Safety and Efficacy of Fiber Supplements Like Metamucil (Psyllium) for Constipation

Fiber supplements are by far the most commonly used treatment for constipation and are recommended as first-line management by American, European, and global guidelines. Soluble nonfermentable fibers, such as psyllium (also known as is-puh-GHOUL-la and sold as Metamucil) seems to be the most appropriate first choice. It traps water in the intestine, increasing stool water content and bulk to ease defecation, but as such, it’s important to take psyllium as directed, with sufficient fluid intake. Otherwise, psyllium itself can cause its own intestinal obstruction.

Overall, the efficacy of psyllium has been described as “modest.” A meta-analysis of fiber supplementation trials found that 77 percent of constipation sufferers responded to the fiber, but so did 44 percent in the placebo group. Fiber supplements significantly improved stool frequency and softened stools compared to placebo, but 50 percent of hundreds of fiber supplement users report not feeling their constipation was completely relieved. The same, however, was true of prescription laxative drugs. The advantage of psyllium may lie in its ancillary benefits. 

In diabetics, a meta-analysis of studies using an average dose of nine grams of psyllium a day for 12 weeks significantly improved both short- and long-term blood sugar control, dropping fasting blood sugars over 30 points and hemoglobin A1c by .9 percent, even without a significant change in body weight. Although Metamucil markets psyllium for “appetite control,” an average of ten weeks of viscous fiber supplementation drops body weight less than a pound and waist circumference only about a quarter inch. 

The diabetes meta-analysis also found a 19-point drop in triglycerides and a 9-point drop in LDL cholesterol, especially important in diabetics, who are at elevated risk of dying from cardiovascular disease. Across the board in diabetics and nondiabetics alike, 28 randomized controlled trials found an average dose of 10 grams of psyllium for eight weeks cut LDL cholesterol 13 points, presumably by facilitating the body’s own natural mechanism for flushing excess cholesterol out of the system. It even works if you’re already on a statin drug, reducing LDL cholesterol as much as effectively doubling the drug dose. The blood pressure benefit is small (reducing both top and bottom numbers by about two points among hypertensives), but most people need all the help they can get. 

Psyllium has also been tested head-to-head against the proton pump inhibitor drug omeprazole (sold as Prilosec) for the treatment of acid reflux disease (or GERD, Gastroesophageal Reflux Disease). Two months of taking the drugs twice a day or five grams of psyllium dissolved in water twice a day both similarly and effectively control symptoms in about 9 out of 10 GERD patients. The drug started working sooner—three days as opposed to seven for the psyllium, but the most striking difference occurred after the two months were over. The GERD recurred in 70 percent of the drug group, starting after an average of about two weeks, but in only 24 percent of those after two months on psyllium, starting an average of 10 weeks later.