Obesity of politicians may be a good indicator of that country’s corruption

Maybe it's that fat people have low self-discipline. A collection of fat people will likely also have low self-discipline, ie, a group of fat people may not care about fiscal discipline. It seems like a short road from not caring about fiscal discipline to corruption.

Trust is not so simple as "don't trust fat people". I might trust a fat person to cook a great meal for me, but not trust them to handle grocery shopping on a strict budget.