In a review article published in the journal Frontiers in Sports and Active Living, scientists discussed the impact of diet and exercise on gut microbiota composition, diversity, and functions in older adults.
Study: Growing old together: What we know about the influence of diet and exercise on the aging host's gut microbiome. Image Credit: Christoph Burgstedt / Shutterstock
The human gut microbiota refers to an enormous collection of bacteria and other microorganisms that symbiotically reside inside the intestinal tract. These microorganisms and the metabolites produced by them collectively play an important role in influencing human health and immune functioning.
The immune system is vital for defending against various invading pathogens, including bacteria and viruses. Individuals with a weakened immune system, such as older people, are more vulnerable to infections and autoimmune and inflammatory diseases. An imbalance in gut microbiota (dysbiosis) is associated with many age-related diseases.
It is well-documented in the literature that gut microbiota composition changes with increasing age. Moreover, diet and exercise play a vital role in shaping gut microbiota composition and diversity.
In this review, scientists have analyzed available literature to provide an overview of the impact of diet and exercise on gut microbiota and its functions in older adults.
Impact of diet on aging gut microbiota
Diet is one of the main factors responsible for regulating gut microbiota composition and diversity. Individuals residing in different geographical locations exhibit significant variations in gut microbiota structure because of the differences in their dietary habits.
A loss of microbial diversity has been observed among residents of non-western countries who have migrated to the United States. Similarly, diets enriched with food emulsifiers are known to change the gut microbiota composition, which subsequently induces low-grade inflammation.
Dietary macro- and micronutrients are digested in the gastrointestinal (GI) tract, and the metabolites are absorbed through the intestinal mucosa into the bloodstream. The gut microbiota plays a vital role in regulating digestion and absorption of dietary compounds. Evidence indicates that diets lacking healthy nutrients can induce various health adversities by changing gut microbiota composition. While fiber-rich and low-calorie diets are known to increase longevity, consumption of high-fat and low-fiber diets has been found to associate 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 induce immune responses through pathogen-associated molecular patterns. In contrast, the Mediterranean diet that contains high amounts of vegetables, fruits, nuts, fibers, olive oil, and red wine can increase bacterial community that produces beneficial metabolites, including short-chain fatty acids (SCFAs).
An alteration in diet and nutrient intake is commonly observed among older adults because of changes in appetite, digestion ability, food sensitivity, or access to proper nutrition. Studies have shown that older adults consume less than recommended amounts of vitamins and minerals vital for anti-inflammatory responses and immune regulation. A reduction in protein consumption has also been noticed in older adults, leading to various health complications, such as loss of lean body mass.
In older adults, changes in dietary patterns induce gut microbiota dysbiosis, characterized by reduced microbial diversity and butyrate-producing microbes and increased facultative anaerobic microbes. These changes collectively 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 bacterial populations and reduce the growth of opportunistic bacteria in older adults. Similarly, prebiotic galacto-oligosaccharides have been found to restore gut microbiota composition and reduce inflammation in older adults.
As mentioned by the scientists, more studies are needed to understand the extent to which dietary patterns can influence gut microbiota structure and function in older adults. Well-controlled trials are also needed to identify effective dietary interventions that can improve the overall health of aging populations by modulating gut microbiota.
Impact 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 older adults, inflammation and immune senescence are the significant 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 functions, and increasing autophagy (a cellular process to degrade and remove cellular debris).
There is evidence showing that regular exercise influences gut microbiota composition and diversity. However, because of a lack of control for diet and age and exercise training regimen, these studies could not conclusively determine the mechanisms and the extent to which exercise influences gut microbiota.
In this context, one well-controlled animal study has shown that six weeks of voluntary wheel running reduces gut microbiota richness in young mice compared to that caused by forced treadmill running or sedentary conditions. Mice performing forced treadmill running, on the other hand, exhibit enrichment of certain endotoxin-producing bacteria that are associated with GI tract pathologies.
The study's outcomes indicate that exercise could have both beneficial and detrimental effects on gut microbiota, depending on the type of stimulus.
Human studies involving professional rugby athletes have indicated that exercise increases the functional capacity of gut microbiota. Moreover, evidence shows that athletes' cardiorespiratory fitness level is highly correlated with gut microbiota composition and diversity. Moreover, a direct association has been observed between cardiorespiratory fitness level and genes related to SCFA biosynthesis, bacterial chemotaxis, and motility.
Endurance exercise conducted for six weeks has been found to alter gut microbiota composition and SCFA levels in young people depending on the body mass index (BMI). Healthy adults undergoing endurance exercise and resistance exercise for 8 weeks have been found to exhibit only minimal changes in gut microbiota composition and function and no change in microbial diversity.
Based on the findings of these studies, scientists highlight the need for more longitudinal studies to understand to which extent exercise modulates gut microbiota and the outcome of these modifications, especially in elderly populations.