We know that fiber intake is important for gut health, but do we know why?
Microbial diversity in our bodies is important, and with current technology we can determine types of microorganisms present as well as changes in composition and functions of the different communities. The majority of the microbiota in most adults are Firmicutes and Bacteroidetes type, but the ratio is different from person to person. An imbalance of Firmicutes to Bacteroidetes is associated with chronic disease and obesity, and a larger population of Firmicutes leads to greater energy yield from food. Greater diversity of the microbiota is one indication of a healthy gut.
Diet and exercise are two main factors leading to change in the microbiota, along with environment, illness, medication usage (antibiotics), etc. These microorganisms derive energy from metabolizing the nutrients passing through the GI tract and fermenting dietary fiber. Fermentation of indigestible fibers by the colonic bacteria creates short-chain fatty acids, which act as an energy source for the cells of the colon, and decrease the pH of the colon. This more acidic environment prevents growth of pathogenic bacteria.
The human microbiota is established early in life. Babies born naturally are first exposed to bacteria characteristic of the vagina and colon, while babies born by C-section are exposed to bacteria present on the skin and in the environment. The composition of the gut microbiota shifts dramatically when a child begins to eat solid foods and rely less on breast milk or formula for its nutritional needs. Its composition then remains fairly similar throughout adulthood, but does change in response to various factors such as changes in BMI and aging.
Studies in humans and in animals have indicated that even short-term changes to diet can have significant effects on gut microbiota composition. A short-term decrease in fiber intake can also have marked detrimental effects. A good example of this is lower carbohydrate consumption (which generally leads to lower fiber consumption) often seen in many weight loss diet approaches. For those on low carbohydrate diets, supplementation with prebiotic fiber may be of benefit. A short-term diet trial of high fiber intake can cause quick and dramatic changes to the microbiota, but individual results vary and are not permanent. Longer-term interventions have more significant and longer lasting changes.
Limited mobility and functionality as well as malnutrition related to aging can also have detrimental effects on the gut microbiota.
There’s still so much we don’t know about how weight status and gut microbial population are related, but they likely are related in a significant way. Long-term adherence to Western-style diets high in sugar and fat and low in fiber may increase risk for colonic disease.
Are you inspired to eat your fiber now? Recommended daily intakes are 38g per day for most men, and 25g per day for most women.
-Katy Hair, RD, LDN, CNSC
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