The new study, published in the journal NeuroImage, adds to the idea that the body may respond differently to caloric and non-caloric sweet foods by suggesting that the energy content of a beverage (in this case orangeade) affects the activation of the amygdala and ventral striatum areas of the brain.
“A possible explanation for our finding is that the sucrose-containing orangeade is rewarding due to its caloric content while the non-caloric drink is sweet but not metabolically rewarding, i.e., less biologically relevant,”,” said the researchers, led by Dr Paul Smeets from the University Medical Center Utrecht in The Netherlands. However, the researchers note the complexity of making stimuli that only differed in caloric content, and stressed the need for additional research to confirm their observations.
Dr Smeets and his co-workers added that the implications for the effectiveness of non-caloric sweeteners in decreasing energy intake need to be established.
The regulation of food intake is driven by a combination of sensory signals, including gastric signals of fullness, signals indicative of nutrient depletion, and sensory specific satiety, explained the researchers.
Sensory-specific satiety (the decrease in perceived pleasantness of a consumed food relative to that of an uneaten food) has been shown to be associated with altered neuronal activation of brain areas in response to odour and taste stimuli.
Smeets and his colleagues noted that higher degrees of oro-sensory stimulation – attributes relating to overall sensing, including taste and smell, but including other senses such as sight, sound, and touch) – promote sensory-specific satiety. Adding that degree of oro-sensory stimulation achieved by a food or beverage depends on its physical properties, including tastant concentration and viscosity.
“It has been found that increasing the amount of oro-sensory stimulation results in lower ad libitum intake,” said the researchers.
Previous studies have also suggested that tasting a caloric (sucrose) solution activates taste areas, including reward areas (such as the amygdala), stronger than a similar tasting non-caloric (sucralose) solution, they said.
The amygdala, which is implicated in emotional processing of stimuli, it is thought to influence behaviour by processing sensory cues associated with reward and by linking such cues to emotion.
Smeets and his co-workers noted that previous work has shown that food odours predicting the delivery of their associated drink activate the amygdala, whilst amygdala deactivation has been reported to occur in response to pleasant taste stimuli.
“By measuring the effects of the controlled consumption of caloric and non-caloric versions of a soft drink on taste activation, we aimed to dissociate the effects of sensory-specific satiety from metabolic satiety effects (i.e., energy repletion),” said the authors.
The researchers tested the activation of the amygdala and ventral striatum areas of the brain in response to caloric and non caloric orangeade using functional magnetic resonance imaging (fMRI) in ten male volunteers – finding that the brain responds differentially to caloric and non-caloric versions of a sweet drink.
The caloric orangeade was sweetened with sucrose, whilst the non-caloric orangeade with aspartame, acesulfame K, sodium cyclamate and sodium saccharin, to create beverages with caloric contents of 177 kJ and 0 kJ per 100 g, respectively.
Before consumption, they reported that the right amygdala was more activated by non-caloric orangeade than by caloric orangeade. They observed that the amygdala deactivated in response to caloric orangeade, while it activated in response to the non-caloric drink.
The caloric drink was also found to elicit stronger striatal activation than the non-caloric drink.
“This is in line with recent findings that the striatum responds to carbohydrates but not non-caloric sweeteners,” said the researchers.
The researchers noted that that their finding that the amygdala deactivates in response to an energy-containing drink while it activates in response to a non-caloric drink “warrants further research.”
“Studies in rats have suggested that when sweet taste is no longer predictive of caloric content, this may promote energy intake. Therefore, a particular topic of interest is in how far the lack of an association between sweet taste and calories affects food intake regulation,” they said.
Volume 54, Issue 2, Pages 1367-1374, doi: 10.1016/j.neuroimage.2010.08.054
“Consumption of caloric and non-caloric versions of a soft drink differentially affects brain activation during tasting”
Authors: P.A.M. Smeets, P. Weijzen, C. de Graaf, M.A. Viergever