well. it is always "food" we choose to eat that makes our body change. the book talks about "who" chooses these foods and "why". not that adhd is the
"cause" he is talking about connections.
Honestly, I think it is our culture of fatty deep fried foods that causes obesity. I bet the obesity rates are just as high for those who are non ADHD.
Read the review of the book. It seemed like a pretty sensible book since it attempted to break down why one would have weight problems and then how to deal with that specific cause - instead of the traditional one diet fits all approach.
As to the link with ADHD. Many with ADHD are very lean because they are so active. However, due to jobs or job focus, meds, spontaneity, anxiety, depression, etc. I can certainly see how weight management could be a problem.