How much protein should I actually eat?

Seven answers, and they are not answers to one question. Campbell's 10 percent of calories is a whole-population chronic-disease target for general adults over decades.

Greger's caution is about the animal share and, in its strongest form, about midlife: the cohort behind it (Levine and colleagues, Cell Metabolism, 4 March 2014) found high intake tracked higher mortality between 50 and 65 and lower cancer and overall mortality after 66. Longo's number inverts at roughly 65 for the same reason. Norton's 1.6 g/kg is a breakpoint for maximising muscle in people doing resistance training, Attia's gram per pound is aimed at people already training hard, and Schwarcz's 1.1 to 1.5 g/kg comes with the condition that protein without lifting does nothing.

Lyon is advising an ageing adult, often a woman in or near menopause, whose risk is lost muscle rather than long-term disease. For a 70 kg adult eating 2,200 kcal, 10 percent of calories is roughly 55 g and 1.6 g/kg is roughly 112 g, so the spread is about twofold, and most of it is explained by two facts about you: your age, and whether you do resistance training.

More than a seven-way split suggests. Campbell and Norton both hold that protein quality scores measure the biological efficiency of utilisation rather than a health outcome, and that plant protein can meet the requirement at a higher total intake; Norton's own reading of the mortality literature is that plant protein associates with lower mortality. Campbell, Greger and Longo all prefer plant and fish protein to red and processed meat.

Nobody here is arguing that protein does the work on its own. Schwarcz makes lifting a condition of his own number, Lyon says protein and resistance training are inseparable, and Greger's reading of the trials he cites is that the exercise arm gained the muscle. Longo and Lyon are far apart on the daily total and land on the same figure around hard training, roughly 30 g in the meal after it.

The live disagreement is narrower than how much protein: it is whether a high intake carries an independent long-term cost, and for whom.

No single trial settles this, because the seven are not asking one question. A long-duration randomised trial of higher against lower protein with hard outcomes rather than lean mass would move Norton, Attia and Schwarcz, who all rest on body-composition endpoints.

Greger has pre-committed to a standard that would move him: a randomised trial in adults over 70 measuring muscle by MRI or CT rather than by lean mass, showing that protein above the RDA improves function on top of resistance training. Campbell says his position rests on convergence, so what would move him is evidence that the rodent casein promotion effect does not generalise across protein sources, which is exactly what his critics argue the whey and fish-protein studies already show.

Longo and Lyon both turn on the age inflection: replicating it in a larger cohort adjusted for socioeconomic status, smoking and obesity would move one of them, and failing to replicate it would move the other.