How should I eat or work out as an ectomorph / mesomorph / endomorph?

The same way as everyone else, because there is no such thing. Collectively referred to as “somatotypes”, these classifications are the result of a now debunked theory of psychology and had nothing to do with predicting how one gained fat or muscle.

These concepts unfortunately stick around because they are powerful marketing tools to sell products and programs to those who don’t know better – be wary of anyone who treats these terms as legitimate.