LogFAQs > #957348232

I think in the most literal sense, you gain weight if you have a caloric surplus and lose weight if you have a caloric deficit. I'm not an expert so feel free to correct me if I'm wrong.

There definitely is still a concept of good and bad calories. Obviously if you have mass nutrient deficiencies your body will respond in bad ways. Not all calories are equal and eating 100 calories of sugar water won't fill you up nearly as much as 100 of vegetables, so sugar water generally causes you to eat more calories. And in the long run what you eat can also affect your metabolism which affects what amounts you need to target for a surplus/deficit.

McDonald's has a lot of "bad" calories but he kind of biased that by IIRC always getting at least a large fries and soda, which are the emptiest kind of calories they have there.