Diet high in soluble fiber may prevent weight gain

While high-fat diets are considered a primary cause of weight gain, a new study by researchers from Georgia State University suggests a diet low in soluble fiber may also be a key culprit.

Researchers suggest adding soluble fiber to one's diet may promote good gut health and prevent weight gain.

Published in the American Journal of Physiology-Gastrointestinal and Liver Physiology, the study found mice fed a diet lacking soluble fiber experienced poor gut heath and gained weight.

Soluble fiber absorbs water in the gut, forming a gel-like substance that can bind to cholesterol and bile acids, helping to eliminate them from the body. 

As such, soluble fiber helps to lower cholesterol. The gel-like substance it forms also helps to slow digestion and regulate blood sugar.

Foods rich in soluble fiber include oat bran, barley, nuts, seeds, beans, lentils, peas and certain fruits and vegetables, such as apples, blueberries and carrots.

According to researchers from the Institute for Biomedical Sciences at Georgia State, past research has indicated that a diet low in soluble fiber may alter the gut microbiome - the community of microorganisms living in the intestines - triggering inflammation and leading to weight gain. They decided to investigate further.

The research team fed mice a series of diets that varied in levels of soluble and insoluble fiber, proteins and fat. They assessed how each diet impacted the structure of the mice's intestines, their microbiome, fat accumulation and weight gain.

Compared with mice fed a diet high in soluble fiber, those fed a diet that lacked soluble fiber had higher weight gain and greater fat accumulation. They also showed significant differences in gut structure as little as 2 days after initiating the soluble fiber-deficient diet; their intestinal walls were thinner and shorter.

However, the researchers found that switching insoluble fiber to soluble fiber among mice fed a high-fat diet prevented fat accumulation and weight gain.

Soluble fiber increases production of SCFAs to improve gut health

What is more, on introducing soluble fiber to the diets of mice, the team found the changes in gut structure were reversed, though the same could not be said on introducing insoluble fiber to their diets.

The team found the improvement in gut structure was down to changes in gut bacteria triggered by soluble fiber, which led to greater production of short-chain fatty acids (SCFAs); the mice fed a diet lacking soluble fiber had low levels of SCFAs, but levels increased with introduction of soluble fiber.

On supplementing the mice fed a soluble fiber-deficient diet with SCFAs, they found it produced similar effects to supplementation with inulin - a soluble fiber found in chicory roots and Jerusalem artichokes. However, they found it only improved gut structure for normal mice, not those without gut bacteria.

Overall, the researchers say their findings indicate that adding soluble fiber to a diet may promote good gut health and regulate weight by triggering the production of SCFAs.

The research team adds:

"If our observations were to prove applicable to humans, it would suggest that encouraging consumption of foods with high soluble fiber content may be a means to combat the epidemic of metabolic disease.

Moreover, addition of inulin and perhaps other soluble fibers to processed foods, including calorically rich obesogenic foods, may be a means to ameliorate their detrimental effects."

References:

1.  Lack of soluble fiber drives diet-induced adiposity in mice, Benoit Chassaing et al., American Journal of Physiology-Gastrointestinal and Liver Physiology, doi:10.1152/ajpgi.00172.2015, published online 10 October 2015.
2.  American Physiological Society news release, accessed 30 October 2015 via Newswise.
3.  Additional source: Mayo Clinic, Dietary fiber: Essential for a healthy diet, accessed 30 August 2015.