The effects of catechin rich teas and caffeine on energy expenditure and fat oxidation: a meta-analysis.

Different outcomes of the effect of catechin-caffeine mixtures and caffeine-only supplementation on energy expenditure and fat oxidation have been reported in short-term studies. Therefore, a meta-analysis was conducted to elucidate whether catechin-caffeine mixtures and caffeine-only supplementation indeed increase thermogenesis and fat oxidation. First, English-language studies measuring daily energy expenditure and fat oxidation by means of respiration chambers after catechin-caffeine mixtures and caffeine-only supplementation were identified through PubMed. Six articles encompassing a total of 18 different conditions fitted the inclusion criteria. Second, results were aggregated using random/mixed-effects models and expressed in terms of the mean difference in 24 h energy expenditure and fat oxidation between the treatment and placebo conditions. Finally, the influence of moderators such as BMI and dosage on the results was examined as well. The catechin-caffeine mixtures and caffeine-only supplementation increased energy expenditure significantly over 24 h (428.0 kJ (4.7%); P < 0.001 and 429.1 kJ (4.8%); P < 0.001, respectively). However, 24 h fat oxidation was only increased by catechin-caffeine mixtures (12.2 g (16.0%); P < 0.02 and 9.5 g (12.4%); P = 0.11, respectively). A dose-response effect on 24 h energy expenditure and fat oxidation occurred with a mean increase of 0.53 kJ mg(-1) (P < 0.01) and 0.02 g mg(-1) (P < 0.05) for catechin-caffeine mixtures and 0.44 kJ mg(-1) (P < 0.001) and 0.01 g mg(-1) (P < 0.05) for caffeine-only. In conclusion, catechin-caffeine mixtures or a caffeine-only supplementation stimulates daily energy expenditure dose-dependently by 0.4-0.5 kJ mg(-1) administered. Compared with placebo, daily fat-oxidation was only significantly increased after catechin-caffeine mixtures ingestion.

Uncoupling proteins: their roles in adaptive thermogenesis and substrate metabolism reconsidered.

During the past few years, there have been two major developments, if not revolutions, in the field of energy balance and weight regulation. The first at the molecular level, which was catalysed by developments in DNA screening technology together with the mapping of the human genome, has been the tremendous advances made in the identification of molecules that play a role in the control of food intake and metabolic rate. The second, at the systemic level, which centered upon the use of modern technologies or more robust analytical techniques for assessing human energy expenditure in response to starvation and overfeeding, has been the publication of several papers providing strong evidence that adaptive thermogenesis plays a much more important role in the regulation of body weight and body composition than previously thought. Within these same few years, several new members of the mitochondrial carrier protein family have been identified in a variety of tissues and organs. All apparently possess uncoupling properties in genetically-modified systems, with two of them (uncoupling protein (UCP) 2 and UCP3) being expressed in adipose tissues and skeletal muscles, which are generally recognised as important sites for variations in thermogenesis and/or in substrate oxidation. Considered as breakthrough discoveries, the cloning of these genes has generated considerable optimism for rapid advances in our molecular understanding of adaptive thermogenesis, and for the identification of new targets for pharmacological management of obesity and cachexia. The present paper traces first, from a historical perspective, the landmark events in the field of thermogenesis that led to the identification of these genes encoding candidate UCP, and then addresses the controversies and on-going debate about their physiological importance in adaptive thermogenesis, in lipid oxidation or in oxidative stress. The general conclusion is that UCP2 and UCP3 may have distinct primary functions, with UCP3 implicated in regulating the flux of lipid substrates across the mitochondria and UCP2 in the control of mitochondrial generation of reactive oxygen species. The distinct functions of these two UCP1 homologues have been incorporated in a conceptual model to illustrate how UCP2 and UCP3 may act in concert in the overall regulation of lipid oxidation concomitant to the prevention of lipid-induced oxidative damage.

Green tea and thermogenesis: interactions between catechin-polyphenols, caffeine and sympathetic activity.

The thermogenic effect of tea is generally attributed to its caffeine content. We report here that a green tea extract stimulates brown adipose tissue thermogenesis to an extent which is much greater than can be attributed to its caffeine content per se, and that its thermogenic properties could reside primarily in an interaction between its high content in catechin-polyphenols and caffeine with sympathetically released noradrenaline (NA). Since catechin-polyphenols are known to be capable of inhibiting catechol-O-methyl-transferase (the enzyme that degrades NA), and caffeine to inhibit trancellular phosphodiesterases (enzymes that break down NA-induced cAMP), it is proposed that the green tea extract, via its catechin-polyphenols and caffeine, is effective in stimulating thermogenesis by relieving inhibition at different control points along the NA-cAMP axis. Such a synergistic interaction between catechin-polyphenols and caffeine to augment and prolong sympathetic stimulation of thermogenesis could be of value in assisting the management of obesity. International Journal of Obesity (2000) 24, 252-258

Efficacy of a green tea extract rich in catechin polyphenols and caffeine in increasing 24-h energy expenditure and fat oxidation in humans.

BACKGROUND: Current interest in the role of functional foods in weight control has focused on plant ingredients capable of interfering with the sympathoadrenal system. OBJECTIVE: We investigated whether a green tea extract, by virtue of its high content of caffeine and catechin polyphenols, could increase 24-h energy expenditure (EE) and fat oxidation in humans. DESIGN: Twenty-four-hour EE, the respiratory quotient (RQ), and the urinary excretion of nitrogen and catecholamines were measured in a respiratory chamber in 10 healthy men. On 3 separate occasions, subjects were randomly assigned among 3 treatments: green tea extract (50 mg caffeine and 90 mg epigallocatechin gallate), caffeine (50 mg), and placebo, which they ingested at breakfast, lunch, and dinner. RESULTS: Relative to placebo, treatment with the green tea extract resulted in a significant increase in 24-h EE (4%; P < 0.01) and a significant decrease in 24-h RQ (from 0.88 to 0.85; P < 0.001) without any change in urinary nitrogen. Twenty-four-hour urinary norepinephrine excretion was higher during treatment with the green tea extract than with the placebo (40%, P < 0.05). Treatment with caffeine in amounts equivalent to those found in the green tea extract had no effect on EE and RQ nor on urinary nitrogen or catecholamines. CONCLUSIONS: Green tea has thermogenic properties and promotes fat oxidation beyond that explained by its caffeine content per se. The green tea extract may play a role in the control of body composition via sympathetic activation of thermogenesis, fat oxidation, or both.

Poststarvation hyperphagia and body fat overshooting in humans: a role for feedback signals from lean and fat tissues.

An increase in the sensation of hunger and overeating after a period of chronic energy deprivation can be part of an autoregulatory phenomenon attempting to restore body weight. To gain insights into the role of fat and lean tissue depletion as determinants of such a hyperphagic response in humans, we reanalyzed the individual data on food intake and body composition available for the 12 starved and refed men in the classical Minnesota Experiment after a shift from a 12-wk period of restricted refeeding to an ad libitum refeeding period of 8 wk. For each individual, the following were determined: 1) the total hyperphagic response during the ad libitum refeeding period, calculated as the energy intake in excess of that during the prestarvation (control) period; 2) the degree of fat recovery and that of fat-free-mass (FFM) recovery before ad libitum refeeding, calculated as the deviation in fat and FFM from their respective prestarvation values (ie, the amount of fat or FFM before ad libitum refeeding as a percentage of fat or FFM during the control period); and 3) the deficit in energy intake before ad libitum refeeding, calculated as the difference between the energy intake during the period of restricted refeeding and that during the control period. The results indicate that 1) the total hyperphagic response is inversely correlated with the degree of fat recovery (r = -0.6) as well as with that of FFM recovery (r = -0.5), 2) the correlation between hyperphagia and FFM recovery persists after adjustment for fat recovery, and 3) the correlations between hyperphagia and fat recovery or FFM recovery persist after adjustment for the variance in the energy deficit during the preceding period of restricted refeeding. Taken together, these results in humans suggest that poststarvation hyperphagia is determined to a large extent by autoregulatory feedback mechanisms from both fat and lean tissues. These findings, which have implications for both the treatment of obesity and for nutritional rehabilitation after malnutrition and cachexia, have been integrated into a compartmental model of autoregulation of body composition, and can be used to explain the phenomenon of poststarvation overshoot in body fat.

Influence of dietary composition on energy expenditure during recovery of body weight in the rat: implications for catch-up growth and obesity relapse.

The influence of dietary composition on whole-body energetics was examined during the first 2 weeks of isocaloric refeeding after low food intake in a rat model. The high energetic efficiency and energy partitioning toward fat accretion characteristic of this refeeding period were unaltered by (1) dietary fat levels varying between 6% and 30% of energy intake; (2) protein levels between 15% and 40%; (3) carbohydrate types (glucose v fructose v sucrose v starch v unrefined carbohydrate); and (4) diets containing 30% fat but differing in fatty acid composition (long-chain triglycerides [LCT] v medium-chain triglycerides [MCT] v oleic v linoleic v alpha-linolenic metabolites eicosapentaenoic acid [EPA] and docosahexaenoic acid [DHA] omega-3 fatty acids). Changes were only observed for extreme diets, ie, those deficient in protein or very high in fat. Low-protein diet was the only condition in which the high metabolic efficiency characteristic of the refeeding period was partially suppressed, and this occurred despite a lack of concomitant reduction in body fat deposition. On the contrary, with high-fat diets (> 30% of dietary energy consumption) the elevated efficiency was further increased, an effect that was only partially accounted for by the lower energy cost of body fat gain from high-fat diets. These studies indicate that during body weight recovery, the mechanisms underlying the adaptive increase in metabolic efficiency favoring the replenishment of body fat stores override any effect of food type on thermogenesis, and suggest some convergence in the controlling neural pathway. The implications of these findings vis-a-vis nutritional rehabilitation (catch-up growth) and obesity relapse are discussed.

Dietary supplementation with fish oil enhances in vivo synthesis of tumor necrosis factor.

Studies reported here investigate the influence of dietary fat types on cytokine production in response to endotoxin (LPS) challenge. Tumor necrosis factor (TNF) serum levels were markedly higher (by 10-fold) in mice fed chronically a diet rich in fish oil rather than either a diet rich in corn or coconut oil or a low fat diet. This in vivo hyper-responsiveness in LPS-induced TNF production following fish oil consumption concorded with similar exaggerated in vitro TNF release from macrophages exposed to LPS. These data suggest that high consumption of fish oils, by virtue of their high content of omega-3 polyunsaturated fatty acids, can lead to an exaggerated production of mediators of inflammation with potentially adverse consequences on the outcome and severity of infectious diseases.

Screening of drugs for thermogenic anti-obesity properties: antidepressants.

Twelve antidepressant drugs, currently in clinical use, were screened for thermogenic properties on the basis of their ability to stimulate the activity of the sympathetic nervous system via an inhibitory effect on noradrenaline reuptake into the sympathetic neurons. Drug screening was carried out on mice made obese by hypothalamic lesioning using monosodium glutamate. Preliminary experiments, based on changes in body weight and food intake in response to increased doses of the drugs, indicate that most of the twelve antidepressants possess thermogenic potential. In particular, butriptyline, protriptyline and nortriptyline were most effective in causing marked losses in body weight without altering the food intake of the mice. The potent anti-obesity thermogenic properties of these three antidepressants were confirmed during a 10-week energy balance study involving measurements of energy expenditure over the entire period by the comparative carcass method, as well as by measurement of 24 h oxygen consumption. These studies indicate that the methodology employed in the preliminary screening is valid for identifying drugs with thermogenic potential, and demonstrate that many antidepressants currently in clinical use have marked thermogenic properties, and could therefore influence the nutritional status of patients under drug therapy.

Thermogenic drugs for the treatment of obesity: sympathetic stimulants in animal models.

Thirty-three drugs known to stimulate the sympathetic nervous system have been screened for thermogenic properties. The results presented are for seven of them. The drugs were tested in five animal models of obesity (genetic (mice and rats), hypothalamic (mice) and dietary (mice and rats] as well as in lean mice. Energy-balance studies were undertaken using the comparative-carcass technique as well as by measurement of daily oxygen consumption. All seven drugs in obese animals tended to reduce body-weight and fat without loss of body protein: they acted by increasing metabolic rate without increasing food intake. They were much less effective in lean animals. These findings lend support to the concept that obesity is due to a diminished activity of the sympathetic nervous system. Differences in the effectiveness of the drugs are discussed in relation to differences between the animal models of obesity. Ephedrine and tranylcypromine were found to be the most effective drugs in this series of experiments and a prima facie case is made for human clinical trials.