All vegetables that grow underground are modified roots. One job of a root in nature is to store nutrients for the plant above. Starch is one of nature's best food storage mechanisms, and it promotes storage on our bodies, too (fat). These foods are too excessively high in starch and cellulose to be considered optimal. They are also low in nutrients. They are commonly cooked because of their indigestibility in the raw state, which is no answer because cooking causes harmful oxidation and destruction of nutrients. While these foods are not optimal, they can be helpful in transition (eaten raw) because, like nuts, they can provide a feeling of "fullness".