How do I avoid offending fat people?

Several of my coworkers are extremely sensitive about their weight. My simple existence constantly reminds them that they are failing at a very important aspect, especially for women.

I think one thinks I'm judging her, but I really don't care.

Any tips on how to navigate her insecurity?

I initially tried to avoid food and diet and exercise topics, but naturally, it's impossible, because we have to eat every day.