This is the sort of thing that turns a lot of people off to the whole movement, I’d guess. At its best it’s pure sophistry. But, more likely, it’s just self-deception.
Almost anyone who’s ever had fluctuations in their own weight, or knows even the basics about nutrition or biology can see that overeating and lack of exercise cause weight gain. Yes, that doesn’t mean that every fat person overeats or fails to exercise enough, but on average, and for the majority, that is true.
It’s fantastically silly to think otherwise. I’ve run into friends who I hadn’t seen in a while who’d lost weight, and asked them about it. I’ve never had someone answer “Oh, I didn’t really change anything. I have exactly the same eating and activity patterns I always have.” They almost invariably mention that they’ve been more physically active and more wholesomely nourished.
I’ve seen the effect of insufficient exercise and a sedentary lifestyle in my own body. I weigh about 25 lbs. more than I’d like to (10 lbs into the “overweight” BMI category), and it’s a result of insufficient exercise and less-than-stellar eating habits over the past four years. I also know that I felt better, had more energy, and was more attractive when I weighed a bit less than I do now.
I agree that people should focus on being healthy and not on being thin. However, I find it hard to believe that there are really people much heavier than I am who feel that they are healthy. I used to be able to run a 6-minute mile, and then run another two (slightly slower). I used to be able to do 50 push-ups, and 20 pull-ups, and lift more than I can now. I used to ride my bike 50 miles a week and go to the gym 4 times and swim and dance and run. That was healthy. I’m trying to get back there.
One of the things that scares me the most about any kind of fat-acceptance thinking is that I’ll forget what it really feels like to be in good shape, to really feel healthy and active. People tend to adapt to their current lifestyles, and I fully believe that there are fat people who once were in better shape, but have convinced themselves that there’s no reason to strive for that again. And it’s not that they’re bad people, or that they’re in medical danger, it’s just that they’ve become complacent. And talking about how there’s no link between being fat and exercise or diet is just setting yourself up to feel good about bad decisions.