This can be confusing, but sweet tasting-low calorie foods may actually fool the body into expecting a high-calorie intake, making you more hungry when the calories don't arrive.
Scientists say that the low-calorie substitutes in food and drink may actually make dieters gain weight.
Researchers claim that the taste of fat and sugar prepares the body up to expect the high-calories.
When the high calories don't show up, the body process for controlling food intake becomes confused, and we want to eat more.
When we taste something, that normally alerts the body to expect calories, and when those calories aren't there the experts believe the systems become ineffective and one of the body's mechanisms to control food intake can become ineffective.
Professor Swithers from the Ingestive Behaviour Research Centre, says: 'We didn't study this in people, but we found that when rats consumed a fat substitute, learned signals that could help control food intake were disrupted, and the rats gained weight as a result.'
Researchers fed laboratory rats with crushed crisps as a supplement to their diet, and they were then divided into two groups that were given either a low-fat diet or a high-fat diet.
These groups were then each split into two smaller groups. One group on each diet was fed a mixture of high-fat crisps and the fat-substitute crisps, containing olestra, which is a synthetic fat with no calories, while the other group received only high-fat crisps.
Researchers fed laboratory rats combinations of normal and low fat crisps - those eating low and high fat together gained more weight than those eating high fat alone
After 28 days, of the animals maintained on the high-fat diet, the rats given fat-substitute crisps gained more weight and developed more fatty tissue than those on regular high-fat crisps.
Study co-author Professor Terry Davidson said: 'We are looking at an animal model, but there are similarities for humans, and based on what we found, we believe that our findings question the effectiveness of using fat substitutes as part of a long-term weight loss strategy.'
