This is certainly not true. I had no idea how much it bothered my wife that I was gaining weight until she told me. Heck, I had no idea that I had put on so much weight. Her honesty allowed me to see what was happening to my body for the first time, and act to reverse it before it was too late. I think the difference is in my self-image. I was confident enough in myself that I just saw it as a problem to be overcome...
I cannot tell you how much I admire your wife for being able to tell you, and for you for hearing her and doing something about it. Seriously, that's awesome.
One of the two worst days of my marriage was when I finally sat DH down and told him that he had gained way too much weight, and I really needed him to do something about it, and that he was just not healthy. That was one of DH's worst days too; he still gets upset about it (I should state here that we found out 2 years later that a big underlying issue was a pituitary gland tumor causing his body to make the nursing mother hormone, so he is VERY emotional plus he's a sensitive guy to begin with), BUT he heard me and found a scale, and was horrified to see what it said. He is glad I told him, but also so sad.
I actually lost a friend, partially because of that amount of communication. She just doesn't get it; thinks that all negativity in her head is BAD, that she must medicate it ALL away, and if she ever told her husband something like that (or he told her) her marriage would likely end. They keep on doing the "little white lies", and she tried to spark a fight between us by "telling on me" to DH; she just didn't believe that I had told him first, before posting it on my journal.
Anyway, OP, DH's mom is like yours, except she gets even MORE aggressive than yours (and I kind of agree with a PP that your mom isn't passive at all). Second time I saw her, I was happy in a new relationship and had gained a few pounds, and she went OFF on me about how fat I was (I was about 20 lbs above my WW goal, and I'm a very muscular person who has always weighed much more than I look), "how you get so fat", etc etc.
A visit to her isn't complete without her commenting on DH's weight.
And the problem is...she *started* his weight problems by force-feeding him as an infant and toddler, and then growing up the rest of the years, she would plate his food, he had to eat ALL of his food, and then she would get on him if he gained weight. Oh, and it took her until about his junior year of HS to let him do any other sports than martial arts, not even running except for in PE.
And for a long time as an adult, every time she would comment, it would spark a binge. He still looks for food when he's upset (food was given when he was sad or hurt as a kid), and it's not usually an apple!
MIL and I are getting along better now, but she's not giving in on the weight thing. DH eats SO well now, and we're exercising and getting healthier. His bloodwork is getting better and better, he's finally dropping the bulk he had put on (which is something prolactinomas do), but she STILL comments on it.
And worse, and this might be something for you to think about, she comments on DS's weight. Right now, it's all positive, because the kid is all muscle, with a bit of a belly, he's very active and trim. My MIL refuses to understand how that could be. She says that *my brother's* genes must have somehow come through, because my brother is trim and a marathoner. She doesn't know that my brother was a chubby toddler/kid until his sophomore year of HS, and I was actually the very active, trim one! It's just a tiny step from "you're thin because of your uncle" to commenting on any gain, should he get more bulk on him. And bulk is likely to happen, because when we dress him in clothes like MIL put DH in, DS actually looks heavier, just like his dad did when he was little!
Just one more little "share", so you can feel the pain of others.... My MIL knew DH's size when he was little. She KNEW it. But EVERY time they went shopping, she would pick out jeans and shirts in too-small sizes, make DH try them on, and then make a big huge deal about going and getting the Husky sizes. Awful! She knew he had a tummy, and it is just flat out rotten of her to have done that.
I figure that you're either going to need to be absolutely direct...that is rude, that is NOT helping me, you need to stop, etc...or just leave when it starts up.