I have cousins who were severely overweight as kids-as adults, one is still pretty heavy, the other one would never get mistaken for thin. Their parents are heavy and they always ate all kinds of crap and never got any exercise. I think if they had been taken away from their parents, they would have been worse off, because then they would feel like they are being denied something.
My mom put me on a diet when I was about 7, because she thought I was going to be fat. I wasn't fat, I just looked like her mother overall, and she was fat. So, I felt denied, because my siblings were allowed to eat whatever they wanted in front of me. My response was to go to Stop and Rob and buy candy bars, which was worse than eating her homemade goodies. Putting me in foster care wouldn't have changed that behavior, it would have only made it worse-foster kids hoarde food in their rooms for various reasons, but most of them do it to some degree.