Carb-starve diets have fortunately fallen out of fashion, replaced by a more sensible approach to their consumption. Not only are carbs -- especially slow-digesting carbs -- essential for proper muscle function, growth, and repair, but they may also play a role in your willpower.

British researchers found that drinking a carbohydrate-rich beverage during prolonged, high-intensity exercise reduced the perception of effort being put forth. By comparison, exercisers who drank artificially sweetened beverages claimed to experience no such reduction.

In addition, the exercisers who consumed the carb-rich beverage during exercise demonstrated an increased focus and level of persistence. Again, this experience was not claimed by those who drank artificially sweetened beverages.

One thing to bear in mind, though -- all carbs are not created equal. Fast-digesting, high-GI carbs may provide you with a temporary sugar boost, but you will experience a precipitous drop in energy shortly thereafter. Slow-digesting, low-GI carbs, by contrast, will provide you with sustained energy throughout their slow digestion.