By John McDougall MD

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 largely mythical1

Fish Fat

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).

Fish Cholesterol

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 Protein

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

Infectious Agents

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.

Environmental Contaminants

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

I wrote this article just before leaving to go SCUBA diving on the Great Barrier Reef in Australia. 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.

Full citations for this article can be found online at http://www.nealhendrickson.com/mcdougall/030200.htm.