Low-calorie energy drink improves physiological response to exercise in previously sedentary men: a placebo-controlled efficacy and safety study

Journal Title (Medline/Pubmed accepted abbreviation):  J Strength Cond Res
Year:  2010
Volume: 24
Number: 8
Page numbers: 2227-2238
doi (if applicable):  

Summary of Background and Research Design

Hypothesis/purpose of study:Assess the effects of 10 weeks of once-daily consumption of a low-calorie energy drink, either alone or in combination with exercise, on body composition, cardiorespiratory fitness, upper- and lower-body strength, mood, and safety variables 

Subjects:There were a total of 37 sedentary men (<30 min of physical activity per week, 18-45 years of age) in the study. 

Experimental design:Independent groups, between subjects design (no crossover), double-blind, placebo-controlled

Treatments and protocol: Subjects were randomly assigned to one of 4 groups for the course of this 10-week study: Low calorie energy drink plus exercise (Ex-A, n = 10), low calorie energy drink without exercise (NEx-A, n = 8), placebo drink plus exercise (Ex-B, n = 9), placebo drink without exercise (NEx-B, n = 10). Those provided with the low calorie energy drink drank one 12-ounce can per day for the duration of the study. The drink provided 10 kcal, some water-soluble B-vitamins, and 1.8 g of a “thermogenic” blend of taurine, guarana extract, green tea leaf extract, caffeine, glucuronolactone, and ginger extract (200 mg total caffeine per serving). The placebo drink was isocaloric, but with none of the additives of the energy drink. The exercise program consisted of aerobic exercise 3 times per week (cycling on an ergometer) and resistance training (9 different exercises) 2 times per week. On exercise days, the drink was consumed 15 min before activity-otherwise, it was consumed any time of day. The intensity and duration of the aerobic exercise was gradually increased from 15-20 min @ 40-50% of heart rate reserve (HRR) in week 1 to 30-35 min@60-70% HRR by weeks 8-10. The level of resistance was also gradually increased as subjects were consistently able to do ³ 10 repetitions at a given resistance. At the beginning and end of the 10 weeks, body composition, strength, cardiorespiratory fitness parameters, mood, and safety variables were measured. 3-day dietary records were also obtained at baseline and weekly during the study.

Summary of research findings:
  •   The energy drink, by itself, had no meaningful impacts on body composition, strength, or cardiorespiratory fitness.
  • The low calorie energy drink, when combined with exercise, reduced body fat mass more than did exercise alone, despite that reported energy intakes for the groups were not different. However, muscle mass increases were similar in the exercise groups with and without the energy drink
  •   The combination of the low calorie drink plus exercise also increased several cardiorespiratory fitness parameters (VO2, power output, time to exhaustion, and energy expenditure at ventilatory threshold).
  • Upper- and lower-body strength increased comparably for both the Ex-A and Ex-B groups
  • There were no differences in mood ratings among the 4 groups.
  • The low calorie energy drink was not associated adverse cardiovascular effects, although there were some verbal reports of restless sleep in the Ex-A group.       

Interpretation of findings/Key practice applications:

The low calorie energy drink provided some additional benefits to the exercise program with regard to body fat loss and metabolic adaptation to exercise and was not associated with safety concerns. Additional studies of the effects of the low calorie energy drink on both metabolic rate and exercise performance variables may be warranted. A key limitation of this study is that only men were included, so it is not clear if these results would also apply to women.
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