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Exercise looks harmful short term
Exercise looks bad
Described without its name, exercise would sound like something to avoid. Every acute response on that list looks bad, and each of those markers improves with long-term exercise.
The macronutrient trap
The same trap applies in nutrition. Any single macronutrient can be argued, mechanistically, to shorten life: fat can reduce flow-mediated dilation, which matters for heart health in the short term, and carbohydrates stimulate insulin, which is pro-inflammatory. Even scientists make the mistake of assuming an acute response relates to long-term outcomes.
The protein and mTOR case
Protein stimulates mTOR, and the argument that this makes it a risk for early death rests on that mechanism. Human outcome data supporting the claim is very thin. A year-long randomized trial by Jose Antonio, albeit only a year, tracked a range of biomarkers and found no negative health outcomes even at protein intakes up to about 4 grams per kilogram of body weight, other than that people felt so satiated they ate fewer calories.
Why does short-term exercise stress make people stronger?
Biologists call it hormesis: a small dose of stress triggers repair processes that overshoot. Exercise raises free radicals briefly, which activates antioxidant defenses in muscle. Muscle damage activates satellite cells, stem cells that fuse to muscle fibers and add nuclei. The result is a body better equipped for the next bout of the same stress.
Why did people suspect mTOR shortens life?
Inhibiting mTOR extends lifespan in yeast, worms, flies, and mice. In a 2009 paper in Nature, David Harrison and colleagues found that the mTOR inhibitor rapamycin extended lifespan in mice even when started late in life. Since protein activates mTOR, some researchers proposed that high protein might shorten life. Human outcome data for that idea remain limited.
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