The identification of brown adipose tissue (BAT) in adult humans and importance in the determination of levels of obesity has led to a renaissance in this field, particularly in relation to the potential for it to be targeted as an anti-obesity therapy. Furthermore, dietary macronutrients have been shown to be unequal in terms of their impact on food intake; however, the outstanding question is how different macronutrients drive energy expenditure. These experiments aim to characterize the impact of specific macronutrient groups on energy expenditure in BAT and gain an insight into the underlying mechanism(s).

Adult male Sprague Dawley rats were surgically implanted with a cannula directed into the stomach and exteriorized subcutaneously in the dorsal region of the neck. At the same time, a telemetric device was implanted between the interscapular lobes of the BAT to measure shifts in local temperature, indicative of thermogenic activity. Macronutrients (glucose, lipid, protein) were matched for calories and volume and infused 1) directly into the stomach or 2) towards the brain (via carotid artery). 

The administration of glucose, lipid or protein, both peripherally or towards the brain causes a differential activation of BAT thermogenesis. There was a significant impact of all macronutrients, with the most profound effect on BAT activity derived from lipid, followed by protein and glucose. 

These data provide a framework for the formulation of “smart diets” that will allow the effective control of body weight through modulation of energy expenditure.