Research explained: systematic review and meta-analysis
Eating 25-29 g of fiber a day is linked to lower risk of heart disease, diabetes and early death
A WHO-commissioned review of 185 cohort studies and 58 trials remains the clearest evidence on how much fiber to aim for.
People who ate the most fiber had a 15-30% lower risk of dying early and of developing heart disease, stroke, type 2 diabetes and colorectal cancer than people who ate the least, according to a review commissioned by the World Health Organization and published in The Lancet. The biggest benefits showed up at 25-29 g of fiber a day.
What the researchers did
The team pooled 185 prospective cohort studies, which follow large groups of people over years, and 58 clinical trials with about 4,600 adults. Cohort studies show associations, not cause and effect, but the trials pointed the same way: higher fiber intake lowered body weight, systolic blood pressure and total cholesterol.
How strong is the evidence?
Strong for an observational question. The results were consistent across many populations and there was a dose-response pattern: more fiber, lower risk. The limits are the usual ones for diet research. People who eat more fiber also tend to exercise more and smoke less, and studies adjust for this only partly.
What it means for you
Most adults eat around 15-20 g of fiber a day. Closing the gap does not take supplements. A cup of cooked lentils gives about 16 g, a cup of black beans about 15 g, 40 g of oats 4 g, and two tablespoons of chia seeds about 8 g. Increase slowly and drink water to avoid bloating.
See every food ranked by fiber in our list of foods high in fiber.