Clinical Pearls for Prescribing Fiber and Fiber Supplements

Lillian White, MD
September 29, 2025

Although dietary fiber has many known health benefits, data from the National Health and Nutrition Examination Survey reported that <5% of children and adults consume the recommended amount. Fiber-rich foods include fruits, vegetables, legumes, nuts, and whole grains. The Academy of Nutrition and Dietetics recommends 14 g per 1,000 kcal/day for children and older adults (eg, 28 g of fiber is recommended for an older adult with a 2,000 kcal daily caloric intake), 25 g/day for women, and 38 g/day for men of dietary fiber.

Current guidelines recommend dietary fiber as part of nutrition therapy for treatment of hyperlipidemia and cardiovascular disease (CVD) prevention. Dietary fiber specifically reduces total cholesterol, triglycerides, and low-density lipoprotein (LDL). Fiber appears to reduce the re-absorption of cholesterol from the gastrointestinal tract, resulting in lower levels of circulating cholesterol. This causes up-regulation of LDL receptors on the liver, resulting in further removal of LDL cholesterol from the bloodstream.

Adequate fiber intake has been associated with improved blood pressure, blood sugar, and reduced risk of breast cancer. It is uncertain whether increased dietary fiber reduces the risk of colon adenomas or colorectal cancer. Fiber supplementation is recommended as a first-line treatment for chronic constipation. Legumes in particular (4 servings vs 1 serving per week) have been associated with reduced risk of CVD as well as improved blood sugar, weight, and longevity.

Psyllium fiber appears to be particularly effective for the treatment of chronic constipation at a dose of >10 g per day over a period of at least 4 weeks. Psyllium has also demonstrated benefits in treating hyperlipidemia, diabetes, and hypertension, making it one of the more versatile options for fiber supplementation. Notably, combining psyllium (10 g/day) with simvastatin (10 mg/day) can double the LDL-lowering effect—comparable with increasing simvastatin to 20 mg/day. Similar results have been observed with atorvastatin. On its own, fiber supplementation typically lowers LDL by 5% to 10%.

Other fiber supplements with evidence of benefit include β-glucan (found in oats, barley, etc.) and galactomannan (produced from guar gum). Galactomannan at a dose of 10 g/day appears to be the most effective form of fiber supplementation for lowering blood sugar levels in patients with diabetes according to a recent meta-analysis, with a mean difference of -1.5 in A1C.

Physicians should exercise caution in recommending fiber supplementation for patients with active inflammatory bowel disease, although evidence of harm is lacking. Without sufficient fluid intake or in patients with slow transit constipation, fiber supplementation may increase the risk of bowel obstruction. Therefore, prescribe fiber with caution in patients who have an increased risk of bowel obstruction (eg, history of severe gastroparesis, known intestinal strictures). Excessive fiber supplementation may lead to diarrhea.

A common adverse effect of fiber supplementation is flatulence and bloating. Starting low and gradually increasing the dose may help avoid these unwanted effects. American Family Physician has published additional patient education regarding increasing dietary fiber intake.