You should stay away from sugar free items as they do contain artificial sweeteners.
James would prefer that you use products with Stevia in them. The sugar free sugar substitutes don't hurt weight loss its the long term health effects that James is concerned with. If you eat things with other sugar substitutes it won't effect the program. He just doesn't like what studies have shown that these substitutes do in the long term. In moderation it will be fine.
According to the latest research, artificial sweeteners like Splenda, Equal, and NutraSweet have been shown to "hijack" your metabolism. This forces you to crave unhealthy foods.
And when you give into your cravings... those foods get turned to fat. Fat that ends up in your belly, your thighs, butt, or any place you happen to store it.
Not only that, these sweeteners spike your blood sugar, harm your digestion, and destroy your friendly gut bacteria (i.e. bad news if you've got diabetes or pre-diabetes).
Stevia is the best type of sweetener to use. It's natural so it doesn't come with the potential side effects of artificial sweeteners such as Splenda and Nutrasweet.
If you looking for a beverage I do know that there is product out there that makes different beverages with Stevia. They are all natural, vegetarian/vegan friendly, gluten free, and are one of the best "diet" beverage out there. Its called Zevia. You check the product out at www.Zevia.com.