Based on evidence from tightly-controlled, short-term clinical trials that showed that HDL levels fell and triglyceride (TG) levels rose when dietary carbohydrate replaced fat, the National Cholesterol Education Program’s Adult Treatment Panel III recently recommended that people who have the metabolic syndrome, also known as syndrome X, should consume a diet with 35 percent fat instead of a low-fat diet.Because excessive body fat stores play a major role in the development of the metabolic syndrome, short-term studies in which calorie intake and body weight are tightly controlled provide a dubious basis upon which to recommend the addition of more fat to the diet because they are not a model for real life. People eat until they feel full. For this reason, I have argued that a very-low fat, high-fiber diet consisting largely of minimally processed fruits, vegetables and whole grains would likely prove best for reducing the risk of heart disease in patients with the metabolic syndrome in large part because it would promote weight loss without chronic hunger.1 The type of high-carbohydrate foods used in short-term studies showing the presumably adverse metabolic effects of high-carbohydrate diets (relative to higher-fat diets) tended to be high in refined grains and sugar. Diets higher in sugar and refined grains are less likely to promote weight loss and more likely to lead to adverse effects on blood lipids than a diet higher in complex carbohydrates.A new study examined the long-term effects of a low-fat, high-complex-carbohydrate (LF-CC) diet and a low-fat, high-sugar (LF-HS) diet to a higher-fat control diet.2 After six months, those on the higher-fat control diet had gained an average of 2.3 pounds. Those on the LF-HS diet lost a little more than1/2 pound, but those on the LF-CC diet lost an average of 9.4 pounds. This study found higher TG levels on the LF-HS diet, but not on the LF-CC diet compared to the higher-fat control diet. HDL levels were similar on all 3 diets and total and LDL cholesterol were lowest on the LF-CC diet.The authors of this study conclude “A low-fat, (high-complex carbohydrate) diet in overweight individuals led to moderate weight loss and some improvement in serum cholesterol.” The results of this study also suggest that neither a higher-fat diet nor a low-fat diet, high in sugar, is desirable for patients with the metabolic syndrome.1. CFFH Newsletter 2001;July/August:852. Am J Clin Nutr 2002;75:11-20