Building material for muscle, organs, enzymes, hormones, antibodies and transport proteins.
Switzerland age 18–65: 0.83 g/kg/day; age 65+: 1.0–1.2 g/kg/day.
Legumes, tofu/tempeh, dairy, eggs, fish, meat, seitan, nuts and seeds.
Too little protein can cause muscle loss, weakness, slower wound healing and, when severe, oedema and impaired immunity.
In older age, low intake together with inactivity increases sarcopenia risk; resistance training remains the key stimulus.
Loss of muscle and strength is more relevant than hair or nail changes but is not diagnostic on its own.
Higher in older adults, very restrictive diets, illness, weight loss and high training loads.
Consider intake in g/kg, weight trend, muscle strength and clinical context together.
Food first. Protein powder is simply a convenient food supplement when the target is otherwise hard to reach.
Very high intake usually adds no benefit beyond needs; individualise in kidney disease.