Observational studies on cardiovascular disease support Lupton’s claim. The massive Nurses’ Health Study and Health Professionals Follow-up Study, among others, found that adults who consumed the most total fiber, near the recommended 25 grams per day for women and 38 grams for men (double what typical Americans consume) are much less likely to suffer heart problems. “Collectively, it’s about a 30 percent risk reduction in heart disease,” Lupton says.
The big disappointment, however, is that current research has found no connection between fiber and colorectal cancer. That news undercuts the safety net of many people with a family history of colon cancer since doctors, depending upon intuition and encouraging animal studies, have long recommended high-fiber diets. Still, there may be some as-yet-unknown factor in fiber that produces a positive effect, says John Baron, an epidemiologist at Dartmouth Medical School.
Lupton says the data are stronger for type 2 diabetes, since a high-fiber diet has been linked to lower risk in several major studies. Other research shows that eating fiber may help prevent obesity and, of course, constipation.
In the end, many experts believe total fiber may really just be a proxy for healthy eating habits. “My feeling is that fiber itself has an effect, but other things—known or not—in healthy foods are also important,” says Denis Lairon, the researcher who conducted the French study.
“High-fiber foods are nutritious foods,” adds Lupton. “If you were to meet your recommended intake for fiber from foods and not exceed your calorie allotment, it would be extremely difficult to not eat a good diet.”