Can diet and exercise improve gut bacteria and the health of older adults?

In a review article published in the journal Frontiers in sports and active lifeScientists have discussed the impact of diet and exercise on the composition, diversity, and function of the gut microbiota in older adults.

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The human gut microbiota refers to the enormous group of bacteria and other microorganisms that live symbiotically within the intestine. Together, these microorganisms and the metabolites they produce play an important role in influencing human health and immune function.

The immune system is vital to defend against various invading pathogens, including bacteria and viruses. Individuals with weakened immune systems, such as the elderly, are more susceptible to infections, autoimmune diseases, and infections. An imbalance in the gut microbiota (dysbiosis) is associated with many age-related diseases.

It is well documented in the literature that the composition of the gut microbiota changes with age. Furthermore, diet and exercise play a vital role in shaping the composition and diversity of the gut microbiota.

In this review, scientists analyzed the available literature to provide an overview of the effect of diet and exercise on gut microbiota and function in the elderly.

Effect of diet on the aging gut microbiota

Diet is one of the main factors responsible for regulating the composition and diversity of the gut microbiota. Individuals residing in different geographic locations show significant differences in the structure of their gut microbiota due to differences in their dietary habits.

Loss of microbial diversity has been observed among residents of non-Western countries who immigrated to the United States. Similarly, diets enriched with food emulsions are known to alter the composition of the gut microbiota, which subsequently leads to low-grade inflammation.

Dietary macro- and micronutrients are digested in the gastrointestinal (GI) tract, and metabolites are absorbed through the intestinal mucosa into the bloodstream. Gut bacteria play a vital role in regulating digestion and absorption of food compounds. Evidence suggests that diets lacking in healthy nutrients can cause many health afflictions by altering the composition of the gut microbiota. While high-fiber, low-calorie diets are known to increase longevity, consumption of high-fat, low-fiber diets has been found to be associated with reduced longevity.

Western diets with low fiber content and high fat, sugar and salt content can significantly increase endotoxin-releasing bacteria, which in turn can stimulate immune responses through molecular patterns associated with pathogens. In contrast, a Mediterranean diet that includes high amounts of vegetables, fruits, nuts, fiber, olive oil, and red wine can increase the bacterial community that produces beneficial metabolites, including short-chain fatty acids (SCFAs).

A change in diet and nutrient intake is commonly observed among the elderly due to changes in appetite, ability to digest, food sensitivity, or access to proper nutrition. Studies have shown that older adults consume less than the recommended amounts of vitamins and minerals that are essential for anti-inflammatory responses and immune regulation. A decrease in protein consumption has also been observed in the elderly, which leads to various health complications, such as a loss of lean body mass.

In the elderly, changes in dietary patterns lead to dysbacteriosis of the intestinal flora, which is characterized by a decrease in microbial diversity and butyrate-producing microbes and an increase in facultative anaerobic microbes. Together, these changes lead to the development of a chronic, low-grade inflammatory state, which is the hallmark of many age-related diseases.

Some studies have been done to identify dietary interventions that can improve gut microbiota structure and function in older adults. Some probiotics have been found to increase the growth of beneficial bacteria and reduce the growth of opportunistic bacteria in the elderly. Similarly, galacto-oligosaccharides prebiotics have been found to repopulate the gut microbiota and reduce inflammation in the elderly.

As the scientists stated, more studies are needed to understand the extent to which dietary patterns affect gut microbiota structure and function in older adults. Well-controlled trials are also needed to identify effective nutritional interventions that can improve the overall health of the elderly population by modulating the gut microbiota.

Effect of exercise on aging gut microbiota

Regular physical activity improves cardiorespiratory fitness and overall health by reducing the risk of chronic diseases (cardiovascular and metabolic diseases) and all-cause mortality. In the elderly, inflammation and immune aging are important determinants of various diseases associated with high mortality rates. Regular exercise can significantly reduce the risk of these diseases by reducing chronic low-grade inflammation, improving immune function, and increasing autophagy (a cellular process of breaking down and removing cellular debris).

There is evidence to suggest that regular exercise affects the composition and diversity of the gut microbiota. However, due to a lack of control for diet, age, and exercise, these studies were unable to determine the mechanisms and extent of the effect of exercise on the gut microbiota.

In this context, one well-controlled animal study showed that six weeks of voluntary wheel running reduced the gut microbiota richness of young mice compared to that induced by forced running or sitting conditions. On the other hand, mice running a forced treadmill show enrichment of certain endotoxin-producing bacteria associated with gastrointestinal disease.

The results of the study indicate that exercise can have both beneficial and harmful effects on gut microbes, depending on the type of stimulus.

Human studies involving professional rugby players have indicated that exercise increases the functional capacity of the gut microbiota. Moreover, evidence indicates that the level of cardiorespiratory fitness of athletes is closely related to the composition and diversity of the gut microbiota. Moreover, a direct correlation was observed between the level of cardiorespiratory fitness and genes related to SCFA biosynthesis, bacterial chemotaxis, and motility.

Endurance exercise performed for six weeks was found to alter the composition of the gut microbiota and SCFA levels in young men depending on their body mass index (BMI). Healthy adults undergoing endurance and resistance exercise for 8 weeks were found to show only slight changes in the composition and function of their gut microbiota and no change in microbial diversity.

Based on the results of these studies, the scientists highlight the need for more longitudinal studies to understand the extent to which exercise modifies the gut microbiota and the consequences of these modifications, particularly in the elderly population.