Is It Healthy to Eat Once a Day and Exercise Twice a Day?

If someone eats a banana for breakfast runs for 30 minutes eats for lunch at work something small and healthy and nothing for dinner and runs again is healthy? My partner thinks he’s fat and he’s not. I have tried to call a nutritionist and states that it sounds like a eating disorder. he feels weak at times dizzy I just don’t know what to do. what is it that I can do? I don’t want him to get an sick. . I don’t think his body gets enough energy and vitamins if he eats the way he does

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