Effect of Gender on the Metabolic Impact of a Commercially Available Thermogenic Drink

EFFECT OF GENDER ON THE METABOLIC IMPACT OF

A COMMERCIALLY AVAILABLE THERMOGENIC DRINK

VINCENT J. DALBO,1 MICHAEL D. ROBERTS,2 JEFFREY R. STOUT,2 AND CHAD M. KERKSICK2

1School of Medicine and Applied Sciences, Central Queensland University, Rockhampton, Queensland, Australia; and2Department of Health and Exercise Science, University of Oklahoma, Norman, Oklahoma

ABSTRACT

Dalbo, VJ, Roberts, MD, Stout, JR, and Kerksick, CM. Effect

of gender on the metabolic impact of a commercially available

thermogenic drink. J Strength Cond Res 24(6): 1633–1642,

2010—The purpose of this study was to examine the gender

effect of daily consumption of a thermogenic drink (TD)

containing caffeine, epigallocatechin gallate, and taurine. In a

single-blind, matched-pairs, placebo-controlled study, 60 par-

ticipants (n = 30 men and n = 30 women) were matched in a

balanced fashion according to age and body mass. Participants

completed determination of body composition, resting energy

expenditure (REE), and serum levels of glycerol and free fatty

acids before and after ingesting either 336 mL of a TD or a

noncaloric, noncaffeinated placebo (PLA). Participants were

supplemented daily with 336 mL of either the TD or PLA and

repeated identical testing procedures on day 28. Area under

the curve (AUC) analysis on days 0 and 28 were calculated

for all blood variables (e.g., glycerol and free fatty acids) and

analyzed with REE, respiratory exchange ratio, dietary records,

and body composition with separate repeated-measure anal-

yses of variance. On days 0 and 28, REE AUC (p, 0.001) was

greater in all men compared with in women. Women ingesting

the TD had significantly greater free fatty acid AUC values

(p = 0.002) when compared with those of men. A significant

interaction for glycerol AUC (p = 0.02) revealed greater glycerol

concentrations in the male PLA group, which decreased in all

other groups from days 0 to 28. The male TD group lost

significantly more percent body fat (p = 0.02) than did the

female PLA group. The popularity of thermogenic drinks to

promote weight loss and body composition changes has grown

exponentially. Gender differences after drink ingestion may

impact the resulting adaptations and how successful their

inclusion impacts weight loss and body-composition changes

in those following a regular diet and exercise program.

KEY WORDS metabolism, thermogenesis, caffeine, EGCG,

energy drink

INTRODUCTION

The use of nutritionally supplemented drinks withthermogenic ingredients forweight loss and relatedimprovements while following a diet and exerciseprogram has increased significantly. Specifically,

the thermogenic ‘‘energy’’ drink (thermogenic drink [TD])market was estimated to be a $5.7 billion industry in 2006with over 500 TDs beingmarketed worldwide (7). As a result,the need to investigate the efficacy of TDs has increased inan attempt to explain associated efficacy and mechanismsof action (10,15,29).Common ingredients in TDs include caffeine, epigalloca-

techin gallate (EGCG), and taurine. Caffeine increaseslipolysis through stimulation of adenosine and b-adrenergicreceptors resulting in increases in circulating epinephrine(13,26) and serum free fatty acids (26). Epigallocatechingallate enhances fat oxidation (6), alters food digestibility(20,27), and can downregulate stearoyl-CoA desaturase geneexpression (20); an effect linked to a reduction of adiposityand lipid synthesis. Consequently, caffeine and EGCGshould work synergistically because epinephrine secretion(from caffeine ingestion) enhances metabolism, whereasEGCG reduces net energy intake and offsets further increasesin adiposity. Taurine ingestion may facilitate lipolysis byincreasing peroxisome proliferator–activated receptor-gcoactivator-1a in white adipose tissue (37), an effect thatwarrants the addition of taurine to the weight-loss products.Recent researchhas reported thatproductscontainingcaffeine

andEGCGas primary ingredients (or in combination) increasesmetabolism and promotes lipolysis (6,10–12,29,31). Althoughless research is available on taurine, studies have suggested it topositively influence mood, lipid metabolism, and weight lossand when combined with caffeine to influence memory, mood,and information processing (1,34,39,42). Our laboratory hasrecently found a TD containing caffeine, EGCG, and taurine tosignificantly increase metabolism and promote lipolysis (10,29).Specifically, acute consumption of this TD significantly

Address correspondence to Dr. Chad M. Kerksick, [email protected].

24(6)/1633–1642

Journal of Strength and Conditioning Research� 2010 National Strength and Conditioning Association

VOLUME 24 | NUMBER 6 | JUNE 2010 | 1633

increased resting energy expenditure (REE) and serummarkersof lipolysis assessed by free fatty acid and glycerol appearance(10). In a follow-up investigation, our laboratory reported on theeffects of chronic TD consumption. Free fatty acid area underthe curve (AUC) values were significantly greater after TDingestion compared with a noncaffeinated, noncaloric placeboafter 28 days of supplementation, and percent body fat and fatmass were significantly decreased in the TD group whencompared with the placebo group independent of exercise (29).The majority of research conducted on TDs has examined

the efficacy of the product compared with a noncaffeinated,noncaloric placebo (10,23,30), but no studies to our knowl-edge have directly examined the physiological differencesthat may occur between genders. This is important as currentformulations of TDs do not standardize the dosage of activeingredients relative to body mass; thus making it likely thatdivergent responses may occur between genders given thatmen generally possess more body mass relative to women(23). Further support to this hypothesis has shown thatwomen tend to oxidize less fat for energy at rest and duringexercise compared with men (25,31). The present inves-tigation involves a retrospective analysis to a previouslypublished data set (29) in which no gender effect wasinvestigated. The initially published report examined theoverall efficacy of the TD without a gender-specific analysis.The purpose of this investigation was to examine if genderdifferences were evident between a group of men and womenwho consumed a commercially available TD for a period of4 weeks for changes in body mass, body composition, energyexpenditure, and markers of lipolysis.

METHODS

Experimental Approach to the Problem

This study was conducted as a single-blind, parallel,matched-pair, placebo-controlled investigation. Upon re-cruitment, subjects were matched into clusters according toage and body mass before beginning the study. In a balancedformat, all subjects (N = 60) were assigned to ingest ona daily basis either a TD (men: n = 15 and women: n = 15) ora placebo drink (men: n = 15 and women: n = 15) for theduration of the study. All participants were tested at baseline(day 0) and after 28 days (day 28) for changes in free fattyacids, glycerol, REE, respiratory exchange ratio, body mass,and body composition. To determine metabolic changes inall groups, the response to ingestion of a single 336 mL drinkon days 0 and 28 was measured by repeated blood samples,energy expenditure, and substrate oxidation measurementsbefore (0 minutes) and 60, 120, and 180 minutes after drinkingestion. Primary outcome variables were gender-specificresponses to metabolic indicators (e.g., free fatty acid,glycerol, respiratory exchange ratio, and REE), whereassecondary outcomes were changes in body mass and bodycomposition. It is hypothesized from these data that dailyingestion of a TD for 4 weeks will result in gender-dependent outcomes relative to changes in biochemical

markers of lipolysis (e.g., free fatty acids and glycerol),substrate oxidation, energy expenditure, and body mass andbody composition changes.

Subjects

Healthy college-agedmen (mean6 SE; 23.26 0.74 years; 177.26 1.12 cm; 81.76 2.07 kg; 22.86 1.33%; n = 30) and women(236 1 years, 23.46 0.56 years; 165.66 1.59 cm; 62.16 1.18kg; 28.36 1.36%; n = 30) chose to participate in this study. Alltesting was conducted after the participant completed theinformed consent and comprehensive medical history ques-tionnaires in compliance with the Institutional Review Board atthe University of Oklahoma. Participants were excluded if they(a) had any history of metabolic, hypertension, hepatorenal,musculoskeletal, autoimmune, or neurological disease; (b) werecurrently taking thyroid, antihyperlipidemic, hypoglycemic,antihypertensive, or androgenicmedications; and (c) had takennutritional supplements or regularly consumed foods that maycontain ingredients or bioactive compounds that may affectmetabolism (i.e., over 100 mg�d21 of caffeine, ephedrine alka-loids, guggulsterones, etc.) or muscle mass (i.e., creatine,protein, amino acids, androstenedione, dihydroepiandroster-one, etc.) within 3 months of starting the study.

Procedures

In a single-blind fashion, participants were randomly assignedto ingest 336 mL of a TD that was provided by themanufacturer (CELSIUS, Celsius, Inc., Delray Beach, FL,USA) or a noncaffeinated noncaloric PLA (Caffeine-FreeDietCoke, CocaCola) after baseline testing at any point during theday for the duration of the investigation. The TD containeda proprietary blend of guarana extract (seed), green tea leafextract (leaf ) standardized to 10% EGCG, 200 mg caffeine,taurine, glucuronolactone, and ginger extract (root) (Table 1).The randomly assigned drinks were stripped of all identifyinginformation before administration and compliance wasmonitored by having participants pick up drinks from thelaboratory on a weekly basis and completing an ingestionlog throughout the duration of the study. Additionally,participants were instructed to avoid regular consumption offoods known to be high in caffeine such as caffeinated softdrinks and coffee. Dietary intake was monitored with 3 daydietary recalls (2) (2 week days and 1 weekend day) com-pleted before day 0 and day 28 testing sessions to ensurebetween-group homogeneity for energy and macronutrientconsumption and were assessed using the Food Processor IIINutrition Software version 8.6 (ESHA Nutrition Research,Salem, OR, USA).During days 0 and 28, each subject reported to the

laboratory after a 12-hour fast. Upon arrival, participants wereasked to void their bladder and change into a tight fittingswimsuit. Participants were barefoot for measurement ofheight that was conducted using a standiometer (Detecto,Webb City, MO, USA). Assessment of body mass, fat mass,fat-free mass, and percent body fat was done using airplethysmography (BOD POD�, Life Measurement Inc.

1634 Journal of Strength and Conditioning Researchthe TM

Gender Effect and Thermogenic Drinks

Concord, CA, USA). Before each test, the device wascalibrated according to the manufacturer’s instructions, andpercent body fat was estimated using the Brozek equation (8).Our laboratory colleagues have previously demonstratedtotal error of measurement values of 0.66% body fat using thistechnique (29). After body composition assessment, partic-ipants rested in a quiet room for 5 minutes where heart rateand blood pressure were determined using an electronicsphygmomanometer (HEM-757, Omron HealthCare Inc.,Vernon Hills, IL, USA), which has been reported to have anSD of63 mmHg for blood pressure and to be within65% ofpulse rate.Resting energy expenditure and respiratory exchange ratio

were determined using indirect calorimetry (True One 2400�Metabolic Measurement System, ParvoMedics Inc., Sandy,UT, USA). Before each testing session, the metabolic cart wascalibrated according to the manufacturer’s specification. Fortesting, a clear, hard plastic breathing hood with a plasticdrape was attached to a metabolic cart and was placed overthe participant’s head and upper torso. To ensure accuracy ofREE assessment, percent CO2 values were maintained within1.0–1.2% by manual adjustment of flow rate. Mean oxygenuptake ( _VO2) and carbon dioxide output ( _VCO2) weremeasured for each breath and averaged over 15-secondintervals. Resting energy expenditure and respiratory

TABLE 2. Dietary intake normalized to body mass (kg).

Variable Group Day 0 Day 28 Within group Between group

Caloric intake (kcal�kg�d21) Male TD 26.4 6 2.4 24.5 6 3.0 0.37 Group = 0.25Female TD 24.9 6 2.2 23.2 6 2.2 0.44 Time = 0.07Male PLA 24.9 6 2.2 25.0 6 2.6 0.97 G 3 T = 0.41Female PLA 33.1 6 4.3 27.4 6 1.9 0.11

Protein intake (g�kg�d21) Male TD 1.18 6 0.13 1.13 6 0.11 0.65 Group = 0.25Female TD 1.15 6 0.10 1.05 6 0.11 0.30 Time = 0.10Male PLA 1.00 6 0.08 1.05 6 0.09 0.48 G 3 T = 0.20Female PLA 1.53 6 0.26 1.22 6 0.12 0.11

Carbohydrate intake (g�kg�d21) Male TD 3.23 6 0.34 2.93 6 0.41 0.43 Group = 0.33Female TD 3.24 6 0.28 2.74 6 0.27 0.06 Time = 0.003Male PLA 3.19 6 0.37 2.91 6 0.40 0.46 G 3 T = 0.38Female PLA 4.23 6 0.49 3.19 6 0.27 0.02*

Fat intake (g�kg�d21) Male TD 0.93 6 0.10 0.91 6 0.13 0.75 Group = 0.22Female TD 0.87 6 0.11 0.83 6 0.10 0.67 Time = 0.67Male PLA 0.92 6 0.08 0.99 6 0.11 0.48 G 3 T = 0.78Female PLA 1.20 6 0.21 1.09 6 0.10 0.57

Caffeine (g�kg�d21) Male TD 0.13 6 0.05 2.54 6 0.11† ,0.001* Group , 0.001Female TD 0.20 6 0.13 3.30 6 0.16 ,0.001* Time , 0.001Male PLA 0.14 6 0.06 0.06 6 0.03 0.57 G 3 T , 0.001Female PLA 0.28 6 0.20 0.41 6 0.16 0.57

TD = thermogenic drink; PLA = placebo.Values are expressed as mean 6 SE.*Significant difference from days 0 to 28, p , 0.05.†Male TD group significantly different from female TD group, p , 0.05.‡Male PLA group significantly different from female PLA group, p , 0.05.

TABLE 1. Nutritional content of assigned drinks.*

Nutritional composition TD† PLA

Calories 5 kcal 0Protein ;1 g 0Carbohydrates ,1 g 0Fat ,1 g 0Vitamin C 60 mg 0Niacin 20 mg 0Vitamin B6 2 mg 0Vitamin B12 6 mcg 0Biotin 300 mcg 0Pantothenic acid 10 mg 0Calcium 50 mg 0Chromium 50 mcg 0Sodium 6 mg 0Caffeine‡ 200 mg 0

*TD = thermogenic drink; PLA = placebo; EGCG =epigallocatechin gallate.

†The product contains a proprietary blend of taurine,guarana extract, green tea leaf extract (standardized to10% EGCG), glucuronolactone, and ginger extract.

‡Caffeine comes from anhydrous caffeine, green tea,and guarana.


Journal of Strength and Conditioning Researchthe TM

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exchange ratio were measured for 20 minutes, but the datareported represent a 5-minute window at the end of thecollection period in which a criterion variable ( _VO2) deviatedby less than 5%. Test–retest correlations (r) using this devicewere in the range of 0.550–0.747 with a mean intraclasscoefficient of 0.893, p , 0.001. Before drink ingestion, aninitial measurement (0 minute) was made, and after drinkingestion, participants had their REE and respiratoryexchange ratio determined at 60, 120, and 180 minutes afterdrink ingestion.Participants then donated approximately 6 mL of fasting

blood from an antecubital vein by using standard venipunc-ture techniques. All blood samples were collected in 6-mLserum separation vacutainer tubes (BDVacutainer�, FranklinLakes, NJ, USA). Each vacutainer was inverted several timesand immediately centrifuged at 3,500 rpm for 15 minutes atroom temperature. The resulting supernatant was thenaliquoted into 2 microcentrifuge tubes and stored at 220�Cfor subsequent analysis of glycerol and free fatty acids. Beforedrink ingestion, an initial blood sample (0 minutes)was collected, and after drink ingestion, subjects donatedadditional blood samples 60, 120, and 180 minutes after drinkingestion. After day 0 testing, participants ingested 1 dailydose of the randomly assigned drink per day for 27 daysbefore returning to the laboratory on day 28 at the same time

of the day as baseline testing and performed identical testingprocedures as was conducted on day 0.Lipolysis was determined in duplicate by the assessment of

serum concentrations of glycerol and free fatty acids. Glycerolwas assessed using a calibrated commercial oxidase enzymereaction analyzer and reagents (Analox GM7, AnaloxInstruments, London, United Kingdom). Free fatty acidswere assessed using a commercial colorimetric assay (Roche,Penzeberg, Germany) and read with a spectrophotometer(SmartSpecTMPlus, Bio-Rad, Hercules, CA, USA) at a wave-length of 546 nm. Assay precision (coefficient of variation[CV]) and accuracy (percent of nonrecovery) were calculatedusing control samples for glycerol and free fatty acids by 8replicate determinations. The reported CV and percent ofnonrecovery for glycerol (0.24 mM control serum: 2.5 and1.2%) and free fatty acids control serums (0.35 mM controlserum: 8.9 and 3.6%) were found to be within acceptableranges (4,14).

Statistical Analyses

Separate AUC analyses using the trapezoidal method wereperformed for free fatty acids, glycerol, and REE on days0 and 28. Respiratory exchange ratio analysis data obtainedfrom each time point (pre, 60, 120, and 180 minutes) wereaveraged to attain a 3-hour value for each group of

Figure 1. A) Free fatty acid area under the curve analysis for all study groups (thermogenic drink [TD] men: n = 15; TD women: n = 15; placebo [PLA] men:n = 15; PLA women: n = 15). Similar letters signify there is no significant difference (p . 0.05) between groups. B) Day 0 and day 28 response graphs of men(n = 15) and women (n = 15) who ingested the TD. † = Male TD group: significant difference (p, 0.05) between days 0 and 28 at designated time point. ‡ = MaleTD group: significantly different (p , 0.05) from the female TD group on day 28. All data are presented as mean 6 SE.



participants on both days 0 and 28. Thus, all nutritional data,body composition, respiratory exchange ratio, and all AUCdata were analyzed using separate 43 2 (group3 time point[days 0 and 28]) repeated-measures analysis of variance,Bonferroni post hoc comparisons were performed to de-lineate within group changes, and Tukey post hoc compar-isons were used to delineate between-group changes. Toclearly delineate between-gender responses according to ourhypothesis, free fatty acid, glycerol, REE, and respiratoryexchange ratio data were compared between genders on days0 and 28 using separate independent t-tests. Within-genderresponses were evaluated using separate dependent t-test. Allstatistical analyses were performed using SPSS (version 16.0,SPSS Inc., Chicago, IL, USA). Data are presented as mean6

SE, and significance for all statistical analyses was determinedusing an alpha level of #0.05.

RESULTS

Nutritional Data

Nutrient consumption was normalized for body mass (inkilograms) and is presented in Table 2. No significant inter-actions (p . 0.05) were found for energy, protein, carbo-hydrate, or fat consumption. There was a main effect for timebecause there was a significant decrease in carbohydrateconsumption (p , 0.05) from days 0 to 28. Within-group

analyses revealed a significant decrease in carbohydrateconsumption in the female PLA group. A significant inter-action was found for caffeine consumption (p, 0.001). Therewas a main effect for group (p , 0.001), because the TDgroups consumed significantly more caffeine than did thePLA groups and time (p , 0.001) because caffeine con-sumption was significantly greater on day 28 compared toon day 0 in the male and female TD groups.

Day 0 and Day 28 Thermogenic and Lipolytic Response

Acute and chronic thermogenic and lipolytic data using AUCanalysis with day 0 and day 28 response graphs for free fattyacids, glycerol, and REE are presented in Figures 1–3,respectively. There was no significant interaction (p = 0.11)for free fatty acid AUC analysis, but there was a significantgroup effect (p = 0.002) as the male PLA group mobilizedsignificantly less free fatty acids than every other group onday 0 and the female TD group mobilized significantly morefree fatty acids than every other group on day 28. Theresponse graph indicated that the male TD group hadsignificantly greater serum free fatty acid concentrations at60, 120, and 180 minutes post–drink consumption comparedto on day 28. Additionally, the female TD group hadsignificantly greater serum free fatty acid concentrations thandid the male TD group at 120 and 180 minutes post–drinkconsumption on day 28. There was a significant interaction

Figure 2. A) Glycerol area under the curve analysis for all study groups (thermogenic drink [TD] men: n = 15; TD women: n = 15; placebo [PLA] men: n = 15; PLAwomen: n = 15). Similar letters signify that there is no significant difference (p. 0.05) between groups. —– = significant difference from days 0 to 28, p, 0.05. B)Day 0 and 28 response graphs of men (n = 15) and women (n = 15) who ingested the TD. All data are presented as mean 6 SE.



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Figure 4. A) Mean respiratory exchange ratio analysis for all study groups (thermogenic drink [TD] men: n = 15; TD women: n = 15; placebo [PLA] men: n = 15;PLA women: n = 15). Similar letters signify that there is no significant difference (p . 0.05) between groups. —– = significant difference from days 0 to 28, p ,

0.05. B) Days 0 and 28 response graphs of men (n = 15) and women (n = 15) who ingested the TD. ¢ = Male TD group significantly different from the female TDgroup on day 0, p, 0.05. ‡ = Male TD group: significantly different (p, 0.05) from female TD group on day 28. # = Significant difference from days 0 to 28 in thefemale PLA group, p , 0.05. All data are presented as mean 6 SE.

Figure 3. A) Resting energy expenditure (REE) area under the curve analysis for all study groups (thermogenic drink [TD] men: n = 15; TD women: n = 15;placebo [PLA] men: n = 15; PLA women: n = 15). Similar letters signify that there is no significant difference (p . 0.05) between groups. B) Day 0 and 28response graphs of men (n = 15) and women (n = 15) who ingested the TD. ¢ = Male TD group significantly different from the female TD group on day 0, p, 0.05.‡ = Male TD group: significantly different (p , 0.05) from the female TD group on day 28. All data are presented as mean 6 SE.



for glycerol AUC (p = 0.02), because the male PLA groupexperienced a significant increase (p = 0.04) in serum glycerolappearance from days 0 to 28. There was no main effect forgroup (p = 0.82) or time (p = 0.43). No interaction waspresent for REE AUC (p = 0.09), but there was a main effectfor group (p , 0.001). On day 0, the female TD group hada lower REE than did the male PLA and male TD groups,

whereas the female PLA group had a lower REE than didthe male PLA, male TD, and female TD groups. On day 28,the female TD and female PLA groups had significantlylower REE than did the male TD and male PLA groups.Resting energy expenditure was significantly greater in themale TD and male PLA groups compared with the femaleTD and female PLA groups at each time point on days

0 and 28. Acute and chronicrespiratory exchange ratio dataalong with day 0 and 28 re-sponse graphs are presented inFigure 4. There was no signif-icant interaction (p = 0.08),group (p = 0.06), or time effect(p = 0.27). The response graphindicated that the female TDgroup had a significantly higherrespiratory exchange ratio onday 28 compared to on day 0at 120 (p = 0.03) and 180(p = 0.03) minutes post–drinkconsumption. Additionally, thefemale TD group had signifi-cantly greater respiratory ex-change ratio values 120minutes (p = 0.03) post–drinkconsumption on day 0 and 60minutes (p = 0.04) post–drinkconsumption on day 28 com-pared to the male TD group.

Figure 5. A) Delta change (pre–post) for percent body fat for all study groups (thermogenic drink [TD] men: n = 15;TD women: n = 15; placebo [PLA] men: n = 15; PLA women: n = 15). D = Male TD group significantly different fromthe female PLA group, p, 0.05. B) Individual response graph for all study groups (TD men: n = 15; TD women: n =15; PLA men: n = 15; PLA women: n = 15). All data are presented as mean 6 SE.

TABLE 3. Body composition*

Variable Group Day 0 Day 28 Within group Between group

Body mass (kg) Male TD 81.3 6 3.1† 81.0 6 3.0 †§ 0.17 Group , 0.001Female TD 63.9 6 2.8 63.7 6 2.7 0.58 Time = 0.61Male PLA 82.1 6 2.9‡ 82.1 6 2.8‡ 0.94 G 3 T = 0.10Female PLA 60.3 6 2.3 61.1 6 2.3 0.01§

Fat-free mass (kg) Male TD 61.5 6 1.8†§ 62.3 6 1.9† 0.12 Group , 0.001Female TD 45.7 6 1.3 45.3 6 1.3 0.04§ Time = 0.81Male PLA 63.7 6 1.8‡ 63.7 6 1.8‡ 0.98 G 3 T = 0.13Female PLA 42.4 6 1.1 42.1 6 1.1 0.42

Fat mass (kg) Male TD 19.8 6 2.2 18.5 6 2.2 0.007§ Group = 0.98Female TD 18.2 6 2.0 18.2 6 2.0 0.77 Time = 0.51Male PLA 18.3 6 1.9 18.2 6 1.9 0.69 G 3 T = 0.001Female PLA 17.9 6 1.7 18.8 6 1.6 0.04§

Body fat (%) Male TD 23.7 6 2.0† 22.3 6 2.2 0.02§ Group = 0.02Female TD 27.6 6 1.8 27.9 6 1.9 0.36 Time = 0.99Male PLA 21.8 6 1.8 21.7 6 1.8‡ 0.80 G 3 T = 0.002Female PLA 28.9 6 2.0 30.2 6 1.8 0.04§

*Values are expressed as means 6 SE.†Male TD group significantly different from female TD group, p , 0.05.‡Male PLA group significantly different from female PLA group, p , 0.05.§Significant difference from day 0 to day 28, p , 0.05.



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Body Composition

No significant interaction was present for body mass (p =0.10) or fat-free mass (p = 0.13), but there was a main effectfor group in each condition (p , 0.001) as men weresignificantly heavier and had more fat-free mass than didwomen. There was a significant interaction for fat mass (p ,0.001) and percent body fat (p = 0.002) as the male TD grouplost a significant amount of fat mass and the female PLAgroup gained a significant amount of fat mass over theduration of the investigation. A group effect was present forpercent body fat (p = 0.02) as women had significantly morepercent body fat than men (Table 3). Figure 5A, B display thedelta change (prevalue2 postvalue) for percent body fat andan individual response graph, respectively.

DISCUSSION

The purpose of the present study was to investigate gender-specific metabolic responses to prolonged of a commerciallyavailable TD. The primary findings from this study suggestedthat women tended to mobilize greater amounts of fat(Figure 2), whereas men tended to oxidize more fat (Figure 4)and experienced improvements in body composition(Figure 5). Previous investigations have examined themetabolic response of TD ingestion; however, none of thesestudies examined any gender-related outcome (10,16,19).Our laboratory has reported increases in energy expenditureand fat mobilization after acute and prolonged ingestion ofa TD containing caffeine, EGCG, and taurine (10). Theprolonged study of this data set investigated mixed-gendereffects (29) but failed to investigate any gender-specificoutcomes; a potential effect that was brought to light bya recent report of Lockwood et al. (23). This study indicatedthat with exercise over a 12-week period, men may experi-ence greater changes in body composition than do women(23). Thus, the decision was made to perform a retroactiveanalysis of the Roberts et al. data set (29) to determine theimmediate metabolic changes for each gender that occurafter acute ingestion of a TD before and after 28 days of dailyingestion. It was hypothesized that women would experiencea greater metabolic effect because of greater relative dosing(milligrams per kilogram body mass) of active ingredientsand gender differences in substrate use at rest and duringexercise (17,25). As expected, men in the TD group receiveda significantly lower relative dose of caffeine compared tothe women in the TD group (male TD = 2.5 6 0.39, femaleTD = 3.3 6 0.59, p = 0.001). Specific delivered dosages ofEGCG and taurine could not be calculated because of theirinclusion in a proprietary blend of the ingredients; however,popular over-the-counter thermogenic drinks containaround 90 mg of EGCG (28) and 1–2 g of taurine (3).Relative dosing values are important because of thecommonly reported dose-related outcomes associated withthese ingredients (9,22).Caffeine is thought to be the likely candidate for the

metabolic action seen between the genders. Briefly, the

lipolytic mechanisms associated with caffeine ingestioninclude the following: (a) an enhanced secretion of epine-phrine (5) and greater production of cAMP-mediatedactivation of hormone-sensitive lipase and the subsequentliberation of glycerol and free fatty acids into the plasma (38),(b) phosphodiesterase inhibition, leading to further sustain-ment of cAMP and subsequent activation of lipolysis, and (c)antagonism of peripheral adenosine (A1) receptors, yetfurther increasing intraadipocyte cAMP levels. It is likelythat caffeine is the primary and only agent resulting inlipolytic actions; however, firm conclusions to this pointcannot be drawn from our study design. It is also possible thatgreater values in serum estrogen in women may work tofurther sustain caffeine levels through its inhibition ofcytochrome P450 1A2 (21,35). Therefore, although plasmacaffeine concentrations were not assessed, women consum-ing the TD may have had greater circulating concentrationsof caffeine than did men allowing for greater fat mobilizationvia the aforementioned lipolytic mechanisms. In support ofthis, day-28 free fatty acid AUC analysis revealed that thewomen who ingested a TD had significantly more serum freefatty acids than did the other 3 cohorts. However, the lackof plasma caffeine, epinephrine, and estrogen assessment isa limitation in the present investigation and limits our abilityto further explore these possibilities. While taurine has beenused as a lipolytic agent that may improve mood (1) anddecrease risk of heart disease (41,42), although it is unknownwhether the dose received in either gender was sufficient toelicit a physiological response. Although Zhang et al. reportedthat a daily 3-g dose for 7 weeks reduced triglycerides andreduced body mass (42), a post hoc analysis revealed no sucheffect from the present study (data not shown).In contrast to the initial hypothesis, the man who ingested

the TD experienced significant reductions in fat mass andpercent body fat in comparison to men who ingested PLAand women who ingested the TD. Although contradictory togreater liberation of free fatty acids in women who ingesteda TD on days 0 and 28, men who ingested the TD lost morefat mass. Respiratory exchange ratio data (Figure 4) suggesta greater oxidation of fat by men who ingested the TDin comparison to women who also ingested the TD on days0 and 28. This is supported previously where women werefound to oxidize less fat for energy than men at rest (25,36).Hence, this between-gender endocrinological phenomenonwould again help explain the significant changes in percentbody fat and fat mass for the male TD group and the lack ofresponse in the female TD group.A lack of internal stability in our body composition mea-

surement or changes in normal dietary intake are potentialconfounding influences; however, we have previously reporteda total error of measurement for body composition using theBOD POD to be approximately 0.66% with a test–retestintraclass coefficient of.0.99 (29). Using minimum differencestandards (40), the 1.18% gender difference (Figure 5) seen inbody composition exceeded the SEM of this device of 0.48%



(24), thus suggesting that this effect was a real difference.Furthermore, a significant decrease in carbohydrate intakeoccurred in the female PLA group; however, no other changesin dietary variables were found (Table 2). It is likely that self-reporting errors may have occurred in the dietary analysis (33),but previous studies have also reported validity with 3-dayfood records (32).In conclusion, findings from this study provide preliminary

biochemical and metabolic evidence of greater increasesin circulating free fatty acids in women (Figure 1), whereasgreater levels of fat oxidation and overall improvements inbody composition were seen in men (Figure 5). Althoughsupportive of other literature (23), the mechanism(s) asso-ciated with these findings are not well understood becauseprevious research has suggested an inhibitory effect ofestrogen over cellular respiration components (35), whereasthe rates of reesterification (18) between genders may havealso impacted the findings from the present investigation.

PRACTICAL APPLICATIONS

Fitness and exercise professionals are faced with a barrage ofefficacy-based questions in their practice regarding exerciseand nutrition. The use of thermogenic ingredients andespecially TDs in the past several years has increased byseveral degrees of magnitude. Completed studies have shownthat immediate effects of these drinks results in an increase inlipolysis and energy expenditure. Outcomes from this studyhelp fitness enthusiasts and professionals understand thegender-specific responses that may occur in response toingesting a commercially available TD. As such, it appearsthat greater increases in free fatty acids (a marker of lipolysis)result in women, whereas men may experience a greaterdecrease in body composition after daily ingestion of a TD for28 days.

ACKNOWLEDGMENTS

The authors would like to thank the study participants andadditional graduate students and faculty in the Department ofHealth andExercise Sciencewhoassisted inpartwith this studyinvestigation. Celsius Inc. (Delray Beach, FL) provided fundingfor this project through an unrestricted research grant to theUniversityofOklahoma.All researchers involved independentlycollected, analyzed, and interpreted the results from this studyand have no financial interests concerning the outcome of thisinvestigation; thus, no conflicts of interest are evident in thisreport. The results from this study do not constitute endorse-ment of the product by the authors, their institution or theNational Strength and Conditioning Association.

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Effect of Gender on the Metabolic Impact of a Commercially Available Thermogenic Drink

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