This may not be very helpful, but this is a case where I’d simply say “too bad, Honey. My health and how *I* feel are more important than a number on a scale.”
You say all he can see is the increased poundage, but if you really are feeling better then that will start to show as your healing progresses. I’ve gained a lot of weight on my journey so far and while my husband doesn’t love it he can see some of the improvements in how I feel so while he is too afraid to go down the road himself because of the weight gain (he needs it desperately: morning temps of BARELY 96F regularly) he isn’t giving me any flak about it either.
I also suggest hiding or throwing out the scale, as has been said a good bit of the weight gain during recovery can be muscle, bone, and organ regrowth none of which look any good on the scale but all of which are awesome reasons to gain weight. I did that here and while my husband whined a bit at first he got over it pretty quickly. :)
I hope you can find a way to help your husband understand as an extra stressor in the form of your husband’s worry does no one any good.