And before I get someone saying "just run at an 'energy deficit' - consume less calories than you burn" - I say, if you want to look and FEEL good, the person who eats 1,500 calories a day of carbohydrates vs 1,500 calories a day of protein, vegetables (carbohydrates largely bound by fiber), etc - will look and feel vastly different. This is why it's not just as simple as calories in - calories out.