Fish is Not Health Food
By: John McDougall M.D.
(While you read this letter, picture me swimming at the
Great Barrier Reef in Australia)
Many health professionals and scientists are
recommending fish to improve your health and especially, to reduce your
risk of suffering from heart disease. Japanese are the most-recognized
example of a fish-eating population enjoying a low incidence of diseases
common to Americans (heart disease, breast cancer, diabetes, etc.), and a
trim appearance. Plus, people living in Japan have the longest life
expectancy of any country in the world. But, I believe these advantages
are in spite of the fish, rather than because of the fish. Japanese are
healthy primarily because they eat a diet based on rice with lots of
vegetables – fortunately for them; they eat fish only as a condiment.
A Muscle is a Muscle
Fish is the muscle of a cold-blooded, animal with fins
and gills. The major components of fish are fat and protein. There is no
carbohydrate, no dietary fiber, or no vitamin C in fish. Because many fish
are high on the food chain they are highly contaminated with environmental
chemicals – it is not unusual to read in the newspaper that certain kinds
of fish, such as swordfish, tuna, or shark, contain sufficient levels to
be considered a health hazard. For example, because of their high content
of mercury, the Food and Drug Administration (FDA) has advised women who
are pregnant or plan to become pregnant to not eat swordfish, king
mackerel, tile fish, shark, or fish from mercury contaminated areas.
The advantages of fish over beef, chicken or pork are
Fish is high in fat – often 60% of the calories come
from fat. This fat is effortlessly incorporated into a person’s body fat –
contributing to the risk of obesity. Fish fat is usually associated with a
low risk of cancer. However, there is considerable evidence that fish fat
(omega-3 fat) will increase a person’s risk of cancer and also will
increase the risk of metastasis (spread of cancer to other parts of the
body).2-5 Fish fat is known to paralyze the actions of insulin and
increase the tendency for high blood sugars and eventually diabetes, known
to suppress the immune system, and known to increase the tendency for
serious bleeding (see below under fish oil supplements).
Like all animal products, fish are high in cholesterol.
Based upon a weight of 100 grams, mackerel contains 95 mg of cholesterol,
haddock 65 mg, tuna 63 mg, and halibut 50 mg. This compares to beef at 70
mg, chicken 60 mg, and pork at 70 mg.1 However, when the comparison is
made based on calories, fish (50 mg/100 calories) is much higher in
cholesterol than pork (24 mg/100 calories), beef (29 mg/100 calories), or
chicken (44 mg/100 calories).1 Comparisons based upon calories are much
more relevant because we eat our diet based upon calories (a 2000 calories
diet) rather than based on the weight of the food (a 5 pound diet).
Feeding fish to people, instead of beef, pork or chicken, causes
predictable increases in their blood cholesterol to levels that are
virtually the same.6
Fish is high in animal protein and the kinds of protein
that make up fish are very acidic in nature. The high acid load caused by
the ingestion of fish results in bone loss, which eventually leads to
osteoporosis.7 Eskimos are among the highest consumers of fish on Earth;
they also have the highest rates of osteoporosis of any people on our
planet. After the age of 40 years, Eskimos of both sexes have from a 10%
to 15% greater bone loss than do whites in the US of the same age.8 The
Eskimos consume up to 2,500 mg of calcium a day, mostly in the form of
fish bones – this large calcium intake is offset by the high protein
content (250 to 400 grams a day) – much of this coming from fish.
I have heard it said that the negative effects of
protein on bone health are only caused by synthetic mixtures of proteins
devised in the laboratory, and are not caused by the real foods that
people eat, such as chicken, turkey, beef or fish. People making such
statements fail to thoroughly review the scientific literature (and by no
coincidence, most are advocates of high-protein diets).
To support their claim of no effect of whole animal
foods on bone loss they will quote the work of Herta Spencer from the mid
1970s. She published 2 often-sited studies on the subject – one was paid
for by the National Dairy Council9 and the other by the National Livestock
and Meat Board.10 Her work has been rightly criticized because close
scrutiny reveals areas of serious inconsistency. For example, in the study
paid for by the National Dairy Council,9 she used inappropriate subjects
and reported conclusions in contrast to her results. Of the six subjects
in the study, one had osteoporosis and the urinary calcium so low as to
suggest calcium malabsorption. Another subject carried a diagnosis of
hypercalcuria (very high levels of calcium in the urine), making his data
invalid. Of the remaining four subjects, three subjects did experience
increased calcium loss during the high protein diet.11
Studies on human subjects using whole foods, such as
beef, chicken and turkey have produced negative calcium balances of 77
mg/day.12 In another study, the addition of 5 ounces of skipjack tuna a
day (34 grams of animal protein) increased the loss of urinary calcium by
23%.13 Furthermore, scientific evidence shows that the body does not
adjust (compensate) with time while on high protein diets, and the losses
continue for as long as the diet is high in animal protein.14
In the United States of America, seafood ranked third on
the list of products which caused food-borne disease between 1983 and
1992.15 Several illnesses are a result of toxic algal blooms; for example,
the most commonly reported marine toxin disease in the world is ciguatera
– associated with consumption of contaminated reef fish such as barracuda,
grouper, and snapper. There are about 20,000 cases world-wide. Ciguatera
presents primarily as diarrhea, abdominal cramps, vomiting, paresthesias,
pain in the teeth, pain on urination, blurred vision, arrhythmias, and
heart block Another common problem from fish is Scombroid poisoning. This
type of food intoxication is caused by consuming scombroid and scombroid-like
marine fish species that have begun to spoil with the growth of certain
types of bacteria. Fish of the Scombridae family are tuna and mackerel.
Fish eat other fish that eat plankton and algae, which
are contaminated with environmental pollutants. Because these chemicals
are attracted and concentrated in the fat of the fish, they become even
more concentrated as the chemicals move up the food chain, by a process
known as biomagnification. The fish most heavily laden with chemicals are
those such as the tuna, swordfish and shark, which are predators of
smaller sea life.
Unfortunately, those most affected by all this
contamination are the ones highest on the food chain – our unborn and
breast-feeding children, living off of their mother. Polychlorinated
biphenyl exposure (PCB) of children born to women who had eaten relatively
large quantities of Lake Michigan fish resulted in poorer intellectual
function of the children, compared to other children, shown by lower
scores on a preschool IQ test, and poorer verbal IQ and reading
comprehension at 11 years of age.17
Mercury Contamination and Heart Disease:
Methylmercury (MeHg) is a global environmental problem
and is listed by the International Program of Chemical Safety as one of
the six most dangerous chemicals in the world's environment. A recent
article in the New England Journal of Medicine warned that many fish
contain such high levels of mercury that they may actually increase your
risk of a heart attack.18 In this study, toenail clippings from men with a
history of a previous heart attack provided evidence of the person’s
accumulation of mercury. Those with high mercury levels had more than
double the risk of a heart attack compared with those who had low levels.
Mercury is known to be toxic to the nervous system and
kidneys, but long-term exposure may also accelerate the development of
arthrosclerosis (hardening of the arteries) by promoting free radical
damage to the arteries. Free radicals are highly reactive species of
common substances, such as fats and LDL-cholesterol, which donate
electrons to tissues and cause severe damage leading to many common
diseases. Fish can be a major source of mercury in a very toxic form
called methylmercury. This substance may counteract all the hypothesized
benefits of omega-3 fats on prevention of heart disease.
Fish Oil Supplements
Unless they have been specially processed to remove
cholesterol, fish oils contain large amounts of cholesterol and will raise
the blood cholesterol of people. Even when the fish oil is purified of
cholesterol, the omega-3 fat itself will cause the LDL-bad cholesterol to
rise.19,20 The final results are published in a study on the effects of
fish oil on artery closure, where the authors concluded, “Fish oil
treatment for 2 years does not promote favorable changes in the diameter
of atherosclerotic coronary arteries.”21
To get the cholesterol lowering effects of fish oil you
need to consume about 2.5 to 3.5 ounces daily, and that represents 675 to
900 extra calories daily.1 Fish fat is easily stored and I have seen
patients of mine gain 5 pounds when they added fish oil to their “heart
disease prevention program.”
Furthermore, fish oils suppress the immune system, which
can promote cancer and increase susceptibility to viral infections; and
can cause severe bleeding.22.23 Fish fat also inhibits the action of
insulin, thus increasing a person’s tendency to suffer from diabetes.24
Our Future and that of the Poor Fish
As you are reading this article, I want you to know, I
am SCUBA diving on the Great Barrier Reef in Australia (February 2003). I
love fish – I love to watch them and I love to photograph them, but I do
not like to kill or eat them. I am very concerned that fish, in too many
minds, has become “health food.” It is not healthy for humans to eat and
it is certainly not healthy for the fish. I have shown my children the
beauty of the oceans on our many adventures to Costa Rica, Panama, Hawaii
and the Cayman Islands. I worry that my children will not have the
opportunity to show their children the same beauty -- unless we start
telling the truth about fish.
1) J Pennington. Bowes & Church’s Food Values of Portions Commonly
Used. 17th Ed. Lippincott. Philadelphia- New York. 1998.
2) Griffini P. Dietary omega-3 polyunsaturated fatty acids promote
colon carcinoma metastasis in rat liver. Cancer Res. 1998 Aug
3) Klieveri L. Promotion of colon cancer metastases in rat liver by
fish oil diet is not due to reduced stroma formation. Clin Exp Metastasis.
4) Young MR. Effects of fish oil and corn oil diets on
prostaglandin-dependent and myelopoiesis-associated immune suppressor
mechanisms of mice bearing metastatic Lewis lung carcinoma tumors. Cancer
Res. 1989 Apr 15;49(8):1931-6.
5) Coulombe J. Influence of lipid diets on the number of metastases and
ganglioside content of H59 variant tumors. Clin Exp Metastasis. 1997
6) Davidson MH. Comparison of the effects of lean red meat vs lean
white meat on serum lipid levels among free‑living persons with
hypercholesterolemia: a long‑term, randomized clinical trial. Arch Intern
7) Barzel US, Massey LK. Excess dietary protein can adversely affect
bone. J Nutr. 1998;128:1051‑3.
8) Mazess R. Bone mineral content of North Alaskan Eskimos. Am J Clin
Nutr. 1974 Sep;27(9):916-25.
9) Spencer H. Effect of a high protein (meat) intake on calcium
metabolism in man.
Am J Clin Nutr. 1978 Dec;31(12):2167-80.
10) Spencer H. Further studies of the effect of a high protein diet as
meat on calcium metabolism. Am J Clin Nutr. 1983 Jun;37(6):924-9.
11) Marcus R. The relationship of dietary calcium to the maintenance of
skeletal integrity in man-an interface of endocrinology and nutrition.
Metabolism. 1982 Jan;31(1):93-102.
12) Cummings J. The effect of meat protein and dietary fiber on colonic
function and metabolism. I. Changes in bowel habit, bile acid excretion,
and calcium absorption.
Am J Clin Nutr. 1979 Oct;32(10):2086-93.
13) Robertson W. The effect of high animal protein intake on the risk
of calcium stone-formation in the urinary tract. Clin Sci (Lond). 1979
14) Allen L. Protein-induced hypercalciuria: a longer term study. Am J
Clin Nutr. 1979 Apr;32(4):741-9.
15) Lipp EK. The role of seafood in foodborne diseases in the United
States of America.
Rev Sci Tech. 1997 Aug;16(2):620-40.
16) Aguilar A. Geographical and temporal variation in levels of
organochlorine contaminants in marine mammals. Mar Environ Res. 2002
17) Jacobson JL. Association of prenatal exposure to an environmental
contaminant with intellectual function in childhood. J Toxicol Clin
18) Guallar E. Mercury, fish oils, and the risk of myocardial
infarction. N Engl J Med. 2002 Nov 28;347(22):1747-54.
19) Harris W. Effects of a low saturated fat, low cholesterol fish oil
supplement in hypertriglyceridemic patients. A placebo-controlled trial.
Ann Intern Med. 1988 Sep 15;109(6):465-70.
20) Wilt TJ. Fish oil supplementation does not lower plasma cholesterol
in men with hypercholesterolemia. Results of a randomized,
placebo-controlled crossover study. Ann Intern Med. 1989 Dec
21) Sacks F. Controlled trial of fish oil for regression of human
coronary atherosclerosis. HARP Research Group. J Am Coll Cardiol. 1995
22) Calder PC. Polyunsaturated fatty acids, inflammation, and immunity.
23) Clarke J. Increased incidence of epistaxis in adolescents with
familial hypercholesterolemia treated with fish oil. J Pediatr. 1990
24) Hendra TJ. Effects of fish oil supplements in NIDDM subjects.
Diabetes Care. 1990 Aug;13(8):821-9.