fortified with vitamin A
and vitamin D
. In these societies individuals who reduce or eliminate consumption of dairy must obtain these nutrients elsewhere; calcium from fortified breakfast foods, for example, potassium and vitamin A from fruit and vegetables and B vitamins from meat and eggs. The human body produces some vitamin D from exposure to direct sunlight.
Congenital lactase deficiency (CLD), the inhibited production of lactase in infants as well as adults, can be dangerous in any society because of infants' nutritional reliance on breast milk. Before the 20th century those born with the condition were not expected to survive infancy but it can be mitigated using soybean
-derived infant formula
e and manufactured lactase-free dairy products. Beyond infancy individuals affected by CLD usually have the same nutritional concerns as other lactose-intolerant adults.
lactase
in the lining of the duodenum
. Lactose
, a disaccharide
molecule found in milk and dairy products, cannot be directly absorbed through the wall of the small intestine into the bloodstream so, in the absence of lactase, passes intact into the colon
. Bacteria
in the colon are able to metabolise lactose and the resulting fermentation
produces copious amounts of gas (a mixture of hydrogen
, carbon dioxide
and methane
) that causes the various abdominal symptoms. The unabsorbed sugars and fermentation products also raises the osmotic pressure
of the colon, resulting in an increased flow of water into the bowels (diarrhea
).
30 minutes but may take up to 2 hours depending on other foods and activities. Substantial variability in response (symptoms of nausea, cramping, bloating, diarrhea, and flatulence) is to be expected as the extent and severity of lactose intolerance varies among individuals.
It is important to distinguish lactose intolerance from milk allergy
, an abnormal immune response (usually) to milk proteins. This may be done in diagnosis by giving lactose-free milk, producing no symptoms in the case of lactose intolerance but the same reaction as to normal milk if it is a milk allergy. An intermediate result might suggest that the person has both conditions. Since lactose intolerance is normal state for most adults worldwide it is not considered a disease and a medical diagnosis is not normally required. However if confirmation is necessary four tests are available.
, after an overnight fast, 25 gram
s of lactose (in a solution with water) is swallowed. If the lactose cannot be digested, enteric bacteria metabolize it and produce hydrogen
which, along with methane
if produced, can be detected on the patient's breath by a clinical gas chromatograph or compact solid-state detector. The test takes about 2 to 3 hours.
After an overnight fast blood is drawn and then 50 gram
s of lactose (in aqueous solution) is swallowed. Blood is then drawn again at the 30 minute, 1 hour, 2 hour, and 3 hour mark. If the lactose cannot be digested blood glucose levels will rise by less than 20 mg/dL.
The infant is given lactose to drink. If the individual is tolerant, the lactose is digested and absorbed in the small intestine, otherwise it is not digested and absorbed and it reaches the colon. The bacteria in the colon, mixed with the lactose, cause acidity in stools. Stools passed after the ingestion of the lactose are tested for level of acidity. If the stools are acidic, the infant is intolerant to lactose.
Lactose intolerance is not usually an absolute condition: the reduction in lactase production, and the amount of lactose that can therefore be tolerated, varies from person to person. Since lactose intolerance poses no further threat to a person's health, the condition is managed by minimizing the occurrence and severity of symptoms. Berdanier and Hargrove recognise four general principles; avoidance of dietary lactose, substitution to maintain nutrient intake, regulation of calcium intake and use of enzyme substitute.
Lactose is present in two large food categories: conventional dairy products, and as a food additive (in dairy and non dairy products).
ling process affect tolerance of foods. After the curd
ling process lactose is found in the water portion (along with whey
and casein
) but not in the fat portion. Dairy products that are "fat reduced" or "fat free" generally have a slightly higher lactose percentage. Low fat
dairy foods, additionally, often have various dairy derivatives such as milk solids added to them to enhance sweetness, increasing the lactose content.
Milk. Human milk has a high lactose percentage at around 9%. Unprocessed cow milk has 4.7% lactose. Unprocessed milk from other bovid
s contains similar lactose percentages (goat milk 4.7%, buffalo
4.86%, yak
4.93%, sheep milk
4.6%)
Butter. The butter-making process separates the majority of milk's water components from the fat components. Lactose, being a water soluble molecule, will largely be removed, but will still be present in small quantities in the butter
unless it is also fermented to produce cultured butter. Clarified butter
, however, has extremely low concentrations of lactose and is safe for most LI patients.
Yogurt, Frozen Yogurt and kefir
. People can be more tolerant of traditionally made yogurt than milk because it contains lactase produced by the bacterial cultures used to make the yogurt. Frozen yogurt, if cultured similarly to its unfrozen counterpart, will contain similarly reduced lactose levels. However many commercial brands contain milk solids , increasing the lactose content.
Cheeses. Traditionally made hard cheese (such as Emmental) and soft ripened cheeses may create less reaction than the equivalent amount of milk because of the processes involved. Fermentation and higher fat content contribute to lesser amounts of lactose. Traditionally made Emmental or Cheddar
might contain 10% of the lactose found in whole milk
. In addition, the traditional aging methods of cheese (over 2 years) reduces their lactose content to practically nothing. Commercial cheese brands, however, are generally manufactured by modern processes that do not have the same lactose reducing properties, and as no regulations mandate what qualifies as an "aged" cheese, this description does not provide any indication of whether the process used significantly reduced lactose.
Soured cream if made in the traditional way, may be tolerable, but most modern brands add milk solids.
Examples of lactose levels in foods. As scientific consensus has not been reached concerning lactose percentage analysis methods (non-hydrated form or the mono-hydrated form), and considering that dairy content varies greatly according to labeling practices, geography and manufacturing processes, lactose numbers may not be very reliable. The following are examples of lactose levels in foods which commonly set off symptoms. These quantities are to be treated as guidelines only.
, milk solids, modified milk ingredients, etc.) is a commercial food additive
used for its texture, flavour and adhesive qualities, and is found in foods such as processed meats (sausage
s/hot dog
s, sliced meats, pâté
s), gravy stock powder, margarine
s, sliced bread
s, breakfast cereals, potato chip
s, processed foods
, medication
s, pre-prepared meals, meal replacement (powders and bars), protein supplements (powders and bars) and even beer
s in the milk stout style. Some barbecue sauces and liquid cheeses used in fast-food restaurants may also contain lactose.
Kosher products labeled pareve or fleishig are free of milk. However, if a "D" (for "Dairy") is present next to the circled "K", "U", or other hechsher
, the food likely contains milk solids (although it may also simply indicate that the product was produced on equipment shared with other products containing milk derivatives).
and derivatives are inherently lactose free: soy milk
, rice milk
, almond milk
, hazelnut milk, oat milk, hemp milk
, peanut milk
, horchata
.
The dairy industry has created low-lactose or lactose-free products to replace regular dairy.
supplements may be used.
Lactase enzymes similar to those produced in the small intestines of humans are produced industrially by fungi of the genus
Aspergillus
. The enzyme, β-galactosidase, is available in tablet form in a variety of doses, in many countries without a prescription. It functions well only in high-acid environments, such as that found in the human gut due to the addition of gastric juices from the stomach. Unfortunately, too much acid can denature it, and it therefore should not be taken on an empty stomach. Also, the enzyme is ineffective if it does not reach the small intestine by the time the problematic food does. Lactose-sensitive individuals can experiment with both timing and dosage to fit their particular needs.
While essentially the same process as normal intestinal lactose digestion, direct treatment of milk employs a different variety of industrially produced lactase. This enzyme, produced by yeast
from the genus Kluyveromyces
, takes much longer to act, must be thoroughly mixed throughout the product, and is destroyed by even mildly acidic environments. Its main use is in producing the lactose-free or lactose-reduced dairy products sold in supermarkets.
Enzymatic lactase supplementation may have an advantage over avoiding dairy products, in that alternative provision does not need to be made to provide sufficient calcium intake, especially in children.
enzyme from being expressed.
Some studies indicate that environmental factors (more specifically, the consumption of lactose) may "play a more important role than genetic factors in the etio-pathogenesis of milk intolerance", but some other publications suggest that lactase
production does not seem to be induced by dairy/lactose consumption.
associated with various autosomal dominant alleles prolonging the activity of lactase beyond infancy; conversely, lactase non-persistence is the phenotype associated with primary lactase deficiency (see above). Among mammals, lactase persistence is unique to humans – it evolved relatively recently (in the last 10,000 years) among some populations, and the majority of people worldwide remain lactase non-persistent. For this reason lactase persistence is of some interest to the fields of anthropology
and human genetics
, which typically use the genetically-derived persistence/non-persistence terminology.
Recognition of the extent and genetic basis of lactose intolerance is also relatively recent. Though the symptoms were recognised as early as Hippocrates
(460-370 B.C.), until at least the 1960s the prevailing assumption in the medical community was that tolerance was the normal condition and intolerance either the result of milk allergy
, an intestinal pathogen
, or else was psychosomatic (it being recognised that some cultures did not practice dairying, and people from those cultures often reacted badly to consuming milk). Many people are still surprised or disbelieving that, from a cross-cultural and evolutionary perspective, lactose tolerance is the "abnormal" condition. There are two reasons for this perception. Firstly Western countries, as a result of their mostly European heritage, have particularly low frequences of lactose intolerance, and an extensive cultural history of dairying, so tolerance actually was the norm in most of the societies sampled by medical researchers. Secondly, in such societies lactose intolerance tended to be under-reported: genetically lactase non-persistent individuals can tolerate varying quantities of lactose before showing symptoms, and their symptoms differ in severity. Most are able to digest a small quantity of milk, for example in tea or coffee, without suffering any adverse effects. Fermented dairy products
, such as cheese, also contain dramatically less lactose than plain milk. Therefore in societies where tolerance is the norm many people who consume only small amounts of dairy, or have only mild symptoms, may be unaware that they cannot digest lactose. Eventually, however, it was recognised that in the United States
lactose intolerance was closely linked to race
. Subsequent research revealed that intolerance was the worldwide norm, and that the variation was genetic. However, as yet there is no comprehensive understanding of either the global distribution of lactase persistence, the number of alleles that cause it, or the reasons for its recent selection
.
Digestion
Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones....
and metabolize
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
lactose
Lactose
Lactose is a disaccharide sugar that is found most notably in milk and is formed from galactose and glucose. Lactose makes up around 2~8% of milk , although the amount varies among species and individuals. It is extracted from sweet or sour whey. The name comes from or , the Latin word for milk,...
, a sugar
Sugar
Sugar is a class of edible crystalline carbohydrates, mainly sucrose, lactose, and fructose, characterized by a sweet flavor.Sucrose in its refined form primarily comes from sugar cane and sugar beet...
found in milk. It is caused by a lack of lactase
Lactase
Lactase , a part of the β-galactosidase family of enzymes, is a glycoside hydrolase involved in the hydrolysis of the disaccharide lactose into constituent galactose and glucose monomers...
, the enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
required to break down lactose in the digestive system, and results in symptoms including abdominal pain
Abdominal pain
Abdominal pain can be one of the symptoms associated with transient disorders or serious disease. Making a definitive diagnosis of the cause of abdominal pain can be difficult, because many diseases can result in this symptom. Abdominal pain is a common problem...
, bloating
Bloating
Bloating is any abnormal general swelling, or increase in diameter of the abdominal area. As a symptom, the patient feels a full and tight abdomen, which may cause abdominal pain sometimes accompanied by increased borborygmus or more seriously the total lack of borborygmus.-Symptoms:The most common...
, flatulence
Flatulence
Flatulence is the expulsion through the rectum of a mixture of gases that are byproducts of the digestion process of mammals and other animals. The medical term for the mixture of gases is flatus, informally known as a fart, or simply gas...
, diarrhea
Diarrhea
Diarrhea , also spelled diarrhoea, is the condition of having three or more loose or liquid bowel movements per day. It is a common cause of death in developing countries and the second most common cause of infant deaths worldwide. The loss of fluids through diarrhea can cause dehydration and...
, nausea
Nausea
Nausea , is a sensation of unease and discomfort in the upper stomach with an involuntary urge to vomit. It often, but not always, precedes vomiting...
and acid reflux.
Most mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s normally become lactose intolerant when they are young but some human populations have developed lactase persistence
Lactase persistence
Lactase persistence is the continued activity of the enzyme lactase in adulthood. Since lactase's only function is the digestion of lactose in milk, in most mammalian species the activity of the enzyme is dramatically reduced after weaning...
, in which lactase production continues into adulthood. It is estimated that 75% of adults worldwide show some decrease in lactase activity during adulthood. The frequency of decreased lactase activity ranges from 5% in northern Europe through 71% for Sicily to more than 90% in some African and Asian countries.
Terminology
"Lactose intolerance" primarily refers to a syndromeSyndrome
In medicine and psychology, a syndrome is the association of several clinically recognizable features, signs , symptoms , phenomena or characteristics that often occur together, so that the presence of one or more features alerts the physician to the possible presence of the others...
having one or more symptoms upon the consumption of food substances containing lactose. Individuals may be lactose intolerant to varying degrees, depending on the severity of these symptoms. "Lactose malabsorption" refers to the physiological concomitant of lactase deficiency (i.e. the body does not have sufficient lactase capacity to digest the amount of lactose ingested). A medical condition with similar symptoms is fructose malabsorption
Fructose malabsorption
Fructose malabsorption, formerly named "dietary fructose intolerance," is a digestive disorder in which absorption of fructose is impaired by deficient fructose carriers in the small intestine's enterocytes. This results in an increased concentration of fructose in the entire intestine.Fructose...
.
Lactase deficiency has a number of causes, and is therefore classified as one of three types:
- Primary lactase deficiency is genetic, only affects adults and is caused by the absence of a lactase persistenceLactase persistenceLactase persistence is the continued activity of the enzyme lactase in adulthood. Since lactase's only function is the digestion of lactose in milk, in most mammalian species the activity of the enzyme is dramatically reduced after weaning...
allele. It is the most common cause of lactose intolerance as a majority of the world's population lacks these alleles. - Secondary lactase deficiency is caused by injury to the small intestineSmall intestineThe small intestine is the part of the gastrointestinal tract following the stomach and followed by the large intestine, and is where much of the digestion and absorption of food takes place. In invertebrates such as worms, the terms "gastrointestinal tract" and "large intestine" are often used to...
, usually in infancy, from acute gastroenteritisGastroenteritisGastroenteritis is marked by severe inflammation of the gastrointestinal tract involving both the stomach and small intestine resulting in acute diarrhea and vomiting. It can be transferred by contact with contaminated food and water...
, diarrheaDiarrheaDiarrhea , also spelled diarrhoea, is the condition of having three or more loose or liquid bowel movements per day. It is a common cause of death in developing countries and the second most common cause of infant deaths worldwide. The loss of fluids through diarrhea can cause dehydration and...
, chemotherapyChemotherapyChemotherapy is the treatment of cancer with an antineoplastic drug or with a combination of such drugs into a standardized treatment regimen....
, intestinal parasites or other environmental causes. - Congenital lactase deficiency is a very rare, autosomal recessive genetic disorder that prevents lactase expression from birth. It is particularly common in FinlandFinlandFinland , officially the Republic of Finland, is a Nordic country situated in the Fennoscandian region of Northern Europe. It is bordered by Sweden in the west, Norway in the north and Russia in the east, while Estonia lies to its south across the Gulf of Finland.Around 5.4 million people reside...
.
Lactose intolerance is not an allergy
Food allergy
A food allergy is an adverse immune response to a food protein. They are distinct from other adverse responses to food, such as food intolerance, pharmacological reactions, and toxin-mediated reactions....
because it is not an immune response
Immune system
An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
but caused by lactase deficiency. Milk allergy
Milk allergy
A milk allergy is a food allergy, an adverse immune reaction to one or more of the constituents of milk from any animal...
is a separate condition with distinct symptoms.
Symptoms
Not all people with lactase deficiency will necessarily present symptoms when exposed to lactose. Most people with lactose intolerance can tolerate some amount of lactose in their diet and the severity of symptoms increases with the amount of lactose consumed. When they do occur, symptoms appear thirty minutes to two hours after consumption of lactose, and typically include abdominal bloatingBloating
Bloating is any abnormal general swelling, or increase in diameter of the abdominal area. As a symptom, the patient feels a full and tight abdomen, which may cause abdominal pain sometimes accompanied by increased borborygmus or more seriously the total lack of borborygmus.-Symptoms:The most common...
and cramps, flatulence
Flatulence
Flatulence is the expulsion through the rectum of a mixture of gases that are byproducts of the digestion process of mammals and other animals. The medical term for the mixture of gases is flatus, informally known as a fart, or simply gas...
, diarrhoea, nausea
Nausea
Nausea , is a sensation of unease and discomfort in the upper stomach with an involuntary urge to vomit. It often, but not always, precedes vomiting...
, borborygmi (rumbling stomach) and vomiting
Vomiting
Vomiting is the forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose...
(particularly in adolescents).
Nutritional implications
While dairy products, being rich in protein, calcium, and carbohydrates, can be a significant source of nutrients, there is no evidence that lactose intolerance has any adverse impact on health in populations where it is the norm amongst adults. In dairy-consuming societies, however, dairy is often the main source of those nutrients and also, for lacto-vegetarians, the main source of vitamin B12Vitamin B12
Vitamin B12, vitamin B12 or vitamin B-12, also called cobalamin, is a water-soluble vitamin with a key role in the normal functioning of the brain and nervous system, and for the formation of blood. It is one of the eight B vitamins...
. Some countries require by law that milk be fortified with vitamin A
Vitamin A
Vitamin A is a vitamin that is needed by the retina of the eye in the form of a specific metabolite, the light-absorbing molecule retinal, that is necessary for both low-light and color vision...
and vitamin D
Vitamin D
Vitamin D is a group of fat-soluble secosteroids. In humans, vitamin D is unique both because it functions as a prohormone and because the body can synthesize it when sun exposure is adequate ....
. In these societies individuals who reduce or eliminate consumption of dairy must obtain these nutrients elsewhere; calcium from fortified breakfast foods, for example, potassium and vitamin A from fruit and vegetables and B vitamins from meat and eggs. The human body produces some vitamin D from exposure to direct sunlight.
Congenital lactase deficiency (CLD), the inhibited production of lactase in infants as well as adults, can be dangerous in any society because of infants' nutritional reliance on breast milk. Before the 20th century those born with the condition were not expected to survive infancy but it can be mitigated using soybean
Soybean
The soybean or soya bean is a species of legume native to East Asia, widely grown for its edible bean which has numerous uses...
-derived infant formula
Infant formula
Infant formula is a manufactured food designed and marketed for feeding to babies and infants under 12 months of age, usually prepared for bottle-feeding or cup-feeding from powder or liquid . The U.S...
e and manufactured lactase-free dairy products. Beyond infancy individuals affected by CLD usually have the same nutritional concerns as other lactose-intolerant adults.
Causes
Lactose intolerance is a consequence of lactase deficiency, which may be either genetic or environmentally induced, depending on whether it is primary, secondary, or congenital. In any case symptoms are caused by insufficient levels of the enzymeEnzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
lactase
Lactase
Lactase , a part of the β-galactosidase family of enzymes, is a glycoside hydrolase involved in the hydrolysis of the disaccharide lactose into constituent galactose and glucose monomers...
in the lining of the duodenum
Duodenum
The duodenum is the first section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms anterior intestine or proximal intestine may be used instead of duodenum...
. Lactose
Lactose
Lactose is a disaccharide sugar that is found most notably in milk and is formed from galactose and glucose. Lactose makes up around 2~8% of milk , although the amount varies among species and individuals. It is extracted from sweet or sour whey. The name comes from or , the Latin word for milk,...
, a disaccharide
Disaccharide
A disaccharide or biose is the carbohydrate formed when two monosaccharides undergo a condensation reaction which involves the elimination of a small molecule, such as water, from the functional groups only. Like monosaccharides, disaccharides form an aqueous solution when dissolved in water...
molecule found in milk and dairy products, cannot be directly absorbed through the wall of the small intestine into the bloodstream so, in the absence of lactase, passes intact into the colon
Colon (anatomy)
The colon is the last part of the digestive system in most vertebrates; it extracts water and salt from solid wastes before they are eliminated from the body, and is the site in which flora-aided fermentation of unabsorbed material occurs. Unlike the small intestine, the colon does not play a...
. Bacteria
Gut flora
Gut flora consists of microorganisms that live in the digestive tracts of animals and is the largest reservoir of human flora. In this context, gut is synonymous with intestinal, and flora with microbiota and microflora....
in the colon are able to metabolise lactose and the resulting fermentation
Fermentation (biochemistry)
Fermentation is the process of extracting energy from the oxidation of organic compounds, such as carbohydrates, using an endogenous electron acceptor, which is usually an organic compound. In contrast, respiration is where electrons are donated to an exogenous electron acceptor, such as oxygen,...
produces copious amounts of gas (a mixture of hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
, carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
and methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...
) that causes the various abdominal symptoms. The unabsorbed sugars and fermentation products also raises the osmotic pressure
Osmotic pressure
Osmotic pressure is the pressure which needs to be applied to a solution to prevent the inward flow of water across a semipermeable membrane....
of the colon, resulting in an increased flow of water into the bowels (diarrhea
Diarrhea
Diarrhea , also spelled diarrhoea, is the condition of having three or more loose or liquid bowel movements per day. It is a common cause of death in developing countries and the second most common cause of infant deaths worldwide. The loss of fluids through diarrhea can cause dehydration and...
).
Diagnosis
To assess lactose intolerance, intestinal function is challenged by ingesting more dairy products than can be readily digested. Clinical symptoms typically appear within30 minutes but may take up to 2 hours depending on other foods and activities. Substantial variability in response (symptoms of nausea, cramping, bloating, diarrhea, and flatulence) is to be expected as the extent and severity of lactose intolerance varies among individuals.
It is important to distinguish lactose intolerance from milk allergy
Milk allergy
A milk allergy is a food allergy, an adverse immune reaction to one or more of the constituents of milk from any animal...
, an abnormal immune response (usually) to milk proteins. This may be done in diagnosis by giving lactose-free milk, producing no symptoms in the case of lactose intolerance but the same reaction as to normal milk if it is a milk allergy. An intermediate result might suggest that the person has both conditions. Since lactose intolerance is normal state for most adults worldwide it is not considered a disease and a medical diagnosis is not normally required. However if confirmation is necessary four tests are available.
Hydrogen breath test
In a hydrogen breath testHydrogen Breath Test
A hydrogen breath test is used as a clinical medical diagnosis for people with irritable bowel syndrome, and common food intolerances. The test is simple, non-invasive, and is performed after a short period of fasting . Even though the test is normally known as a "Hydrogen Breath Test" some...
, after an overnight fast, 25 gram
Gram
The gram is a metric system unit of mass....
s of lactose (in a solution with water) is swallowed. If the lactose cannot be digested, enteric bacteria metabolize it and produce hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
which, along with methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...
if produced, can be detected on the patient's breath by a clinical gas chromatograph or compact solid-state detector. The test takes about 2 to 3 hours.
Blood test
In conjunction, measuring blood glucose level every 10 – 15 minutes after ingestion will show a "flat curve" in individuals with lactose malabsorption while the lactase persistent will have a significant "top", with a typical elevation of 50 to 100%, within 1 – 2 hours. However due to the need for frequent blood sampling this approach has been largely supplanted by breath testing.After an overnight fast blood is drawn and then 50 gram
Gram
The gram is a metric system unit of mass....
s of lactose (in aqueous solution) is swallowed. Blood is then drawn again at the 30 minute, 1 hour, 2 hour, and 3 hour mark. If the lactose cannot be digested blood glucose levels will rise by less than 20 mg/dL.
Stool acidity test
This test can be used to diagnose lactose intolerance in infants, for whom other forms of testing are risky or impractical.The infant is given lactose to drink. If the individual is tolerant, the lactose is digested and absorbed in the small intestine, otherwise it is not digested and absorbed and it reaches the colon. The bacteria in the colon, mixed with the lactose, cause acidity in stools. Stools passed after the ingestion of the lactose are tested for level of acidity. If the stools are acidic, the infant is intolerant to lactose.
Intestinal biopsy
An intestinal biopsy can confirm lactase deficiency following discovery of elevated hydrogen in the hydrogen breath test. Modern techniques have enabled a test to be performed at the patient's bedside identifying the presence/absence of the lactase enzyme in conjunction with upper gastrointestinal endoscopy. However, for research applications such as mRNA measurements a specialist laboratory is required.Management
Lactose intolerance is not considered a condition that requires treatment in societies where the diet contains relatively little dairy. However those living among societies that are largely lactose-tolerant may find lactose intolerance troublesome. Although there are still no methodologies to reinstate lactase production, some individuals have reported that their intolerance varies over time depending on health status and pregnancy).Lactose intolerance is not usually an absolute condition: the reduction in lactase production, and the amount of lactose that can therefore be tolerated, varies from person to person. Since lactose intolerance poses no further threat to a person's health, the condition is managed by minimizing the occurrence and severity of symptoms. Berdanier and Hargrove recognise four general principles; avoidance of dietary lactose, substitution to maintain nutrient intake, regulation of calcium intake and use of enzyme substitute.
Avoiding lactose-containing products
Since each individual's tolerance to lactose varies, according to the US National Institute of Health, "Dietary control of lactose intolerance depends on people learning through trial and error how much lactose they can handle." Label reading is essential, as commercial terminology varies according to language and region.Lactose is present in two large food categories: conventional dairy products, and as a food additive (in dairy and non dairy products).
Dairy products
Lactose is a water-soluble molecule. Therefore fat percentage and the curdCurd
Curds are a dairy product obtained by curdling milk with rennet or an edible acidic substance such as lemon juice or vinegar, and then draining off the liquid portion. The increased acidity causes the milk proteins to tangle into solid masses, or curds. The remaining liquid, which contains only...
ling process affect tolerance of foods. After the curd
Curd
Curds are a dairy product obtained by curdling milk with rennet or an edible acidic substance such as lemon juice or vinegar, and then draining off the liquid portion. The increased acidity causes the milk proteins to tangle into solid masses, or curds. The remaining liquid, which contains only...
ling process lactose is found in the water portion (along with whey
Whey
Whey or Milk Serum is the liquid remaining after milk has been curdled and strained. It is a by-product of the manufacture of cheese or casein and has several commercial uses. Sweet whey is manufactured during the making of rennet types of hard cheese like cheddar or Swiss cheese...
and casein
Casein
Casein is the name for a family of related phosphoprotein proteins . These proteins are commonly found in mammalian milk, making up 80% of the proteins in cow milk and between 60% and 65% of the proteins in human milk....
) but not in the fat portion. Dairy products that are "fat reduced" or "fat free" generally have a slightly higher lactose percentage. Low fat
Diet food
Diet food refers to any food or drink whose recipe has been altered in some way to make it part of a body modification diet...
dairy foods, additionally, often have various dairy derivatives such as milk solids added to them to enhance sweetness, increasing the lactose content.
Milk. Human milk has a high lactose percentage at around 9%. Unprocessed cow milk has 4.7% lactose. Unprocessed milk from other bovid
Bovid
A bovid is any of almost 140 species of cloven-hoofed ruminant mammal at least the males of which bear characteristic unbranching horns covered in a permanent sheath of keratin....
s contains similar lactose percentages (goat milk 4.7%, buffalo
Bovinae
The biological subfamily Bovinae includes a diverse group of 10 genera of medium to large sized ungulates, including domestic cattle, the bison, African buffalo, the water buffalo, the yak, and the four-horned and spiral-horned antelopes...
4.86%, yak
Yak
The yak, Bos grunniens or Bos mutus, is a long-haired bovine found throughout the Himalayan region of south Central Asia, the Tibetan Plateau and as far north as Mongolia and Russia. In addition to a large domestic population, there is a small, vulnerable wild yak population...
4.93%, sheep milk
Sheep milk
Sheep's milk is the milk of domestic sheep. Though not widely drunk in any modern culture, sheep's milk is commonly used to make cultured dairy products. Well-known cheeses made from sheep milk include the Feta of Greece, Roquefort of France, Manchego from Spain, the Pecorino Romano , the Pecorino...
4.6%)
Butter. The butter-making process separates the majority of milk's water components from the fat components. Lactose, being a water soluble molecule, will largely be removed, but will still be present in small quantities in the butter
Butter
Butter is a dairy product made by churning fresh or fermented cream or milk. It is generally used as a spread and a condiment, as well as in cooking applications, such as baking, sauce making, and pan frying...
unless it is also fermented to produce cultured butter. Clarified butter
Clarified butter
Clarified butter is milk fat rendered from butter to separate the milk solids and water from the butterfat. Typically, it is produced by melting butter and allowing the different components to separate by density...
, however, has extremely low concentrations of lactose and is safe for most LI patients.
Yogurt, Frozen Yogurt and kefir
Kefir
Kefir is a fermented milk drink that originated with shepherds of the North Caucasus region, who discovered that fresh milk carried in leather pouches would occasionally ferment into an effervescent beverage...
. People can be more tolerant of traditionally made yogurt than milk because it contains lactase produced by the bacterial cultures used to make the yogurt. Frozen yogurt, if cultured similarly to its unfrozen counterpart, will contain similarly reduced lactose levels. However many commercial brands contain milk solids , increasing the lactose content.
Cheeses. Traditionally made hard cheese (such as Emmental) and soft ripened cheeses may create less reaction than the equivalent amount of milk because of the processes involved. Fermentation and higher fat content contribute to lesser amounts of lactose. Traditionally made Emmental or Cheddar
Cheddar cheese
Cheddar cheese is a relatively hard, yellow to off-white, and sometimes sharp-tasting cheese, produced in several countries around the world. It has its origins in the English village of Cheddar in Somerset....
might contain 10% of the lactose found in whole milk
Milk
Milk is a white liquid produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals before they are able to digest other types of food. Early-lactation milk contains colostrum, which carries the mother's antibodies to the baby and can reduce the risk of many...
. In addition, the traditional aging methods of cheese (over 2 years) reduces their lactose content to practically nothing. Commercial cheese brands, however, are generally manufactured by modern processes that do not have the same lactose reducing properties, and as no regulations mandate what qualifies as an "aged" cheese, this description does not provide any indication of whether the process used significantly reduced lactose.
Soured cream if made in the traditional way, may be tolerable, but most modern brands add milk solids.
Examples of lactose levels in foods. As scientific consensus has not been reached concerning lactose percentage analysis methods (non-hydrated form or the mono-hydrated form), and considering that dairy content varies greatly according to labeling practices, geography and manufacturing processes, lactose numbers may not be very reliable. The following are examples of lactose levels in foods which commonly set off symptoms. These quantities are to be treated as guidelines only.
| Dairy product | Serving size | Lactose content |
|---|---|---|
| Milk, regular | 250 ml | 12 g |
| Milk, reduced fat | 250 ml | 13 g |
| Yogurt, plain, regular | 200 g | 9 g |
| Yogurt, plain, low-fat | 200 g | 12 g |
| Cheddar cheese | 30 g | 0.02 g |
| Cottage cheese | 30 g | 0.1 g |
| Butter | 1 tsp | 0.03 g |
| Ice cream | 50 g | 3 g |
Lactose in non-dairy products
Lactose (also present when labels state lactoserum, wheyWhey
Whey or Milk Serum is the liquid remaining after milk has been curdled and strained. It is a by-product of the manufacture of cheese or casein and has several commercial uses. Sweet whey is manufactured during the making of rennet types of hard cheese like cheddar or Swiss cheese...
, milk solids, modified milk ingredients, etc.) is a commercial food additive
Food additive
Food additives are substances added to food to preserve flavor or enhance its taste and appearance.Some additives have been used for centuries; for example, preserving food by pickling , salting, as with bacon, preserving sweets or using sulfur dioxide as in some wines...
used for its texture, flavour and adhesive qualities, and is found in foods such as processed meats (sausage
Sausage
A sausage is a food usually made from ground meat , mixed with salt, herbs, and other spices, although vegetarian sausages are available. The word sausage is derived from Old French saussiche, from the Latin word salsus, meaning salted.Typically, a sausage is formed in a casing traditionally made...
s/hot dog
Hot dog
A hot dog is a sausage served in a sliced bun. It is very often garnished with mustard, ketchup, onions, mayonnaise, relish and/or sauerkraut.-History:...
s, sliced meats, pâté
Pâté
Pâté is a mixture of ground meat and fat minced into a spreadable paste. Common additions include vegetables, herbs, spices, and either wine or cognac, armagnac or brandy...
s), gravy stock powder, margarine
Margarine
Margarine , as a generic term, can indicate any of a wide range of butter substitutes, typically composed of vegetable oils. In many parts of the world, the market share of margarine and spreads has overtaken that of butter...
s, sliced bread
Bread
Bread is a staple food prepared by cooking a dough of flour and water and often additional ingredients. Doughs are usually baked, but in some cuisines breads are steamed , fried , or baked on an unoiled frying pan . It may be leavened or unleavened...
s, breakfast cereals, potato chip
Potato chip
Potato chips are thin slices of potato that are deep fried...
s, processed foods
Food processing
Food processing is the set of methods and techniques used to transform raw ingredients into food or to transform food into other forms for consumption by humans or animals either in the home or by the food processing industry...
, medication
Medication
A pharmaceutical drug, also referred to as medicine, medication or medicament, can be loosely defined as any chemical substance intended for use in the medical diagnosis, cure, treatment, or prevention of disease.- Classification :...
s, pre-prepared meals, meal replacement (powders and bars), protein supplements (powders and bars) and even beer
Beer
Beer is the world's most widely consumed andprobably oldest alcoholic beverage; it is the third most popular drink overall, after water and tea. It is produced by the brewing and fermentation of sugars, mainly derived from malted cereal grains, most commonly malted barley and malted wheat...
s in the milk stout style. Some barbecue sauces and liquid cheeses used in fast-food restaurants may also contain lactose.
Kosher products labeled pareve or fleishig are free of milk. However, if a "D" (for "Dairy") is present next to the circled "K", "U", or other hechsher
Hechsher
A hechsher is the special certification marking found on the packages of products that have been certified as kosher . In Halakha , the dietary laws of kashrut specify food items that may be eaten and others that are prohibited as set out in the commandments of the Torah...
, the food likely contains milk solids (although it may also simply indicate that the product was produced on equipment shared with other products containing milk derivatives).
Alternative products
Plant-based milksPlant milk
thumb|right|250px|A cup of [[amazake]] .Plant milk is a general term for any milk-like product that is derived from a plant source. There is no formal or legal definition for plant milk...
and derivatives are inherently lactose free: soy milk
Soy milk
Soy milk and sometimes referred to as soy drink/beverage is a beverage made from soybeans. A stable emulsion of oil, water, and protein, it is produced by soaking dry soybeans and grinding them with water...
, rice milk
Rice milk
Rice milk is a kind of grain milk processed from rice. It is mostly made from brown rice and commonly unsweetened. The sweetness in most rice milk varieties is generated by a natural enzymatic process, cleaving the carbohydrates into sugars, especially glucose, similar to the Japanese amazake...
, almond milk
Almond milk
Almond milk is a milky drink made from ground almonds. Unlike animal milk, almond milk contains no cholesterol or lactose. Regular, unsweetened almond milk can be used as a substitute for animal milk in many recipes, and as it does not contain any animal products, is suitable for vegetarians and...
, hazelnut milk, oat milk, hemp milk
Hemp milk
Hemp milk or Hemp Seed Milk, is a drink made from hemp seeds that are soaked and ground into water, yielding a creamy nutty beverage. It is marketed in health and fitness publications as a "new health food darling".- Health claims :According to Dr...
, peanut milk
Peanut milk
Peanut milk is a non-dairy beverage created using peanuts and water. Recipe variations include salt, sweeteners, and grains. It does not contain any lactose and is therefore suitable for people with lactose intolerance...
, horchata
Horchata
Horchata or orxata is the name of several kinds of traditional beverage, made of ground almonds, sesame seeds, rice, barley, or tigernuts .-Etymology:...
.
The dairy industry has created low-lactose or lactose-free products to replace regular dairy.
Lactase supplementation
When lactose avoidance is not possible, or on occasions when a person chooses to consume such items, then enzymatic lactaseLactase
Lactase , a part of the β-galactosidase family of enzymes, is a glycoside hydrolase involved in the hydrolysis of the disaccharide lactose into constituent galactose and glucose monomers...
supplements may be used.
Lactase enzymes similar to those produced in the small intestines of humans are produced industrially by fungi of the genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Aspergillus
Aspergillus
Aspergillus is a genus consisting of several hundred mold species found in various climates worldwide. Aspergillus was first catalogued in 1729 by the Italian priest and biologist Pier Antonio Micheli...
. The enzyme, β-galactosidase, is available in tablet form in a variety of doses, in many countries without a prescription. It functions well only in high-acid environments, such as that found in the human gut due to the addition of gastric juices from the stomach. Unfortunately, too much acid can denature it, and it therefore should not be taken on an empty stomach. Also, the enzyme is ineffective if it does not reach the small intestine by the time the problematic food does. Lactose-sensitive individuals can experiment with both timing and dosage to fit their particular needs.
While essentially the same process as normal intestinal lactose digestion, direct treatment of milk employs a different variety of industrially produced lactase. This enzyme, produced by yeast
Yeast
Yeasts are eukaryotic micro-organisms classified in the kingdom Fungi, with 1,500 species currently described estimated to be only 1% of all fungal species. Most reproduce asexually by mitosis, and many do so by an asymmetric division process called budding...
from the genus Kluyveromyces
Kluyveromyces
Kluyveromyces is a genus of ascomycetous yeasts in the family Saccharomycetaceae. Some of the species, such as K. marxianus, are the teleomorphs of Candida species....
, takes much longer to act, must be thoroughly mixed throughout the product, and is destroyed by even mildly acidic environments. Its main use is in producing the lactose-free or lactose-reduced dairy products sold in supermarkets.
Enzymatic lactase supplementation may have an advantage over avoiding dairy products, in that alternative provision does not need to be made to provide sufficient calcium intake, especially in children.
Rehabituation to dairy products
For healthy individuals with secondary lactose intolerance, it may be possible in some cases for the bacteria in the large intestine to adapt to an altered diet and break down small quantities of lactose more effectively by habitually consuming small amounts of dairy products several times a day over a period of time. Reintroducing dairy in this way to people who have an underlying or chronic illness, however, is not recommended, as certain illnesses damage the intestinal tract in a way which prevents the lactaseLactase
Lactase , a part of the β-galactosidase family of enzymes, is a glycoside hydrolase involved in the hydrolysis of the disaccharide lactose into constituent galactose and glucose monomers...
enzyme from being expressed.
Some studies indicate that environmental factors (more specifically, the consumption of lactose) may "play a more important role than genetic factors in the etio-pathogenesis of milk intolerance", but some other publications suggest that lactase
Lactase
Lactase , a part of the β-galactosidase family of enzymes, is a glycoside hydrolase involved in the hydrolysis of the disaccharide lactose into constituent galactose and glucose monomers...
production does not seem to be induced by dairy/lactose consumption.
Lactase persistence
Lactase persistence is the phenotypePhenotype
A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...
associated with various autosomal dominant alleles prolonging the activity of lactase beyond infancy; conversely, lactase non-persistence is the phenotype associated with primary lactase deficiency (see above). Among mammals, lactase persistence is unique to humans – it evolved relatively recently (in the last 10,000 years) among some populations, and the majority of people worldwide remain lactase non-persistent. For this reason lactase persistence is of some interest to the fields of anthropology
Anthropology
Anthropology is the study of humanity. It has origins in the humanities, the natural sciences, and the social sciences. The term "anthropology" is from the Greek anthrōpos , "man", understood to mean mankind or humanity, and -logia , "discourse" or "study", and was first used in 1501 by German...
and human genetics
Human genetics
Human genetics describes the study of inheritance as it occurs in human beings. Human genetics encompasses a variety of overlapping fields including: classical genetics, cytogenetics, molecular genetics, biochemical genetics, genomics, population genetics, developmental genetics, clinical genetics,...
, which typically use the genetically-derived persistence/non-persistence terminology.
Recognition of the extent and genetic basis of lactose intolerance is also relatively recent. Though the symptoms were recognised as early as Hippocrates
Hippocrates
Hippocrates of Cos or Hippokrates of Kos was an ancient Greek physician of the Age of Pericles , and is considered one of the most outstanding figures in the history of medicine...
(460-370 B.C.), until at least the 1960s the prevailing assumption in the medical community was that tolerance was the normal condition and intolerance either the result of milk allergy
Milk allergy
A milk allergy is a food allergy, an adverse immune reaction to one or more of the constituents of milk from any animal...
, an intestinal pathogen
Pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...
, or else was psychosomatic (it being recognised that some cultures did not practice dairying, and people from those cultures often reacted badly to consuming milk). Many people are still surprised or disbelieving that, from a cross-cultural and evolutionary perspective, lactose tolerance is the "abnormal" condition. There are two reasons for this perception. Firstly Western countries, as a result of their mostly European heritage, have particularly low frequences of lactose intolerance, and an extensive cultural history of dairying, so tolerance actually was the norm in most of the societies sampled by medical researchers. Secondly, in such societies lactose intolerance tended to be under-reported: genetically lactase non-persistent individuals can tolerate varying quantities of lactose before showing symptoms, and their symptoms differ in severity. Most are able to digest a small quantity of milk, for example in tea or coffee, without suffering any adverse effects. Fermented dairy products
Fermented milk products
Fermented milk products, also known as cultured dairy foods, cultured dairy products, or cultured milk products, are dairy foods that have been fermented with lactic acid bacteria such as Lactobacillus, Lactococcus, and Leuconostoc...
, such as cheese, also contain dramatically less lactose than plain milk. Therefore in societies where tolerance is the norm many people who consume only small amounts of dairy, or have only mild symptoms, may be unaware that they cannot digest lactose. Eventually, however, it was recognised that in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
lactose intolerance was closely linked to race
Race
Race is classification of humans into large and distinct populations or groups by factors such as heritable phenotypic characteristics or geographic ancestry, but also often influenced by and correlated with traits such as appearance, culture, ethnicity, and socio-economic status...
. Subsequent research revealed that intolerance was the worldwide norm, and that the variation was genetic. However, as yet there is no comprehensive understanding of either the global distribution of lactase persistence, the number of alleles that cause it, or the reasons for its recent selection
Selection
In the context of evolution, certain traits or alleles of genes segregating within a population may be subject to selection. Under selection, individuals with advantageous or "adaptive" traits tend to be more successful than their peers reproductively—meaning they contribute more offspring to the...
.
See also
- Dairy allergy
- Food allergyFood allergyA food allergy is an adverse immune response to a food protein. They are distinct from other adverse responses to food, such as food intolerance, pharmacological reactions, and toxin-mediated reactions....
- GastroenterologyGastroenterologyGastroenterology is the branch of medicine whereby the digestive system and its disorders are studied. The name is a combination of three Ancient Greek words gaster , enteron , and logos...
- Gluten intolerance
- Soy cheeseSoy cheeseCheese analogues are cheese substitutes made most frequently from soybeans but also made from rice, almonds, nutritional yeast and other non-dairy ingredients. Cheese analogues, just like plant-based milk substitutes, are available in many of the same varieties as their cheese counterparts...
- Soy milkSoy milkSoy milk and sometimes referred to as soy drink/beverage is a beverage made from soybeans. A stable emulsion of oil, water, and protein, it is produced by soaking dry soybeans and grinding them with water...
and Plant milkPlant milkthumb|right|250px|A cup of [[amazake]] .Plant milk is a general term for any milk-like product that is derived from a plant source. There is no formal or legal definition for plant milk... - Sucrose intoleranceSucrose intoleranceSucrose intolerance, also called congenital sucrase-isomaltase deficiency or Sucrase-isomaltase deficiency, is the condition in which sucrase, an enzyme needed for proper metabolization of sucrose, is not produced in the small intestine....