My girlfriend is losing weight, what are the best ways for me to support her?

We've been together for 3 years and while she's always had weight problems she's recently made a decision to lose body fat. I'm eager to support her but I'm not entirely sure what the best way to do it is, so I thought I'd ask for advice. I've already been telling her how proud of her I am and things like that, but I feel like there must be more I can do. She's doing a sugar-free diet.