How simple is this?
"For the complete picture, recognize that any excess calories -- whether they come from carbohydrates, fat, or protein -- are stored in the body as fat. Complex carbohydrates and lean protein supply 4 calories per gram, while fat more than doubles that at 9 calories per gram. BOTTOM LINE: Too much of any food will make you gain weight."
Better Homes & Gardens Low Carb Recipes page 5.