Margaret J. Albrink

Insulin resistance in hyperglyceridemia

The response of the plasma FFA and the blood glucose to intravenous insulin injection, 0.1 unit/Kg. body weight, was measured in 8 normal persons, 9 obese persons, 12 persons with fasting hyperglycemia, and 19 persons with hyperglyceridemia. The rate of immediate decline in the concentration of blood glucose was correlated with the plasma triglyceride concentration (p < 0.05) and with the fasting plasma cholesterol (p < 0.02). The degree of hypoglycemia was inversely related to the degree of obesity (p < 0.05). The blood glucose response to insulin was significantly delayed and prolonged with advancing age. The blood glucose was higher at 15 minutes and lower at 180 minutes after insulin in older subjects. The resistance to exogenous insulin in hyperglyceridemic, obese and elderly persons is considered further evidence of some common etiologic factor(s) in obesity, diabetes, and atherosclerosis.

Dietary fiber, plasma insulin, and obesity.

The relationship between obesity, insulin resistance, and hyperinsulinemia is briefly reviewed. The possibility is considered that excess insulin secretion is the cause rather than the result of insulin resistance and obesity. Glucose administration is one of the most frequently studied of those factors known to stimulate insulin secretion. Much less well documented is the fact that meals of equal protein, fat, and carbohydrate content may cause different responses of plasma glucose and insulin. An experiment is reported in which the effects of a high-carbohydrate, high-fiber meal administered to seven healthy young adults were compared with the effects of a meal equally high in carbohydrate but composed largely of glucose in liquid formula form. The high-fiber meal caused an insulin rise less than half that caused by the liquid formula meal although the plasma glucose response to the two meals was not significantly different. The hypothesis is proposed that a high-carbohydrate, fiber-depleted diet, high in simple sugars, by repeatedly stimulating an excessive insulin response, may lead to insulin resistance and obesity in susceptible individuals and may play a role in the common occurrence of obesity in industrialized societies.

Serum Lipids, Diet, and Cardiovascular Disease

Elevated serum cholesterol value is more atherogenic, although less common, than elevated serum triglyceride level, but both are equally important risk factors in atherosclerotic cardiovascular disease. Unfortunately, the effect of dietary manipulation on cholesterol is small and on triglyceride, uncertain.

Dietary Fiber, Sucrose, and Serum Lipids

The best known effects of diet on serum cholesterol were elaborated during a series of experiments on adult men carried out by Keys and others during the 1960s (Keys et al., 1965; Anderson et al., 1973). The conclusions reached from these experiments were that saturated fat was the most powerful cholesterol-raising dietary component, dietary cholesterol having a small additional effect, and polyunsaturated fat having a cholesterol-lowering effect about half as effective as the cholesterol-raising effect of saturated fat. Pectin, certain vegetables, and plant sterols were also found to have a cholesterol-lowering effect. Most of these studies were carried out using diets of usual Western composition, i.e., moderately high in saturated fat and cholesterol. The amount and type of carbohydrate was found to have little or no effect. When an effect was found, sucrose and other sugars had a cholesterol-raising effect compared to starch. By and large, the type of carbohydrate was thought to be of little significance compared to the large effect of type of fat (McGandy et al., 1967). So strong is this impression that in many studies the type of carbohydrate is not even stated.

Diabetes as a Risk Factor for Arteriosclerotic Vascular Disease

The well known association between diabetes and arteriosclerotic cardiovascular disease (ASHD) suggests that impaired glucose tolerance is a major risk factor for ASHD. The association can be seen from, the point of view of the diabetic, who has increased vascular disease when compared to non-diabetics, or from the point of view of the patient with ASHD, who has increased frequency of diabetes when compared with persons without vascular disease.

Effect of Dietary Fiber on Lipids and Glucose Tolerance of Healthy Young Men

Epidemiologic evidence supports a protective effect of dietary fiber against diabetes (Trowell 1974), obesity (Trowell 1975), and coronary artery disease (Trowell 1972). However, the diet of peoples consuming large amounts of fiber is likely to differ in other important respects, i.e., to be high in carbohydrate, low in fat and cholesterol, and low in sugars. The effect of dietary fiber must be examined in the context of these other variables. Since other chapters in this book deal with the effect of fiber on diabetes (Anderson, Chapter 14) and lipids (Story and Kelley, Chapter 20), these will be only briefly discussed here. The chief emphasis will be on the effect of diet on glucose tolerance of normal young men. Young women appear to be immune to some of the effects of very high carbohydrate diets (Reiser et al., 1979a). Our own studies have therefore been confined to young men.