Epidemiologic studies of cardiovascular mortality rates in different countries have suggested that dietary fiber may play a protective role. Within a similar population, a large intake of fiber is associated with a lower relative risk of death from coronary heart disease. Dietary fiber may be separated into at least two types: insoluble, which includes cellulose, hemicellulose, and lignin; and soluble, including pectin and gums. Laxative effects appear to predominate with insoluble fibers such as wheat bran, with little change in plasma lipid levels in most studies. Pectin, guar gum, and oat bran (soluble fibers) have been reported to have hypocholesterolemic effects in both animals and man, with the effect being proportional to the degree of cholesterol elevation. Other gums, specifically those from locust bean and karaya, have a similar effect, with the decrease in total cholesterol due primarily to a decrease in the low-density lipoprotein cholesterol fraction. While some studies have shown continued improvement over a period of months, this has not been uniformly found. Both normal and elevated triglyceride levels appear to be more resistant to change with dietary fiber. An increase of dietary carbohydrate as a source of fiber may be associated with an increase in triglyceride levels. Fiber may, however, offer some protection against an increase in cholesterol and triglyceride levels in subjects fed diets containing large amounts of sucrose. Although rats fed oat bran, guar gum, or pectin had lower levels of hepatic and blood triglycerides, humans with hypercholesterolemia fed oat bran or guar showed no effect on their triglycerides.(ABSTRACT TRUNCATED AT 250 WORDS)