NUTRITIONAL VALUE OF FISH IN REFERENCE TO ATHEROSCLEROSIS AND CURRENT DIETARY RESEARCH By Charles Butler* ABSTRACT THERE IS MUCH IN TODAY'S NEWS ABOUT ATHEROSCLEROSIS, A DISORDER ARISING FISH AND FISHERY PRODUCTS OFFER A NUMBER OF DEMONSTRATED NUTRITIVE MERITS IN SPECIES (SPECIFIC FLAVORS AND TEXTURES), AND IN MARKET FORM SO THAT EYE AND AP RESEARCH NOW UNDER WAY WILL ACCURATELY PINPOINT WHICH OF THE UNSATURATED A SERIES OF TABLES ARE INCLUDED SHOWING THE CHOLESTEROL CONTENT OF SOME In relationship to diet, you hear much these days about arteriosclerosis, atherosclerosis, and coronary heart disease. As Samuel Johnson would say, these are "foot-and-a-half words." What do they mean? TUNA SHRIMP OYSTERS FIG. 1 Coronary heart disease is a disorder in which fatty deposits form in the arteries that supply blood to the heart. The deposits result in constriction in the artery. If the process continues and the deposits harden, the artery then becomes constricted very considerably. In later stages of the disease, a blood clot may lodge in the artery and further impede the flow of blood. Coronary thrombosis then results. SHOWS THE ADAPTABILITY OF VARIOUS TYPES OF FISH AND SHELLFISH TO DIETS. TWO VIEWPOINTS Beyond this point, you can get an argument on almost any aspect of the problem of atherosclerosis. Let's look at two of the opposing views for further background. CHIEF, BRANCH OF TECHNOLOGY, DIVISION OF INDUSTRIAL RESEARCH AND SERVICES, U. S. BUREAU OF COMMERCIAL FISHERIES, WASHINGTON, D. C. MECHANICAL INJURY: One group contends that atherosclerosis occurs more often and more markedly in areas of stress induced within the artery injured by pressure of blood flow. Such injury may sensitize the tissues to biochemical action that weakens them and allows further mechanical injury. A biochemical agent that weakens the tissues could be (1) a normal food ingredient not properly absorbed or excreted, (2) toxic products ingested or allowed to accumulate because of bodily imbalance, or (3) normally assimilable materials that for some reason build up in the blood above normal levels. CHOLESTEROL DEPOSITS: Another group contends that atherosclerosis results from cholesterol becoming abnormally deposited in the arterial walls along with other lipids (fatty materials), protein, and ultimately, minerals. Table 1 Cholesterol Content of Some Protein Foods 1/ Food Fish: Bluefish Cod Salmon, canned in oil, drained Tuna, canned in oil, drained Cheese: Size 3343 3. Content .07 .06 .07 .072 .077 Croaker Flounder Haddock Halibut 3 .11 .11 Sardines (Atlantic), canned Shrimp, dry-pack, drained .085 .18 .07 .063 Cholesterol is a part of the unsaponifiable fraction of fats and oils along with the fat-soluble vitamins A and D, squalene, and a number of the pigments or "colorbodies" of the fat. Fish oil may contain from from 1 to 2 percent of unsaponifiable matter of which 20 to 25 percent in turn may be cholesterol or about 0.2 to 0.5 percent of the total fish oil. Obviously, cholesterol is a very minor constituent of fish oils. Some foods, such as eggs, contain rather more of it. Table 1 shows the cholesterol content for a serving portion of several protein foods. Among the factors studied by the many workers in this field, that were believed might affect the cholesterol level of blood, were sex, age, racial origin, economic status, body weight, build, obesity or leanness, hormonal balance, composition of diet, and stress. The effects of these factors as measured on test animals, indicate that no conclusive statements can yet be made on any one aspect of atherosclerosis. We are, however, gaining a better concept of the problem. In May 1957, Dr. Wendall Griffith of the University of California Medical Center, while reporting to the American Medical Association, summarized the present state of our knowledge as follows: "Considerable evidence exists to show that under certain circumstances, sources of linoleic acid may lower elevated bloodserum cholesterol levels in man. The evidence favors the concept that essential unsaturated fatty acids are required for normal transport of cholesterol as lipoprotein and possibly phospholipid complexes in the circulatory system. Circumstances under which high cholesterol levels can be prevented remain to be spelled out. No valid effects of surplus dietary calories, of an experiments have yet shown the relative excess of the total dietary fat, of abnormal ratios of linoleic acid to other fatty acids in the diet, or of numerous other nutritive factors that may influence adversely the physical and chemical characteristics of fatty substances in the blood and in the walls of the vascular system. Lacking a clearcut solution for prevention of atherosclerosis, a faulty diet may be one of the causative agents. The role of dietary fat remains to be established. Meanwhile, dietary control to attain and maintain optimum body weight and the choosing of a varied diet containing adequate amounts of those foods, including fats, that are shown to have special nutritive value is indicated." ATHEROSCLEROSIS AND THE MARKETING OF FISH What are the implications of our knowledge of atherosclerosis (although admittedly inconclusive) as it applies to the marketing of fish? If there is any agreement relating to atherosclerosis, at this stage, it is that this disorder is of metabolic origin--with a deficiency, excess, or imbalance of diet possibly playing an obscure role in relation to disturbed lipid metabolism. POSSIBLE BOOMERANG: As Dr. E. Geiger of Van Camp Seafoods Laboratory cogently put it, we can suggest what does not help. He says, in substance, that attempts to exploit preliminary reports may do more harm than good. Earlier, for example, we were told to avoid such cholesterol-containing foods as eggs and the land-animal fats. Next fatfree diets were pushed. Then saturated fats were suspect. Soon the thinking veered to "essential" fatty acids as being the more important of the fats in the diet. Dr. Geiger pointedly indicated that the heart authority who early recommended against canned fish for victims of coronary disease must have regretted this recommendation when the ideas FIG. 2 FISHERY PRODUCTS POSSESS THE IMPORTANT ELEMENTS NECESSARY FOR CHILDREN'S DIETS. Unsaturated Fatty Acids in Pilchard Oils 1/ Table 2 Palmitoleic Oleic Linoleic 2452. 15 on importance of essential GOOD STRATEGY: It would seem that a good, long-range strategy would be to push aggressively the more extensive use of fish and fishery products on demonstrated nutritive merits. Some of the well-established facts are pertinent here. 1. We know that fish are an excellent source of complete and well-balanced protein, essential to optimum nutrition. 2. We know that fish are easily digested and become readily available for assimilation, even for those in convalescence, for children, or for the aged. 3. We know that fish can be prepared with all these desirable qualities, but with very low sodium content, if that feature is essential, as it may be in cases of high blood pressure. Recently, Dr. Claude Thurston of the Bureau's Seattle Labora tory found that pink salmon can be made even more desirable for this purpose by the removal of the dark meat, which he found to contain a disproportionately high amount of sodium. 4. We know that fish oils are uniquely well fortified with more of the unsaturated fatty acids than are vegetable fats or land-animal fats. There is also some evidence that fish fat is easily digested and readily used by the body tissues. Table 2 shows the distribution of the principal unsaturated fatty acids in pilchard oil. At present, those fatty acids tentatively classed as being essential include linoleic, linolenic, and arachidonic. 5. We know that fish, within the approximately 160 marketed varieties and the numerous additional market forms, can supply to the diet any degree of fat desired, whether it be that of such oily species as sablefish, pilchard, or mackerel; that of such species as the very lean cod, haddock, halibut, or shrimp; or that of the numerous intermediate group composed of such species as salmon, tuna, oysters, crab, lobster, yellow perch, or flounder. Thus, proof already is at hand showing that fish is an excellent food, regardless of the outcome of the additional studies now being conducted on the problem of atherosclerosis. It should be pointed out, in passing, that this demonstrated value of fish may be applied to the greater utilization of fish in other areas of disease or malnutrition not specifically touched on here. The well-deserved position gained for fish-liver oils as a source of vitamins A and D is not necessarily an isolated case. OUR KNOWLEDGE MUST CONTINUE TO GROW: Whatever the outcome of continuing worldwide research, we should be alert to benefit from the findings. By corollary, however, it is essential that our presently-limited knowledge of the nutritive value of fish and, specifically, of those factors of greatest importance in current dietary research must continue to grow along with the knowledge being gained in the field of competing products if we are to keep pace. Additional efforts could actually put us ahead, since we are working with products of great merit. Dr. Stare, of the Department of Nutrition, Harvard University, aptly sums up the situation for this phase of the atherosclerosis discussion, thusly: "As a final word, we should like to leave the impression that nutritional researches in this important area of health are most promising, and we are enthusiastic about them. But, we think that such enthusiasm should be directed toward further research, to get the many answers we don't have, rather than toward suggesting changes in our accustomed diets, when we aren't too sure at this time, if, or how they should be changed." FUNDAMENTAL RESEARCH AND THE SALE OF FISH This summation logically leads us into the third phase of our problem--what, specifically, is being done in our research program that will be of effective help? As was stated earlier, we know that fish oils contain a larger amount and a greater diversity of the unsaturated fatty acids than do many other food fats. This information is one of the findings of fundamental technological fishery research begun with funds provided by the Saltonstall-Kennedy Act. The elucidation of the detailed chemical structure of the fatty acids in menhaden oil is now far enough along to predict that fish oils generally possess these unique characteristics. The characterization of other principal fish oils soon will be possible, using the methods developed in this study. There is no reason to expect more than the usual minor variability among species that have a comparable oil content, such as men haden, sardines, and mackerel. For purposes of comparison, table 3 is a compilation showing the unsaturated fatty acid composition of land-animal fats and marine-animal fats and of vegetable oils. FIG. 4 FISHERY PRODUCTS ARE IDEAL FOR GERIATRIC DIETS. LIPOPROTEINS AND PHOSPHOLIPIDS: As a follow-up to a study of the physical-chemical characteristics of all commercially-produced fish oils, we now are setting up a study of the lipoproteins and phospholipids in fish oils. From statements made here, you will recall that these two phases of fat transport and metabolism in the body are believed to be a part of the atherosclerosis problem still unsolved. DEPOSITION OF CHOLESTEROL: Again, you will recall that there is the unresolved problem of the deposition of cholesterol in the body. A new project now under way will include fish-oil fatty acids of known degrees of unsaturation in the diets of miniature pigs to follow the location and extent of deposition of cholesterol in the arteries. (The metabolism of pigs has been found to be similar to that of human beings. Use of miniature pigs reduces the cost of feeding and, therefore, of experimentation.) Ultimately, the pigs will be butchered, and their arteries examined to evaluate the effects of the several diets employed. ESSENTIAL FATTY ACIDS: Another phase of this study is related again to the earlier remark about "essential" fatty acids. The diets of rats are set up (1) to throw further light on which of the several fatty acids are actually essential, (2) to determine whether their beneficial effects are available in fish oils, and (3) to point the way to the significance of these factors in human nutrition and in the related areas of human diseases. UNSAPONIFIABLE COMPONENTS: Still another phase will include the study of the values of another portion of fish oil--the unsaponifiable matter--for pharmaceutical and nutritive purposes. Certain of the unsaponifiable components of fish oil, for example, have been vaguely referred to in the scientific literature as being |