This program is mostly designed for ectomorph body type which generally means that person is having lack of muscle mass and normal / under fat mass. They are usually skinny / lean and their program is completely opposite to weight loss program. This difference is in nutrition rules and intensity / volume of training.What we mean under gaining weight programs is focus d on muscle growth and gaining / keeping fat mass, if necessary. Be Strong approach is based on scientific facts, tests and training methodology related with this specific goal which one is not so common like weight loss program. Underweight condition could lead to so many health issues and we should threat them properly. Changing lifestyle is key and this start with properly physical activity, nutrition, sleep and reduced stress.