Intermittent fasting
Encyclopedia
Intermittent fasting is a pattern of eating
that alternates between periods of fasting
(usually meaning consumption of water only) and non-fasting. A specific form of IF is alternate day fasting (ADF), which is a 48-hour routine typically composed of a 24-hour fast followed by a 24-hour non-fasting period. (ADF is also sometimes referred to as every other day (EOD) fasting, or sometimes every other day feeding (EODF).)
There is some evidence that intermittent fasting may have beneficial effects on the health and longevity
of animals—including human
s—that are similar to the effects of caloric restriction (CR). There is currently no consensus as to the degree to which this is simply due to an (often) concomitant overall decrease in calories. (IF and CR are forms of Dietary Restriction (DR), which is sometimes referred to as Dietary Energy Restriction (DER).)
Scientific study of intermittent fasting in rats (and anecdotally in humans) was carried out at least as early as 1943.
A number of subsequent studies have shown beneficial effects of IF in animals.
" is the name of a book/regime equivalent to "19/5".)
The phase
of the fasting period may also be specified. Practitioners often start the fasting period at the commencement of nightly sleep
.
Unlike the use of IF in scientific experiments, in popular usage the term is sometimes also applied even when the fasting period involves consumption of some calorie-containing beverages.
Another variation on IF is to consume limited calories (e.g., 20% of normal) rather than none at all on fasting days. This regimen may provide many of the benefits of IF.
Diet (nutrition)
In nutrition, diet is the sum of food consumed by a person or other organism. Dietary habits are the habitual decisions an individual or culture makes when choosing what foods to eat. With the word diet, it is often implied the use of specific intake of nutrition for health or weight-management...
that alternates between periods of fasting
Fasting
Fasting is primarily the act of willingly abstaining from some or all food, drink, or both, for a period of time. An absolute fast is normally defined as abstinence from all food and liquid for a defined period, usually a single day , or several days. Other fasts may be only partially restrictive,...
(usually meaning consumption of water only) and non-fasting. A specific form of IF is alternate day fasting (ADF), which is a 48-hour routine typically composed of a 24-hour fast followed by a 24-hour non-fasting period. (ADF is also sometimes referred to as every other day (EOD) fasting, or sometimes every other day feeding (EODF).)
There is some evidence that intermittent fasting may have beneficial effects on the health and longevity
Longevity
The word "longevity" is sometimes used as a synonym for "life expectancy" in demography or known as "long life", especially when it concerns someone or something lasting longer than expected ....
of animals—including human
Human
Humans are the only living species in the Homo genus...
s—that are similar to the effects of caloric restriction (CR). There is currently no consensus as to the degree to which this is simply due to an (often) concomitant overall decrease in calories. (IF and CR are forms of Dietary Restriction (DR), which is sometimes referred to as Dietary Energy Restriction (DER).)
Scientific study of intermittent fasting in rats (and anecdotally in humans) was carried out at least as early as 1943.
Animal studies
The 1945 study by Carlson and Hoelzel, referenced above, found that the apparent life span of rats in the study was increased by intermittent fasting. Tests in which a group of thirty-three rats were allowed the same food ad libitum and groups of thirty-seven, thirty-seven and thirty rats were fasted 1 day in 4, 3 and 2, respectively, after the age of 42 days, showed that the optimum amount of fasting appeared to be fasting 1 day in 3 and this increased the life span of littermate males about 20% and littermate females about 15%. However, the pre-experimental condition of the individual rats was also found to be an important factor determining the life spans. No drastic retardation of growth was produced by the intermittent fasting but the development of mammary tumors was retarded in proportion to the amount of fasting.A number of subsequent studies have shown beneficial effects of IF in animals.
- "Reduced serum glucose and insulinInsulinInsulin is a hormone central to regulating carbohydrate and fat metabolism in the body. Insulin causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle....
levels and increased resistance of neurons in the brain to excitotoxic stressExcitotoxicityExcitotoxicity is the pathological process by which nerve cells are damaged and killed by excessive stimulation by neurotransmitters such as glutamate and similar substances. This occurs when receptors for the excitatory neurotransmitter glutamate such as the NMDA receptor and AMPA receptor are...
" - "Enhance[s] cardiovascular and brain functions and improve[s] several risk factors for coronary artery disease and strokeStrokeA stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...
including a reduction in blood pressureBlood pressureBlood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...
and increased insulin sensitivity" and that "cardiovascular stress adaptation is improved and heart rate variability is increased in rodents" and that "rodents maintained on an IF regimen exhibit increased resistance of heart and brain cells to ischemic injuryIschemiaIn medicine, ischemia is a restriction in blood supply, generally due to factors in the blood vessels, with resultant damage or dysfunction of tissue. It may also be spelled ischaemia or ischæmia...
in experimental models of myocardial infarctionMyocardial infarctionMyocardial infarction or acute myocardial infarction , commonly known as a heart attack, results from the interruption of blood supply to a part of the heart, causing heart cells to die...
and stroke." - May "ameliorate age-related deficits in cognitive function" in mice
- Correlation with IF and significantly improved biochemical parameters associated with development of diabetic nephropathyDiabetic nephropathyDiabetic nephropathy , also known as Kimmelstiel-Wilson syndrome, or nodular diabetic glomerulosclerosis and intercapillary glomerulonephritis, is a progressive kidney disease caused by angiopathy of capillaries in the kidney glomeruli. It is characterized by nephrotic syndrome and diffuse...
- Resistance in mice to the effects of gamma irradiationIrradiationIrradiation is the process by which an object is exposed to radiation. The exposure can originate from various sources, including natural sources. Most frequently the term refers to ionizing radiation, and to a level of radiation that will serve a specific purpose, rather than radiation exposure to...
- Lifespan increases of 40.4% and 56.6% in C. elegansCaenorhabditis elegansCaenorhabditis elegans is a free-living, transparent nematode , about 1 mm in length, which lives in temperate soil environments. Research into the molecular and developmental biology of C. elegans was begun in 1974 by Sydney Brenner and it has since been used extensively as a model...
for alternate day (24 hour) and two-of-each-three day (48 hour) fasting, respectively, as compared to an ad libitumAd libitumAd libitum is Latin for "at one's pleasure"; it is often shortened to "ad lib" or "ad-lib"...
diet. - Rats showed markedly improved long-term survival after chronic heart failure via pro-angiogenic, anti-apoptotic and anti-remodeling effects.
Human studies
Similarly, recent studies on humans suggest similar beneficial results.- Alternative day fasting (ADF) may produce significant improvements in several markers such as LDL cholesterol in as little as eight weeks.
- ADF "may effectively modulate several risk factors, thereby preventing chronic disease, and that ADF may modulate disease risk to an extent similar to that of CR".
- SerumBlood plasmaBlood plasma is the straw-colored liquid component of blood in which the blood cells in whole blood are normally suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid...
from humans following an IF diet had positive effects (reduced triglycerides in men and increased HDL in women, as well as reduced cell proliferation and increased heat resistanceHeat shockIn biochemistry, heat shock is the effect of subjecting a cell to a higher temperature than that of the ideal body temperature of the organism from which the cell line was derived.-Heat shock response:...
) in vitroIn vitroIn vitro refers to studies in experimental biology that are conducted using components of an organism that have been isolated from their usual biological context in order to permit a more detailed or more convenient analysis than can be done with whole organisms. Colloquially, these experiments...
on human hepatoma cells. - IF confers protection from toxic chemotherapy treatments, allowing higher doses and therefore more effective treatment for cancers.
- IF may function as a form of nutritional hormesisHormesisHormesis is the term for generally favorable biological responses to low exposures to toxins and other stressors. A pollutant or toxin showing hormesis thus has the opposite effect in small doses as in large doses...
.
As a human diet
A number of individuals are experimenting with different varieties of IF as a dietary regime. In this context, shorthand such as "20/4" is used to denote a repeating pattern of 20 hours of fasting followed by 4 hours of non-fasting. ("Fast-5Fast-5 Diet
The Fast-5 Diet refers to the way of eating endorsed by Bert Herring M.D. in the book "The Fast-5 Diet and the Fast-5 Lifestyle." The Fast-5 Diet is a weight-loss and weight-maintenance plan consisting of a single rule: limit calorie intake to no more than five consecutive hours in each day...
" is the name of a book/regime equivalent to "19/5".)
The phase
Phase (waves)
Phase in waves is the fraction of a wave cycle which has elapsed relative to an arbitrary point.-Formula:The phase of an oscillation or wave refers to a sinusoidal function such as the following:...
of the fasting period may also be specified. Practitioners often start the fasting period at the commencement of nightly sleep
Sleep
Sleep is a naturally recurring state characterized by reduced or absent consciousness, relatively suspended sensory activity, and inactivity of nearly all voluntary muscles. It is distinguished from quiet wakefulness by a decreased ability to react to stimuli, and is more easily reversible than...
.
Unlike the use of IF in scientific experiments, in popular usage the term is sometimes also applied even when the fasting period involves consumption of some calorie-containing beverages.
Another variation on IF is to consume limited calories (e.g., 20% of normal) rather than none at all on fasting days. This regimen may provide many of the benefits of IF.