ObjectiveThe goal of this investigation was to examine the effect of glycemic index on brain function during the late post-prandial period (4-5 hours after eating a meal).
MethodsTwelve overweight men consumed two liquid meals on separate occasions. The meals were identical in calories, macronutrients, and palatability. The only difference between the meals was that one had a glycemic index of 84, and the other had a GI of 37. Brain activity was then measured by MRI four hours after consumption of each meal. Blood glucose, insulin, and hunger were also measured repeatedly during the post-prandial period.
ResultsPlasma glucose was significantly lower and hunger was significantly greater four hours after the high glycemic meal when compared to the low glycemic meal. The high glycemic preload also elicited a greater brain activity centered in the right nucleus accumbens. This area of the brain is associated with reward and food craving.
CommentThis is a fascinating study! We’ve known for years that high glycemic carbs promote a post-prandial dip in blood sugar that leads to an increase in hunger. I always thought that this was governed solely by the endocrine system. This is the first study to show that high glycemic carbs actually change brain activity, particularly in areas that control reward and craving. While this is just one study, it was very well designed.
Take Home MessageIf you work with me or have read my books, you know that a low glycemic approach is the key to losing weight and improving health. This study provides even more reason to strictly limit high glycemic carbs like bread, pasta, white rice and sugar. Instead, focus on lower glycemic carbs like fruits, vegetables, legumes, and whole grains.