Can I/should I do anything?

I think she's got to want to make the change for herself. You can't do much to help other than support her if she makes that decision.

I so identify with this conundrum. My wife and I have been plugging away on diets since May and have lost a lot of weight. My sis is early 60s and extremely obese with declining mobility and all the things that go with being way, way too heavy, including worsening bloodwork and so on. She talks about dieting and almost half makes it sound like she's on a diet, but then we see her exhibiting all the behaviors of someone who's in fact not dieting at all, and she's still getting bigger. We so, so, so want her to get healthier and are very worried about her but she just won't engage with her health in a meaningful way. We hoped that by setting a good example she'd notice and want to be part of the in-crowd, but that hasn't happened at all. We used to bring up dieting with her and she'd get difficult and evasive. All roads lead back to her doing nothing about the problem except complaining about her weight and how much it's made her life suck, while getting fatter. She is stuck in one of those brutal cycles of being depressed about her weight and then soothing her depression with food.

The problem, I think, is that dieting is challenging and you have to really want to do it. It has to come from deep inside, because food is not like alcohol or cigarettes, you can't just go cold turkey, so it's imperative to develop a strong sense of what's important to you and what you value more, the next chips and queso or getting healthy, because you are going to face that choice multiple times every single day. The problem as I see it is, you can't make someone else want to get healthy; they have to want it all on their own. And sometimes, people just don't want it badly enough to do something about it, even when the consequences of not doing so are dire.

There is a good chance that even if she was ready to lose weight she would want to get advice from someone else. If she has tried and failed in the past she may be very uncomfortable involving people who are very close.

Even though I am not the one that brings it up I try not to talk about my own weight loss too much in front of close family members that need to lose weight. I do not want anyone to feel like they are competing with me. I also do not want them to think I am judging what they are eating when we eat together or that they are somehow letting me down if they go through a rough spot or just fail altogether.

Very few people knew when I started this last time. I hid it for as long as I could. I actually kept trying to lie about it even after it was super obvious I was losing.

Continue to be a positive example with how you keep and try to improve yourself. Always be kind and gentle but truthful in your conversations should you continue them. Cite folks like me (I am totally ok with this); here is my story briefly: Until 2019, I lived for years with painful, nearly debilitating mobility due to severely deteriorating hips which being heavy absolutely did not help. For just as long I stubbornly resisted and refused any suggestion to seek appropriate treatment. At the end of 2018, I finally reached my "enough's enough!" point. Everyone has one. Somehow, someway your sister has to find her's and once she does she will do what needs to be done. Help her see that. I saw a surgeon who replaced both my hips in the first half of '19. I spent the next part rehabbing and then ever since trying to live an appropriate (for me at nearly 65) fitness lifestyle to lose and keep weight off for fear of reverting to that immobile mess I was a year ago and with the knowledge and hope that doing so not only extends the lifespan of my implants, but ME as well. I wish and hope for the very best for your sister and your efforts. I had sibs that never gave up on me. Don't give up on her!