On your concern for your fat friend’s health.
Your Fat Friend

Actually equating fat people with ill health is not accurate. Studies show that thin people who diet and don’t exercise are more likely to die of any cause than a person who fits in the “overweight” or even “mildly obese” categories who exercises. Don’t believe me? Simply do a google search. There are plenty of recent studies on this topic. So if illness is risk of dying, being “fat” (as long as not more than mildly obese), is not actually unhealthy. So essentially a overweight or mildly obese person who exercises is less likely to die from any cause than a thin person who diets and exercises. Dieting isn’t actually healthy for you. It suggests that you are restricting your nutrients. You can’t judge health by calories. Your body needs many nutrients to run well. Restricting those nutrients is actually bad for you. You can be eating more than enough calories to sustain your energy requirements, but still not be getting enough calcium, or vitamin b6, or essential fatty acids, etc. Fat itself, until it starts impeding the internal organs, is rather harmless. Look at women’s breasts. They are just big blobs of fat. They are not dangerous. They are not “unhealthy.” So, eat when your body tells you it needs food. A scale in your bathroom is not more sophisticated than millions of years of evolution in devising a method to tell you when you need food. The drive to eat could come from caloric need or a nutritional need. Eat nutrient rich food of a wide variety that is low in sugar. Then add exercise and simply be the weight you are. Don’t worry if you are fat or thin.