Feeding children diet food and low-calorie drinks may, paradoxically, spur overeating and weight gain, a new Canadian study suggests.
That's because humans, like most animals, are able to instinctively match calorie intake with the body's needs, and are conditioned to associate food tastes with calories ingested.
But when children ingest diet or calorie-wise versions of foods normally high in calories, this can distort these important connections between taste and caloric content and lead to overeating, according to the research.
"Essentially, they are tricked or fooled by the taste, and conditioned to think it will always be low in calories," said David Pierce, a sociologist at the University of Alberta in Edmonton.
He is also the lead author of the study, published in Wednesday's edition of the journal Obesity.
The research was conducted on laboratory rats. However, Pierce said it is probably applicable to people because the "taste-conditioning process" is identical in rodents and humans.
He said the message for parents is straightforward: Feed children a healthy, well-balanced diet with sufficient calories to meet their energy needs. That way their bodies will be able to use taste-related cues to assess the energy value of their food correctly.
"I'm not saying people should not eat diet foods," he said. "I'm cautioning that it might be best to not give youngsters diet foods because it risks conditioning their tastes in a way that isn't beneficial."
To conduct the study, researchers carried out a series of elaborate experiments. Young rats were given sweet or salty Jell-O-like cubes that either contained high-calorie starch or were artificially sweetened and contained no starch. This was done to condition tastes.
Later, the rats were fed snacks, then regular meals, and food consumption was measured. Those who associated the taste of "diet" snacks with fewer calories routinely overate at meals.
The same experiment was conducted with lab rats that were bred to be lean or obese, with the same results. However, the additional calories (and weight gain) were more detrimental to the obese rats.
That suggests that children prone to obesity for genetic or other reasons will be worse off in the long run if they consume diet foods in their formative years.
Pierce noted that the experiments were conducted on young rats, whose development is the equivalent of human children's. When the tests were done on juvenile and adult rats, the outcome was not the same.
"We think that older animals rely on many sensory dimensions of food aside from taste to judge caloric content," he said.
The researcher also noted that adults can also read packages and calculate calories in food if they want to, whereas "children tend to eat what they're given."
Pierce said it is important to realize that the changes that occur in conditioning taste are fairly subtle and the effects are small, yet cumulative over time.
"What you're going to see is children eating a little more than they should at dinner because of this conditioning. But it can add up to a lot of extra calories, and extra weight, over time."
Diet foods and their effects on taste buds are only a small part of the puzzle that is the current obesity epidemic; there are complex genetic, environmental and social factors that influence the way we eat and the way we gain weight.