There exists a system of body type classification called “somatotypes”. It was originally dreamed up by a psychologist in the 1930s to link personality to body shape.
While this link has been largely shelved, possibly because not quite all ectomorphs on the planet have turned out to be introverted psychopaths, the concept of 3 basic body types, the ectomorph, endomorph and mesomorph has persisted in the world of diet and fitness.
Ectomorphs are the “hard gainers”. They are slim and find it hard to put on weight, whether than weight be muscle or fat.
Many people envy their skinny ectomorph friends who can “eat anything”.
However if you are an ectomorph and shoveling junk food down your gullet in a daily feeding frenzy, your health is going to fail. Big time.