The aging muscle story is more complicated — and more hopeful — than you’ve been told.

“Anabolic resistance” refers to the blunted MPS response to protein intake and exercise that occurs with aging. It’s real — but recent research has challenged how severe it is and how much of it is actually due to aging itself versus lifestyle factors.

Katsanos et al. (2005) was the landmark study that established the concept: elderly subjects showed significantly less muscle protein accretion than young subjects after ingesting a small (6.7g) bolus of EAAs. This suggested a “resistance” to the anabolic signal.

However, Paddon-Jones et al. (2004) showed that when a larger dose (15g) of EAAs was provided, both young and elderly subjects increased MPS by approximately the same amount (~0.04%/h). The resistance could be partially overcome by simply providing more amino acids.

More recently, Shad et al. (2016) reviewed the evidence in Experimental Gerontology and argued that much of what’s attributed to “anabolic resistance” in aging may actually reflect reduced physical activity, chronic low-grade inflammation, and suboptimal protein intake — factors that are modifiable, not inevitable consequences of biological aging.

What this means practically

The practical implication is straightforward: older adults may need to be more intentional about hitting the full threshold dose at each eating occasion. Aiming for 12–15g of EAAs per serving (vs. the 10g that’s sufficient for young adults) helps compensate for any age-related blunting. Resistance exercise remains the most potent stimulus for maintaining muscle sensitivity to amino acids at any age.

References

1. Katsanos CS, Kobayashi H, Sheffield-Moore M, et al. Aging is associated with diminished accretion of muscle proteins after the ingestion of a small bolus of essential amino acids. Am J Clin Nutr. 2005;82(5):1065-1073. PubMed
2. Paddon-Jones D, Sheffield-Moore M, Zhang XJ, et al. Amino acid ingestion improves muscle protein synthesis in the young and elderly. Am J Physiol Endocrinol Metab. 2004;286(3):E321-E328. PubMed
3. Shad BJ, Thompson JL, Breen L. Does the muscle protein synthetic response to exercise and amino acid-based nutrition diminish with advancing age? A systematic review. Am J Physiol Endocrinol Metab. 2016;311(5):E803-E817. PubMed
4. Kumar V, Selby A, Rankin D, et al. Age-related differences in the dose-response relationship of muscle protein synthesis to resistance exercise in young and old men. J Physiol. 2009;587(1):211-217. PubMed