Fiber Supplements

The best place to get fiber is not the supplement aisle, but the produce section, and there you should focus primarily on beans and whole grains. In addition to regular bowel movements, a high-fiber diet brings a reduced risk of heart disease, cancer, obesity, diabetes, depression, and early death in general. Every intake of 7 grams of fiber daily means a 9 percent lower risk of heart disease, our number-one killer. So if we reduce our risk by taking in 77 grams of fiber by 99 percent? That’s about how much fiber people used to eat in Uganda, a country where heart disease was virtually unknown.

Among people in Uganda on their traditional plant-based diet, heart disease was so rare that there were articles with titles like “A Case of Coronary Heart Disease in an African.” After 26 years in East Africa, physicians practicing there finally had their first case of coronary heart disease. (The patient was a judge with a “partly Westernized diet,” in which fiber-free foods, meat, dairy products, and eggs—some of the foods of his traditional diet—had been displaced.) Since dietary habits across the African continent have become more like those in the West, cardiovascular disease has of course now become there, too, the noncommunicable disease from which most people die—a path from virtually nonexistent to epidemic.

The fact that formerly typical Western diseases were so rare in rural regions of sub-Saharan Africa led to the fiber hypothesis, which holds that whole plant foods offer such great protection against chronic disease because they contain so much fiber. As expected, this gave rise to a multibillion–US-dollar market for fiber products. However, there is a problem: They don’t work.

Such fiber supplements may help with constipation, but they have no additional benefit against chronic diseases. In fact, studies that find an association between high fiber intake and lower risk of disease and death refer exclusively to fiber from food—not isolated fiber or supplements. Maybe that’s because fiber is a marker for healthy whole plant foods, or because of its role as a smuggler.

The main job of fiber in food could be to enclose nutrients and bring them to the microbiome in the gut. Fiber is the building material of plant cell walls, and these cell walls function as indigestible physical barriers. So when you eat structurally intact plants, some of the nutrients remain enclosed. You can chew as much as you want; the starch still remains completely surrounded by fiber and brings a livelihood to the friendly part of the gut flora. The good gut flora then gets not only the fiber, but also all the food contained within it. Agents like psyllium, however, cannot bring such treasures to the gut bacteria and are not even fermentable themselves, so our microbiome misses out on all the additional benefits of a high-fiber diet.

Flaxseed and rye

Ground flaxseed is an excellent whole-food source of fiber. In a randomized study, people with diabetes ate cookies for twelve weeks that either contained a tablespoon of ground flaxseed daily or not, if they were placebos. The flaxseed not only improved constipation symptoms such as pain with bowel movements, straining, and hard stool, but compared with the placebo group, the flaxseed group lost eight pounds, their fasting blood sugar fell by 25 points, HbA1c by an astonishing 1.8 percent, and LDL cholesterol by 17 points. For a direct comparison of flaxseed and psyllium husk, there was also a cookie group with 10 grams of psyllium. Flaxseed came out ahead; it beat psyllium on constipation, weight loss, blood sugar levels, and cholesterol values. (In addition, flaxseed is four times cheaper than psyllium, even the most ordinary kind.) Flaxseed also won the head-to-head comparison with the laxative lactulose; it increased the frequency of bowel movements from two to seven times per week, lactulose to six.

Rye bread with a high fiber content of 5 grams of fiber per slice was also tested; some of the study participants ate eight slices a day. Unlike the group eating white bread, which contains only one gram per slice, “the high-fiber rye clearly relieved constipation”; participants had more frequent bowel movements, felt better in the process, the stool was softer, and intestinal transit took less time. In the first week, however, the rye group reported more flatulence and bloating, but once the gut flora had adapted and a balance between gas-producing and gas-utilizing bacteria had been established, these symptoms diminished. (Small aside: The label “old fart” is not only derogatory, but perhaps also inaccurate. A survey of 16 000 Americans found that older people have less flatulence than younger people.)

Prunes and mangoes

A few decades ago, an article appeared in the scientific journal Geriatric Nursing with the title “A Special Recipe for Constipation,” which anecdotally presented the effectiveness of a particular mixture. Their basic recipe was two cups of applesauce, two cups of wheat bran, and one cup of 100-percent prune juice, and it was dispensed in small medicine cups to residents of a nursing home. A regimen like that costs half as much as psyllium (calculations put it at 77 instead of 147 US dollars per year). But how reliable is our scientific evidence on prunes?

I discuss the facts in see.nf/prune. Basically, ten prunes daily beat psyllium husk in a head-to-head comparison in frequency of bowel movements and stool consistency; they increased bowel regularity from twice to four times per week in the prune group; in the psyllium group it was only three times. (To keep things in perspective: Those who eat a plant-based diet average about eleven bowel movements per week.) The researchers, who openly stated that their study was funded by the California prune growers’ association, concluded that prunes should be “used first” for chronic constipation.

A trial with figs came to nothing, but a study funded by mango growers found that fresh mangoes also beat psyllium. Men and women with chronic constipation ate, in randomized groups, either one mango daily or the corresponding amount of fiber in the form of psyllium, which corresponded to one teaspoon per day. After a month, the mangoes not only had a more favorable effect on relieving constipation, but also had a distinctly anti-inflammatory effect: Blood IL-6 levels fell by more than 20 percent. On the basis of microbiome studies in mice, it was assumed that the cause lay in the prebiotic effect of the mango flesh, and that was confirmed in 2020 in a human trial, when one mango a day caused the amount of the beneficial gut bacterium Lactobacillus to rise significantly.