A new study from the University of Illinois suggests that adding fiber to the diet can influence the growth of two kinds of bacteria in your gut (known collectively as the microbiome) toward a ratio typically seen in lean people. Unfortunately, the researchers observed, most Americans consume only 12 to 14 grams of fiber a day, which is half the recommended amount of 25 to 38 grams. The investigative team had previously studied whether adding fiber to the diet would cause gut bacteria to shift toward "lean." They gave snack bars to 20 men whose reported daily fiber intake was about 14 grams a day. About one third of the men received snack bars with no fiber; another third were given bars containing 21 grams of polydextrose, a common fiber food additive, and the remainder of the participants received bars with 21 grams of corn fiber. The researchers reported significant positive shifts in the ratio of gut bacterial populations toward more bacteriodetes (associated with being lean) and fewer firmicutes (associated with overweight and obesity) with the addition of fiber. However, they also found that the beneficial changes didn't last when the participants went back to their normal diets. Earlier research had shown that a high fiber diet is protective against obesity. The take-home message from lead researcher Kelly Swanson is that if you want a healthier gut and hope to lose weight, you have to make lasting changes to your diet.
My take? It's well established that a diet high in fiber influences health for the better: it prevents constipation, and reduces the risks of colon cancer, heart disease and diabetes. We've also known for some time that fiber helps to maintain ideal weight. This new study adds to the growing body of evidence demonstrating the importance of fiber in the diet, and especially as it pertains to weight. I recommend getting 40 grams a day from bran cereals, beans, vegetables, fruit and whole grains. Freshly ground flaxseed and psyllium seed are also excellent sources of fiber.