About two thirds of people in the US are either overweight or obese (1).
However, there are also many people with the opposite problem of being too skinny (2).
This is a concern, because 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 are clinically underweight or simply a “hard gainer” struggling to gain some muscle weight, the main principles are the same.
This article outlines a simple strategy to quickly gain weight, the healthy way.
What Does “Underweight” Really Mean?
Being underweight is defined as having a body mass index (BMI) below 18.5. This is estimated to be less than the body mass needed to sustain optimal health.
Conversely, over 25 is considered overweight and over 30 is considered obese.
Use this calculator to see where you fit on the BMI scale (opens in new tab).
However, keep in mind that there are many problems with the BMI scale, which only looks at weight and height. It does not take muscle mass into account.
Some people are naturally very skinny but still healthy. Being underweight according to this scale does not necessarily mean that you have a health problem.
Being underweight is about 2-3 times as common among girls and women. In the US, 1% of men and 2.4% of women 20 years and older are underweight (2)