Anabolic Resistance: Why We Lose Muscle As We Age, And How To Fight Back

Despite our best efforts, we still haven’t cracked the code to cease aging. No matter how well you eat, how active you are, or how diligently you prioritize mental health and wellness, the body breaks down more and more with each passing year. Molecular damage leads to reduced cell function, which in turn leads to deterioration of tissue, organs, and health. One of the many pitfalls of aging is muscle loss, or trouble maintaining the same lean muscle mass and functional strength capacity. This phenomenon can be attributed, in part, to anabolic resistance.

What Is Anabolic Resistance?

Anabolic resistance refers to a reduced level of sensitivity to protein ingestion as you get older. Nutrient sensitivity to amino acids is brought on by physical activity, which is reduced in older people due to either lifestyle changes or physical limitations that make exercising difficult. As physical activity is reduced, there is a corresponding reduction in the muscle’s ability to take in amino acids, which are the building blocks of protein. In addition to other age-related factors like microvascular preclusion, this is a primary cause of anabolic resistance. Even in aging folks who maintain healthy, active lifestyles, the body is still less able to break down protein into amino acids or absorb amino acids through the muscle than is a younger person of similar fitness levels.

Inactivity And Its Link To Muscle Loss

“Skeletomuscular is very plastic—us nerds call it plasticity,” says Alex James Kitson, a Master’s degree candidate in Sports and Exercise Nutrition. “It changes and adapts by different levels of intensities, frequencies, and durations.” During periods of inactivity, “it adapts by having skeletomuscular atrophy.” According to research by sports scientist Dr. Benjamin Wall, in cases of bed rest and immobilization, a person loses up to 0.5% lean body mass per day and 1.5% functional strength capacity per day. Other health implications of inactivity cited by Kitson include reductions in metabolic rate, decreases in insulin sensitivity, increases in fat mass, and, as discussed above, lowered amino acid sensitivity.

How To Prevent Muscle Loss As You Age

You can’t stop the march of time, but you can slow its effect on the body by maintaining a healthy, balanced lifestyle, one that includes a dedicated, regular training regimen that emphasizes whole-body fitness: endurance/aerobic, strength/resistance, flexibility exercises, and balance training.

While we can fight muscle loss by boosting our intake of protein adding more protein to the diet isn’t enough. Muscle loss is also linked to a digestive component. Stomach acid levels decrease as we age, which affects the body’s ability to break down and properly utilize dietary protein. As mentioned above, the absorptive process for bioavailable nutrients also dips with age.

The Proper Amount Of Protein Intake

When strategizing optimal protein intake, it is important to consider how age and anabolic resistance factor into your situation. For young, healthy subjects, Kitson states that 0.24 grams of protein per kg of body weight is generally ideal to maximally trigger rates of muscle protein synthesis in the body, even while at rest. For older adults, anabolic resistance prevents optimal protein synthesis. As a result, an older person would require a higher amount of protein to trigger target rates of muscle protein synthesis, as high as 2.4 g/kg.

It is hard, if not impossible, to get that amount of protein from your daily diet. An amino acid supplement can help bridge the gap where diet is not enough. As we age and protein deficiency becomes more of a pressing issue due to factors like anabolic resistance, finding a quality protein source is essential.