Age-related muscle loss has a substantially negative effect on our later years. It reduces quality of life, decreases resilience, and leads to significant disability.

Clearly, exercise is essential to help hold on to as much muscle as possible. Regular strength training at 3-4x/wk covers this base.

Getting adequate protein is also important. Unfortunately, the dose of protein required to simulate muscle protein synthesis increases with age. So a dose of protein that is effective when we’re young isn’t as we age, a process known as anabolic resistance.

Identifying other factors that can help preserve muscle for as long as possible is crucial. Aging related changes to our physiology make building and holding on to muscle much more difficult.

The gut-muscle axis and age related muscle loss

You’ve likely heard of the gut-brain axis. It’s a bi-directional communication line between the brain and gut that can affect cognition and mood.

In the same way, there is a gut-muscle axis where the gut and muscle communicate with one another that affects muscle metabolism and function. For a review on the topic, click here.

An important way that the aging gut can affect our ability to maintain muscle mass is through systemic inflammation. As we age, there is a progressive increase in inflammation know as inflammaging.

Consequently, the gut is a rich source of inflammation, and there are changes to the gut as we age that can promote it. This affects hormones that regulate muscle mass as well as amino acid availability in muscle.

Effectively, the ability to maintain muscle mass is a fight between muscle protein synthesis(MPS) and muscle protein breakdown(MPB). When MPB exceeds MPS, we lose muscle mass.

Short chain fatty acids and the gut-muscle axis

One of the proposed ways in which the gut-muscle axis protects against muscle loss is through the production of short chain fatty acids(SCFAs). SCFAs are produced when our microbiome breaks down soluble dietary fiber.

Dietary fiber makes it’s way in to our colon where most of our microbiome resides. There, networks of microbes breakdown fiber into metabolites that other microbes use to make SCFAs.

SCFAs impact both ends of the gut-muscle axis. First, they create an anti-inflammatory environment in the gut and decrease intestinal permeability to keep inflammation low.

Secondly, they enter the bloodstream and alter muscle physiology by:

• Activating receptors that activate MPS, mTOR in particular
• Enhancing fat and carb metabolism
• Increasing mitochondria
• Increasing insulin-like growth factor-1(IGF-1)

Recent evidence in humans seems to support the benefits of dietary fiber on age related muscle loss.

Age related muscle loss and dietary fiber

Studies in younger men show no real benefit of dietary fiber to muscle mass. However, a couple studies find that increased dietary fiber intake protects muscle mass in otherwise healthy older people.

A recent paper found that increased dietary fiber intake correlated to greater muscle mass and lower fat mass. This was in men and women above the age of 40. There were additional benefits to muscle strength and glucose metabolism.

Another paper looking only at postmenopausal women over 40 found similar results. However, this second study dug quite a bit deeper to support a CAUSAL relationship rather than an association. In other words, it showed that increased fiber intake caused increased muscle mass.

Furthermore, it found out how it all worked. People with genes associated with increased fiber intake saw an increase in bacteria that ferment fiber into the SCFA butyrate. They also had increased levels of the SCFA butyrate.

As a result, there was an increase in genes that regulate carbohydrate metabolism in muscle. The key here is that the muscle fiber type that metabolizes carbohydrate, type II fibers, are also the ones most most prone to growth.

For more on this study including the microbes doing the legwork, check out our Youtube short on the topic.

Conclusion

The gut-muscle axis may be an important way in which we can preserve muscle mass and protect against age related muscle loss. In particular, increasing SCFAs such as butyrate may help maintain muscle mass by decreasing inflammation and reinforcing muscle protein synthesis.

Consuming more dietary fiber is the tried and true way to increase production of butyrate by our microbiome. Interestingly, a new study found that supplementing with high doses of a common vitamin may provide similar benefit.

This will be the topic of our next Youtube Short, so stay tuned! And don’t forget to subscribe to our Youtube channel by clicking the red Youtube button in the righthand margin of this page!