A high intake of dietary fiber is associated with a wide array of health benefits, including a reduced mortality rate, according to a massive systematic review reported in 2019 in The Lancet.
Researchers analyzed data from 58 clinical trials and 185 observational studies. People who consumed the most dietary fiber (at least 25 to 30 grams [g] a day) had a 15 percent to 30 percent lower death rate and incidence of heart disease, stroke, diabetes, and colorectal cancer than those who ate the least fiber (less than about 15 g a day). High fiber intake was also linked to lower blood cholesterol, blood pressure, and body weight. Similar benefits were seen for whole grains.
The scientists included only studies with healthy participants, so the findings cannot be applied to people with existing chronic diseases. It’s also true that people who consume healthier diets tend to smoke less, move more, and not abuse alcohol—factors that can be difficult to control for.
For every 8-g increase of dietary fiber eaten per day, total deaths and incidences of coronary heart disease, type 2 diabetes, and colorectal cancer decreased by 5 percent to 27 percent. Protection against stroke and breast cancer also increased. Consuming 25 to 29 g each day was adequate, but the data suggest that higher intakes could provide even greater protection. The average American consumes only about 15 g of fiber a day. (If you increase fiber intake, you should also drink more water.)