Blood flow into brown fat of rats is greater after a high carbohydrate than after a high fat test meal.

Postprandial oxygen uptake of whole animals and rate of blood flow into the scapular and cervical brown adipose tissue (BAT) of Osborne-Mendel male rats (200 g) were compared for those receiving a high carbohydrate meal or an equicaloric high fat meal. Blood flow was determined by the use of radiolabeled microspheres injected into the left ventricle of anesthetized animals, 2-3 hours after the test meal. In vivo oxygen uptake was elevated by about 10% (P less than 0.05) and blood flow by more than 100% (P less than 0.05) in the group receiving the high carbohydrate meal compared to the high fat meal. The rate of blood flow into tissues other than brown fat was not significantly altered by the composition of the test meal. These tissues included heart, gastrocnemius and soleus muscles, GI tract and white adipose tissue. Our data suggest that a high carbohydrate meal is more thermogenic than a high fat meal, and that the difference in the magnitude of the thermic effect produced by the two meals is paralleled by a corresponding difference in brown fat thermogenesis.