Essential fatty acids are fatty acids that cannot be synthesized within the human body, and therefore must be obtained from the diet. There are two families of essential fatty acids: omega-3 (n−3) and omega-6 (n−6) fatty acids. As these fatty acids are not saturated with hydrogen (H) atoms (and contain more than one double bond between the atoms) they are called ' polyunsaturated fatty acids ' (PUFAs). Most PUFAs are of plant and fatty fish origin.

 

There are three major types of omega-3 fatty acids that are ingested in foods and used by the body: alpha-linolenic acid (ALA), an essential fatty acid, whose primary utility is its ability to be converted into the long-chain polyunsaturated fatty acids (LCPUFAs) eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). While the body can convert ALA to EPA and DHA, the conversion rate is generally inadequate to provide sufficiency of EPA and DHA. Hence, EPA and DHA are referred to as “conditionally essential.”

 
Most omega-6 fatty acids are consumed in the diet from vegetable oils such as linoleic acid (LA). Linoleic acid is converted in the body to the long-chain polyunsaturated fatty acids gamma-linolenic acid (GLA) and arachidonic acid (AA). AA can also be consumed directly from meat and GLA can be ingested from several plant-based oils. AA is the precursor for prostaglandin and related bioactive components. The typical Western diet provides relatively low levels of DHA and EPA and high levels of AA compared with diets from other industrialized nations.

A sufficient intake of polyunsaturated fatty acids (omega-3 and omega-6 fatty acids) is important as they play a critical role in

 

• development and maintenance of proper brain function
• the vision process
• immune and inflammatory responses
• production of hormone-like molecules.

 

The European Food Safety Authority (EFSA), which provides scientific advice to assist policy makers, has confirmed that clear health benefits have been established for the dietary intake of the polyunsaturated omega-3 fatty acids docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) in contributing to:

 

• the maintenance of normal blood pressure;
• the maintenance of normal blood triglyceride levels (2 grams/day);
• the normal function of the heart (250 mg/day).

 

In addition, DHA contributes to:

 

• the maintenance of normal blood triglyceride levels (2 grams/day);
• the maintenance of normal brain function (250 mg/day);
• the maintenance of normal vision (250 mg/day).

 

Health in pregnancy and lactation
The months of gestation and the early months of life are periods of rapid brain growth, development, and incorporation of DHA. The mother is the primary source of long-chain polyunsaturated fatty acids (LCPUFA) via the placenta to the fetus and through breast milk for the infant. Studies of DHA supplementation during pregnancy and lactation show improvements in infant DHA status and higher scores on measures of visual and cognitive processes.

Infant Health
The long-chain omega-3 fatty acid docosahexaenoic acid (DHA) is a major and essential building block of membranes of the brain and other nervous tissues, including the retina. Moreover, DHA appears to be functionally important for visual and neurological processes. Preterm and term infant formula containing at least 0.3% of the total fatty acids, such as DHA and 0.6% of the long chain n-6 fatty acid arachidonic acid (AA), have been shown to aid visual maturation when compared to unsupplemented formula. In addition, neurological development and function show benefits from including this level of DHA and ARA in preterm or term infant formula as compared to an unsupplemented formula.

Cardiovascular disease
The European Food Safety Authority, the American Heart Association, and other scientific and regulatory bodies confirm that eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are important for cardiovascular health. Studies show that their presence in the diet maintains healthy blood pressure, blood lipids, and heart rate as compared to diets low in n-3 fatty acids. EPA and DHA also maintain healthy immune functions and inflammatory responses.

Studies of heart attack victims have found that supplementing the diet or increasing consumption of omega-3 fatty acids daily can reduce the risk of stroke, follow-on heart attacks, and death.

Cancer
The balance between omega-3 and omega-6 fatty acids appears to play an important role in the development and growth of some cancer forms, such as breast, colon, and prostate cancer.

While further research is still needed to understand the effect that omega-3 fatty acids may have on cancer prevention or treatment, researchers speculate that omega-3 fatty acids in combination with other nutrients (e.g. vitamin C, vitamin E, beta-carotene, and coenzyme Q10) may be of particular value in the prevention and treatment of breast cancer.

Some studies have shown the slowing or reversing of the progression of colon cancer with daily consumption of long-chain omega-3 fatty acids (eicosapentaenoic acid [EPA] and docosahexaenoic acid [DHA]).

One animal study has shown that in rats with spreading colon cancer, omega-3 fatty acids (specifically the omega-3 fatty acid alpha-linolenic acid, ALA) promoted the growth of cancer cells in the liver. The reason for this is not clear and needs further investigation.

While higher levels of omega-3 fatty acid alpha-linolenic acid (ALA) has been seen in individuals with prostate cancer in one study – which suggests that ALA may have a cancer-promoting role – more recent studies that were specifically designed to look for prostate cancer risk factors in humans and a systematic review found no such link.

 

Age-related eye disease
A study that compared people with age-related macular degeneration, a serious eye condition that can progress to blindness, to individuals without the eye disease found that those with a healthy dietary balance of omega-3 and omega-6 fatty acids and higher intake of fish in their diets were less likely to have this particular eye disorder.

Another larger epidemiological study confirms that consuming long-chain omega-3 fatty acids (eicosapentaenoic acid, EPA, and docosahexaenoic acid, DHA) from fish four or more times per week may reduce the risk of developing macular degeneration. Notably, however, this same study suggests that omega-3 fatty acid alpha-linolenic acid (ALA) may actually increase the risk of this eye condition. The reason for this is not clear.

Alzheimer’s disease
Multiple epidemiological studies have shown that an insufficient intake of long-chain omega-3 fatty acids (docosahexaenoic acid, DHA) may be a risk factor for Alzheimer's disease and other types of dementia. Higher intake or plasma levels of DHA are significantly correlated with lower risk of cognitive decline, all-cause dementia, and Alzheimer’s disease. The Agency for Healthcare Research and Quality (AHRQ) report issued in 2005 stated that “total omega-3 fatty acid consumption and consumption of DHA (but not ALA or EPA) were associated with a significant reduction in the incidence of Alzheimer’s disease.” The report also stated that “due to the small number of studies, further research is needed before a strong conclusion can be drawn.” Since 2005, other systematic reviews of the literature have also supported this association. Clinical trials of omega-3 fatty acid supplementation have begun to emerge that show cognitive benefits in very mild Alzheimer disease, mild cognitive impairment, and age-related cognitive decline.

 

* see also Principles – The complexity of micronutrient research

Please note:
Any dietary or drug treatment with high-dose micronutrients needs medical supervision.

 

Diabetes
Individuals with diabetes tend to have high blood fat (triglyceride) levels. Studies have shown that omega-3 fatty acids from fish oil can help to lower triglycerides, so people with diabetes may benefit from eating foods or taking supplements that contain long-chain omega-3 fatty acids (eicosapentaenoic acid [EPA], and docosahexaenoic acid [DHA]).

 

The omega-3 fatty acid alpha-linolenic acid (ALA) may not have the same benefit as DHA and EPA because some people with diabetes lack the ability to efficiently convert ALA to a form of omega-3 fatty acids that the body can readily use.

 

Inflammatory diseases
Several studies investigating the use of omega-3 fatty acid supplements for inflammatory joint conditions (e.g., rheumatoid arthritis) concluded that the supplements reduce tenderness in joints, decrease morning stiffness, and allow for a reduction in the amount of medication needed for people with rheumatoid arthritis.

 

In addition, some studies suggest that diets rich in omega-3 fatty acids (and low in the inflammatory omega-6 fatty acids) may benefit people with other inflammatory disorders, such as Crohn’s disease and asthma. However, study results have been mixed and more evidence is needed to draw any definitive conclusions.*

 

Mental disorders
Omega-3 fatty acids are important components of nerve cell membranes; they help nerve cells communicate with each other, which is an essential step in maintaining good mental health. In particular, the long-chain omega-3 fatty acid docosahexaenoic acid (DHA) is involved in a variety of nerve cell processes. These include the modulation of signal transduction molecules and G-protein coupled receptors, synaptogenesis, neuronal differentiation, and generation of active metabolites such as docosanoids.

 

Levels of omega-3 fatty acids were found to be measurably low and the ratio of omega-6 to omega-3 fatty acids were particularly high in a clinical study of patients hospitalized for depression. In a clinical study of individuals with depression, those who ate a healthy diet consisting of fatty fish 2–3 times per week for 5 years experienced a significant reduction in feelings of depression.

 

In a clinical study in people with bipolar disorder, those who were treated with the long-chain omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in combination with their usual mood stabilizing medications experienced fewer mood swings and recurrence of either depression or mania than those who received a placebo. However, another study treating individuals with bipolar depression did not find evidence of efficacy for the use of EPA in these patients.*

 

Preliminary clinical evidence suggests that people with schizophrenia experience an improvement in symptoms when given omega-3 fatty acids. However, a recent well-designed study concluded that EPA supplements are no better than placebo in improving symptoms of this condition. The conflicting results suggest that more research is needed before conclusions can be drawn.*

 

Children with attention deficit/hyperactivity disorder (ADHD) may have low levels of certain essential fatty acids (including EPA and DHA) in their bodies. A clinical study using omega-3 and omega-6 fatty acid supplementation in children with ADHD or developmental coordination disorder found improvements in reading, spelling, and behavior in the children. More studies, including comparisons with drug therapies, are needed to evaluate these results.*

 

Clinical studies suggest that men and women with the eating disorder anorexia nervosa have lower than optimal levels of polyunsaturated fatty acids (including omega-3 fatty acid alpha-linolenic acid [ALA] and long-chain omega-6 fatty acid gamma-linolenic acid [GLA]). To prevent the complications associated with essential fatty acid deficiencies, some experts recommend that treatment programs for anorexia nervosa include polyunsaturated fatty acid-rich foods such as fish and organ meats.

 

Osteoporosis
Studies suggest that long-chain omega-3 fatty acid eicosapentaenoic acid (EPA) may help increase calcium levels in the body, deposit calcium in the bones, and improve bone strength.

 

In a study of women over 65 with osteoporosis, those given EPA and long-chain omega-6 fatty acid gamma-linolenic acid (GLA) supplements experienced significantly less bone loss over a three-year period than those who were given a placebo.

 

Positive correlations between dietary intake of AA and ALA and reduced hip fracture rate in older men have also been recently reported. Benefits from LCPUFA intake related to bone health may vary depending upon age and gender.

 

Weight loss
Clinical studies suggest that overweight people who follow a weight loss program that includes exercise tend to achieve better control over their blood sugar and cholesterol levels when fish rich in omega-3 fatty acids (such as salmon, mackerel, and herring) is a staple in their low-fat diet.

 

*see also Principles – The contradictory science of micronutrients

A number of recommendations regarding the intake of fatty acids – and n-3 LCPUFA in particular – have been made by scientific, governmental, and regulatory bodies. The primary source of n-3 LCPUFA is fish. Most health agencies which include nutrition guidelines, promote the consumption of two fish meals per week. Due to allergy, concern over contamination or sustainability, many people limit their fish consumption. Fish oil and algal oil supplements along with foods which have been fortified with the oils are commercially available to supply the recommended levels of n-3 LCPUFA.

 

European health authorities have established intake recommendations for polyunsaturated fatty acids for adults:

 

• an omega-3 fatty acid intake of 2 g/day alpha-linolenic acid (ALA) and 250 mg/day long-chain omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)
• an omega-6 fatty acid intake of 10 g/day linoleic acid (LA).

 

Scientists have suggested a minimum daily intake of 500 mg EPA and DHA combined for healthy individuals.

 

In the U.S., adequate intakes for adults have been set at 1.6 g omega-3 fatty acids (ALA) per day for men, 1.1 g/day for women respectively, and 17 g omega-6 fatty acids (LA) per day for men (19–50 years of age), 12 g/day for women (19–50 years of age) respectively.

 

The American Heart Association recommends eating fish (particularly fatty fish such as mackerel, lake trout, herring, sardines, albacore tuna, and salmon) at least twice a week.

 

It is advised that pregnant women and mothers, nursing mothers, young children, and women who might become pregnant not eat several types of fish, including swordfish, shark, and king mackerel, which have higher levels of contaminants (e.g., mercury). They are advised to consume polyunsaturated fatty acid supplements.

 

It is important to maintain an appropriate balance of omega-3 and omega-6 in the diet, as these two substances work together to promote health. Omega-3 fatty acids, for example, help reduce inflammation, and most omega-6 fatty acids tend to promote inflammation. An inappropriate balance of these essential fatty acids contributes to the development of disease whereas a proper balance helps maintain and even improve health.

 

A healthy diet should consist of roughly 2–4 times more omega-6 fatty acids than omega-3 fatty acids. The typical diet in developed countries (‘Western diet’) tends to contain 14–25 times more omega-6 fatty acids than omega-3 fatty acids, and many researchers believe this imbalance is a significant factor in the rising rate of inflammatory disorders. In contrast, the ‘Mediterranean diet’ consists of a healthier balance between omega-3 and omega-6 fatty acids, and many studies have shown that people who follow this diet are less likely to develop heart disease.

In general, dietary intakes of omega-6 fatty acids are well above the recommendations defined in most European countries, while the intakes of long-chain omega-3 fatty acids, such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are mostly lower than recommended by national authorities.

 

A similar situation exists in the U.S.: while a healthy diet should consist of roughly 2–4 times more omega-6 fatty acids than omega-3 fatty acids, the typical American (Western) diet tends to contain 14–25 times more omega-6 fatty acids than omega-3 fatty acids.

Essential fatty acid deficiency has been found to occur in patients with a chronic poor absorption of fat from food, some patients nourished intravenously, and in patients with cystic fibrosis.

 

Because the last three months of pregnancy are a critical period for the accumulation of the omega-3 fatty acid docosahexaenoic acid (DHA) in the brain and retina, preterm infants are thought to be particularly vulnerable to adverse effects of insufficient DHA. Therefore, it has been proposed that preterm infant formulas be supplemented with enough DHA to bring blood and cellular DHA levels of formula-fed infants up to those of breast-fed infants.

 

True deficiency of essential fatty acids manifests as skin problems. Less than optimal intakes of essential fatty acids have been associated with poor memory, poor circulation, depression, and other mental health problems.

 

Infants who do not get enough omega-3 fatty acids from their mothers during pregnancy are at risk of developing less than optimal vision and cognitive development.

Omega-3 fatty acids can be found in fatty fish, such as salmon, tuna, anchovies, and sardines, and other marine life like algae and krill. Nut oils are a good source of alpha-linolenic acid (ALA), but not of docosahexanoic acid (DHA) or eicosapentaneoic acid (EPA).

 

Food sources of omega-6 fatty acids include vegetable oils, such as soybean, safflower, and corn oil, nuts, seeds, and ─ in small amounts ─ in meat, poultry, and eggs.

 
In addition, supplements containing omega-3 fatty acids (with a fish oils or algae basis) and omega-6 fatty acids (with a borage, black current seed oil, or evening primrose oil basis) are available. In addition, there are many commercially available foods that are fortified with DHA and EPA.

Omega-3 fatty acids
High doses of omega-3 fatty acids, docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA) should be used cautiously by people who bruise easily, have a bleeding disorder, or take blood-thinning medications, because excessive amounts of omega-3 fatty acids may lead to bleeding. Bleeding may be a problem when > 3 grams/day of DHA and EPA are consumed.

 

Fish oil can cause flatulence, bloating, belching, and diarrhea.

 

Individuals with type 2 diabetes may experience increases in fasting blood sugar levels while taking high doses of fish oil supplements; supervision by a health care provider is recommended.

 

Studies have shown that some long-chain omega-3 fatty acids, especially DHA, may reduce the risk of developing macular degeneration. In contrast, some studies suggest that high doses of the shorter-chain omega-3 fatty acids, such as alpha-linolenic acid (ALA), may increase the risk of developing this disorder. Clearly, more research is needed to evaluate any potential risk.

 

Some studies have shown that omega-3 fatty acids may reduce the risk of developing certain cancers. In contrast, an analysis has suggested that consumption of high doses of ALA may increase the risk of prostate cancer. However, more recent studies and a systematic review found no such link.

 

Fish (and fish oil supplements) may contain potentially harmful contaminants, such as heavy metals (including mercury), dioxins, and polychlorinated biphenyls (PCBs). Excessive exposure to those toxic substances can cause brain and kidney damage. The developing fetus, infants, and young children are especially vulnerable to the toxic effects of mercury on the brain. In order to limit the exposure of these groups to mercury, health authorities recommend women who are considering pregnancy, pregnant women, and breast-feeding women to not eat fish that contain high mercury levels (e.g., shark, swordfish, king mackerel, or golden snapper), and instead to consume a variety of fish that are lower in mercury (e.g., tuna, shrimp, salmon, catfish, and pollock).

 

Omega-6 fatty acids
Omega-6 fatty acids should not be used in individuals with seizure disorder because there have been reports of these supplements (e.g., evening primrose oil) inducing seizures.

 

Borage seed oil, and possibly other sources of gamma-linolenic acid (GLA), should not be used during pregnancy because they may be harmful to the fetus and induce early labor.

 

Doses of GLA greater than 3 g per day should be avoided because, at that point, production of arachidonic acid (AA) increases, which may cause and increase inflammation.

 

Side effects of evening primrose oil can include occasional headache, abdominal pain, nausea, and loose stools.

 

Animal studies have shown that omega-6 fatty acids (linoleic acid and arachidonic acid), such as the fat found in corn oil, promote the growth of prostate tumor cells. More research is needed to evaluate potential cancer-promoting effects in humans. 

 

Drug interactions
Please note:
Because of the potential for interactions, dietary supplements should not be taken with medication without talking to an experienced healthcare provider first.

 

Nutrient interactions
It has been suggested that the amount of vitamin E required increases with the amount of polyunsaturated fatty acids consumed.