A lot of people have had problems with the hunger/thirst thing, but honestly it never bothered me.
The indicators are not about giving you “facts” as such, but “feelings”.
Try to think of it in a real world way. If you drank a lot of water, your hunger would go away very fast, but come right back. You wouldn’t consider that a fluctuation cause you understand why. In the same way, I can eat a lot of dinner, till I am full and want no more. But that doesn’t mean I cant eat more when I see some chocolate.
As Junknown said, the best thing you can do if you are worried about weight is eat when you are “very hungry”, as that indicator won’t show until you are getting calorie deficient. If that keeps popping up, keep eating as much calorie dense foods as you can.
If you are playing on the newer builds, keep in mind that they are actively messing with more lifelike calorie burning from strenuous activities. Activities such as killing lots of zombies, or dragging around a 150 pound shopping cart all day, make you burn many more calories then before. As I understand it, the amount of food you can eat without barfing is off, and may cause you to burn way more calories then you can actually eat, if you don’t take a lot of rest days in between active days.