@greenean71, I think it can happen at any age change, but I just noticed it recently with my toddler aging to child. But that is because I was testing genetics and needed to age up the baby to a teen in a short amount of time, but at the time I posted earlier I had only gotten to the child stage. And if I don't have her loose some weight, I won't know if aging her to teen will make her heavy or not. This time around it seems to be a problem with female Sims. I think in the past it happened to both females and males. 🤔
As for foods making your Sims gain weight, some do have more calories, but other foods have zero, which seems to be an accident, since some of these foods are fattening in real life. The best food to eat (that still has some calories) is Garden Salad. The worst is Lobster Thermidor. Check the list from Carl's Sims 4 Guide for the list of foods and calories. https://www.carls-sims-4-guide.com/tutorials/calories.php (I think the previous link that I gave in the other post is broken.😳🤭 ) You will also see the section of foods that accidentally have no calories, so you can make those dishes as well . Bacon and Eggs aren't too bad in the game, but not as good as salad. And all of this depends on which packs you have added to your game. Also, some foods aren't listed (like the food stall dishes that come with City Living, or the Grand Feasts that come with Seasons. But the Grand Feasts can make your Sims fat very quickly! And as with real life, the best way to loose weight is a combination of diet and exercise. Just make sure you do cardio activites -- jog and use the treadmill. ( @SheriGR & I love the treadmill combined with a TV for raising the Fun need (and Cooking skill if you have them watch the Cooking Channel) or the 2 treadmill combo for the added socialization they can get. But some gyms have these set ups too!
Punching bag and training dummy (Strangerville) raise both cardio and muscle tone. And if you have Fitness Stuff you can do a cardio workout. I'm not too sure how swimming and skating affect weight loss.🤔 I've used those more for fun so far. 😃
I hope this is of some help to you! 🙂 Hopefully they will fix the bug soon! 🤞