Don't worry if nature is anything to go by then the fats will end up breeding themselves out of existence when they eventually find that they can't procreate together or with an attractive mate. Unfortunately that most likely won't happen for many years to come and by then who knows what kind of things will be invented to help these sacks of lard outlive their 40s. Anyone can get fat but those who have the will power to actually exercise and eat healthily will pass on some resilience to getting fat traits to their children at the very least.