Nutritional Background

The Big Heart Disease Lie

Chinese Treatments for Cardiovascular Disease

Get Instant Access

Up to the 1970s, the issue of fat in the diet and its effect on health was hardly considered, except in cases of obesity where an overall reduction in energy was recommended. Reduced-calorie foods, therefore, were mainly a small niche market directed toward a minority of consumers who were obese or otherwise wished to lose body weight, and thus were interested in reducing their calorie intake. Moreover, the nutritional advice for weight loss at that time tended to focus more on carbohydrates than on fat, despite the fact that fat is the most dense source of calories (9 kcal/g vs. 4 kcal/g for carbohydrates and proteins). By the 1980s, a radical change had taken place in consumers' attitudes. This can be traced directly to developments in the science of nutrition, and to a better understanding of the relationships between diet and health, which, in the developed countries, led to significant changes in official nutritional recommendations.

In the U.K., this reevaluation was brought to public attention by the publication of two major reports which were, respectively, the so-called "NACNE Report," produced in 1983 by the National Advisory Committee on Nutrition Education (NACNE, 1983), and Diet and Cardiovascular Disease, known as the "COMA Report," produced in 1984 by the Committee on Medical Aspects of Food Policy (COMA) (Department of Health and Social Security, 1984). The recommendations of the NACNE Report were oriented toward a diet that would benefit the nation's health generally, whereas those of the COMA Report were intended more specifically to prevent coronary heart disease (CHD). The major recommendation of both reports was to reduce the intake of fat from the 42% at the time to 34% (NACNE) or 35% (COMA) of total food energy in the diet. Furthermore, they recommended that the intake of saturated fat should be reduced to 10% (NACNE) or 15% (COMA) of food energy. They also advised a reduction in salt intake and increased consumption of complex carbohydrates and dietary fiber. The recommendations were widely debated and given extensive publicity in the media. The reports, therefore, had a significant impact on increasing consumer awareness of the relationship between diet and health.

Similar developments took place in the United States. In 1988, the U.S. Surgeon General published a major review on nutrition and health. It proposed that energy in the diet derived from fat should be reduced to 30% (USDHHS, 1988). A further review carried out on behalf of the Food and Nutrition Board of the National Academy of Sciences (NAS, 1989) provided a broad scientific consensus for the U.S. government report: Nutrition and Your Health: Dietary Guidelines for Americans (USDA/USDHHS, 1990). The recommendations of the Surgeon General were supported by a number of health-related organizations such as the American Heart Association and the American Cancer Society, on the basis that the incidence of coronary heart disease and cancer would be reduced by decreasing the amount of fat and cholesterol in the diet (Przybyla, 1990). By the end of the 1980s, the governments of most developed countries in the western hemisphere had drawn up nutritional recommendations advising consumers to reduce fat intake from the prevailing level of 40 to 49% (depending on the country) to approximately 30% of total energy in the diet. In most cases, the goal was set to reduce fat consumption to the recommended level by the year 2000.

In 1992, the U.K. government issued a set of targets to reduce the incidence of coronary heart disease (CHD) in the White Paper The Health of the Nation: A Strategy for Health in England (Department of Health, 1992). One target was to reduce the number of premature deaths (in people under 65 years old) by 40% by the year 2000 (using 1990 figures as a baseline). Dietary targets were set on the basis of the recommendations given in a second report by the Committee on Medical Aspects of Food Policy on dietary reference values (Department of Health, 1991), which, in the case of fat, was that it should not exceed 35% of total food energy in the diet (the same as in the COMA Report of 1984), with the consumption of saturated fatty acids no more than 11% of total food energy (4% lower than in the COMA 1984 Report). At the time, the average fat intake of the British population was at 40% of total food energy and 17% of food energy was derived from saturated fats.

It would appear, therefore, that relatively little progress has been made in achieving the targets suggested by NACNE and COMA in the mid-1980s, despite the concurrent increase in sales of low-fat foods (see Chapter 3). Dietary fat in the American diet is considered to account for 36% of energy content (Buss, 1993), indicating that greater progress in adopting dietary recommendations has been made on average compared with the U.K. However, the analysis of a nutritional survey among British adults (Ministry of Agriculture, Fisheries and Food, 1994a) found that 10% of the adult population had less than 35% of their food energy derived from fat, thus indicating a significant segmentation in consumers' response to nutritional guidelines. The extent to which consumers might be compensating for low-fat intakes when consuming low-fat products remains to be established (see Chapter 2). If that is so, a further point of interest would be to find out the extent to which the process was a physiological, as opposed to a psychological, response.

Meanwhile, scientific research oriented toward understanding better the relationship between diet and health was a major growth area. One noteworthy study was that carried out by Watts et al. (1992), which was the first to support the hypothesis that a low-fat diet can actually prevent narrowing of the coronary arteries.

More recently, the complex relationship between diet and heart disease has been reviewed by Ashwell (1993). While it is acknowledged that CHD is a multifactorial disorder, it is considered that diet is one component which can be modified by everybody. The report concludes that the development of CHD can be viewed simplistically as a three-stage process starting from an initial arterial injury that is followed by atherosclerosis and the formation of a blood clot which eventually blocks the artery thus causing a heart attack. Each stage can be influenced by several physiological conditions (e.g., high blood pressure, high levels of plasma lipids, and low levels of antioxidants), and these can be affected by controllable factors, including diet. A "round table model" was derived to elucidate the relationships between the stages of the disease, physiological conditions, and dietary components. The level and composition of the fats consumed is shown to be of importance at all three stages, and overall the dietary advice given includes reduction of fat intake through the consumption of low-fat products and increased intake of fish oils.

There is a general consensus that the type of fat consumed is of importance in relation to the aetiology of chronic diseases. In particular, increasing the proportion of polyun-saturated fats in the diet, e.g., through the consumption of oil-rich fish, appears to play a protective role against CHD, as evident from the fact that Eskimos subsisting on a high fat diet based on fish are less prone to heart disease and thrombosis than people on high fat diets based more on saturated fats (Dyerberg et al., 1978; Dyerberg and Bang, 1979). The crucial factor, it seems, is the effect of consumption of different fats on the proportion of serum cholesterol associated with high-density lipoproteins (HDL cholesterol) vs. that associated with low-density lipoproteins (LDL cholesterol). Thus, consumption of fats favoring a higher proportion of HDL cholesterol and/or a lower proportion of LDL cholesterol, such as diets in which a higher proportion of fats consumed are polyunsat-urated (e.g., from fish or certain vegetable sources) or monounsaturated (e.g., from olive oil), tend to reduce risk from CHD (helped also by the consumption of dietary antioxidants such as Vitamin E, which blocks the oxidative modification of LDL). Conversely, a higher proportion of saturated fats in the diet tends to increase the ratio of LDL cholesterol to HDL cholesterol, thus increasing risk of CHD (Grundy, 1994). However, it is now evident that different saturated fats and dietary sources of saturated fat vary in their influence on the level of LDL cholesterol (Richardson, 1995). For instance, butter and other dairy products, which are high in myristic acid (14:0), appear to strongly increase levels of LDL cholesterol, whereas beef fat, containing palmitic (16:0) and stearic (18:0) acids does so to a lesser extent, and cocoa butter, with a high proportion of stearic acid, increases LDL cholesterol only slightly.

In addition, there has been increasing concern and controversy on the consumption of trans fatty acids in relation to health (Mensink and Katan, 1990; Grundy, 1994). Epidemiological data (Willett et al., 1993) have shown a positive association between higher intakes of trans isomers (derived from partially hydrogenated vegetable oils) and the risk of CHD. Wahle and James (1993) have published a comprehensive review on this topic, and concluded that some evidence exists to suggest that trans fatty acids have deleterious effects on blood plasma lipids (i.e., they tend to increase the levels both of LDL and HDL cholesterol present, as well as the concentration of lipoprotein a (which is a genetic marker for CHD acting as an independent risk factor). However, other studies have given conflicting results, so that the issue at present remains unresolved, with a majority of studies implicating trans fatty acids. Clearly, more research is required on this issue. Meanwhile, the FAO/WHO Expert Committee concluded that the effects on plasma cholesterol concentrations exerted by trans unsaturated fatty acids are similar to saturated fatty acids and hence they have recommended that in order to improve plasma lipid profile, the intake of trans fatty acids should be cut back when the intake of saturated fats is reduced (Sanders, 1995).

In short, while our knowledge of the relationship between diet and health continues to progress, the adoption of dietary recommendations derived from that knowledge consistently lags behind. It is possible that a better consumer response could be achieved primarily by more extensive nutritional education and secondly, by improving the quality of existing or new low-fat foods. On the other hand, it is likely that as the market matures, with increasing availability of low-fat foods to a wider range of social strata, consumers might more readily adhere to the guidelines regarding fat consumption.

Was this article helpful?

0 0
Low Carb Diets Explained

Low Carb Diets Explained

You can burn stored body fat for energy and shed excess weight by reducing the carbohydrate intake in your diet. Learn All About The Real Benefits of Low Carb Diets And Discover What They Can Really Do To Improve The Quality Of Your Life Today.

Get My Free Ebook

Post a comment