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Acute Effects of a Thermogenic Nutritional Supplement on Energy Expenditure and Cardiovascular Function at Rest, During Low-Intensity Exercise, and Recovery from Exercise

Ryan, Eric D; Beck, Travis W; Herda, Trent J; Smith, Abbie E; Walter, Ashley A; Stout, Jeffrey R; Cramer, Joel T

Journal of Strength and Conditioning Research: May 2009 - Volume 23 - Issue 3 - p 807-817
doi: 10.1519/JSC.0b013e3181a30fb8
Original Research
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Ryan, ED, Beck, TW, Herda, TJ, Smith, AE, Walter, AA, Stout, JR, and Cramer, JT. Acute effects of a thermogenic nutritional supplement on energy expenditure and cardiovascular function at rest, during low-intensity exercise, and recovery from exercise. J Strength Cond Res 23(3): 807-817, 2009-The purpose of present study was to examine the acute effects of a thermogenic nutritional supplement on energy expenditure (EE) and cardiovascular function at rest, during low-intensity exercise, and recovery from exercise. Twenty-eight healthy sedentary participants (mean ± SD; age, 22.3 ± 1.9 years; body mass index, 24.0 ± 3.7) volunteered for this randomized, double-blinded, placebo-controlled, crossover study. Each experimental trial was divided into 4 phases: (a) 30 minutes of initial resting, followed by the placebo or thermogenic nutritional supplementation, (b) 50 minutes of postsupplementation resting, (c) 60 minutes of treadmill walking (3.2-4.8 km·h−1), and (d) 50 minutes of postexercise recovery. Gas exchange variables measured by indirect calorimetry and heart rate (HR) were recorded during all 4 phases, blood pressure was only measured at rest, and rating of perceived exertion (RPE) was only recorded during exercise. EE and oxygen consumption rate (V̇o2) were greater for the supplement than the placebo at 50 minutes after supplementation. Also, during the postsupplementation period, diastolic blood pressure (DBP) was higher at all time periods, whereas the respiratory exchange ratio (RER) was higher at 20 and 30 minutes for the supplement. During exercise, only V̇o2 and minute ventilation (V̇E) were greater for the supplement than the placebo, with HR being less than the placebo at 20 minutes for the men. Postexercise EE, V̇o2, systolic blood pressure (SBP), DBP, and HR (men only) at 10, 20, 30, and 50 minutes were greater for the supplement than the placebo. These findings indicated that the thermogenic nutritional supplement increased resting EE and exercise V̇o2 with only minimal effects on blood pressure and HR and no meaningful effects on RER or RPE. These results suggested that the combination of thermogenic ingredients in this nutritional supplement may be useful to help maintain a negative caloric balance but may not influence substrate use or perceived exertion.

Department of Health and Exercise Science, University of Oklahoma, Norman, Oklahoma

Address correspondence to Joel T. Cramer, jcramer@ou.edu.

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Introduction

Within the past several decades, the United States has experienced large increases in the prevalence of obesity (32,41). Obesity is often associated with comorbidities, including cardiovascular disease, type 2 diabetes, and hypertension, whereas also reducing life expectancy (35). In addition, obesity has been linked to increased health care costs (4), making it a major public health concern (44).

Recent literature reviews have proposed that certain nutritional ingredients may increase resting energy expenditure (EE); therefore, supplementing the diet with these ingredients may be useful for obesity management (12,25). Such nutritional supplements have been marketed as “thermogenic aids.” Theoretically, if nutritional supplementation can increase resting EE, negative energy balance could be achieved (assuming no changes in energy intake), which may help dieters improve body composition and prevent weight gain (25). Recent authors (12,25) have also suggested that thermogenic nutritional supplements may help counteract the reduction in resting EE that is present during dieting (2), thereby contributing further to maintenance of a negative energy balance and weight loss.

It has been suggested that foods containing caffeine, capsaicin, bioperine, and certain B vitamins may be safer alternatives than ephedrine-containing supplements for weight loss (11,12). In fact, these alternative ingredients have been considered “…functional agents that could help in preventing a positive energy balance and obesity” (43). For example, caffeine is one of the most widely consumed compounds in the world (19), with reported (5) daily intakes in the United States ranging from 3 to 7 mg·kg−1 of body weight. Several previous studies have suggested that caffeine may increase resting EE (3,16,24), and that this thermogenic affect may be dose-dependent (3). Capsaicin, the pungent component of red pepper, has also been shown to increase resting EE by nearly 32% when added to a standard breakfast (46). Under similar conditions, Lim et al. (27) also reported plasma epinephrine and norepinephrine levels to be greater 30 minutes after a hot red pepper meal when compared with a standard meal without hot red peppers. Like capsaicin, the thermogenic ingredient in black pepper (piperine) has also been reported to increase EE in rats (23,37). Furthermore, preliminary evidence has suggested that niacin may be a metabolically-active vitamin because niacin intake was found to be lower in adolescents that were overweight when compared with those that were not overweight (20). Overall, since the banning of ephedra as a legal nutritional supplement (36), scientists have been seeking safer alternative nutritional strategies for enhancing the body's metabolic rate (12,43).

Recent studies have suggested that combinations of thermogenic nutritional supplements may act synergistically to improve resting EE (7,8,45). For example, Belza and Jessen (8) stated that caffeine may be a “…potent amplifier of thermogenesis in humans when given in conjunction with agents stimulating (sympathetic nervous system) SNS. In addition, Yoshioka et al. (45) found that adding caffeine and capsaicin to daily meals increased daily energy expenditure by approximately 3%. More recent studies have examined the effects of a combination of thermogenic supplements (i.e., caffeine, capsaicin, catechins, L-tyrosine, and calcium) on acute (4 hour) and daily (24 hour) EE (7,8). The authors reported that the supplement increased acute EE by 90 kJ (2.4%) (7) and daily EE by approximately 200 kJ (2%) (8). In general, however, little is known about the acute effects of thermogenic nutritional supplements on resting EE, aerobic power, and other markers of cardiovascular function. Therefore, to extend our knowledge regarding the physiological effects of a combination of various thermogenic ingredients, the purpose of the present study was to examine the acute effects of a caffeine-, capsaicin-, bioperine-, and niacin-containing nutritional supplement on EE and cardiovascular function at rest, during low-intensity exercise, and recovery from exercise.

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Methods

Experimental Approach to the Problem

This study used a randomized, double-blinded, placebo-controlled, crossover design. Each subject visited the laboratory on 3 separate occasions: once for a familiarization session and (2-4 days later) 2 experimental trials, which were separated by 6-8 days (Figure 1). During the familiarization session, subjects were screened for their exercise and health history status, and height and weight were recorded.

Figure 1

Figure 1

As shown in Figure 1, subjects arrived at the laboratory for the experimental trials after a 12-hour overnight fast and rested supine for 30 minutes on a padded table (Earthgear Therapeutic Innovations™, Taichung Hsien, Taiwan). All measurements for each subject were performed at the same time of day for both experimental trials. The laboratory was kept quiet with the lights off during all resting measurements. After the 30-minute resting period, the subjects were fitted with a heart rate monitor (Polar Electro Inc., Lake Success, N.Y.) for the 30 minutes presupplementation resting EE measurements. The supplement was then administered, and the postsupplementation resting EE measurements continued for 50 minutes. Subjects then walked on a treadmill for 60 minutes at a self-selected, predetermined speed between 3.2 and 4.8 km·h−1, which remained constant for both experimental trials. After the exercise, subjects returned to the padded table for the final postexercise resting energy expenditure measurements, which lasted 50 minutes (Figure 1).

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Subjects

Thirteen women (mean ± SD: age = 22.2 ± 1.3 years; height = 166.5 ± 8.1 cm; weight = 63.5 ± 11.8 kg; BMI = 22.9 ± 3.7) and 15 men (age = 22.1 ± 2.3 years; height = 178.5 ± 9.1 cm; weight = 79.4 ± 14.2 kg; BMI = 24.9 ± 3.6) volunteered for this investigation. Each subject completed a pre-exercise health status questionnaire and signed a written informed consent document. Eighteen of the 28 subjects participated in 3.2 ± 2.0 hours of aerobic exercise, 14 of the 28 subjects participated in 2.4 ± 1.5 hours of resistance exercise, and 5 of the 28 subjects participated in 3.0 ± 1.4 hours of recreational sports per week, but none of the participants were competitive athletes. None of the subjects reported or exhibited (a) a history of medical or surgical events that might have significantly affected the study outcome, including cardiovascular disease or metabolic, renal, hepatic, or musculoskeletal disorders; (b) use of any medication that might have significantly affected the study outcome; (c) use of nutritional supplements (e.g., creatine, protein drinks, amino acids, or vitamins) in the 6 weeks before the beginning of the study; or (d) participation in another clinical trial or ingestion of another investigational product within 30 days before screening and enrollment. All procedures were approved by the University Institutional Review Board for Human Subjects Research.

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Physiological Measurements

Oxygen consumption rate (V̇o2), carbon dioxide production rate (V̇co2), and minute ventilation rate (V̇E ) were measured continuously during the resting and exercise conditions via indirect calorimetry using a calibrated metabolic cart (Parvo Medics TrueOne® 2400 Metabolic Measurement System, Sandy, Utah). The resting measurements were performed using a ventilated-hood (Vacu Med, Ventura, Calif.) that was placed over the head of the subject, whereas plastic sheeting attached to the hood was carefully tucked around the subject to form a seal between the hood and the outside air in accordance with the user's manual (Vacu Med 5.04, Canopy Cat #17). The subjects were instructed to remain supine and awake, while not talking or fidgeting for the duration of the resting measurements. For the exercise conditions, subjects were fitted with a nose clip and a head-mounted 3-way valve (Hans-Rudolph, Kansas City, Mo.). Before each trial, the oxygen and carbon dioxide gas analyzers were calibrated with a known gas mixture. Energy expenditure (EE) (kilojoules per minute) was derived from the respiratory exchange ratio (RER) data by using the Weir (42) conversion for nonprotein RER during the resting measurements. In addition, the subject's arterial blood pressure (i.e., systolic [SBP] and diastolic [DBP]) was measured during the resting conditions using an automated digital blood pressure system (Omron Healthcare, Inc. HEM-773, Vernon Hills, Ill.). Ratings of perceived exertion (RPE) were also recorded during the exercise trials using the Borg RPE Scale (9). All indirect calorimetry measurements were recorded breath by breath and reported as 10-minute averages (14). Arterial blood pressure was taken every 15 minutes at rest, and RPE was taken every 10 minutes during the exercise. The dependent variables in the current study were chosen to determine if the thermogenic supplement had any effect on specific metabolic (EE, RER, V̇o2, and V̇E), cardiovascular function (HR,SBP, and DBP), and perceived exertion (RPE) benefits during rest, exercise, and recovery from exercise.

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Supplementation

For the two experimental trials, subjects received either the supplement or the placebo in random order (Table 1). Both the supplement and the placebo capsules were dark, opaque, and similar in appearance to maintain the double-blind nature of the experiment. In addition, third-party random laboratory testing (Nutra Manufacturing Inc., Greenville, S.C.) was performed to confirm that the ingredients in the supplement and placebo capsules were ±5% of the manufacturer claims.

Table 1

Table 1

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Statistical Analyses

Separate 3-way repeated-measures analyses of variance (ANOVAs) (condition × time × sex) were used to analyze the EE, HR, V̇o2, RER, V̇E, SBP, DBP, and RPE data. The V̇o2, HR, and RER data were analyzed separately for each individual time period (resting and exercise). The EE, SBP, and DBP data were analyzed for all resting conditions, and the V̇E and RPE data were analyzed during exercise. When appropriate, follow-up analyses included 1-way ANOVAs and paired samples t-tests with Bonferroni-corrected post-hoc comparisons. SPSS software version 14.0 (SPSS Inc., Chicago, Ill.) was used for all statistical analyses. An alpha of 0.05 was considered statistically significant for all comparisons.

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Results

Energy Expenditure

The results for EE indicated that for the presupplementation period, there was a 3-way interaction (p = 0.024; condition × time × sex). At 30 minutes, the women's EE was greater for the placebo than the supplement. EE decreased within the 30 minutes before supplementation for both the supplement and placebo conditions. During the postsupplementation period, there was no 3-way interaction (p = 0.139; condition × time × sex), no 2-way interaction for condition × sex (p = 0.291) or time × sex (p = 0.817) but a 2-way interaction for condition × time (p < 0.001), where EE values were greater for the supplement than the placebo at 50 minutes. For the postexercise period, there was no 3-way interaction (p = 0.247; condition × time × gender), no 2-way interaction for condition × time (p = 0.091), condition × sex (p = 0.291), or time × sex (p = 0.419), but there were main effects for condition (p < 0.001), time (p < 0.001), and sex (p < 0.001). EE decayed over time after the exercise for both the supplement and placebo conditions; however, EE was greater for the supplement than the placebo and greater for men than women during the entire postexercise period. See Figure 2 for significant mean differences in EE among time points. In addition, Figure 3 displays the change in EE from baseline (30-minute time point during presupplementation) for the postsupplementation and postexercise periods for both the supplement and placebo.

Figure 2

Figure 2

Figure 3

Figure 3

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Oxygen Consumption

The results for V̇o2 indicated that for the presupplementation period, there was no 3-way interaction (p = 0.182; condition × time × sex), no 2-way interaction for condition × time (p = 0.948), condition × sex (p = 0.701), or time × sex (p = 0.086), and no main effect for condition (p = 0.327) and sex (p = 0.156), but there was a main effect for time (p < 0.001). Oxygen consumption decreased over the 30 minutes before supplementation for both the supplement and placebo conditions. During the postsupplementation period, there was no 3-way interaction (p = 0.145; condition × time × sex) and no 2-way interaction for condition × sex (p = 0.618) or time × sex (p = 0.873), but there was a 2-way interaction for condition × time (p = 0.005), where V̇o2 values were greater for the supplement than the placebo at 50 minutes. During exercise, there was no 3-way interaction (p = 0.793; condition × time × sex), no 2-way interactions for condition × time (p = 0.473), condition × sex (p = 0.236) or time × sex (p = 0.453), and no main effect for time (p = 0.619) and sex (p = 0.214), but there was a main effect for condition (p = 0.014). Oxygen consumption was greater for the supplement than the placebo at all times during exercise. During the postexercise period, there was no 3-way interaction (p = 0.302; condition × time × sex) and no 2-way interaction for condition × sex (p = 0.725) or time × sex (p = 0.186), but a 2-way interaction (p = 0.008; condition × time), where V̇o2 for the supplement condition was greater than that for the placebo condition at all time points. See Figure 4 for significant mean differences in V̇o2 among time points.

Figure 4

Figure 4

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Respiratory Exchange Ratio

The results for RER indicated that for the presupplementation period, there was no 3-way interaction (p = 0.328; condition × time × sex), no 2-way interaction for condition × time (p = 0.467), condition × sex (p = 0.430), or time × sex (p = 0.366), and no main effect for condition (p = 0.941) and sex (p = 0.440), but there was a main effect for time (p < 0.001). RER decreased over time during the 30 minutes before supplementation for both the supplement and placebo conditions. During the postsupplementation period, there was no 3-way interaction (p = 0.406; condition × time × sex) and no 2-way interaction for condition × sex (p = 0.255) or time × sex (p = 0.109), but there was a 2-way interaction for condition × time (p = 0.044), where RER values were greater for the supplement than the placebo at 20 and 30 minutes postsupplementation. For the exercise period, there was no 3-way interaction (p = 0.472; condition × time × sex), no 2-way interaction for condition × time (p = 0.326), condition × sex (p = 0.319), or time × sex (p = 0.487), and no main effects for condition (p = 0.333) and sex (p = 0.111), but there was a main effect for time (p < 0.001). RER was higher from 20-50 minutes when compared with the 10-minute period. During the postexercise period, there was no 3-way interaction (p = 0.221 condition × time × sex), no 2-way interactions for condition × time (p = 0.428), condition × sex (p = 0.412), or time × sex (p = 0.431), and no main effect for condition (p = 0.706) or sex (p = 0.776), but there was a main effect for time (P < 0.001). RER initially decreased and then gradually increased for both the supplement and placebo conditions over the 50-minute period. See Figure 5 for significant mean differences in RER among time points.

Figure 5

Figure 5

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Minute Ventilation

The results for V̇E indicated that during exercise, there was no 3-way interaction (p = 0.658; condition × time × sex), no 2-way interaction for condition × time (p = 0.143), condition × sex (p = 0.882), or time × sex (p = 0.413), and no main effect for sex (p = 0.396), but there were main effects for condition (p < 0.001) and time (p < 0.001). Minute ventilation increased over the 60-minute period for both the supplement and placebo conditions, and the supplement elicited a greater V̇E response than the placebo over the entire exercise period. See Figure 6 for significant mean differences in V̇E among time points.

Figure 6

Figure 6

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Heart Rate

The results for HR indicated that for the presupplementation period, there was no 3-way interaction (p = 0.465; condition × time × sex), no 2-way interaction for condition × time (p = 0.629), condition × sex (p = 0.544), or time × sex (p = 0.824) and no main effect for condition (p = 0.691) or sex (p = 0.175), but there was a main effect for time (p = 0.007). HR decreased within the 30-minute period before supplementation for both the supplement and placebo conditions. During the postsupplementation period, there was no 3-way interaction (p = 0.429; condition × time × sex), no 2-way interaction for condition × time (p = 0.146), condition × sex (p = 0.568), or time × sex (p = 0.205), and no main effects for condition (p = 0.896), time (p = 0.375), or sex (p = 0.112). During exercise, there was a 3-way interaction (p = 0.038; condition × time × sex), where HR was greater for the placebo condition than for the supplement condition at 20 minutes for men. For the postexercise period, there was a 3-way interaction (p = 0.031; condition × time × sex). HR was greater for the supplement than the placebo at 10, 20, 30, and 50 minutes during the postexercise period in men. See Figure 7 for significant mean differences in HR among time points.

Figure 7

Figure 7

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Systolic Blood Pressure

The results for SBP indicated that for the presupplementation period, there was no 3-way interaction (p = 0.765; condition × time × sex), no 2-way interactions for condition × time (p = 0.372), condition × sex (p = 0.334), or time × sex (p = 0.247), but there were main effects for condition (p = 0.025), time (p < 0.001) and sex (p < 0.001). SBP decreased over the 30 minutes before supplementation for both the supplement and placebo conditions, but the mean SBP values for the placebo were greater than those for the supplement during this time. In addition, SBP was higher for men than women over all time periods. During the postsupplementation period, there was no 3-way interaction (p = 0.994; condition × time × sex), no 2-way interaction for condition × time (p = 0.818), condition × sex (p = 0.520), or time × sex (p = 0.900), and no main effects for condition (p = 0.223) or time (p = 0.067), but there was a main effect for sex (p < 0.001). SBP was higher for the men when compared with the women over all time periods. For the postexercise period, there was no 3-way interaction (p = 0.303; condition × time × sex), no 2-way interaction for condition × time (p = 0.144), condition × sex (p = 0.551), or time × sex (p = 0.426), and no main effect for time (p = 0.094), but there was a main effect for condition (p = 0.001) and sex (p < 0.001). The supplement elicited higher mean SBP values than the placebo during the postexercise period, whereas SBP values were higher for men than women over the entire postexercise period. See Figure 8 for significant mean differences in SBP among time points.

Figure 8

Figure 8

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Diastolic Blood Pressure

The results for DBP indicated that for the presupplementation period, there was no 3-way interaction (p = 0.524; condition × time × sex), no 2-way interaction for condition × time (p = 0.631), condition × sex (p = 0.644), or time × sex (p = 0.127), and no main effect for condition (p = 0.441) or sex (p = 0.745), but there was a main effect for time (p = 0.008). DBP decreased over the 30-minute presupplementation time period for both the supplement and placebo conditions. During the postsupplementation period, there was no 3-way interaction (p = 0.632; condition × time × sex), no 2-way interaction for condition × time (p = 0.188), condition × sex (p = 0.708), or time × sex (p = 0.408), and no main effect for time (p = 0.253) or sex (p = 0.597), but there was a main effect for condition (p = 0.013). DBP values for the supplement were greater than those for the placebo over the entire postsupplementation period. For the postexercise period, there was no 3-way interaction (p = 0.711; condition × time × sex), no 2-way interaction for condition × time (p = 0.994), condition × sex (p = 0.298), or time × sex (p = 0.751), no main effect for time (p = 0.109) or sex (p = 0.523), but there was a main effect for condition (p = 0.009). The mean DBP values for the supplement were greater than those for the placebo during the postexercise period. See Figure 9 for significant mean differences in DBP among time points.

Figure 9

Figure 9

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Rating of Perceived Exertion

The results for RPE indicated that during exercise, there was no 3-way interaction (p = 0.191; condition × time × sex), no 2-way interaction for condition × time (p = 0.391), condition × sex (p = 0.131), or time × sex (p = 0.483), and no main effect for condition (p = 0.337) or sex (p = 0.526), but there was a main effect for time (p < 0.001). RPE increased over the 60-minute period for both the supplement and placebo conditions. See Figure 10 for significant mean differences in RPE among time points.

Figure 10

Figure 10

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Discussion

Energy Expenditure

The primary results of the present study were that resting EE was 6% greater at 50 minutes postsupplementation and 4-8% greater during the entire postexercise period for the supplement compared to the placebo (Figure 2). Although no previous studies have examined the acute effects of a caffeine-, capsaicin-, niacin-, and bioperine-containing nutritional supplement on resting EE, several studies have investigated the effects of caffeine (3, 16, 24, 34) or capsaicin (27, 46). Less is known about the thermogenic influences of niacin (11, 20) and bioperine (43) on resting EE.

It is difficult to directly compare the results of studies that have examined the effects of supplements that contain multiple ingredients. Often, the supplements are similar, but contain slightly different ingredients or different doses. For example, Engels et al. (16) reported a 7% greater resting EE after a 5 mg·kg−1 dose of caffeine, which is equivalent to an average dose of 371 mg (based on the subjects' average body mass). In the present study, the relative caffeine dosages ranged from 1.9 to 4.1 mg·kg−1 of body weight and resulted in similar increases in resting EE when compared with those of Engels et al. (16), despite using an average of 54% less caffeine. Koot and Deurenberg (24) used a 200 mg (~2.7 mg·kg−1) dose of caffeine and reported a 7% increase in resting EE over the entire postsupplement period (3 hours). It has been suggested, however, that blood plasma levels of caffeine peak at 45 minutes after ingestion (26). Therefore, our results may not be directly comparable to those of Koot and Deurenberg (24), who measured resting EE for 3 hours after ingestion, whereas we stopped at 50 minutes postsupplementation to begin the exercise protocol. Although we can only speculate, it may have been possible to observe greater increases in EE if we had continued our postsupplementation resting EE measurements beyond 50 minutes.

Several studies have also examined the effects of capsaicin and/or caffeine on resting EE. For example, Yoshioka et al. (46) found that when compared to a control group, there was a 23% increase in resting EE 30 minutes after the administration of 30 mg of capsaicin. There was no difference, however, between the capsaicin and control groups for the remaining 120 minutes. In addition, 3 studies have examined the combined effects of caffeine and capsaicin on resting EE. For example, Yoshioka et al. (45) added caffeine (200 mg) and capsaicin (6 mg) to regular meals and observed a 3.2% increase in resting EE over a 24-hour period. A similar study by Belza et al. (8) reported a 2% increase in daily EE after subjects ingested a supplement containing capsaicin (0.6 mg), caffeine (151 mg), catechins, tyrosine, and calcium. The same combination of ingredients was examined in another recent study (7), which reported a 2.4% increase in resting EE during a 4-hour period. Therefore, our findings supported the results from previous studies that have suggested that EE can be enhanced after ingesting relatively small doses of caffeine and other thermogenic ingredients.

Although no human studies have examined the effects of bioperine (black pepper extract) on resting EE, previous investigations (23, 37) have found that it has a thermogenic effect in rats. For example, Kawada and associates (23) administered piperine (the principle ingredient in bioperine) to rats, and found increases in catecholamine secretion and metabolic rate. In addition, Eldershaw et al. (15) reported that piperine stimulated resting V̇o2 in the rat hind limb. Several studies have also suggested that the thermogenic mechanisms of action for black pepper extract may be controlled through sympathetic nervous system stimulation (23) or increased ATPase activity of the mitochondria (37). Although the results from the present investigation do not provide information regarding the potential mechanism(s) of action for bioperine, they did suggest that it may contribute to an increase in resting EE. Interestingly, previous studies (11,20) have suggested that niacin may also have an effect on mitochondrial function. Specifically, Hassapidou et al. (2006) suggested that supplemental niacin may improve body composition because of its role in mitochondrial energy transfer (11). However, future research is required to further elucidate the individual and combined abilities of bioperine and niacin for improving metabolism.

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Oxygen Consumption Rate and Respiratory Exchange Ratio

The results from the present investigation showed that the supplement increased V̇o2 during the postsupplementation, exercise, and postexercise periods (Figure 4). There were also significant increases in RER 20 and 30 minutes after ingestion of the supplement, but not the placebo (Figure 5). Previous studies have suggested that caffeine supplementation may increase V̇o2 and decrease RER, which, in turn, may reflect a greater reliance on lipid metabolism during rest (34), exercise (29), and postexercise recovery periods (10,14). For example, Chad and Quigley (10) and Donelly and McNaughton (14) reported that caffeine ingestion before 90 minutes of treadmill walking and cycling at 55% of V̇o2max increased postexercise V̇o2 and decreased RER. The authors (10,14) suggested that the increase in V̇o2 and decrease in RER may have been caused by the stimulatory effect of caffeine on lipolysis (40) or increased central nervous system activity (6). However, Ahrens et al. (1) recently found increases in V̇o2, with no changes in RER during both rest and low-intensity treadmill walking, which suggested that caffeine may not influence substrate use. In addition, a comprehensive review by Graham (18) stated that “…in a wide variety of circumstances, there is little support for the theory that caffeine increases fat oxidation, even though it may well promote adipose tissue lipogenesis at rest” (p. 799). Despite the increases in RER that occurred at 20 and 30 minutes after the supplementation, the results of the present study supported the findings of Ahrens et al. (2007) and the overview of Graham (2001) in that the supplement did not cause any sustained changes in RER. It is possible that the increase in RER at 20 and 30 minutes postsupplementation may have been caused by a capsaicin-induced stimulation of visceral afferent sensory neurons (28). For example, Lim et al. (27) reported a similar transient increase in RER 30 minutes after a capsaicin-containing meal, which was attributed to a digestion-related autonomic nervous system response. Therefore, our findings indicated that RER was transiently affected by the caffeine-, capsaicin-, niacin-, and bioperine-containing supplement. However, this effect may have been caused by the capsaicin-induced autonomic nervous system response, rather than a shift in substrate utilization.

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Heart Rate and Blood Pressure

Our findings also showed that when compared with the placebo, the supplement resulted in greater DBP over the entire postsupplementation period and greater DBP and SBP over the entire postexercise recovery period. In addition, for the men, the supplement resulted in a lower HR at 20 minutes during the postsupplementation period, whereas during the postexercise period, the supplement was greater than the placebo at 10, 20, 30, and 50 minutes. Previous studies have demonstrated similar responses after the consumption of caffeine (30,33). For example, small doses of caffeine have been reported to reduce HR and increase blood pressure at rest and during exercise (33,38,39), which has been attributed to adenosine receptor antagonism (17). Other studies have shown that capsaicin (46) and bioperine (23) ingestion increased sympathetic nervous system activity. Although, sympathetic nervous system activity was not directly measured in the present study, it is possible that the effects of the supplement on HR and blood pressure were at least partially caused by increased drive from the sympathetic nervous system. However, previous studies have shown that larger doses of caffeine (400-500 mg) elicit dose-dependent increases in HR, blood pressure, and a number of other self-reported side effects (i.e., anxiety, irritability, nausea, headache, and dizziness) (3,22,31). Therefore, our findings tentatively supported the suggestion that the use of other thermogenic ingredients (such as capsaicin, niacin, and bioperine), in conjunction with smaller doses of caffeine (~200 mg) could minimize the potentially adverse side effects associated with larger doses of caffeine.

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Rating of Perceived Exertion

A recent meta-analysis that examined the influence of caffeine on RPE during exercise suggested that caffeine may reduce the perception of exercise difficulty at intensities ranging from 50 to 125% of V̇o2max (13). It has been hypothesized that caffeine may alter central drive (21), cause a hypoalgesia effect (31), and improve cardiorespiratory dynamics (13), which may help to explain the previous reports of caffeine-induced decreases in RPE. However, the results of the present study indicated that caffeine had no effect on RPE, which is consistent with the findings of Ahrens et al. (1) during treadmill walking. Thus, it is possible that caffeine ingestion may have little or no influence on RPE at low exercise intensities.

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Practical Applications

With the increasing rise of obesity (41), it is important to identify thermogenic nutritional supplements that can be used in conjunction with exercise to increase EE and act as a weight management tool. Previous studies have suggested that caffeine, capsaicin, bioperine, and niacin may increase EE (16,23,46) and improve body composition (20) separately, whereas others (7,8,45) have shown that various combinations of thermogenic supplements may act synergistically to increase EE. The results of the present study suggested that relatively small doses of caffeine combined with other thermogenic ingredients (i.e., capsaicin, bioperine, and niacin) increased resting EE, low-intensity exercise V̇o2, and recovery EE with no change in substrate use. Thus, it is possible that the thermogenic supplement used in the current study may aid in weight management when combined with long duration (60 minutes) low intensity (walking) exercise.

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Acknowledgments

This study was funded by a research grant from General Nutrition Corporation.

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Keywords:

thermogenesis; oxygen consumption rate; blood pressure; caffeine; capsaicin

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