Does your tween eat relatively healthy? I am struggling with my 12 yo overeating. I’m not sure how to help her and sometimes lose my patience with her. I’m always reminding her how diabetes runs in our family so she has to watch her sugar intake and limit desserts to once a week. Or how she should have more protein and less carbs for dinner because it will keep her fuller longer. How does everyone else deal with this? TIA.

Wow sounds tough. Re "dessert after huge dinner" -- for a long time we did dessert in the middle of dinner -- eat your vegetables, then you can have dessert, then continue to eat. Also "listen to your belly" is a huge refrain in our house. We don't forbid anything, just emphasize listening to when you are actually hungry, eating majority healthy foods, and thinking about long term health.
my 12 yo is skinny but younger one has a weight gain tendency. I have made both of them exercise during this pandemic. And I always talk about different foods and how it affects us. I have talked about weight gain but in terms of health, not in terms of appearance. we have obesity in our family and i talk about it
Don’t buy any of it. My son is 12 and I can’t get over how overweight some of these kids are, it’s terrible.
Dessert once a week? I eat dessert almost every night and I am a healthy weight. It’s all about moderation. I also eat very light through the day because I know i would rather snack and indulge after dinner. I wouldn’t make anything forbidden. It’s more about total food consumed over the day. Sorry, I know that’s not all that helpful but if someone told me I could only have dessert once a week, all I would crave would sweets.
"If sugar had been discovered ten years ago instead of in antiquity, it would be a felony offense to possess it. Cocaine's pretty damn unhealthy, but at least it isn't half of our children's diet..."
For 10 yo DD, I have just railed against sugar her whole life. If she wants a dessert I ask her whether she's had healthy food throughout the day. I am not sure if it will work as she gets more independent. Fingers crossed.
I'm French, and I have no issues with the fat talk, but I have no issues around food either, i.e there's no "emotional eating", or "special treats" in our home. DD eats without guilt whatever she fancies outside the 3 main meals/day, and when she puts on weight and starts to be pudgy, I just tell her to reduce the crap eating for a while, so she doesn't get fat.
But to answer your question, bc what I said was not helpful in your situation : go cold turkey, make all the meals yourself, (=she doesn't get to choose), do not buy anything sugary or junk for a while, even if you want to eat that. Increase the protein intake, lower the carbs, don't bother about the fat. I noticed that it always takes 3 days to get over sugar/carbs cravings, so the difficult part is to last 4 days. Do not limit fruits and full fat yoghurts. Do not consume splenda or similar. The only sugars you get come from fruits.
Stop the talk about "1 treat allowed/week".
Exercise is also really helpful for controlling blood sugar and insulin signaling.
I have a just turned 13 year old dd. It's a tough subject especially during the pandemic when kids aren't as active. Our motto is everything in moderation. I wouldn't harp on it all the time (not sure if you are but I can't tell by the post). This is just going to turn into negative body issues. Make sure there are healthy foods in the house for snacks, meal times, etc. Also, we don't make any food "forbidden." Not sure this is helpful - sorry!