Caffeine and metabolism - Metabolism

Nutrition Research Newsletter, Feb, 2004

It is well known that caffeine and coffee can stimulate energy expenditure to varying degrees. The use of caffeine alone or in combination with ephedrine has been proposed as a treatment for obesity. The increase in energy expenditure and the alterations in plasma substrates, following caffeine ingestion, are similar to those caused by the increased activity of the sympathetic nervous system.

In an attempt to further investigate the metabolic effects of caffeine, a combination of slow-release caffeine and normal caffeine were used to obtain and maintain high plasma caffeine concentrations. Measurements of energy expenditure, lipid oxidation, and lipid turnover were performed in a group of healthy, young, male volunteers before and after caffeine ingestion and in the presence or absence of beta-adrenoceptor blockade with propranol.

Respiratory exchange and [1-[sup.13]C] palmitate were utilized to trace lipid oxidation and free fatty acid (FFA) turnover for 90 minutes prior to and 240 minutes after the ingestion of placebo, caffeine (10 mg/kg), or caffeine during beta-adrenoceptor blockade.

During fasting conditions, there were few differences in measured variables between the 3 tests. During steady state condition (last hour of the test) after ingestion of caffeine, lipid turnover increased two-fold (P < 0.005), and the mean ([ or -] SEM) thermic effect was 13.3 [ or -] 2.2% (P < 0.001), both of which were greater than after ingestion of the placebo or caffeine during beta-adrenoceptor blockade. Following the ingestion of caffeine, oxidative FFA disposal increased 44% (236 [ or -] 21 [micro]mol/min to 340 [ or -] 16 [micro]mol/min), whereas nonoxidatvie FFA disposal increased 2.3-fold (455 [ or -] 66 [micro]mol/ min to 1054 [ or -] 242 [micro]mol/min; P < 0.01). In postabsorptive conditions, 34% of lipids were oxidized and 66% were recycled. Caffeine ingestion increased energy expenditure 13% and doubled the turnover of lipids, of which 24% were oxidized and 76% were recycled.beta-adrenoceptor blockade decreased, but did not inhibit, these variables.

It is concluded that many, but not all, of the effects of caffeine are mediated via the sympathetic nervous system. The impact of caffeine on lipid mobilization can be mediated by two scenarios: lipid mobilization alone is insufficient to drive lipid oxidation, or large increments in lipid turnover result in small increments in lipid oxidation.

K. Acheson, G. Gremaud, I. Meirim, et al. Metabolic effects of caffeine in humans: lipid oxidation or futile cycling? Am. J. Clin. Nutr.79:40-46 (January 2004) [Correspondence: KJ Acheson, Nestle Research Center, PO Box 44, Vers-chez-les-Blanc, CH-1000 Lausanne 26, Switzerland E-mail: Kevin.acheson@rdls.nestle.com.]