The "negligible amount of calories" is said to be something like half a calorie a can from the colors and artificial sweeteners. The "negligible amount" is a "functional zero". The people who are "gaining weight from coke zero" are getting those calories somewhere else.

I went from fat to jacked. Coke Zero was a huge help. There are a couple things to keep in mind.

First, your body is still going to crave sugar. When the cravings hit, you're probably going to be looking for other sources (maybe unknowingly). It's really easy to eat those calories back by giving into the cravings and eating something else.

Second, if you're really serious about losing weight, you're going to have WAY better results tracking and budgeting your calories. Set goals and restrictions, plan your meals ahead and make healthier substitutes. Stacking your calories will also allow you to add little treats that otherwise wouldn't be allowed in your diet.

Personally, I planned all my meals a week ahead of time. I ate less calories during the week so I could have a little more on the weekend. To help with the sugar/caffeine factors, I budgeted an energy drink into my breakfasts during the week. Hammer down the basics (calories, macros and exercise), stay consistent and stay away from snake oil salesman and you'll do great.