Alzheimer’s disease
In population studies, high dietary intake of fat and calories was
associated with an increased risk for Alzheimer’s disease, whereas high intake of fish
was associated with a decreased risk. Whether these associations represent a cause-and-effect
relationship is unknown.
Angina
Fish oil, which contains the
beneficial fatty acids known as EPA and DHA, has been studied in
the treatment of angina. In some studies, 3 grams or more of fish oil three times per day
(providing a total of about 3 grams of EPA and 2 grams of DHA) have reduced chest pain as well
as the need for nitroglycerin, a common medication
used to treat angina; other investigators could not confirm these findings. It is not known if
eating fish will confer any benefits for people with angina.
Asthma
There is evidence that children who eat oily fish may have a much
lower risk of getting asthma. Moreover, in a double-blind trial, children who received 300 mg
per day of fish oil (providing 84 mg of EPA and 36 mg of DHA) experienced significant
improvement of asthma symptoms. It should be noted that these benefits were obtained under
circumstances in which exposure to food allergens and environmental allergens was strictly
controlled. Though the evidence supporting the use of fish oils remains somewhat conflicting,
eating more fish and supplementing with fish oil may still be worth considering, especially
among children with asthma.
Atherosclerosis
Supplementation with fish oil, rich in omega-3 fatty acids, has been
associated with favorable changes in various risk factors for atherosclerosis and heart
disease in some, but not all, studies. A double-blind trial showed that people with
atherosclerosis who took fish oil (6 grams per day for 3 months and then 3 grams a day for 21
months) had significant regression of atherosclerotic plaques and a decrease in cardiovascular
events (e.g., heart attack and stroke) compared to those who did not take fish oil. These results
contradict the findings of an earlier controlled trial in which fish oil supplementation for
two years (6 grams per day) did not promote major favorable changes in the diameter of
atherosclerotic coronary arteries. It is not known if eating fish will confer similar
benefits. However, the original fish oil research was stimulated by population studies that
showed a remarkably low incidence of atherosclerosis among Inuit people, whose diets contain
large quantities of fresh fish.
Bipolar disorder
People diagnosed with
depression may have lower blood levels of omega-3 fatty acids. A recent double-blind trial
evaluated the effect of omega-3 fatty acid supplementation on people with bipolar disorder.
Patients in this study were given 9.6 grams of omega-3 fatty acids from fish oil, or a
placebo, in addition to their conventional medications. Those receiving this large amount of
fish oil had significant improvements compared to those taking placebo, including a longer
period between relapses. It is not known if eating fish will confer similar benefits.
Bronchitis
Dietary factors may influence both inflammatory activity and antioxidant status in the body. Increased inflammation and
decreased antioxidant activity may each lead to an increased incidence of chronic diseases,
such as chronic bronchitis. People suffering from chronic bronchitis may experience an
improvement in symptoms when consuming a diet high in anti-inflammatory fatty acids, such as
those found in fish.
Cancer
Fish eaters have
been reported to have low risks of cancers of the mouth, throat, stomach, colon, rectum, pancreas, lung, breast, and
prostate. The omega-3 fatty acids found in fish
are thought by some researchers to be the components of fish responsible for protection
against cancer. Many doctors recommend fish as part of an anticancer diet.
Fish Oil Supplements and the Treatment of
People with Weight Loss Associated with Late-Stage Cancer
In a controlled trial, late-stage cancer patients were given fish oil
supplements, which increased patients’ survival time by several months. Among those
patients who were terminal or near terminal at the beginning of the trial, immune status also
improved. It is not known if eating fish would produce similar effects.
In a preliminary report, 18 late-stage pancreatic cancer patients were given fish oil
supplements. Before supplementation, weight loss averaged over six pounds per month. After
three months of supplementation, patients had gained an average of two-thirds of a pound per
month. Fish oil supplementation appears to be a promising therapy for slowing weight loss in
late-stage cancer patients. It is not known if eating fish would produce similar effects.
Cancer (Breast)
Fish is a source of
a type of dietary fat considered potentially helpful in protecting against breast cancers.
Why do some research findings suggest fat increases the risk of cancer and other studies
find no association? Some studies finding dietary fat unrelated to cancer risks have not
factored out the effects of olive oil and fish fat. Both may protect against cancer. Adding
them to the total dietary fat intake and then studying whether “more fat causes more
cancer” is, therefore, a mistake. Some studies finding no association between fat intake
and breast cancer have made this error.
Scientists know cancers caused by diet most likely occur many years after the causative
food is consumed. When researchers compared dietary intakes to cancer rates occurring ten
years after the consumption of food, and also factored out the effect of fat from fish
consumption, they found a high degree of correlation between consumption of animal fat (other
than from fish) and the risk of breast cancer death rates for women at least 50 years of
age.
In the debate over whether dietary fat increases breast cancer risks, only one fact is
indisputable: women in countries that consume high amounts of meat and dairy fat have a high
risk of breast cancer, while women in countries that mostly consume fish (instead of dairy fat
and meat) have a low risk of breast cancer.
Cancer (Colon)
Several human studies have found that supplementation with fish oil
leads to a reduction in markers for the risk of colon cancer. Despite these promising reports,
no trial has yet investigated whether dietary fish consumption or continuous supplementation
with fish oil would actually help prevent colon cancer, or effectively treat people who
already have been diagnosed with colon cancer.
Cardiac arrhythmia
In a double-blind trial, people with a type of arrhythmia known as
ventricular premature complexes were given fish oil supplements or a similar placebo. Persons
taking the fish oil had a significantly reduced frequency of abnormal heartbeats, compared to
those receiving placebo. It is not known if eating fish would produce similar results.
Chronic
Obstructive Pulmonary Disease (COPD)
A greater intake of the omega-3 fatty acids found in fish and fish
oils has been linked to reduced risk of COPD, though research has yet to investigate whether
dietary fish consumption or fish oil supplements would help people with COPD.
Crohn’s disease
Inflammation within the gut occurs in people suffering from
Crohn’s disease. EPA and DHA, the omega-3 fatty acids found in fish and fish oil, have
anti-inflammatory activity. A two-year trial compared the effects of having people with
Crohn’s disease eat 3.5 to 7 ounces of fish high in EPA and DHA per day or a diet low in
fish. In that trial, the fish-eating group had a 20% relapse rate compared with a 58% rate in
those not eating fish. Salmon, herring, mackerel, albacore tuna, and sardines are all high in
EPA and DHA. Some types of fish oil supplements may also be helpful.
Depression
The amount and type of dietary fat consumed may influence the
incidence of depression. A high intake of omega-6 fatty acids relative to omega-3 fatty acids
and an inadequate intake of omega-3 fatty acids (e.g., from fish and fish oils) have both been
associated with increased levels of depression. People who eat diets high in omega-3 fatty
acids from fish have a lower incidence of depression and suicide.
Omega-3 fatty acids found in fish and fish oil, particularly DHA, are needed for normal
nervous system function. Depressed people have been reported to have lower omega-3 fatty acid
levels (e.g., DHA) than people who are not depressed. Low levels of the other omega-3 fatty
acid from fish, EPA, have correlated with increased severity of depression. In a double-blind
trial, people with manic depression were given a very high intake of supplemental fish oil for
four months. Although some scores of depression levels fell as much as 48% in the omega-3
fatty acid group, it is not known if eating fish could produce similar results, because it is
a far less concentrated source of EPA and DHA.
Diabetes
Eating fish may afford some protection from diabetes. Incorporating a
fish meal into a weight-loss regimen was effective at improving glucose and insulin metabolism
and lowering high cholesterol.
Glucose tolerance improves in healthy people taking fish oil supplements. However, other
studies report that cholesterol increases and diabetes worsens with fish oil supplements.
Until this issue is resolved, people with diabetes should feel free to increase their fish
intake, but they should consult a doctor before taking omega-3 fish oil supplements.
Dysmenorrhea
Diets low in omega-3 fatty acids (EPA and DHA) from fish and fish oil
have been associated with more menstrual pain. Fish oil supplements have helped relieve
dysmenorrhea in some studies. However, it is not known if eating fish would produce a similar
effect.
Eczema
Fish oil supplements have been shown to be helpful for people with
eczema. It is not known whether eating fish rich in omega-3 fatty acids (EPA and DHA) would
have similar effects.
Endometriosis
Animal research suggests that fish oils may reduce the severity of
endometriosis, and fish oils have been shown to improve symptoms of dysmenorrhea (painful
menstruation), which may be caused by endometriosis. However, it is not known whether eating
fish would have similar effects.
Fibrocystic breast disease
Fibrocystic disease has been linked to excess estrogen. When those
with fibrocystic disease are put on a low-fat diet, their estrogen levels decrease. After
three to six months, the pain and lumpiness also decrease. The link between fat and symptoms
appears to be most strongly related to saturated fat. Foods high in saturated fat include meat and dairy products. Fish is
a possible replacement.
Gestational hypertension (GH)
Increased consumption of fish has been associated with reduced risk
of GH in one preliminary trial. In this study, the incidence of GH was significantly higher in
women from communities with lower consumption of fish, and lower in the communities with high
fish consumption. Current evidence is insufficient to recommend the use of fish oil in GH.
Halitosis
Access by oral bacteria to sulfur-containing amino acids will enhance
the production of sulfur gases that are responsible for bad breath. This effect was
demonstrated in a study in which concentrations of these sulfur gases in the mouth were
increased after subjects used a mouth rinse containing the amino acid cysteine. Cleaning the
mouth after eating sulfur-rich foods such as fish may help remove the food supporting these
bacteria.
Heart attack
Several trials report that eating fish decreases heart attack deaths
and reduces the size of the heart injury, though some researchers have not confirmed these
findings. The link between fish eating and heart attack prevention is supported by research
showing that fish oil supplements help reverse atherosclerosis.
Making positive dietary changes immediately following a heart attack is likely to decrease
one’s chance of having a second heart attack. In one study, people began eating more vegetables and
fruits, and substituted fish, nuts, and legumes for meat and eggs 24–48 hours after a heart
attack. Six weeks later, the diet group had significantly fewer fatal and nonfatal heart
attacks than a similar group who did not make these dietary changes. This trend continued for
an additional six weeks.
Many doctors tell people trying to reduce their risk of heart disease to avoid all meat,
margarine, and other processed foods containing hydrogenated oils and dairy fat. Fish are
often suggested instead of meat.
Fish oil supplementation has led to partial reversal of atherosclerosis and a reduction in
incidence of heart attacks in double-blind trials. Fish oil may reduce the amount of heart
muscle damage from a heart attack and enhance the effect of blood-thinning medication.It is
not known if eating fish would produce similar results.
High cholesterol
Eating fish has been reported to increase HDL cholesterol and is
linked to a reduced risk of heart disease in most but not all studies. Fish contains very
little saturated fat, and fish oil contains EPA and DHA, omega-3 fatty acids that appear to
protect against heart disease.
High triglycerides
Some, but not all, studies have found that increasing consumption of
fish is associated with a lower risk of heart disease. Significant amounts of TG-lowering
omega-3 fatty acids (EPA and DHA) can be found in the flesh and oil of salmon, herring,
mackerel, sardines, anchovies, albacore tuna, and black cod. Many doctors recommend that
people with elevated TGs increase their intake of these fatty fish.
Many double-blind trials have consistently demonstrated that fish oil supplements lower TG
levels. Cod-liver oil, another source of omega-3 fatty acids, has also been found to lower
TGs. It is not known if eating fish can effectively reduce TG levels.
Hypertension
EPA and DHA, the omega-3 fatty acids found in fish oil, lower blood
pressure, according to an analysis of 31 trials. The effect was dependent on the amount of
omega-3 oil used, with the best results occurring in trials using unsustainably high levels
such as 15 grams per day—the amount often found in 50 grams of fish oil. It is not known
if eating any amount of fish can control hypertension. In any case, it would be impossible to
eat enough fish on a daily basis to provide an equivalent amount of omega-3 fatty acid as was
used in the studies cited above.
Immune function
Research on the immune effects of the omega-3 fatty acids from fish
and fish oils is conflicting. Liquid diets containing omega-3 fatty acids used in hospitals
for critically ill people have been shown to improve immune function and reduce infections.
However, in one controlled study in healthy people, a low-fat diet improved or maintained
immune function, but when fish was added to increase omega-3 fatty acid intake, immune
function was significantly inhibited.
Insulin resistance syndrome (IRS)
The effect of dietary fat on insulin resistance seems to depend on
the type of fat eaten. Preliminary studies in animals and humans suggest that insulin
resistance is worsened with increased use of saturated fat and improved with increased
unsaturated omega-3 fatty acids from fish. Recently, a low-fat diet allowing fish was shown to
decrease insulin resistance in people with IRS.
In two controlled studies, a combined program of a weight-loss diet lower in fat and higher
in fish, along with exercise three times per week, improved several measures of insulin
resistance, blood triglycerides and cholesterol, and blood pressure in a group of people with
IRS.
Iron-deficiency anemia
Iron deficiency is not usually caused by a lack of dietary iron
alone. Nonetheless, a lack of iron in the diet is often part of the problem, so ensuring an
adequate supply of iron is important. The most absorbable form of iron, called
“heme” iron, is found in meat, poultry, and fish. Non-heme iron is also found in
these foods.
Lupus
(SLE)
Foods high in omega-3 fatty acids, such as fish, may decrease
lupus-induced inflammation.
The omega-3 fatty acids in fish oil decrease inflammation and may be beneficial for persons
with SLE. To date, however, all studies on fish oil have used supplements and not fish.
Nonetheless, many doctors recommend their SLE patients eat several servings of fatty fish each
week.
Macular degeneration
According to preliminary research, people who eat fish more than once
per week have half the risk of developing age-related macular degeneration compared to people
who eat fish less than once per month.
Migraine headaches
Fish oil containing EPA and DHA may reduce the symptoms of migraine
headaches. It is not known if eating fish would have similar effects.
Multiple sclerosis (MS)
A survey of people in 36 different countries found that people who
ate more fish had less risk of developing MS, while those who ate pork, hot dogs, and other
foods high in animal (saturated) fats were at greater risk. Although some doctors recommend
fish oil capsules for people with MS, few investigations have explored the effects of this
supplement.
Night blindness
Night blindness can be an early sign of vitamin A deficiency. Such a deficiency can result from inadequate
intake of animal foods (the main source of vitamin A), including some fish.
Osteoporosis
A preliminary trial found that elderly women with osteoporosis who
were given supplements containing 4 grams of fish oil per day for four months had improved calcium absorption and resulted in evidence of new bone
formation. It is not known if eating fish would have similar effects.
Pancreatic insufficiency
A few preliminary reports suggest that food allergy may cause some
cases of acute pancreatitis. Food allergies identified in these cases included fish and fish
eggs. No research has investigated the possible role of food allergy in other causes of
pancreatic insufficiency.
Parasites
Undercooked fish can contain parasites.
Phenylketonuria (PKU)
A PKU diet is low in protein, providing no more than the minimum
amount of phenylalanine needed by the body. All high-protein foods, including fish, are
usually eliminated.
Photosensitivity
In a preliminary study, supplementation with fish oil for three
months reduced photosensitivity in nine of ten people suffering from polymorphous light
eruptions. It is not known if eating fish would help with this condition.
Preeclampsia
Fish oil supplementation has been proposed to lower the incidence of
preeclampsia. However, blinded trials suggest that fish oil does not reduce symptoms or
protect against preeclampsia. The effects of dietary fish consumption on preeclampsia are not
known. Supplementation with fish oil significantly reduced recurrence of premature delivery,
according to data culled from six clinical trials involving women with a high risk for such
complications. Fish oil supplementation did not prevent premature delivery of twin
pregnancies, nor did it have any preventive effect against intrauterine growth retardation or
pregnancy-induced hypertension. Fish oils should be free of contaminants, such as mercury and
organochlorine pesticides. It is not known if eating fish would have similar health
benefits.
Women who eat substantial amounts of certain types of seafood (e.g.,
swordfish, tuna) may be ingesting contaminants that
can increase the risk of brain and nervous system abnormalities in their offspring. Exposure
to mercury and polychlorinated biphenyls (PCBs) was found to be increased in relation to
maternal intake of seafood. Higher exposure to these toxic contaminants has been linked to an
increased risk of deficits in the developing brains and nervous systems of the children.
Psoriasis
In double-blind trials, fish oil and purified eicosapentaenoic acid
(EPA, one of the fatty acids found in fish oil) supplements have improved psoriasis. It is not
known if eating fish would have similar effects.
Raynaud’s disease
In a double-blind study, supplementation with fish oil for 6 or 12
weeks reduced the severity of blood-vessel spasm in people with Raynaud’s phenomenon.
Fish oil was effective in people with primary Raynaud’s disease, but not in those whose
symptoms were secondary to another disorder. It is not known if eating fish would have similar
effects.
Rheumatoid arthritis (RA)
Many double-blind trials have proven that omega-3 fatty acids in fish
and fish oil, called EPA and DHA, partially relieve symptoms of RA. The effect results from
the anti-inflammatory activity of fish oil. It is not known if eating fish would have similar
effects.
Rickets
Fish liver oil is among the few foods that contain vitamin D. Vitamin
D is required to prevent rickets, a disease of vitamin D deficiency.
Ulcerative colitis (UC)
Because ulcerative colitis is an inflammatory condition and fish oil
has anti-inflammatory activity, fish oil has been tested as a potential remedy for people with
UC. Clinical trials of fish oil for UC have yielded mixed results. It is not known if eating
fish would provide any benefits for persons with UC.
