Striatal dopamine signaling is involved in reward and the motivation to eat. Animal studies showed that nutritional signals that arise following the ingestion of nutrients induce striatal dopamine release. These post-ingestion nutritional signals may therefore play an important role in the rewarding aspects of food consumption and the regulation of feeding behavior. To study this in humans, we assessed the taste- and preference- independent effects of glucose and lipids on striatal activity in lean humans.
In 15 lean humans, we assessed the effects of direct intragastric infusions of glucose 50% (250ml, 500kcal), Intralipid ® (250ml, 500kcal) and water (250ml) on the BOLD signal of striatal subregions (the nucleus accumbens, the caudate nucleus and the putamen), using functional MRI.
Relative to the infusion of water, intragastric glucose infusion induced a significant decrease in BOLD signal in the nucleus accumbens (p<0.001), caudate nucleus (p=0.049) and putamen (p=0.006). The intragastric Intralipid® infusion induced a significant decrease in the nucleus accumbens (p=0.025) and putamen (p=0.025). There was no difference between the effects of glucose and Intralipid® infusion on neuronal activity in these striatal regions.
These findings show that, in lean individuals, striatal neuronal acitivity is reduced following the intragastric infusion of macronutrients in a taste- and preference independent manner. These data suggest an important role for post-ingestion nutritional signals in the regulation of hedonic eating behavior. We are currently assessing these post-ingestion nutritional effects in obese individuals before and after weight loss.