What Is The Gut-Muscle Axis?

Welcome to my blog post ‘What Is The Gut-Muscle Axis And How Are They Connected?’. This blog is the first in a new category of my blog called muscle science where I will discuss the research showing the health benefits of muscle, and the links between muscle and the rest of the body.

What Is The Gut-Muscle Axis?

We have heard about the gut-brain axis, the gut-skin axis, the gut-lung axis, the but-bone axis, the gut-liver axis, the gut-thyroid axis. Well now we have the gut-muscle axis.

The gut-muscle axis is simply the connection between gut health and function, and muscle health and function.

Optimal gut microbiome composition may have an impact on muscle protein synthesis and mitochondrial biogenesis and function, as well as muscle glycogen storage.

How Does The Gut Microbiome Influence Muscle?

The gut microbiome supports muscle health via:

• The production of nutrients including certain vitamins and amino acids.
• Modulating the immune system and reducing inflammation and oxidative stress.
• Supporting of glucose metabolism.
• Mitochondrial function.

Antibiotics And The Gut-Muscle Axis

One study determined, in mice, the consequences of gut microbiome depletion after treatment with a mixture of a broad spectrum of antibiotics for 21 days and after 10 days of natural ‘reseeding’ (reestablishing a microbiome). The authors found that, in gut microbome-depleted mice, running endurance was decreased. Importantly, the muscle endurance capacity was efficiently normalised by natural reseeding. These endurance changes were not related to variation in muscle mass, fiber typology, or mitochondrial function (2).

Our results strongly support the hypothesis that gut bacteria are required for host optimal skeletal muscle function (2).

Probiotics And The Gut-Muscle Axis

Supplementation with probiotics may have some beneficial effect on aerobic and anaerobic performance (1)

The intestinal microbiome may also contribute to oxidative stress reduction. Some bacterial strains have antioxidant properties through various mechanisms. These include the expression of antioxidant enzymes, modulation of inflammation caused by pro-inflammatory cytokines or presence of pathogens, and metabolism regulation through greater absorption of antioxidants.

Specifically, some studies have shown that bacterial species such as Lactobacillus plantarum, Lactobacillus gasseri, Lactobacillus fermentum, Lactococcus Lactis and Streptococcus thermophilus are able to increase SOD activity. Here is a quick summary of some studies:

• Lactobacillus, Lactococcus, and Bifidobacterium have all been shown to elevate intestinal glutathione levels, which is the master antioxidant in the body.
• Animal studies have demonstrated that individuals whose microbiota was richer in Escherichia coli and Enterococci, while being poorer in Lactobacilli, had higher susceptibility to oxidative stress.
• Martatelli et al. conducted a trial with athletes, showing that a Lactobacillus rhamnosus and Lactobacillus paracasei probiotic species supplementation increased plasma antioxidant levels as a response to high-intensity exercise.

Overall, these findings clearly support the essential need to balance a proper diet, an adequate exercise regime, and a healthy microbiome to promote higher glycogen storage to increase mitochondrial function and muscle building (1).

• Jäger et al. have demonstrated the beneficial effect of using the probiotic strains Streptococcus thermophilus FP4 and Bifidobacterium breve BR03, to regulate the inflammation state and enhance muscle training adaptation. The study showed that 21 days of probiotic supplementation period decreased the inflammatory molecule IL-6 in the blood, 48 hours after exercise in 15 trained men. It also reduced the movement limitations caused by training, contributing to a shortening of the regeneration period.
• The positive effects on inflammation and muscle functions were also demonstrated by Wen-Ching et al. They have noticed that long-term supplementation with the probiotic Lactobacillus plantarum PS128 in triathletes resulted in the reduction of plasma creatine kinse (CK) level. Additionally, other significant improvements were found across various markers of inflammation and oxidative stress.
• The effectiveness of probiotic supplementation was also demonstrated by Townsend et al., who showed that 12 weeks of Bacillus subtilis DE111 reduced TNF-α levels (a marker of inflammation), without altering other inflammation parameters.
• Another study, conducted by Roberts et al., clearly displayed the positive effect of using a multi-strain probiotic (Lactobacillus acidophilus CUL-60, Lactobacillus acidophilus CUL-21, Bifidobacterium bifidum CUL-20, and Bifidobacterium animalis) for 12 weeks on the intestinal permeability of triathlonists. The probiotic combined with the prebiotic fructooligosaccharides and the anti-oxidant α-lipolic acid supplementation was associated with a reduction in blood endotoxin level compared to the control group. Endotoxins in the blood may indicate leaky gut, and may contribute to inflammation.

The Gut Microbiome And Anabolic/Catabolic Processes

The intestinal microbiome may affect the metabolism of muscles through several pathways. Evidence regarding the relationship between gut microbiome composition and muscle function have been described in the development of age-related sarcopenia. It was noted that muscle atrophy correlates with a decrease in the number of bacterial species sending anti-inflammatory and pro-anabolic mediators.

Sarcopenia and systemic weakness among the elderly have been correlated with imbalances in the gut microbiome, contributing to increased intestinal barrier permeability (leaky gut), elevated blood LPS levels, activation of the immune system, and a reduction of insulin sensitivity.

In addition, Buigues et al. demonstrated 13-week multistrain Lactobacillus and Bifidobacterium probiotic mixture supplementation enhanced endurance and muscular strength in older individuals. The study showed that older patients who received the prebiotics fructooligosaccharides and inulin experienced a significant improvement in hand grip strength and self-reported exhaustion level.

The lack of homeostasis was associated with an increased abundance of gram-negative bacteria responsible for the systemic inflammation. It has also been noticed that the bacteria Escherichia, Klebsiella, and Citrobacter significantly contribute to the inflammation.

Summary

• Gut microbiome intervention may have beneficial effects on the human body, resulting in better athletic performance.
• Modulation of the immune response, oxidative stress, metabolic processes, and nutrients bioavailability are considered the main mechanisms.
• The microbiome may also have an impact on muscle protein synthesis and mitochondrial biogenesis and function, as well as muscle glycogen storage.
• Imbalances in the gut microbiome may reduce physiological adaptation, increase inflammatory markers as well as free radical macromolecules devastation, all contributing to skeletal muscle atrophy.
• Numerous studies indicate the beneficial effect of probiotics supplementation on aerobic and anaerobic performance in athletes.
• Not all of these processes are well understood, and there is a clear need for future studies to explore this gut-muscle connection.

References For ‘What Is The Gut-Muscle Axis And How Are They Connected?’:

1. Gut-Muscle Axis Exists and May Affect Skeletal Muscle Adaptation to Training: click here.
2. Gut bacteria are critical for optimal muscle function: a potential link with glucose homeostasis: click here.
3. The Role of the Gut Microbiome on Skeletal Muscle Mass and Physical Function: 2019 Update: click here.
4. Exercise and immune system as modulators of intestinal microbiome: implications for the gut-muscle axis hypothesis: click here.
5. Aging Gut Microbiota at the Cross-Road between Nutrition, Physical Frailty, and Sarcopenia: Is There a Gut-Muscle Axis?: click here.
6. Gut Microbiota, Muscle Mass and Function in Aging: A Focus on Physical Frailty and Sarcopenia: click here.
7. Investigation of the Diet-Gut-Muscle Axis in the Osteoporotic Fractures in Men Study: click here.
8. Muscle strength is increased in mice that are colonized with microbiota from high-functioning older adults: click here.