I once heard a radio interview with an obesity researcher who told that counterintuitively becoming fat didn't have that much to do with overeating. His point was that people becomes obese over the course of several years. If excess calorie consumption alone was responsible for the weight gain, the excess weight accounted for a daily excess food intake equal to a teaspoon of sugar.

His findings were that the human body is capable of either storing or shedding energy reserves and that the body will store as much energy as possible if it predicts a shortage of food. This capability evolved back when food was scarce and survival and flood gathering depended on being part of a group and he claimed that although the mechanism had not been studied in detail there was evidence that suggested a link between obesity and mental well-being.

To me it makes sense. Fear of being excluded is ultimately fear of death. It wouldn't be that surprising if that fear had physiological impacts by triggering survival mechanisms.

The professor didn't make a directly anti-capitalist argument but I think there is one to be made. Under late capitalism you don't have the sense of security in your position in society you had at previous iterations. Back in the old days if you became a mailman you could count on being a government employee for life and it was common to stay in the same workplace for decades. Unions provided networks of solidarity, community and security.

Today neoliberalism has ravaged the welfare state. Unions are a shadow of their former glory and workers are constantly monitored and assessed. Meanwhile capitalist propaganda paints an image where you have to live up to ridiculously high standards of beauty, wealth etc. to be acceptable.

All this leads to people feeling insecure and feeling they're not good enough. I don't think it is unreasonable to think that this contributes to the obesity epidemic.

TLDR: Capitalism makes you feel like shit and that is making you fat.