Popeye may have been on to something. A steroid found in leafy greens ramps up protein synthesis in muscles.

extracted phytoecdysteroids from spinach

on samples of cultured human muscle, it sped up growth by 20 per cent. Rats were also slightly stronger after a month of injections of the extract

Unfortunately, you would need to eat more than a kilogram of spinach every day to gain equivalent amounts of the steroid.