For athletes, these sweeteners provide much-needed energy. For the rest of us, they're high-calorie, zero-nutrition temptations that can lead to obesity and a host of related conditions—diabetes, high cholesterol, heart disease.

When sugar has a rap sheet like this, alternative sweeteners start to look appealing. For diabetics, most of these substitutes don't cause the dramatic blood sugar spikes associated with the real thing. For weight watchers, zero (or dramatically reduced) calories are a dieter's boon.

But which to choose? There are scores of sugar substitutes; most fall into one of four categories: natural sweeteners, artificial sweeteners, dietary supplements, and sugar alcohols. And there's a new hybrid sweetener—tagatose—that is natural and has fewer calories than sugar.

As a category, natural sweeteners are a less