Scientists have found that if people eat high-protein foods then they do not get as hungry.
The exact reason is not known, but it is thought a protein triggers particular signals from the gut to the brain that it is full.
The weight lost on a high-protein diet is fat instead of muscle or water.
Dr Alex Johnstone, from the Rowett's Metabolic Health Group, is conducting studies to see if vegetable-based proteins such as soya work as well as dairy and meat.
If successful it could result in a high-protein weight loss plan diet that is healthier and more environmentally-friendly.
The study subjects are currently on a diet made up of around 30 per cent protein.
The diet is not low carb, but contains moderate amounts of carbohydrate at each meal such as rice, bread or pasta as well as meat and dairy substitutes such as soya meatballs or bacon and soya milk, margarine, bread and yoghurts.
For two weeks they ate meat and for a further two a vegetarian diet. So far they have lost up to a stone each in a month.
"One of the main reasons why people fail to lose weight is because of hunger, so how can we design diets in order to achieve that," the Scotsman quoted Johnstone as saying.
"High-protein diets don't have to be low in carbs. I am looking at whether you can have the same control of appetite from vegetarian sources as from meat, which would be good for health. I want to find out if you can get the same modification of appetite from a vegetarian source as from a meat source.
"We ask them how hungry they feel every waking hour. They come in and get their breakfast made for them and scoot away with a packed lunch and dinner. They have really enjoyed the study and as traditional Scottish meat-eating men were quite surprised that the vegetarian diets were extremely palatable and some will go on to make a conscious choice to make changes in their own diet," Johnstone added.