[28M] [32F] How do I get my ignorant gf to listen to me?

She’s had a history of yo-yo dieting and sometimes compares herself to super thin girls. She got in to going to the gym more when she was about 16. Then when she went off to university she put on weight, and dealing with the loss of a close family member caused more weight gain. I think at this point she became very insecure. After discovering her love for running, naturally she shed a lot of weight, and currently has an athletic build as she lifts weights too.

She was unable to exercise for 6 months due to injury this year and so she gained a bit of weight. Then a close family member passed away so her weight fluctuated more. At the moment she looks how she did pre-injury, but she says she doesn’t fit in to some of her jeans and can tell her body is a lot less toned. She is back to exercising now.

Her diet over the last few years has been OK, but she doesn’t eat enough. She has porridge w almond milk at 12pm, then fruit a bit later, then dinner. She often complains she feels lightheaded especially during running and can only run 2 miles now as she lacks energy and she often complains about hunger, not being able to focus. She is taking her vitamins and getting some nutrients in but I feel she definitely isn’t eating enough especially considering the amount she trains. When we spend time together, go on holiday etc and I try and get her to eat 3 meals through the day (like I do) she really struggles with it and gets super full… but I think day to day this would be good for her and drastically increase her energy. I want to help her but she is ignorant. What do you think?