Either you believe in the reality of people or your idea of their reality. When it comes to fat people and the widely touted ideas about them, you either believe in the ideas, or the entirety of people.
You have to make a choice and you make a choice through the one which feels more compelling to you. People or the ideas you have about people.
The distance between the failure of expected and actual result is too great.
It is not possible to believe fat people are as fully human as any others and believe a lifestyle centred around calorie expenditure is tolerable and can make and keep them slim.
One or other has to give. Either you'll move towards accepting the inherent failure of the lifestyle, or you'll move towards the inherent faultiness of (fat) human beings.
The difference is like that between humanism or deity-which if you aren't a believer must be an abstraction of the mind.