We compared the effects of a diet in which approximately 25% of the carbohydrate was replaced by high-amylose starch with those of a similar diet high in oat bran or low-amylose starch in 23 hypertriglyceridemic subjects who were overweight mostly because of abdominal adiposity. Each diet was consumed for 4 wk in random order and in a crossover fashion. Overall, the diets were high in carbohydrate (> 55% of energy) and low in fat (< 30% of energy); the amount of resistant starch in the foods containing high-amylose starch was 17 g in women and 25 g in men. The metabolic effects of specific starches on plasma lipids, fasting and postprandial glucose and insulin profiles, and bowel function were assessed at the end of each intervention. Plasma triacylglycerols (triglycerides) were significantly lower after the oat bran diet than after the other two diets (P < 0.02). No other effects on fasting plasma lipids, glucose, or insulin were noted. However, when the high-amylose starch comprised 33% of the carbohydrate content in a test meal, there was a significant but biologically small reduction in the overall postprandial plasma insulin concentration by 17% relative to the low-amylose diet (P < 0.01). Both the oat bran and the high-amylose diet resulted in an increased frequency of bowel actions and lower fecal pH (P < 0.02) relative to the low-amylose diet. However, unlike the oat bran diet, the high-amylose diet increased short-chain fatty acid concentrations in fecal water by 32% (P < 0.001).