Journal Title (Medline/Pubmed accepted abbreviation): J Strength Cond Res
Page numbers: 2227-2238
doi (if applicable):
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.
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.