Very high levels of soluble fiber slightly reduced cholesterol levels in adults with high cholesterol levels who were on a low-fat, low-cholesterol diet
ACP J Club. 1993 Nov-Dec;119:68. doi:10.7326/ACPJC-1993-119-3-068
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Jenkins DJ, Wolever TM, Rao AV, et al. Effect on blood lipids of very high intakes of fiber in diets low in saturated fat and cholesterol. N Engl J Med. 1993 Jul 1;329:21-6.
To determine if high intake of soluble rather than insoluble fiber can further reduce plasma lipid levels in persons with diets already low in saturated fats and cholesterol.
Randomized, controlled, crossover trial.
A nutrition clinic at a Canadian university hospital.
43 healthy persons (mean age 58 y, 53% postmenopausal women) who had a mean percentage of ideal body weight of 107% and mild-to-moderate hyperlipidemia after following a National Cholesterol Education Program Step II diet for ≥ 2 months. Follow-up was complete.
Participants were assigned to each diet for 4 months separated by 2 months. Both diets aimed to provide ≥ 20% calories as fat, 20% as protein, and at least 60% as available carbohydrate (2.5 to 3.0 g of fiber/100 kcal) and included low-fat dairy foods and vegetable-protein products. Participants chose amounts of food. The soluble-fiber diet included barley, dried lentils, peas, beans, oat bran, and a commercial cereal with added psyllium. The insoluble-fiber diet included wheat-bran breakfast cereal, high-fiber crackers, and bread with wheat bran and gluten. All diet foods were packaged centrally and delivered weekly. 22 participants received the soluble-fiber diet first.
Main outcome measures
Total, high-density lipoprotein (HDL), and low-density lipoprotein (LDL) cholesterol levels; triglyceride levels; and serum apolipoprotein levels.
Plasma total, LDL, and HDL cholesterol and serum apolipoprotein levels decreased during both periods with lowest levels by week 4. Compared with the insoluble-fiber diet, the soluble-fiber diet period had a 4.9% greater decrease in total cholesterol levels ( P< 0.001), 4.8% greater reduction in LDL cholesterol ( P< 0.001), and 3.4% greater reduction in HDL cholesterol levels ( P = 0.01). The total cholesterol in the soluble-fiber period differed from the insoluble-fiber period by 7.5% in the men and 3.4% in the women (P = 0.03).
Very high intakes of soluble fiber compared with insoluble fiber resulted in additional small reductions in blood cholesterol in people with hyperlipidemia who were already consuming a low-fat and low-cholesterol diet.
Sources of funding: Heart, Lung, and Blood Institute and Loblaw Companies Limited.
For article reprint: Dr. D.J. Jenkins, Clinical Nutrition and Risk Factor Modification Center, St. Michael's Hospital, 61 Queen Street East, Toronto, Ontario M5C 2T2, Canada. FAX 416-867-7495.
Jenkins and colleagues addressed an important issue: the comparative effects of soluble and insoluble fiber in patients already on a strict low-fat diet. Interpreting crossover trials such as this one can be difficult, but conferral with the statistical consultant on this trial has given me confidence in the analytic integrity of the results.
Assuming the results are valid, 2 questions remain. First, are the effects clinically important? After a step II diet had already been tried, high intakes of soluble fiber lowered mean total cholesterol (TC) level from 267 mg/dL at baseline to 230 mg/dL, a modest but useful decrease. HDL, however, also decreased and the changes in TC to HDL ratio were variable and small (from 5.15 to 4.88). Many more persons must be studied for a precise appraisal of potential, let alone actual, effect on clinical events.
Second, are the diets feasible for routine practice? Data on side effects, such as flatulence and abdominal cramping, were not provided, but compliance was good. The participants were motivated volunteers in a specialty clinic to whom prepackaged foods were delivered each week. The feasibility of widespread adoption of very high fiber intakes is therefore uncertain.
These findings highlight the potential role of soluble fiber in dietary management of dyslipidemias, but more information is needed before practice recommendations can be made. Practitioners should also remember that only persons at very high risk for coronary heart disease events (e.g., persons with preexisting coronary heart disease or several risk factors) are likely to gain any all-cause mortality benefit from treatment of dyslipidemias by any means (1).
C. David Naylor, MD, DPhil
Sunnybrook Health Science CentreToronto, Ontario, Canada