Low-Calorie Snacks May Not Help the Young Keep Pounds Off

EDMONTON, Alberta, Aug. 10 -- Diet food may train young rats-and children-to overeat by confusing calorie-content cues, researchers said.

Low-calorie food and drink are usually assumed to help in the obesity battle, but an animal study reported in the August issue of the journal Obesity shows that low-calorie snacks can distort the way the young learn to correlate flavor with calorie content.

That leads to overeating at meals, said W. David Pierce, Ph.D., of the University of Alberta here, and colleagues. And, they theorized, their findings likely translate to children.

"As a result of early experience, children learn about tastes and other gustatory cues that signal the caloric contents of foods and beverages," they wrote.

"Children from 'diet conscious' families or families with concerns about body weight would be exposed to a supply of 'calorie-wise' food items and drinks, along with energy dense foods, perhaps making these children more susceptible to learning that food flavors do not predict caloric content," they added. "These youngsters might not be adept at energy balance and have increased risk for overeating and obesity."

An earlier study of heart patients in Texas found that diet soft drinks more strongly correlated with obesity than regular soft drinks, which led the researchers to attempt to unravel the reason.

They conditioned one group of lean or obesity-prone juvenile rats to calorie-dense sweet gelatin cubes or low-calorie salty gelatin cubes before standard laboratory chow meals. Another group was conditioned to calorie-dense salty gelatin and low-calorie sweet gelatin.

After eight days of conditioning, the rats were put on normal food without snacks for three days to stabilize their body weight. Then after 10 hours of fasting, both groups were given salty rice cakes as a snack before being returned to their cage with food and water as normal to test for overeating.

The same process was repeated with sweetened rice cakes.

In this overeating test, juvenile rats ate similar amounts of the "before-dinner snacks" regardless of whether it was paired to their earlier conditioning.

But, rats whose snack flavor predicted fewer calories actually ate more afterward for "dinner" than those whose conditioning prepared them for the high-calorie content of the snack (7.0 versus 5.6 g, P<0.01).

"These results indicate an overeating effect for juvenile rats," the researchers concluded.

For the subset of obese rats, again chow intake after the rice cake snack was greater when calorie content did not match flavor conditioning than when it did (7.7 versus 6.9 g, P<0.05).

Comparing the obese and lean rats, the effect tended to be stronger in those genetically prone to obesity, but the difference was not significant (P=0.065).

Nevertheless, "it is likely that overeating in obesity-prone animals is actually of more concern from a health perspective," Dr. Pierce and colleagues wrote. "Thus, compared with lean rats, the consistent ingestion of a small number of extra calories, induced by subverting the taste-calorie relationship, could be more devastating to weight regulation and health in the obesity-prone animals."

Adolescent rats did not show a pattern of overeating after the same conditioning routine. Chow intake after the rice cake snack was similar when it was paired with conditioned expectations as when it was not (5.5 versus 5.6 g for lean rats and 6.7 versus 6.7 for obese rats).

The difference between the age groups could suggest that "tastes and sensory cues by themselves as well as the taste-caloric content relationship come to regulate the food intake as animals mature," the researchers speculated, whereas for younger animals "the subversion of the relationship between taste and calories disrupts the developing physiological and behavioral energy balance."

The same would likely be true of human children, the investigators said.

Further research is necessary to assess the link in humans, they concluded.