It contains Aspartame, which Dr. Atkins is against. I basically drink water as my beverage of choice and only very occasionally drink caffeine free diet coke as a mixer if I'm having an alc. beverage.

According to a nutritionist I heard before ever starting LC, the body cannot distinguish nutrasweet from actual sugar and falsely perceives that your blood sugar has been raised and releases insulin to combat that. This lowers your blood sugar to lower than normal, which triggers feelings of hunger. I quit drinking Diet coke several years before starting LC b/c the last thing I needed was a drink to make me feel hungrier.

As a side benefit, I stopped getting headaches as frequently as I had been (another possible side effect from aspartame/nutrasweet).