Hang on, Anomaly, I NEVER said all fat people sit in the pub eating junk food! I said that if that was a way of life for someone overweight it would be unattractive, but said that the OP clearly exercised and was healthy. Don't put words in my mouth that weren't there and use me an example of someone who makes horrible assumptions about overweight people. I have an underactive thyroid, so understand perfectly well that some weight gain is nothing to do with overeating.
However, a lot of obesity is caused by poor food choices and lack of exercise, and the NHS 12 week weight loss plan clearly states: We will help you learn to make healthier food choices, suggest exercise plans to help you lose weight, help you adopt a healthier lifestyle [...] If people are overweight, it’s usually because they eat and drink more calories than they need.
So, those 'assumptions fat people eat junk food and lounge about all day' do have some grounding in medical evidence because a sedentary lifestyle and poor food choices do cause weight gain. I think the DH of OP is using a terrible approach to encourage healthier eating (constantly nagging, withholding sex, making her feel crap). Clearly, to him, fat is a huge issue. However, I don't agree that he is totally out of his mind to make some associations with being fat (not the OP as she isn't, but the other people that she says he thinks as fat) and making unhealthy choices / not being active enough.
OP, the worry here isn't that he cares for your health, or wants you to be active: we all want our DH/DWs to live a long healthy life. It's not that he dislikes 'fat': so do most heart surgeons and nutritionists, not because they have horrible stereotypes about fat being a sign of laziness, but because they know the problems that an excess can cause. The problem, to me, is solely the way that he is pushing his views on you, upsetting you and making out that there is a huge problem when you are actually quite active and health conscious. The weight is more of an issue for him than it is any sort of health concern for you. That implies that it is more for 'aesthetic' reasons than genuine fears for your health, and that's what I would be annoyed about. Childbirth and age affect most bodies, but he doesn't seem to get that.