I'm a little late to the game on this thread @kirbz but I thought it'd be helpful to give you a little bit insight. My mother is one of the most unhealthy people I know, the first being my stepdad and the others being my extended family. The last Thanksgiving I spent with them (now 2 years ago).. I told my mom I never wanted to join them again because I thought I was going to throw up from watching him eat. I seriously stopped eating the idea of it made me so sick, and I had already had a decent amount of Thanksgiving goodies at this point. Growing up, my dad was always the advocate for knowing how much food you needed at a meal, you had better eat all of it, and treats were in small portions. After that divorce, my mom, my brother and I gained a bunch of weight. I was 14 when I decided enough was enough, and decided to refuse the food my stepdad would bring home. It was all too unhealthy. When I moved to California it made me appreciate fresh food and all of the outdoor activities even more, and that's all I would spend my money on in college. I'm the only one who regularly works out and constantly trying to analyze the way my lifestyle is affecting my moods/well-being.
It's not easy, telling people that you won't eat certain things because of the way that it affects your own body. It takes a lot of practice, and some thick skin when it's your own family doing it. I clearly fell off the wagon the last few years (career life + being over 21 = more money = more opportunities = slippery slope), and am trying to get back on it. At this point, I've learned that my happiness and how I feel is way more important than feeling my food habits are accepted by them. In the end, my health and strength makes me happier than their support on the matter. But like I said - that's not easy.