avoiding obesity

Not to be pedantic, but I thought this might be of interest: As I understand it, amount of exercise is a better predictor of lifespan than weight. That is, I would expect someone overweight but who exercises regularly to outlive someone skinny who never exercises.

For example, this life expectancy calculator outputs 70 years for a 5"6" 25 year old male who weighs 300lbs, but exercises vigorously daily. Changing the weight to 150 lbs and putting in no exercise raised the life expectancy by only 1 year. (a bit less than I was expecting, actually. I was about to significantly update, but then it occurred to me that 300 lbs isn't the definition of obesity. I knew this previously, but apparently hadn't fully internalized that.) EDIT: This calculator may not work well for weights over ~250 lbs. See comment below.

So, my top two recommendations to friends would be quit smoking and exercise regularly. I'd recommend Less Wrongers either do high intensity workouts once a can read or watch Khan Academy or listen to The week to minimize the amount of time spent on non-productive activities, or pick a more frequent but lower intensity activity they Sequences audiobook while doing. I'm not an expert or anything. That's just the impression I've gotten from my own research.