Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
SUMMATION AND RECOMMENDATIONS Fats are the most concentrated energy sources in man's diet. They provide the essential fatty acids and important amounts of vitamins A, D, and E, facilitate their absorption, and contribute to palatability and satiety. Most Americans obtain about 40 per- cent of their calories from fat, more of which, in recent years, has been from oils than from solid fats. In the conversion of a vegetable oil to a solid fat, partial hydrogenation leads to formation of isomers of the unsaturated fatty acids and decreases the essential fatty acid content. No obviously harmful nutritional effects of such processing have been demonstrated, although further studies of the effects of these or other possible changes caused by processing are needed. A large amount of information has accumulated relating dietary fats to the etiology of human atherosclerosis and its complications, particularly coronary artery disease. As yet, the causes and course of development of atheroma and its relation to coronary heart disease in man are imperfectly known. Disorders of fat transport or metabolism or both certainly participate, but are not the only factors. Heredity is involved in individual suscepti- bility. Disorders of blood flow and blood clotting are implicated in atheroma formation in addition to contributing to the fatal complications of the disease. Evidence to support the concept that increased plasma con- centrations of cholesterol are atherogenic is considerable but not conclusive. The type and quantity of dietary fat and the amount of cholesterol eaten influence the cholesterol concentration in the blood. Fats high in saturated fatty acids support a somewhat higher plasma cholesterol concentration than do those richer in polyunsaturated fatty acids. Many, but not all, population studies indicate that diets high in fat, among other nutrients, are cor- related with higher concentrations of plasma cholesterol and with increased prevalence of cardiovascular disease. However, proof of a causal relationship is lacking. In the majority of the adult population the concentration of plasma cholesterol can usually be reduced by increase in the quantity of polyunsaturated fat in 42
Summation and Recommendations the diet at the expense of saturated fat. That this degree of re- duction in plasma cholesterol is beneficial is still uncertain. Increased plasma triglyceride concentrations, not necessarily dependent upon the plasma cholesterol, have recently been related to atherosclerosis. Triglycerides in the plasma do not respond to dietary changes in a manner identical with that of chol- esterol. In some individuals, replacement of dietary fat with carbohydrate causes plasma triglycerides to rise while chol- esterol falls. Caloric excess, regardless of the form, may elevate plasma triglyceride as well as cholesterol concentrations. Thus, in spite of the large amount of information accumulated in recent years about atherosclerosis and its pathogenesis, many gaps in knowledge remain. Results of recent studies, while valuable and thought provoking, do not provide sufficient data for firm recommendations for radical dietary changes. The attractiveness and availability of rich or fatty foods, how- ever, place the American consumer in danger of overnutrition and dietary imbalance. The Food and Nutrition Board considers that, for many Americans, moderate reduction in total fat intake and some substitution of polyunsaturated for saturated fat may be indicated. The degree to which this is done must be judged on an individual basis and, in adjustment of the diet, other changes in caloric and nutrient intake must be taken into consideration. The food industry, communication media, and official regulatory agencies, meanwhile, can be powerful constructive forces: (a) in prevention of obesity by making known the importance of exercise and the restriction of calories after adult years are attained; (b) by restraining exaggerated claims that particular foods or classes of foods are necessary daily in large quantities for health; and (c) by clearly labeling the composition of packaged foods and those promoted in advertising. Until we learn more about which fats are desirable nutritionally, the Board recommends that the American consumer should partake of the foods that make up a varied, adequate, and not overly rich diet and maintain a normal body weight by judicious control of caloric intake and by daily exercise. 43