After 55, is more protein protective or risky?

Joel KahnMD · cardiologist; MD and Michigan licence confirmed in NPPES, stated triple board certification in internal medicine, cardiovascular medicine and interventional cardiology not confirmed against any certifying body

Do not push protein to 1.8 g per kg a day or beyond once you are past 55.

What it rests onA UK Biobank cohort of 19,420 people without chronic disease at baseline, followed 256,259 person-years with 967 major adverse cardiovascular events, in which intake at or above 1.8 g per kg per day carried 21 percent higher event risk overall, higher all-cause mortality, heart failure, myocardial infarction and cardiovascular death by up to 73 percent, and a 36 percent excess in people over 55 with no significant association under 55. He offers mechanisms as plausible rather than demonstrated: raised IGF-1, saturated fat, absent fibre and phytonutrients, TMAO, Neu5Gc, inflammation, insulin resistance and farming residues. He states the limitation himself: there are always limitations to database studies such as this one.

Layne NortonPhD · nutrition scientist, coach, and competitive powerlifter

Do not restrict protein for longevity reasons on the current evidence.

What it rests onHis read of the mortality literature is that a large meta-analysis found decreased mortality risk associated with total protein intake and with plant protein intake and a neutral effect for animal protein, and that studies finding harm are likely confounded because higher animal protein intakes travel with higher fat and calorie intakes. He separately holds that human randomised trials show high-protein diets do not harm healthy kidneys, with 'healthy' doing necessary work. He grades his own claim Contested rather than Established and acknowledges in his own writing that the mTOR and IGF-1 argument on the other side is real.