Sugar-free energy drinks may contain as few as 12 calories per 8-ounce can, but that still doesn't mean they'll help you lose weight. Diet beverages have links to weight gain, according to NPR, possibly because of the way your body responds to them. These drinks contain artificial sweeteners that trick your body into releasing natural sugar-processing hormones. Over time, you may start to release fewer of these hormones, which may affect your appetite as well as blood-sugar management.
Energy drinks sometimes cause side effects, mainly due to high caffeine content. Caffeine can cause jitteriness, sleeplessness, heart palpitations and other adverse reactions, especially in high doses. Energy drinks typically contain 80 to 100 milligrams of caffeine per 8-ounce serving; moderate caffeine intake is set at 200 to 300 milligrams of caffeine per day, according to MedlinePlus, so drinking more than two to three energy drinks daily isn't advisable. People who have low tolerance for caffeine may experience side effects from consuming just one energy drink.