It is not just your stomach that registers the amount of food you have eaten. It's your brain. Here is an example:
The cheese I am going to use on my tuna salad at lunch time is 10g of a really tasty strong cheddar. Calories are just 40. The flavour enhancement to my meal is powerful and satisfying, so why do I need more? I grate the cheese using the fine grater - it looks more, as you can see in the picture. The piece of cheese on the right hand side is the same weight, but looks pathetic in comparison and let's be honest, something you can pop in your mouth without thinking. To get the idea of the size of the piece of cheese, I've stuck a cherry tomatoe on the plate. So which looks more.
My salad is now going to benefit from a 40 calorie taste explosion.