McDougall points out at one point that it's common for people to gain weight after their doctor tells them to lose weight and puts them on insulin. Insulin promotes weight gain.
If you spend a lot of time around diabetics you'll met many people who have lost appendages and continue to live an morbidly unhealthy lifestyle.
I have spent a lot of time around 4 diabetics in my family, none of which had morbidly unhealthy lifestyles. Sure, they could all use a little more exercise and moderation in their diet, but then again most people can.
https://www.joslin.org/info/why_did_i_gain_weight_when_i_sta...