I think the temporary single-food diet is to break you of the addiction of sugar and other foods, and then once you've habituated your body to an extremely limi

I think the temporary single-food diet is to break you of the addiction of sugar and other foods, and then once you've habituated your body to an extremely limited diet, you can safely re-introduce some variety again. In his case it was potatoes, but I think eating solely any one item would have served the same purpose.