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Emerging research suggests that muscle is more than bulk. It’s a metabolically active, endocrine tissue comprised of more than 500 skeletal muscles making up about 40-50% of body weight. In addition to its well-known role in physical performance, skeletal muscles are involved in numerous metabolic pathways. They are the primary site for glucose uptake and help maintain glucose homeostasis, are involved in fatty acid metabolism, and provide a place for glycogen synthesis, making them one of the main energy storage sites in the body. A somewhat newer finding is that they excrete myokines, hormones produced by the skeletal muscle. Furthermore, much like there has been the long-term recognition of “neuronal plasticity,” there is discussion about “muscle plasticity,” or the ability of the muscle to switch to different muscle fibers as being connected to one’s fitness level.

Each of these factors makes skeletal muscle mass a vital health aspect for individuals. However, with increasing age, muscle loss can lead to physical limitations that increase the risk of falls, hospitalization, and even premature death. In addition to a reduction in muscle mass, a decline in muscle strength and quality accompany the aging process and can decrease quality of life. Muscle loss associated with aging can be accelerated by poor nutrition, particularly inadequate protein, and calorie intake. But there are many other factors related to muscle health that are now getting recognition.

The Impact of Whole Grains on Muscle

While there is debate over whether or not whole grains are to be eaten or avoided by various individuals, there is science to suggest they have merit for muscle health. Whole grains contain a plethora of bioactive compounds, including ferulic acid, quercetin, catechins, carotenoids, beta-glucan, betaine, and others. There is growing support for these compounds’ role in enhancing muscle tissue formation and metabolic function through mechanisms such as exerting anti-fatigue effects, improving mitochondrial function, and altering muscle-fiber-type conversion.

For example, the bioactive compound ferulic acid, which is found in oats, rice, quinoa, wheat, and corn, has shown anti-fatigue effects on muscle by decreasing lactate dehydrogenase and increasing succinate dehydrogenase activity. Quercetin, known for its antioxidative and anti-inflammatory effects, is found in buckwheat (among other foods such as apples and onions) and has anti-fatigue effects by way of improving muscle glycogen content, decreasing oxidative stress, and increasing mitochondrial fatty acid beta-oxidation. Anti-fatigue effects are also seen with resveratrol and rutin, both present in buckwheat. In a small study on men and women between the ages of 65 and 80, resveratrol was shown to act synergistically with exercise to improve mitochondria density, oxygen uptake, and muscle function. In the study, the participants engaged in 12 weeks of exercise and took either a placebo or a supplement containing 500 mg of resveratrol.

Bioactive compounds in whole grains can help in the transformation of fast-twitch muscle fibers to slow-twitch muscle fibers, which are relatively fatigue resistant. Some of these compounds include ferulic acid, resveratrol, quercetin, and beta-glucan.

Several bioactive compounds can enhance mitochondrial function in skeletal muscle. These actives include catechins, which are known to be found in green tea but also present in wheat, buckwheat, and barley; and tocotrienols, present in buckwheat, oat, rye, and rice. In addition to benefits related to mitochondria, catechins can inhibit protein degradation, increase muscle protein synthesis, increase oxygen consumption in muscle tissue during endurance training, and induce GLUT4 translocation to increase glucose uptake in skeletal muscle.

The impact of bioactive compounds on glucose is seen in other instances as well. For example, beta-sitosterol in wheat, oat, barley, and quinoa, is shown to positively impact glucose metabolism and improve insulin sensitivity by facilitating GLUT4 translocation. Quercetin, on the other hand, is shown to increase adiponectin signaling. Adiponectin is a peptide secreted by fat cells that can target skeletal muscle and improves both glucose utilization and fatty acid oxidation.

Finally, general fiber intake is associated with increased muscle strength, improved muscle glucose homeostasis, and improved exercise capacity. According to NHANES data from 2011-2018 on adults 40 years and older, dietary fiber was associated with an increase in lean body mass, decrease in fat mass, improved grip strength, and improved blood sugar regulation and insulin sensitivity. There is additional evidence of a relationship between diet quality and muscle mass. For example, higher intake of soy products and green and yellow vegetables decreases age-related decreases in muscle strength in women.

Interestingly, in the case of sarcopenia, muscle quality is thought to be a key factor. This is because muscle strength decreases faster than muscle mass as a person ages – even as much as three times faster. This finding further emphasizes the importance of foods, such as whole grains, that can improve muscle quality and increase muscle strength. Further, whole grains and the antioxidant compounds they contain may reduce the risk of sarcopenia, which is not only related to anabolic resistance to feeding and exercise, but to systemic inflammation. Fortunately, for those individuals not eating whole grains, several of these phytochemicals can be found in other food groups.

The Microbiome and Muscle

Emerging evidence suggests a “gut-muscle” axis, which explains how the microbiome in the gut can impact muscle. One animal study examined the effects of different antibiotic regimens on muscle in mice involved in progressive weighted wheel running for exercise. Researchers separated mice into four groups: the first group was untreated and did not run; the second group was untreated but did run; the third group was treated with antibiotics and did not run; and the fourth group was treated with antibiotics and did run. While there was no difference in bacterial species in the gut microbiome of mice before antibiotic treatment, the mice who received antibiotic treatment had significantly reduced bacterial species compared to those who did not. Results showed that mice who had antibiotic-induced dysbiosis experienced blunted hypertrophy and impaired muscle fiber type conversion, ultimately showing that the gut microbiome plays a role in the adaptation of skeletal muscle to exercise.

The gut microbiome has many roles, but one of those roles is to produce short-chain fatty acids (SCFAs) that result from the fermentation of complex resistant carbohydrates by gut bacteria. SCFAs primarily provide energy to colonocytes but may play a role in muscle, too. SCFAs that are not taken up by colonocytes are metabolized in the liver, and those not metabolized in the liver can be taken up by other tissues, including muscle cells, where SCFAs are involved in lipid, carbohydrate, and protein metabolism. A cell study assessed the effect of SCFAs on myotubes, which are formed from myogenic cells during muscle differentiation and generate force by contraction. In this study, myotubes were exposed to single SCFAs and mixtures of SCFAs (acetate, propionate, and butyrate). Researchers found that glucose uptake in myotubes – an essential role of energy homeostasis – was increased by a particular ratio of SCFAs, even more so than what was seen with metformin-induced glucose uptake. Additionally, SCFAs aid in the release of Ca2+, which triggers muscle contraction.

Finally, older adults with normal muscle mass have been shown to have higher levels of butyrate, a type of SCFA, compared to those with low muscle mass, presumably because of the role butyrate plays in promoting mitochondrial synthesis and therefore muscle function.

Probiotics and prebiotics may support muscle. Types of probiotics to reduce muscle loss due to aging and cancer include Lactobacillus and Bifidobacillus species. Additionally, in a small study involving six older adults with sarcopenia, it was found that an increase in Bifidobacterium longum after prebiotic administration was associated with increased skeletal muscle mass and reduced body fat percentage.

The Circadian Rhythm and Muscle

The circadian rhythm influences various processes within the body. It involves the “master clock” in the hypothalamus’ suprachiasmatic nucleus (SCN) as well as the peripheral clocks, which includes the musculoskeletal system with approximately 1600 circadian genes expressed in skeletal muscle. In fact, the skeletal muscle has the most significant number of peripheral clocks in the body. These peripheral clocks rely on the regulation of a 24-hour schedule and work in tandem with the central clock to support “rhythmic function” in the body.

Bmal1 is a clock protein involved in SCN regulation and is impacted by sleep quality, exercise, and diet. Bmal1 is involved in the regulation of the musculoskeletal system, and disruption can result in muscle-specific loss. In mice, the absence of Bmal1 expression led to weak skeletal muscles and muscle atrophy. In mice studies, muscle strength is also reduced by constant and long-term light exposure, indicating that the circadian rhythm in muscle is important in homeostasis.

Additionally, past research has shown that time-restricting feeding (TRF), which involves consuming the day’s calories during the “active” hours of the day without altering total energy consumption, can benefit metabolism and attenuate obesity. Additionally, TRF could modulate skeletal muscle structure, function, and metabolism. In the case of circadian rhythm disruption, TRF may increase muscle performance and decrease ectopic adiposity via its impact on glucose metabolism.

Genetics and Muscle

TAS1R2 is a gene that contributes to the activity of sweet taste receptors and is active on the tongue and in skeletal muscle. In a study with mice, muscle-specific deletion of this gene resulted in an increase in lean mass independent of total body mass. It was associated with an increase in muscle strength and running endurance compared to controls. The mice with the deleted TAS1R2 gene also exhibited lower oxygen consumption during moderate-intensity exercise and improved mitochondrial function. Beneficial effects on obese mice and aged mice were observed as well.

In older obese humans, it was found that those with reduced function of the TAS1R2 gene had improved responses to exercise training, increased skeletal mass, improved mitochondrial capacity, and improved aerobic performance after a 6-month trial of weight loss through diet and exercise. This study concluded that TAS1R2 has a role in regulating muscle function and structure and may be useful as an approach to muscle dysfunction in obesity and aging.

Final Remarks

While the basis of building muscle through adequate energy and protein consumption paired with exercise holds true, you can take additional steps to support your muscle mass.

These steps include the following:

• incorporating whole grains such as oats, quinoa, and buckwheat in the diet (or other polyphenol-rich plant foods if whole grains are not able to be eaten);
• supporting your gut microbiome with a variety of plant foods, especially those rich in prebiotic fibers, and fermented products;
• eating colorful fruits and vegetables to reduce inflammation; and
• supporting your circadian rhythm with regular sleeping routines.

If you have questions about supporting your muscle, talk to your doctor, nutritionist, dietitian, or another healthcare professional for personal options based on your circumstances.