A good rule of thumb is to look at the labels and check the carb levels. For instance, splenda is derived from sugar but spree and diet classic cola show low carbs, even though sweetened with splenda.

If the choc label says the carbs are low it is ok. Look at the ingredients list as well. If it says palm oil run like hell. Most choc has a high glycemic index (this determines how much insulin will be generated if you eat it, the curse of LC). The best GI is from belgian dark chocolate, but it must also be LC. This is why it is so hard to find a good one. Only cocolate made from cocao butter(not cocoa) is good. The rest have evil and nasty additives.