@Gwenhwyfar
"I also think that when someone is slim/fit etc it highlights that others are fatter and they don't like it."
Yes, sometimes it's just jealousy.
This. ^
Whenever I tried to lose weight in the past, (when I was around 2-3 stone overweight,) I would go on a diet, and DH ALWAYS went on one a few days later. And EVERY SINGLE TIME the weight would drop off him three times faster than it dropped off me.
He would be 2 stone lighter within 3 months, and I would be ten pounds lighter. Everyone who saw us commented on HIS weight loss, but never mine (as he had lost the most, and it was more obvious.)
He would smile, and puff his chest out at the compliments, and I would be like
For some reason he couldn't bear me losing weight, and him not losing any. So he'd go on a diet too. I think it was insecurity, and maybe jealousy, but it really fucked me off.
After 4 or 5 times (over about 8-9 years of him doing it,) I stopped telling him I was going on a diet. I would just announce that I didn't feel like much to eat... and I wouldn't snack between meals or have high fat/high carb food.
He'd say 'you're making me look bad you are.. I am sitting here eating chocolate biscuits and you are eating hardly anything.' I got annoyed and said 'don't blame ME if you're feeling greedy or like you're eating too much. I'm not going to eat more to make you feel better about yourself.'
Anyway, for the last 15 years or so, he hasn't bothered dieting. I have a few times, but not much. But he did have this annoying trait of instantly going on a diet when I went on one, and ALWAYS lost much more weight, and much faster too. It made me so disheartened that I quit my diet after a couple of months.
Glad he doesn't do it now!
@WorraLiberty
Weight loss often provokes jealousy and insecurity in some people. You only have to read a few MN threads to see that. Lots people have been dropped by friends, put up with PA comments and they've had their partners start acting possessive/jealous.
This. ^ In spades.