About two thirds of people in the US are either overweight or obese (1Trusted Source).

However, there are also many people with the opposite problem of being too skinny (2Trusted Source).

This is a concern, as being underweight can be just as bad for your health as being obese.

Additionally, many people who are not clinically underweight still want to gain some muscle.

Whether you’re clinically underweight or simply struggling to gain muscle weight, the main principles are the same.

This article outlines a simple strategy to quickly gain weight — the healthy way.