As we get older or if we're inactive or sick, our muscles don't build new protein as well after eating — and that's a big reason why we lose muscle, not because of changes in how our muscles work when we're not eating.

The study shows that as people age or become inactive, their muscles don’t build protein as well after eating, which helps explain muscle loss. This supports the idea that it’s not about constant muscle breakdown, but about not repairing and growing muscle after meals.