The National Cholesterol Education Program has suggested people with insulin resistance (IR) and the Metabolic Syndrome (MetS ) avoid diets high in carbohydrates (CHO). This recommendation is based on many studies showing high-CHO diets tend to raise serum triglyceride levels, increase the proportion of small dense LDL particles, and lower HDL levels – known collectively as dyslipidemia. People with IR, the MetS, and Type 2 diabetes mellitus (DM) are more CHO sensitive than those without IR and so are more prone to dyslipidemia and atherosclerosis when consuming a low-fiber, high-CHO diet and are inactive and fail to lose weight.By contrast, epidemiological studies of people living in places where high-fiber, high-CHO diets are the norm, such as rural China, rarely develop type 2 DM and have far less atherosclerosis than Americans. Indeed, as their diets Westernize and become lower in percent of CHO and fiber, and higher in fat and animal products, the prevalence of type 2 DM and atherosclerotic diseases increase dramatically.No doubt the increasing body weight and reduced activity levels often seen in human populations adopting a more Westernized diet both play a role in promoting IR, the MetS, Type 2 DM, and the accompanying dyslipidemia. However, Americans who come to the Pritikin Longevity Center and adopt a high-CHO diet often experience marked drops in insulin levels and serum triglyceride levels in a week or two and long before much body fat is lost. How can we explain what on the surface appears as conflicting data?Muscles May Be Key To Dyslipidemia of High-CHO DietsA recent article by Dr. Gerald Shulman1 sheds light on the important role of skeletal muscle in the development of dyslipidemia seen in people with the MetS. Dr. Shulman screened 400 young, healthy, normal-weight but sedentary subjects. He selected half the subjects who had normal glucose tolerance and insulin sensitivity and the other half had reduced insulin sensitivity (or were IR). Despite differences in insulin sensitivity, the two groups had a similar amount of abdominal fat. Both groups of subjects were then fed a standard liquid meal or the same meal enriched with added sucrose. Compared to the insulin sensitive subjects, those with IR in their skeletal muscle responded to the higher CHO diet by increasing fat synthesis from CHO in their livers while the muscles of the insulin sensitive subjects responded by synthesizing more muscle glycogen. The authors state “These data demonstrate that IR in skeletal muscle, due to decreased muscle glycogen synthesis, can promote atherogenic dyslidemia….”Research has shown that exercise reduces muscle glycogen stores. Until the muscle glycogen is replenished, the muscle cells remain far more sensitive to insulin.Last month we discussed how diets high in fructose tend to raise serum triglyceride levels by delaying the clearance of fat-rich lipoprotein particles from the blood stream. The authors stated that “The similarity of fructose-induced hypertriglyceridemia to certain forms of endogenous hypertriglyceridemia is also suggestive of potential cardiovascular risk.”2 Because fructose goes primarily to the liver for metabolism in sedentary individuals, instead of to the muscles, it is more likely to stimulate fat synthesis in the liver.Bottom Line:Those genetically prone to develop IR should remain active, thin, and limit their intake of refined CHO and especially those containing fructose or they will likely develop a more atherogenic blood lipid profile. By contrast, a diet high in unrefined CHO and limited in fructose when combined with regular exercise can promote weight loss, improve insulin sensitivity, and reverse the dyslipidemia associated with the MetS and Type 2 DM.By James J. Kenney, PhD, RD, FACNReferences1. The role of skeletal muscle insulin resistance in the pathogenesis of the metabolic syndrome. www.pnas.org2. Am J Clin Nutr 2007;85:1511-20Focus on Diet and ExerciseExercise every dayExercising every day is important for your health. The Dietary Guidelines for Americans says that 30 minutes a day is essential for good health. But 60-90 minutes a day is optimal especially if you need to lose weight or maintain weight loss. Now we can see from this study that exercise helps you reduce glycogen stores and that during the period of time when your body refills those, it helps the cells become more sensitive to the insulin that regulates blood sugar. Additionally, the energy you consume will go back into your muscle glycogen stores instead of directly to the liver to produce more cholesterol and other undesirable lipids that clog your arteries.Eat a diet that is high in fiber and low in fatEat more whole grains, vegetables, legumes and fruits and less fat and meat.A diet higher in carbohydrate will likely have more fiber, and certainly less saturated fat than a diet high in fat. It is also likely to have fewer calories when it is low in sugar and higher in fiber; this helps you consume fewer calories over the long term.