This came up for discussion at the lunch table once. Each grade's teachers ate together at the same table every day.
Myself and another teacher were on the chunky side, not hugely obese, but maybe stuck between the end of misses sizes and the beginning of Plus sizes, about size 18. The other two teachers were skinny minis.
We were talking about weight one day and the skinnies remarked on how little the chunkies ate. I ate a piece of fruit, a yogurt and a premier protein drink. If I could even get that much down. I just don't have much of an appetite and neither did my chunky colleague.
The skinnies ate unhealthy microwave dinners and all kinds of crap. One of them whom I shared an office with snacked all day from snacks in her lunch box. She loved chocolate.
The other chunky and I had diagnosed endocrine disorders and were both on thyroid medication. We ate little, but our bodies hold onto fat like it's going out of style! And we were all physically active! You never get a chance to sit down when teaching elementary school. The other chunky even taught dance after school!
The point being that you can't tell if someone is overeating unless you see them eating every day. The physical result doesn't always correlate.
I have my thyroid checked and it seems to be getting worse as I get older. I think my lack of appetite might be related to that. I have trouble cooking dinner now because I am just not hungry and don't judge well how much everyone else will want to eat. Just like when you go grocery shopping on an empty stomach you buy more. I'm never hungry and don't buy enough.