If you Google "do sugar-free energy drinks cause weight gain" in Google you'll find millions of results written by a ton of gurus all claiming different things. I've sifted through the information so you don't have to, and here's the bottom line:
You'll lose weight when you consume less calories than your body needs, so if you eliminate calories with an energy drink like EarlyBird, it helps with weight loss, especially considering a can of Monster can pack a whopping 400 calories.
But it's not that simple - just because you're lowering your caloric intake doesn't mean the calories you're eating are good for you.
If you ate one Big Mac with fries and chicken nuggets a day, you'd probably be in the range of ~1500 calories. Assuming a 2000 calorie diet, you'd be in a caloric deficit and would lose weight.
But are the calories from McDonald's actually good for your body? Of course not! When it comes to weight loss, the quality of calories matters just as much if not more than the quality of calories.
You have to make sure the ingredients in your energy drink are actually good for you, and most of the time, that's not the case. Here are some major drawbacks of mainstream "sugar-free" energy drinks:
1. Your body will produce more insulin
Your pancreas releases insulin, which is how the body store sugar. Artificial sweeteners trick your body into thinking it needs more insulin, so your pancreas does its thing, telling the body to use the sugar as food or store it as fat.
But when your body realizes there isn't any sugar to store, it gets confused. This can screw up your metabolism, which is the last thing you want.
If your body thinks it's getting sugar, it may accidentally store more of your normal calories as fat than it would before, which means you'll have to eat even less each day to maintain your caloric deficit.
2. You get used to sweetness
Artificial sweeteners, although free of real sugar, still condition you to enjoy sweet things. Considering sugar is so bad for you, feeding your sweet tooth isn't a good idea.
Believe it or not, artificial sweeteners are actually much sweeter than real sugar, even if it doesn't taste that way. Your body will crave even more sugary foods after tasting artificial sweeteners.
But you'll find that, once you do stop eating sugar, having a commercially available sugary snack will probably throw you off.
For example, now that I've stopped drinking soda, having a can of Coke normally makes me feel terrible.
However, it's not all bad. Not all energy drinks were created equal, and if the energy drink isn't loaded with sugar or artificial sweeteners, and has other nutrients your body actually needs, it can be a good way to start your day.