Fatties are very good consumers. They purchase a lot of food and buy into fake fads to make them less fat only to give up on them quickly in favor of another fad. Either that or some celeb affirming fatties that they are beautiful while taking their money. Over time their unhealthy lifestyle leads to health issues, and that means more money for pharma and medical industries. People who are morbidly obese need special tools to accomplish regular daily tasks. Imagine needing a special stick just to wipe your ass.
Extra body fat affects brain too. There is correlation between lower IQ and obesity. Getting fat could lower your IQ, alter prefrontal cortex activity, and it interferes with how brain's reward system and memory work. In short, fat people are on average dumber and have lower self control than those at healthy weight. Thus fatties are perfect targets for ads and scams.
Then you can go into schizo things based on consequences of high body fat on brain. Fat masses are easier to control due to their lower intelligence and how easily they succumb to their cravings. They can't be a physical threat either. Not only are they lazy, slow, and weak, but also overly reliant on modern comforts. Fat proles won't be able to rebel, and that's even if they manage to realize that they are being exploited.
Another schizo angle is that fatties are a tool prevent nationalized healthcare and prop insurance industry. They are one of the go to examples to turn the people against the idea of universal health care in the U.S.