Well a website might be more 'up to date' information than even the most recently published book. (I assume it's the www.atkinscenter.com website?)

Dr. Atkins never did like aspartame as an aritificial sweetener. He preferred us to use Splenda (sucralose) or Stevia. I think it was because of the possible, although unproved, side effects.

Lots of people use it and have no problem and do lose successfully. Perhaps you could use Sugar Twin which is saccharin in the US. (In Canada, Sugar Twin is made from cyclamate.)

I think the major consumption of aspartame is in diet pop or 'soda'. These also contain citric acid as part of the flavour & Atkins said that citric acid can be a staller.

So if you need something sweet, it's probably better to have something with Aspartame than with sugar. You'll just have to see how things go for you.