Nutrition Recommendations for the General Population: Where Is the Science?

Abstract

During the 1990s dietary guidelines for the US and many other countries promoted a diet low in fat and high in “complex” carbohydrates. However, there was little evidence then that such a diet would promote health and reduce risk of chronic disease, and subsequent data have not supported benefits for cardiovascular disease, cancer, or weight control. Instead, the combination of controlled feeding studies of intermediate risk factors and prospective epidemiologic studies has indicated that the type of dietary fat and dietary carbohydrate have major impacts on risks of these diseases. Specifically, higher intake of trans fatty acids has adverse effects on blood lipids and inflammatory factors, and has also been associated with greater risks of coronary heart disease and type 2 diabetes. In contrast, both types of studies have indicated beneficial effects of unsaturated fats, especially polyunsaturated fats. The replacement of saturated fat with carbohydrates has little effect on the ratio of serum total to HDL cholesterol, and is minimally associated with risk of heart disease. Similarly, higher intake of refined starches and sugar, represented by dietary glycemic load, has adverse effects on blood lipids and inflammatory factors and is related to higher risks of coronary heart disease and type 2 diabetes. Conversely, higher consumption of whole grains is related to lower risks of these diseases. Regrettably, this evidence has yet to be translated clearly into dietary guidance for many populations.