Reference
Anabolic Resistance
**Anabolic resistance** is the reduced stimulation of muscle protein synthesis (MPS) in response to a given dose of dietary protein or amino acids — a condition associated with aging, inactivity, and obesity that contributes to the gradual loss of muscle mass known as sarcopenia.
How it works
In a younger, active person, ingesting protein produces a reliable rise in muscle protein synthesis. With aging, that same dose produces a smaller and slower response. Aging is characterized by a blunted increase in muscle protein synthesis rates following protein intake, a condition defined as anabolic resistance (PMID:23558692). The phenomenon is not limited to feeding: the synergistic effect of resistance exercise combined with protein ingestion is also delayed with age, with the peak synthetic response occurring later in older adults than in the young (Journal of Applied Physiology, 2008, PMID:18323467).
Anabolic resistance does not present uniformly. Some individuals show resistance to elevated amino acids, others to exercise, and some to both, which is why personalized nutritional and exercise interventions are recommended (PMID:34026802). At the cellular level, anabolic stimuli normally trigger mTORC1 translocation to the lysosome and to peripheral regions of the muscle fiber; a diminished sensitivity of this signaling to feeding is part of the resistant state.
Why it matters
Anabolic resistance is central to age-related muscle loss and to the delivery of clinical nutrition care (PMID:29389741). Because muscle becomes less responsive per gram of protein consumed, the practical compensation is a higher intake. Expert recommendations suggest older adults require 1.0–1.5 g/kg/day of protein to offset anabolic resistance, above the figure used for younger sedentary adults. Inactivity compounds the problem: decreased physical activity, even in young subjects, can produce anabolic resistance that cannot be overcome by increasing dietary protein alone. The implication is that both adequate protein and resistance exercise are required, not one or the other. For a fuller treatment of intake targets across the lifespan, see the guide on protein after 40.
The role of leucine
Leucine content helps explain why protein source matters once resistance sets in. In a 2024 trial, a 20 g plant-based blend supplied 1.5 g of leucine — half that of an equivalent whey dose — and produced a lower synthesis response; adding free leucine to bring the blend to 3.0 g raised the response (0.049%/h) to a level statistically indistinguishable from whey (0.046%/h), indicating leucine fortification closed the anabolic gap (J Nutr, PMC11153912, 2024). Potato protein isolate has been shown to stimulate muscle protein synthesis at rest and after resistance exercise in young women (Nutrients, 2020, PMID:32349353).
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