Most investigators into the causes of obesity believe that eating too much high fat, high-calorie food is the primary cause of obesity and obesity-related diseases, including diabetes. The excess calories consumed directly causes fat accumulation; scientists believe that a low-grade inflammation due to an altered gut microbiome (A microbial biome, such as the community of microbes within the human gut.) may also be involved. A new study published in the American Journal of Physiology—Gastrointestinal and Liver Physiology finds in mice lacking soluble fiber encourages inflammation in the intestines and poor gut health, inducing weight gain. On the other hand, introducing soluble fiber into the diet can restore gut health.
“The gut microbiota is a community of bacteria and other microorganisms that live in the intestines. Microbiota also exists elsewhere on the body, including the skin and mouth. The gut microbiota has an important role in maintaining intestinal health and functions, including helping the body digest food, producing vitamins and fighting foreign microorganisms. Changes to the gut microbiota have been linked to the development of gastrointestinal diseases, including inflammatory bowel disease, and metabolic diseases, including type 2 diabetes and obesity.” (Brooks, 2015)
There are two different types of fiber — soluble and insoluble. Both are important for health, digestion, and preventing diseases.
Soluble fiber attracts water and turns to gel during digestion. This slows digestion. Soluble fiber is found in oat bran, barley, nuts, seeds, beans, lentils, peas, and some fruits and vegetables. It is also found in psyllium, a common fiber supplement. Some types of soluble fiber may help lower risk of heart disease.
Insoluble fiber is found in foods such as wheat bran, vegetables, and whole grains. It adds bulk to the stool and appears to help food pass more quickly through the stomach and intestines. (Soluble vs. insoluble fiber, 2014)
A research team at Georgia State University looked at the effects of diets varying in amounts of soluble and insoluble fiber, protein, and fat on the structure of the intestines, as well as fat accretion for weight gain in mice. Crucial observations from this study are:
Mice on a diet lacking soluble fiber gained weight and had more fat compared with mice on a diet that included soluble fiber. The intestines of mice on the soluble fiber-deficient diet were also shorter and had thinner walls. These structural changes were observed as soon as two days after starting the diet.
Introducing soluble fiber into the diet restored the gut structure. Supplementing with soluble fiber inulin ( ) , certain plants that undergoes used chiefly to increase kidney function alant starch.)
restored the intestinal structure in mice on the soluble fiber-deficient diet. Mice that received cellulose, an insoluble fiber, however, did not show improvements. Moreover, in mice fed a high-fat diet, switching the type of fiber from insoluble to soluble protected the mice from the fat accumulation and intestinal wasting that occurs with excess fat consumption. The data suggest a difference in health benefits between soluble and insoluble dietary fibers, the researchers stated.
Improvements in gut structure with soluble fiber were due to changes in the gut microbiota and the gut microbiota’s production of molecules called short-chain fatty acids, which are used as fuel by intestinal cells and have anti-inflammatory properties. Mice consuming a soluble fiber-deficient diet had lower levels of short chain fatty acids and introducing soluble fiber into their diet boosted their levels. Supplementing the soluble fiber-deficient diet with short chain fatty acids had similar effects as inulin supplementation, although not to the same extent. Inulin supplementation increased the size of the intestines in normal mice but not in mice with no gut microbiota, supporting that the gut microbiota is involved in the intestinal health effects of soluble fiber. According to the researchers, the data support that soluble fiber promotes gut health by encouraging the gut microbiota to produce short chain fatty acids.
“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, the 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,” the researchers stated. (Brooks, 2015)
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Brooks, S. (2015, October 30). Diet Lacking Soluble Fiber Promotes Weight Gain, Mouse Study Suggests. Retrieved November 9, 2015, from The American Physiological Society Press Release: http://www.the-aps.org/mm/hp/Audiences/Public-Press/2015/59.html
Soluble vs. insoluble fiber. (2014, August 11). Retrieved November 9, 2015, from MedlinePlus: https://www.nlm.nih.gov/medlineplus/ency/article/002136.htm