The gut-muscle axis: potential implications for athletes

We’ve all heard of the gut-brain axis (the bidirectional signalling between our gut/microbiome and central nervous system), that regulates mainly stress-related responses and our mood. But now a new axis has emerged from increased research interest into sarcopenia and cachexia: the gut-muscle axis, in which our gut microbiota are thought to be deeply interlinked with muscle function and metabolism.

An athlete could be eating the ‘perfect’ diet that meets all their dietary requirements, but if their gut bugs are unbalanced, this can wreak havoc on the process of nutrient absorption and extraction, with downstream negative effects on skeletal muscle. This is where the gut-muscle axis comes into play. An athlete with compromised skeletal muscle mass and function will struggle with their body composition, performance and recovery.

Although there is evidence that athletes may have a more diverse gut microbiota than general population, which is associated with better health and metabolic function, they are also prone to dysbiosis (an imbalance between ‘good’ and ‘bad’ bacteria) and increased intestinal permeability if they are not careful with their training load. This dysbiosis would promote body-wide inflammation and undesirable metabolic effects, such as catabolism.

While the research is still in its infancy, there is some indirect evidence that the composition of our gut microbiota can influence anabolic drive and subsequent muscle function. Several possible pathophysiological mechanisms and negative effects may occur because of dysbiosis, as discussed in this recent paper:

  • - Compromised bioavailability of dietary amino acids, translating into less muscle protein synthesis.
  • - Reduced synthesis of vital vitamins, including folate, vitamin B12 and riboflavin, which influence ATP production and anabolic drive in skeletal muscle.
  • - Increased intestinal permeability, which can cause absorption of by-products and toxins such as lipopolysaccharides (LPS), produced by the gut bacteria. LPS has been shown to activate the NF-kB pathway, reducing insulin sensitivity, increasing catabolism and inflammation.
  • - Decreased biotransformation of polyphenols (e.g. resveratrol), which may lead to reduced antioxidant capacity.

The most studied mediators involved in the gut-muscle axis are those produced by our gut bacteria. A healthy gut microbiota produces secondary bile acids, known to play a key role in activating an anabolic pathway by stimulating the farnesoid X receptor. Short-chain fatty acids (SCFAs), derived from dietary fibre, are also produced by our gut bacteria and display various beneficial metabolic effects such as promoting lipolysis, stimulating skeletal muscle glucose uptake, increasing insulin sensitivity and modulating systemic inflammation – all of which influence an athlete’s anabolic/catabolic balance. With dysbiosis, these mediators would also likely be compromised.

Three tips to improve your gut health

If you’re an athlete struggling with your body composition, performance and/or recovery, despite eating enough, some sort of gut imbalance may be likely.

Reflect on your diet and training regime, because these are usually the first lever of change. Eating good-quality and diverse foods is a good start and consider adding a ‘Yin Yang’ balance to your training.

You can also incorporate some fermented foods, filled with beneficial bugs, that will diversify your gut microbiota. Easy ways to do this are adding a tablespoon of sauerkraut to your salad, or using dairy kefir as a base for your recovery smoothie.

Finally, avoid anti-inflammatory drugs to manage muscle soreness, as these can compromise your gut lining and gut microbiota. Instead, focus on having a range of foods with anti-inflammatory properties (ginger, turmeric, tart cherry juice, pineapple, green tea, etc.), and on active recovery techniques like gentle stretching, foam rolling, massage, applying ice and/or heat – whatever works for you.