Oily fish have oil

Fish oil

Fish oil is oil derived from the tissues of oily fish. Fish oils contain the omega-3 fatty acids eicosapentaenoic acid , and docosahexaenoic acid , precursors of certain eicosanoids that are known to reduce inflammation throughout the body, and are thought to have many health benefits.Fish do not...

 in their tissues and in the belly cavity around the gut

Gut (zoology)

In zoology, the gut, also known as the alimentary canal or alimentary tract, is a tube by which bilaterian animals transfer food to the digestion organs. In large bilaterians the gut generally also has an exit, the anus, by which the animal disposes of solid wastes...

. Their fillet

Fillet (cut)

A fillet is a cut or slice of boneless meat or fish.- Meat :In the case of beef, in the USA, the term most often refers to beef tenderloin, especially filet mignon.- Chicken :...

s contain up to 30 percent oil, although this figure varies both within and between species. Examples include small forage fish

Forage fish

Forage fish, also called prey fish or bait fish, are small fish which are preyed on by larger predators for food. Predators include other larger fish, seabirds and marine mammals. Typical ocean forage fish feed near the base of the food chain on plankton, often by filter feeding...

, such as sardines, herring

Herring

Herring is an oily fish of the genus Clupea, found in the shallow, temperate waters of the North Pacific and the North Atlantic oceans, including the Baltic Sea. Three species of Clupea are recognized. The main taxa, the Atlantic herring and the Pacific herring may each be divided into subspecies...

 and anchovies, and other larger pelagic fish

Pelagic fish

Pelagic fish live near the surface or in the water column of coastal, ocean and lake waters, but not on the bottom of the sea or the lake. They can be contrasted with demersal fish, which do live on or near the bottom, and reef fish which are associated with coral reefs.The marine pelagic...

, such as salmon

Salmon

Salmon is the common name for several species of fish in the family Salmonidae. Several other fish in the same family are called trout; the difference is often said to be that salmon migrate and trout are resident, but this distinction does not strictly hold true...

, trout

Trout

Trout is the name for a number of species of freshwater and saltwater fish belonging to the Salmoninae subfamily of the family Salmonidae. Salmon belong to the same family as trout. Most salmon species spend almost all their lives in salt water...

, hilsa

Hilsa

Ilish , also spelled Elish, is the most popular fish to Bengalis. Its the national fish of Bangladesh and extremely popular in parts of India such as West Bengal, Orissa, Tripura, Assam as well. Ilish also can be found at India's Assamese-, Bengali- Oriya-speaking regions and in Telugu-speaking...

 and mackerel

Mackerel

Mackerel is a common name applied to a number of different species of fish, mostly, but not exclusively, from the family Scombridae. They may be found in all tropical and temperate seas. Most live offshore in the oceanic environment but a few, like the Spanish mackerel , enter bays and can be...

.

Oily fish can be contrasted with whitefish

Whitefish (fisheries term)

Whitefish or white fish is a fisheries term referring to several species of demersal fish with fins, particularly cod , whiting , and haddock , but also hake , pollock , or others...

, which contain oil only in the liver

Liver

The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...

, and much less overall than oily fish. Examples of whitefish are cod

Cod

Cod is the common name for genus Gadus, belonging to the family Gadidae, and is also used in the common name for various other fishes. Cod is a popular food with a mild flavor, low fat content and a dense, flaky white flesh. Cod livers are processed to make cod liver oil, an important source of...

, haddock

Haddock

The haddock , also known as the offshore hake, is a marine fish distributed on both sides of the North Atlantic. Haddock is a popular food fish and is widely fished commercially....

 and flatfish

Flatfish

The flatfish are an order of ray-finned fish, also called the Heterosomata, sometimes classified as a suborder of Perciformes. In many species, both eyes lie on one side of the head, one or the other migrating through and around the head during development...

. Whitefish are usually demersal fish which live on or near the seafloor, whereas oily fish are pelagic

Pelagic fish

Pelagic fish live near the surface or in the water column of coastal, ocean and lake waters, but not on the bottom of the sea or the lake. They can be contrasted with demersal fish, which do live on or near the bottom, and reef fish which are associated with coral reefs.The marine pelagic...

, living in the water column away from the bottom.

Oily fish are a good source of Vitamin

Vitamin

A vitamin is an organic compound required as a nutrient in tiny amounts by an organism. In other words, an organic chemical compound is called a vitamin when it cannot be synthesized in sufficient quantities by an organism, and must be obtained from the diet. Thus, the term is conditional both on...

s 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 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 ....

, and are rich in Omega 3 fatty acids (whitefish contain the same nutrients but at a much lower level). For this reason the consumption of oily fish rather than whitefish can be more beneficial to humans, particularly concerning cardiovascular diseases, but oily fish are known to carry higher levels of contaminants (such as mercury

Mercury (element)

Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...

 or dioxin

Dioxin

Polychlorinated dibenzodioxins , or simply dioxins, are a group of organic polyhalogenated compounds that are significant environmental pollutants. They are commonly but inaccurately referred to as dioxins for simplicity, because every PCDD molecule contains a dioxin skeletal structure as the...

) than whitefish. Amongst other benefits, studies suggest that the Omega 3 fatty acids in oily fish may help sufferers of depression

Clinical depression

Major depressive disorder is a mental disorder characterized by an all-encompassing low mood accompanied by low self-esteem, and by loss of interest or pleasure in normally enjoyable activities...

and improve inflammatory conditions such as arthritis

Arthritis

Arthritis is a form of joint disorder that involves inflammation of one or more joints....

.

Dementia

French research published in 2002 in the British Medical Journal

British Medical Journal

BMJ is a partially open-access peer-reviewed medical journal. Originally called the British Medical Journal, the title was officially shortened to BMJ in 1988. The journal is published by the BMJ Group, a wholly owned subsidiary of the British Medical Association...

followed 1,674 elderly residents of southern France

France

The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

 for seven years, studying their consumption of meat versus seafood and the presence of dementia

Dementia

Dementia is a serious loss of cognitive ability in a previously unimpaired person, beyond what might be expected from normal aging...

 symptoms. The conclusion was that people who ate fish at least once a week had a significantly lower risk of being diagnosed with dementia over a seven-year period. However the study was unclear as to whether fish consumption protected against dementia, or if dementia prevented the participants from wanting more fish. There was also a possible confounding factor in that individuals with higher education have both a lower risk of dementia and higher consumption of fish.

Ocular health

A 2009 study in the British Journal of Ophthalmology

British Journal of Ophthalmology

The British Journal of Ophthalmology is a peer-reviewed medical journal covering clinical investigations, clinical observations, and clinically relevant laboratory investigations related to ophthalmology...

concluded that the Omega-3 fatty acids in oily fish were beneficial both in preventing the onset and slowing the progression of age-related macular degeneration in the elderly. The researchers suggested that people at risk should eat two portions of oily fish per week.

Cardiovascular health

Consuming oily fish twice per week may also help prevent sudden death due to myocardial infarction

Myocardial infarction

Myocardial 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...

 by preventing cardiac arrhythmia. The eicosapentaenoic acid

Eicosapentaenoic acid

Eicosapentaenoic acid is an omega-3 fatty acid. In physiological literature, it is given the name 20:5. It also has the trivial name timnodonic acid...

 found in fish oils appears to dramatically reduce inflammation through conversion within the body to resolvins

Resolvins

Resolvins are compounds that are made by the human body from the omega-3 fatty acids eicosapentaenoic acid and docosahexaenoic acid . They are produced by the COX-2 pathway especially in the presence of aspirin...

, with beneficial effects for the cardiovascular system and arthritis

Arthritis

Arthritis is a form of joint disorder that involves inflammation of one or more joints....

.

Recommended consumption

In 1994, the UK

United Kingdom

The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

 Committee on Medical Aspects of Food and Nutrition Policy (COMA) recommended that people eat at least two portions of fish per week, one of which should be oily fish.

In 2004 the UK Food Standards Agency

Food Standards Agency

The Food Standards Agency is a non-ministerial government department of the Government of the United Kingdom. It is responsible for protecting public health in relation to food throughout the United Kingdom and is led by a board appointed to act in the public interest...

 published advice on the recommended minimum and maximum quantities of oily fish to be eaten per week, to balance the beneficial qualities of the Omega 3 fatty acids against the potential dangers of ingesting methylmercury (MeHg).
The United States Environmental Protection Agency

United States Environmental Protection Agency

The U.S. Environmental Protection Agency is an agency of the federal government of the United States charged with protecting human health and the environment, by writing and enforcing regulations based on laws passed by Congress...

's (EPA) Exposure Reference Dose (RfI) for MeHg is 0.1 micrograms per kg body weight per day. The corresponding limit of blood mercury is 5.8 micrograms per liter. The restrictions apply to certain oily fish – "marlin, swordfish, shark and, to a lesser extent, tuna"

The recommendations on maximum consumption of oily fish were up to four portions (1 portion = 140g, or approx 4.9 ounces) a week for men, boys, and women past childbearing age, and up to two portions a week for women of childbearing age, including pregnant and breastfeeding women, and girls. There is no recommended limit on the consumption of white fish

Whitefish (fisheries term)

Whitefish or white fish is a fisheries term referring to several species of demersal fish with fins, particularly cod , whiting , and haddock , but also hake , pollock , or others...

.

The EPA and 2007 U.S. Department of Agriculture guidelines sets a limit only on consumption of fatty fish with greater than one part per million of methylmercury. Specifically tilefish

Tilefish

Tilefishes, also known as blanquillo, are mostly small perciform marine fish comprising the family Malacanthidae.They are usually found in sandy areas, especially near coral reefs....

, king mackerel

King mackerel

The king mackerel is a migratory species of mackerel of the western Atlantic Ocean and Gulf of Mexico. It is an important species to both the commercial and recreational fishing industries.-Description:...

, shark

Shark

Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....

 and swordfish

Swordfish

Swordfish , also known as broadbill in some countries, are large, highly migratory, predatory fish characterized by a long, flat bill. They are a popular sport fish of the billfish category, though elusive. Swordfish are elongated, round-bodied, and lose all teeth and scales by adulthood...

. There are limits, however, for nursing/pregnant women and children under the age of six. This population should completely avoid fish with high risk of Mercury contamination (those listed above) and limit consumption of moderate and low-Mercury fish to 12 ounces or fewer per week. Albacore tuna should be limited to 6 oz or less per week.

Omega-3 content

Concerns about contamination, diet

Vegetarianism

Vegetarianism encompasses the practice of following plant-based diets , with or without the inclusion of dairy products or eggs, and with the exclusion of meat...

 or supply

Overfishing

Overfishing occurs when fishing activities reduce fish stocks below an acceptable level. This can occur in any body of water from a pond to the oceans....

 have led to investigation of plant sources of Omega-3 fatty acids, notably flax, hempseed and perilla oil

Perilla oil

Perilla oil is obtained from the seeds of herbs of the genus Perilla, usually from the species Perilla frutescens. The seeds contain 35 to 45 percent oil which is obtained by pressing. Perilla oil is used along with synthetic resins in the production of varnishes...

. Lactating

Lactation

Lactation describes the secretion of milk from the mammary glands and the period of time that a mother lactates to feed her young. The process occurs in all female mammals, however it predates mammals. In humans the process of feeding milk is called breastfeeding or nursing...

 women who supplemented their diet with flaxseed oil showed increases in blood and breastmilk concentration of alpha-linolenic acid

Alpha-linolenic acid

α-Linolenic acid is an organic compound found in many common vegetable oils. In terms of its structure, it is named all-cis-9,12,15-octadecatrienoic acid. In physiological literature, it is given the name 18:3 ....

 and eicosapentaenoic acid

Eicosapentaenoic acid

Eicosapentaenoic acid is an omega-3 fatty acid. In physiological literature, it is given the name 20:5. It also has the trivial name timnodonic acid...

 but no changes to concentrations of docosahexaenoic acid

Docosahexaenoic acid

Docosahexaenoic acid is an omega-3 fatty acid that is a primary structural component of the human brain and retina. In chemical structure, DHA is a carboxylic acid with a 22-carbon chain and six cis double bonds; the first double bond is located at the third carbon from the omega end...

.

Further reading

• Clover, Charles. 2004. The End of the Line: How overfishing is changing the world and what we eat. Ebury Press, London. ISBN 0-09-189780-7

External links

• Achieving optimal essential fatty acid status in vegetarians: current knowledge and practical implications (American Journal of Clinical Nutrition)
• "What's an oily fish?" from the UK Foods Standards Agency
• BUPA article on oily fish
• George Monbiot on the environmental problems of sourcing omega-3 from fish