Are Starchy Tubers Enough Carbohydrates at the Performance level?

Starchy tubers are only one of many possible choices for carbs at the Performance Level.

You've also got fruit and vegetables. In our experience, relying on a higher percentage of calories from protein and fat causes the body to adapt to utilizing them more (in addition to carbohydrates) for energy.

This process is best accomplished gradually. An athlete who is used to eating high-density carbohydrates regularly might be better served to start at the Lifestyle Level, limiting reliance on higher-density carbs, but not eliminating them completely (except yams and legumes).

For some people, going cold-turkey, eliminating all high density carbs except for yams and legumes not only is possible, it works quite well.

So I guess the real answer is that "it depends." How's that for definitive?  :-)