Key Points:
- Twelve weeks of supplementing with 7.5 g of a prebiotic supplement improves older adults’ memory.
- Prebiotic supplementation does not improve muscle strength, as measured by chair rise time.
A new study, published in Nature Communications, has explored the fascinating link between the gut microbiome, cognitive function, and muscle health in older adults. The PROMOTe trial evaluated the effects of prebiotic supplementation on muscle strength and cognitive performance.
While the results did not show significant improvements in muscle strength, the cognitive outcomes were promising. Participants taking prebiotics demonstrated better memory performance, especially on tasks designed to detect early signs of Alzheimer’s disease. These improvements were linked to changes in the gut microbiome, particularly an increase in Bifidobacterium, a beneficial genus of bacteria.
The Study: Gut Microbiome Modulation
The trial involved 36 twin pairs of older adults, half of whom received prebiotics — compounds that promote the growth of healthy gut bacteria and can enhance the gut microbiome. Prebiotics were chosen for their potential to modulate the gut-brain axis—a bidirectional communication network between the gut and brain. Similarly, the hypothetical gut-muscle axis was also explored. The 7.5 g prebiotic intervention contained two types of dietary fiber:
- 3.375 g inulin
- 3.488 g fructo-oligosaccharides (FOS)
Furthermore, to address age-related muscle loss, all participants were given a protein supplement. Compared to young adults, older adults display a blunted response to protein muscle synthesis upon consuming protein. The precise cause of this anabolic resistance is still being explored but could be due to alterations to the gut microbiome. For example, protein absorption may be reduced in older age due to gut microbiome alterations. The protein intervention included all three branched-chain amino acids:
- 1660 mg L-leucine
- 830 mg L-isoleucine
- 830 mg L-valine
Previous research has shown that the gut microbiome influences many aspects of health, including immune function and brain activity. Moreover, in older adults, prebiotics have been shown to counteract frailty, including grip strength and exhaustion, as well as cognitive deficits like memory loss. However, the specific effects of gut modulation on muscle strength and cognitive function in twins have not been studied. Studying twins helps remove some variance from genetic and environmental factors.
Key Findings: Cognitive, but No Muscle Gains
The researchers found no significant differences in muscle strength between the prebiotic group and the placebo group. However, there was a correlation between strength and gut microbiome changes, suggesting that the gut microbiome may affect muscle strength. With these results, the authors suggest that the dose of the prebiotic supplement may need to be higher to see improvements in strength. Also, participants took the prebiotic for only 12 weeks, which may not have been long enough to alter muscle structure.
The cognitive results were more compelling. Participants who took the prebiotic supplement showed improved performance in memory-related tests. The improvements were particularly notable in tasks designed to detect subtle cognitive changes often seen in early-stage Alzheimer’s disease. This finding suggests that gut microbiome modulation could play a role in preserving cognitive function as people age.
Implications for Future Research
While the muscle strength findings were less encouraging, the cognitive benefits open up exciting possibilities for future research. Could prebiotic supplements become part of a larger strategy to protect against cognitive decline in aging populations? Further studies are needed to confirm these findings and explore the potential for personalized microbiome therapies targeting both cognition and overall health.
This study adds to a growing body of evidence suggesting that the gut microbiome plays a crucial role in maintaining brain health. As researchers continue to explore this relationship, we may see new interventions emerge that could help people maintain cognitive function and quality of life as they age. Moreover, higher dietary fiber intake is associated with improved cognition. Thus, dietary fiber — fiber from food — could potentially have similar effects to prebiotic supplementation. Foods containing dietary fiber include:
- Fruits
- Vegetables
- Grains
- Beans
- Peas
- Lentils.
The USDA estimates that 95% of Americans don’t get enough fiber. This is not trivial, considering that higher consumption of total dietary fiber is associated with reduced risk of mortality from all causes, cardiovascular disease, and cancer. It follows that eating a diet rich in fiber can prolong one’s lifespan. The dietary guidelines suggest eating 14 g of fiber for every 1000 calories.
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