Acute effects of ingesting a commercial thermogenic drink on changes in energy expenditure and markers of lipolysis

The prevalence of individuals who are classified as overweight and obese is a primary health concern due to their relationship to various cardiovascular diseases [1, 2] and associated comorbidities [1]. Recent epidemiological data suggests that 31% of the United States (U.S.) population is classified as obese, according to body mass index (BMI) standards, while 65% is classified as overweight [3]. Medical expenses for obesity treatment and its related comorbities in 1998 accounted for 9.1% of total medical expenditures and was reported to be $78.5 billion, which would exceed $100 billion in today's economy [4]. In addition to reducing medical costs, weight loss can reduce risk for cardiovascular disease, improve quality of life and ease the economic burden due to missed work and diminished work productivity [2, 5, 6]. Weight loss can be achieved by maintaining a proper diet and or starting an exercise regime; however, adherence to conventional weight-loss programs has been poor [3]. As a result the use of nutritional supplements to aid weight loss has increased in popularity, with consumers spending an estimated $37.1 billion per year [7].

Many consumers are turning to thermogenic drinks as a means to increase calorie and fat burning, energy levels and weight loss. While the number of TD has increased in recent years, they typically contain a mixture of caffeine, catechins, various herbal extracts, amino acids, neurostimulants and vitamins. Ingredients in these products have been shown to increase metabolism [8‐13], decrease body fat [14, 15] and increase markers of lipolysis [14, 16‐19]. Furthermore, recent work has affirmed that a TD containing caffeine, citrus aurantium, garcinia, cambogia and chromium polynicotinate to increase calorie expenditure [13, 20]. However, limited research has been reported on the impact of ingesting a TD in either an acute or prolonged fashion on energy expenditure and circulating markers of lipolysis. Furthermore, the potential for a TD to promote acute increases in fat metabolism appear promising as a recently published study reported a TD containing tyrosine, capsaicin, catechins and caffeine increased resting metabolism 4 hours post consumption compared to a placebo drink [21]. Therefore, the purpose of this study was to examine the acute effects of ingesting a commercially available TD (Celsius, Celsius, Inc., Delray Beach, FL) for changes in resting energy expenditure (REE) and serum markers of lipolysis. It was hypothesized that acute TD ingestion would increase resting energy expenditure and serum markers of lipolysis when compared to a placebo (PLA).

The purpose of this study examined the acute effects of ingesting a commercially available thermogenic drink (TD) on energy expenditure and lipolysis independent of diet and/or exercise modifications. Upon considering previous animal and human research, we hypothesized that energy expenditure, fat oxidation and serum levels of lipolysis markers would acutely increase after ingestion. Of the active ingredients, caffeine and epigallocatechin gallate (EGCG, an abundant catechin in green tea) [24] are the most common and have been found to increase energy expenditure [8, 10, 11, 25‐29] and increase markers of lipolysis [8‐11]. In this regard, caffeine increases energy metabolism through stimulation of β-adrenergic receptors and adenyl cyclase resulting in activation of cyclic AMP (cAMP), causing subsequent increases in circulating epinephrine [30, 31] and free fatty acids [32]. Caffeine may also enhance lipolysis by inhibiting nucleotide phosphodiesterase resulting in increased tissue concentrations of cAMP and activation of hormone-sensitive lipase, which provides further explanation for the increased circulating levels of free fatty acids seen in the present study [12]. In this regard, caffeine doses of 6 mg·kg^-1 in individuals with impaired epinephrine responses have been shown to increase FFA and glycerol concentration independent of a significant change in epinephrine [33]. An additional bioactive ingredient of importance is the green tea catechin, EGCG. Recent human and animal investigations have demonstrated various positive health effects of EGCG administration. For example, Boschmann gave 300 mg·d^-1 of EGCG alone to six obese men and measured energy expenditure and respiratory quotient changes [34]. While overall energy expenditure did not change, the respiratory quotient numbers did lower in response to EGCG administration leading the authors to conclude that EGCG alone may be beneficial to increase fat oxidation, although no biochemical measures of fat oxidation were measured. Furthermore, Hill and colleagues reported an improved heart rate and glycemic response in obese, postmenopausal women after 12 weeks of EGCG consumption (150 mg·d^-1) along with a walking exercise program [35]. In a more mechanistic fashion, recent studies have also suggested EGCG may alter food digestibility [15, 36] and downregulate stearoyl-CoA desaturase (SCD1) gene expression [15], which may reduce adiposity, decrease lipid synthesis and increase liver fatty acid oxidation, as was found in SCD1 knockout mice [15, 37].

In support of our hypothesis, acute TD consumption significantly increased relative REE at 60, 120 and 180 min post-ingestion when compared to a non-caloric, non-caffeinated placebo. When this data was not normalized to body mass (kcals·d^-1) and expressed relative to baseline levels, the TD group burned an average of 106 more calories when compared to PLC over the 3 h testing period (data not shown). When expressed as a percent increase from baseline, calorie burning in the TD group was increased by an average of 10.45% whereby calorie burning in the PLC group was only 0.89% (data not shown). In accordance with these findings, Rudelle et al. (2007) reported a 4.6% increase of energy expenditure 24 h after ingesting a thermogenic drink containing similar ingredients ([38]. Further, single 100 mg doses of caffeine have been shown to increase metabolic rate 3–4%, while a titrated dosing pattern of 6 × 100 mg over a 12 h period may increase energy expenditure 8–12% [10]. Similar changes to these were found in the present study and are likely due to the combination of caffeine and EGCG provided by the energy drink. In a contrasting fashion, substrate oxidation was hypothesized to change following TD ingestion as prior research has found caffeine to positively increase FFA concentrations [8, 28, 39, 40] and fat oxidation [8, 9, 11, 28]. In support of this research, FFA concentrations from the present study were significantly greater following TD consumption compared to PLA at 30, 60, 120 and 180 min post-ingestion (Figure 3). Increased FFA concentrations in the TD group are likely explained by the stimulatory effects of caffeine on circulating epinephrine [41] and subsequent downstream activation of lipolysis by way of the β-adrenergic receptors.

From a biochemical perspective, changes in serum concentrations of glycerol were not as prominent as FFA concentrations. These results, however, are consistent with prior research which has found FFA concentrations to be significantly elevated up to 180 min post-ingestion while glycerol values were only significantly elevated 60 min post-ingestion [37]. Another study found FFA concentrations to be significantly elevated 60 min post-ingestion with a trend toward increased glycerol concentrations 60 min post-ingestion. There were no changes in glycerol release from skeletal muscle in participants consuming caffeine suggesting fat oxidation was not enhanced in skeletal muscle [42] and that a tissue-specific lipolytic response may impact overall serum concentrations. It has been hypothesized that increased glycerol concentrations following caffeine ingestion are most likely a function adenosine-receptor antagonism, resulting in glycerol release from adipose tissue [37].

The results of this study suggest that the proprietary thermogenic blend contained in the TD may be an effective stimulus to promote weight loss independent of modifications in diet or exercise, as TD consumption increased REE, calorie burning and circulating levels of FFA. Due to the acute nature of this study, however, it is not known if the proprietary blend contained in this TD is effective at decreasing body fat as the effects of the ingredients may diminish with chronic use. As a result more prolonged studies should seek to examine the impact of daily TD ingestion with or without diet and exercise changes to determine changes in body mass as well as body composition along with markers of lipolysis and metabolism.

Acute TD ingestion appears to stimulate significant increases in energy expenditure and circulating levels of FFA while substrate oxidation and circulating levels of glycerol experienced non-significant decreases across time. Additional research needs to further examine the impact of prolonged daily ingestion of TD on energy expenditure, changes in body composition and efficacy of daily ingestion of TD. These studies will provide additional evidence for any role TD may play at promoting weight loss and/or achieving weight maintenance.