Because fat has 9 calories / gram, carbohydrates have 5 and water has zero. So while a tint of olive oil in your salad might have some theoretical health benefi

Because fat has 9 calories / gram, carbohydrates have 5 and water has zero. So while a tint of olive oil in your salad might have some theoretical health benefits if you are skinny, replacing those deep fried chips with baked chips has immediate benefits if you are overweight - you will probably eat the same quantity anyway but half the calories. Fat makes you fat without a proportional decrease in your appetite, it's as simple as that.