Thanks for your insights.
It's true, I did overhear (by chance, not because I was being nosey) and no I don't think he intended for me to hear him, so he wasn't deliberately being cruel with thr comment itself.
I'm glad it's not just me feeling it's somewhat disloyal for him to talk about me like that with someone else and I do feel it's disrespectful.
For those of you asking, he DID say 'fat' and outright compare to when we met in our twenties, which in his opinion was better. He doesn't look like he did then either and while I gave my bmi for context, I'm not hugely overweight, but out of shape through being less active recently. This I'd why I objected to 'depriving myself', which I meant in the sense that if I was more active, I wouldn't need to restrict food. Adding exercise seems to be more sensible in my case, as I know it would make me feel better, even if the scales don't change. My doctor isn't worried about my weight or general health.
Dh's way of 'improving' is slightly obsessive and not really giving him the results he wants. He wasn't referring to my diet meaning general nutrition, he meant obsessive calorie counting and meal replacement like he's doing. I could accept the sentiment a bit more if it was a case of drinking more water or something specifically and undeniably beneficial. However, it really does hurt that he'd tall about me rather than to me.
Still undecided whether to bring it up. I want him to know I feel let down, but if that's his attitude (like I'm too stupid to be able to choose for myself and do something if I want or need to) I don't really want his opinion.