Dietary treatment of hyperlipidemia focuses on reducing saturated fat and dietary cholesterol. Other aspects of diet are not emphasized at present, despite growing evidence that a number of plant components decrease serum cholesterol. We therefore determined whether a combination of two plant components, vegetable protein and soluble fiber, further reduce serum lipids when incorporated into the currently advocated low-saturated-fat diet. Thirty-one hyperlipidemic men and women ate two 1-month low-fat (<7% of total energy from saturated fat), low-cholesterol (<80 mg cholesterol/d) metabolic diets in a randomized crossover study. The major differences between test and control diets were an increased amount of vegetable protein (93% v 23% of total protein), of which 33 g/d was soy, and a doubling of soluble fiber. Fasting blood samples were obtained at the start and end of each phase. On the last 3 days of each phase, fecal collections were obtained. Compared with the low-fat control diet, the test diet decreased total cholesterol (6.2% +/- 1.2%, P < .001), low-density lipoprotein (LDL) cholesterol (6.7% +/- 1.7%, P < .001), apolipoprotein B (8.2% +/- 1.2%, P < .001), and the ratios of LDL to high-density lipoprotein (HDL) cholesterol (6.3% +/- 2.0%, P = .004) and apolipoprotein B to A-I (5.4% +/- 1.5%, P = .001). A combination of vegetable protein and soluble fiber significantly improved the lipid-lowering effect of a low-saturated-fat diet. The results support expanding the current dietary advice to include increased vegetable protein and soluble fiber intake so that the gap in effectiveness between a good diet and drug therapy is reduced.