Eat enough protein if you are training
The one nutrition variable with a large, consistent, well-measured effect.
Do this
Aim for roughly 1.6 grams of protein per kilogram of body weight per day when doing resistance training. Distribute it across meals. Going substantially above that shows little additional benefit in the data.
Why it works
A meta-analysis of 49 studies found protein supplementation significantly increased strength and lean mass gains during resistance training, with benefits plateauing at around 1.6 g/kg/day. This is one of the few nutrition findings with a clear dose-response curve and consistent replication.
Where it fails
It only matters alongside training - protein without a stimulus does very little. Older adults may need more. People with kidney disease should not act on general guidance here.
How you’ll know
Weigh and log your intake for three days. Almost everyone who assumes they eat enough protein is eating less than they think.