Depends on if you wanna do it in a more ethical manner or not. One way you could do it, at least for some places with the resources necessary, is basically forcing tech companies to subtly change your algorithm to slowly push you to believe that you being obese is bad… or that it’s bad in general. Subtly make fatphobic content more accepted by you until you decide to try and change your habits to not be fat. Though, that could just as easily backfire and lead to a spike in suicide for people unable to do it, which is obviously bad.

Though, I think the better option ( at least in my country of the States ) is actual proper education on healthy eating and exercise combined with working on fixing the economy so people have more free time while also having a living wage and access to affordable healthcare.