Average is beautiful. Personally though, I am a leg man.
Thus overweight, underweight, overly-muscled, puny, and any other forms of extremes are all forms of the same ugly. There exist some outliers, as can be seen by those who enjoy fat women (breasts and butts are all fat), those who do not care at all about looks, those who think muscles are hot, and douchebags.
There are many people who simply do not care about their health and take it for granted because that's human nature. Most of us have other shit to worry about. There are many people as well who do not have bad habits which lead to poor health, or who actually enjoy exercise, or simply have the willpower to do force themselves to do something they do not enjoy doing. As a species, advances in technology have allowed people who do not have these traits to survive comparably well, if not better than those without.
The same can be said about people with unhealthy ideals in societies. In more authoritarian societies people with contrary or disagreeable ideals like neverdie usually end up dead. However we have moved from dictatorships to republics/oligarchies where a select few govern, and are much more liberal towards acceptance. Neverdie is a product of that evolution of free society, and only survives here because of it.
There's not much you can do to help your friend other than be supportive of him. I would make fun of him for feeling bad about himself, but I don't give a shit about what other people think and way too much of a thinking introvert, so I'm a bad example.