With a high metabolism, you take in calories but don't see the instant gains on the scale that others who have different hormone profiles and genetic dispositions register. You're likely an ectomorph, a body type characterized by a lanky, long frame, narrow shoulders and little body fat.

It's always better to get the extra calories you need for weight gain from real food. But if you're having a difficult time getting the calories you need from what you eat, you may consider a supplement.