Now, a large new review of studies on fiber, published in the Lancet, shows just how beneficial fiber can be. The nutrient substantially lowers the risk of at least four diseases—many of which don’t even directly relate to the gut.
Compared to those who ate less fiber, people who ate more fiber lowered their risk of heart disease, stroke, type 2 diabetes and colon cancer, as well as their risk of dying early from any cause, by 15% to 30%. And the more dietary fiber people ate, the lower their risk. For every additional 8 grams of fiber consumed, the risk of heart disease, type 2 diabetes and colon cancer dropped by 5% to 27%.
According to the data, people eating 25-29 grams of fiber from foods like fruits and vegetables every day (not from supplements or powders) showed the strongest reductions in risk of the range of diseases, and those eating more tended to show even lower risk. The researchers saw similar benefits among people who ate whole grains.
“Our research indicates that people should have at least 25-29 grams of fiber from foods per day,” says Andrew Reynolds, lead author of the study and a researcher at the University of Otago in New Zealand. “Currently, most people consume less than 20 grams of fiber per day, so being more conscious about choosing high-fiber food options will help reach that target.”
The results come from a thorough analysis of 243 studies — the kind that prospectively asked people about their diets and followed them for a few years to record health issues, as well as clinical trials, in which people volunteered to be studied and were assigned to change their diet or to be part of a control group. The researchers wanted to tease apart the specific health effects of different types of carbohydrates — sugars and fibers from fruits, vegetables and foods like whole grains — so they included studies in which people documented what they ate and their health outcomes. They also included studies that looked at several different health measures, like body weight, blood pressure, cholesterol, blood sugar and inflammation.
While the benefits of eating fiber aren’t a total surprise, the data should help nutrition experts figure out how much fiber people need to eat in order to reap the most benefits. (In fact, the review was requested by the World Health Organization Nutrition Guidance Expert Advisory Group.) The latest Dietary Guidelines for Americans recommend that women eat 25 grams of fiber a day while men should consume 38 grams a day. And the American Heart Association advises that adults eat 25 to 30 grams of fiber in their diet daily, which aligns with the latest data. The average American, however, eats only about 15 grams of fiber a day.
Previous studies have pointed to possible reasons why fiber has such beneficial effects on everything from heart disease to certain cancers. Fiber-rich foods tend to be heavier and require longer to chew, which increases satiety and possibly lowers the risk of obesity, which has been linked to heart disease and cancer. Fiber also stimulates beneficial bacteria in the gut, reducing the risk of colon cancer.
To get more fiber in your diet, base meals and snacks around whole grains, vegetables, beans, legumes and whole fruits, Reynolds says. Getting it from a range of whole-food sources is best.