Professor Terry Davidson and associate professor Susan Swithers at Purdue University suggest their findings may explain why increasing numbers of people in the US lack the natural ability to regulate food intake and body weight.
"This ability may be weakened when this natural relationship is impaired by artificial sweeteners," said Davidson.
Diet soft drinks claim the biggest market share for artificial sweeteners, with over 87 million consumers in the US alone. According to a 1998 survey commissioned by the Calorie Control Council, 144 million American adults consume low-calorie, sugar-free products on a regular basis.
Options for food and beverage makers in artificial sweeteners currently include acesulfame potassium, aspartame and saccharin.
The Purdue researchers' study, published in the July issue of the International Journal of Obesity, also emphasises the crucial role 'mouthfeel' can play in beating weight, and that being able to automatically match caloric intake with caloric need depends on the body's ability to learn that the taste and feel of food by the mouth suggests the appropriate caloric intake.
Much as Pavlov's dogs learned that the sound of a bell signalled food, people learn that both sweet tastes and dense, viscous foods signal high calories. This learning process begins very early in life and perhaps without conscious awareness, according to the researchers.
"Without thinking about it, the body learns that it can use food characteristics such as sweetness and viscosity to gauge its caloric intake. The body may use this information to determine how much food is required to meet its caloric needs," said Davidson.
Over the past 25 years, there has been a dramatic increase in the consumption of artificially sweetened foods and low viscosity, high-calorie beverages, said Swithers, a developmental psychobiologist.
"Our hypothesis is that experience with these foods interferes with the natural ability of the body to use sweet taste and viscosity to gauge caloric content of foods and beverages. When you substitute artificial sweeteners for real sugar, however, the body learns it can no longer use its sense of taste to gauge calories. So, the body may be fooled into thinking a product sweetened with sugar has no calories and, therefore, people overeat," she said.
Swithers added that the loss of the body's ability to gauge caloric intake contributes to increased food intake and weight gain, especially when people do not count calories on their own. A similar dynamic is at work with foods' texture and thickness.
"Historically, we knew that our body learns that if the food is thick, such as whole milk, it tends to have more calories than compared to a thinner liquid such as skimmed milk," commented the scientist. "Our research reinforces this and takes it one step further, showing that our bodies translate this information about perceived calories into a gauge to tell us when to stop eating,"
The researchers based their hypothesis on Pavlovian theory. Ivan Pavlov, known for his work in the early 20th century, is famous for his experiment in training dogs to associate food with the ringing of a bell. After being conditioned to the bell, the dogs salivated when they heard it - even when they did not see or smell food. Davidson and Swithers propose that rats learn a similar relationship between the taste or texture of a food and the calories it contains and may use this information to control food intake and body weight.
The scientists said future studies will need to evaluate if the body and brain can be retrained to naturally measure calories after consuming artificial sweeteners or high-calorie beverages.