Do our bodies learn that low calorie products provide fewer calories – and are therefore less satisfying?
Researchers at Wageningen University in The Netherlands sought to answer this question by studying the reward effect of two drinks sweetened with zero-calorie sweeteners: a nutrient-empty soft drink, and a nutrient-rich yoghurt drink. They hypothesized that the reward effect of a nutrient-rich drink would remain similar to that of a sugar-sweetened yoghurt drink over time, while that of a nutrient-empty soft drink would reduce over time.
However, they found that there was no difference in liking for the drinks, and the brain’s reward centres did not respond differently to the sugar-free versions. On the other hand, they did find that the yoghurt drink was more satiating than the soft drink, even though they had the same caloric value.
The study, published in PLoS ONE, measured the reward effect through MRI (magnetic resonance imaging) scans carried out with 40 participants who consumed either a sugar-sweetened or a sugar-free version of either the yoghurt drink or soft drink for breakfast over a four-week period.
“Our study showed that repeated consumption of a non-caloric sweetened beverage, instead of a sugar sweetened version, appears not to result in changes in the reward value,” they wrote.
The researchers suggested that the perceived difference in satiety might stem from having learned in childhood that thicker drinks are more satiating than thinner soft drinks, regardless of caloric content.
“It cannot be ruled out that learned associations between sensory attributes and food satiating capacity which developed preceding the conditioning period, during lifetime, affected the reward value of the drinks,” they wrote. “Our data indicate that the learned associations between sensory attributes and food satiating capacity are quite robust and difficult to alter.”
The full study is available online here .