To explain how it works, nutrition scientists at the Rowett Institute have made up two dishes of food for me.
One is a vegetable bolognese with spaghetti and a slice of garlic bread. The other is meatballs in tomato sauce, spaghetti and a slice of garlic bread.
"We have two plates of food here," explained Dr Johnstone.
"They're identical in weight and in energy content, but the meatballs are going to help you feel fuller for longer."
The meatballs meal contains 30% protein - twice as much as the vegetable meal but still within dietary guidelines.
Dr Johnstone said: "Protein is an incredibly important nutrient in helping suppress the hunger signals that are produced in the stomach, and relaying fullness signals back to the brain."
High protein diets were made famous by the Atkins diet, which had many celebrity followers, but it has been linked to heart disease.
Dr Johnstone suggested a different approach: eating more protein as part of a balanced, low fat diet.
"Most people could increase their protein intake by about 20%. Both these meals are incredibly healthy, the meatballs dish simply contains a bit less spaghetti."
If you're a veggie, vegetarian sources of protein such as soya, have the same effect.
Later in the week I'll be finding out how the food industry has adapted this science to develop foods that keep you fuller for longer, but on Wednesday I will be investigating whether some of us are born with such a sweet tooth that we're destined to be fat.
How the dishes compare:
Meatballs: 797 calories 27g fat 58g protein
Veggie Bolognese: 797 cals 27g fat 29g protein
Meatballs: 165g pork mince 15g tomato ketchup 15g white bread 45g onions 25g red peppers
Veggie bolognese: 25g red peppers 45g courgette 45g canned mushrooms 40g mange-tout 30g spring onions 32g sweetcorn
For the sauce: 24g carrots 38g mushrooms (canned) 37g green peppers 0.4g chilli powder 0.3g garlic puree 0.3g oregano 0.3g basil 1.2g olive oil 120g tomato pasta sauce 8g tomato chutney 0.4g demerara 2g lemon juice Salt and pepper
Sauce: 19g double cream 0.3g chilli powder 0.3g garlic puree 0.3g oregano 0.3g basil 30g tomato chutney 125g canned tomatoes 2g lemon juice 0.5g demerara sugar salt and pepper
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