It’s the responsibility of your social circle to look after you, the way that manifests in men and women is different. Men or overt about the advice they give, but that shouldn’t be equated with bullying.
Considering the amount of overweight children in the developed world, it’s probably a good thing that they are made aware of it by their peers , since it will motivate them to exercise and eat well.
It’s objectively true that being in good shape is healthy, both mentally and physically.
My experience with the US and the UK is that they don’t have a “body image problem, they have a body problem. Being obese doesn’t only hurts the individual, it also hurts society, since it strips the individual from the energy and health to contribute to it, making him more likely to be a drain on the shared medical and social welfare systems.
Sure, there’s the other extremes at which lie anorexic people and full-time body builders, but we are talking about a 0.x% of the male population in those extremes vs over 50% in the obese camp.