They also found that glucose, but not fructose, had effects on circulating "hunger" hormone levels. Glucose elevated levels of insulin and GLP-1 compared with fructose.
Leptin and ghrelin levels, however, weren't significantly different between the two sugars, the researchers found.
The differences in brain effects between glucose and fructose also appeared to coordinate with ratings of hunger, since there was a significant difference from baseline in terms of fullness and satiety when participants drank glucose, but not fructose.
Sherwin and colleagues cautioned that the study was limited because fMRI doesn't provide a direct measure of neuronal activity, and thus any clinical implications can't yet be determined.
Editorialists Purnell and Fair noted that while some researchers and clinicians warn that the total amount of calories is more important than the type of food when it comes to losing weight, the "reality ... is that hunger and fullness are major determinants of how much humans eat, just as thirst determines how much humans drink. These sensations cannot simply be willed away or ignored."
"The remedy remains eating less," they wrote, "but the means involve reducing the food element, if possible."