How can I convince my girlfriend that her weight isn’t a problem?

My girlfriend of two years is quite self conscious about her weight. She complains that she is fat and should lose weight. And to be fair she is overweight, but I don’t think this is an issue. She is healthy and her body is very hot. But no matter how what I say, she still feels bad about her body. What could I do to change that?
How can I convince my girlfriend that her weight isn’t a problem?
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