Study authors Stephanie Ballard of Nova Southeastern University and colleagues Jennifer Wellborn-Kim and Kevin Clauson say energy drinks typically feature caffeine and a combination of other ingredients -- including taurine, sucrose, guarana, ginseng, niacin, pyridoxine and cyanocobalamin -- but most of the performance-enhancing effects can be linked to caffeine.
"There is conflicting evidence of the impact of energy drinks on weight loss, although some data suggest that combining energy drink use with exercise may enhance body fat reduction," Ballard says in a statement. "Increases in burning calories and losing weight are likely subject to diminishing returns as users become habituated to caffeine."
The U.S. Food and Drug Administration limits caffeine in soft drinks to 71 mg/12 fluid ounces, but energy drinks can have as much as 505 mg of caffeine in a single container, Ballard says.
"Caffeine has been reported to cause insomnia, nervousness, arrhythmias, osteoporosis, cardiovascular disease, pregnancy and childbirth complication, gastrointestinal upset and death," Ballard says.
The findings are published in journal The Physician and Sportsmedicine.