Studies have consistently shown that high intake of dietary fiber improves insulin resistance and lowers the risk of type 2 diabetes by 20–30%. This effect is mainly attributable to grain and cereal fibers, rather than fibers from fruits and vegetables, and may be due in large part to their positive impact on the gut microbiome.^1,2,3 Meta-analyses of randomized controlled trials in people with type 2 diabetes have found that supplementing with approximately 13–15 grams of soluble fiber per day can improve blood glucose control and reduce insulin resistance.^4,5 Psyllium, guar gum, oat bran, and inulin are examples of soluble fibers or soluble fiber sources that have been shown to be beneficial in type 2 diabetes.^6,7,8,9

Numerous clinical trials have shown supplementing with viscous (gel-forming) soluble fibers such as psyllium, guar gum, pectins, glucomannan, and beta-glucans (found in oat bran, mushrooms, and other sources) results in decreased body weight and waist circumference, even in individuals eating a regular diet.^10,11 In addition, although the effects may be small, fiber supplement-related weight loss is more profound in those with overweight and obesity, type 2 diabetes, and metabolic syndrome.¹⁰ It is thought viscous fibers work in part by promoting a sense of fullness and slowing the absorption of glucose from the intestines.^11,14 In addition, some types of fiber may have beneficial metabolic effects due to their prebiotic properties—their ability to build colonies of health-promoting bacteria in the intestines. Byproducts of fiber fermentation by gut microbes include short chain fatty acids and other compounds that help regulate immune function, appetite, fat burning, energy expenditure, insulin sensitivity, and glucose metabolism, all of which can impact weight loss.¹⁴

 

In people with diverticular disease, a fiber supplement may improve constipation. The results of double-blind of fiber supplementation for diverticular disease have been mixed. One study¹³ demonstrated a beneficial effect of fiber supplementation in people who suffered from abdominal pain and pain with bowel movements; whereas a second study¹⁴ indicated no improvement in these symptoms following fiber supplementation. Nevertheless, long-term fiber supplementation may protect against the complications of diverticular disease.¹⁵