Eating fat can help you lose weight on a low carbohydrate diet. But eating fat can make you gain weight on a balanced diet or when you are trying to maintain. Ideally, 70-80% of your calories can come from fat, when you are losing weight on a low carb diet. Keep your total calories under 1500 a day (total caloreies under 1000 is better – 500 a day is too low for most folks to live on for extended periods, not that it’s necessarily unhealthy, they just won’t do it). If you get most of your calories from fat on a low carb diet, you’ll probably feel better, feel fuller, and have fewer carbohydrate cravings. On a balanced diet, or when you are trying to maintain, fat calories tend to pile on pounds. Fat has more than twice as many calories as protein or carbohydrate (9 calories per gram for fat, 4 calories per gram for protein and carbohydrate – there are about 28 grams in an ounce). So if you are eating alot of fat on a balanced diet or while you are trying to maintain, you’re probably in trouble. A good maintenance trick for some patients is to stop using butter or margarine on bread (most are 100% fat), and switch to jam or jelly. Butter has 100 calories an ounce, compared to 25 calories a teaspoon for jam. You can also eat fish (20 calories an ounce) instead of red meat (80 calories an ounce) on maintenance, and you’ll do better because you’re eating fewer (fat) calories.