D-Ribose is a 5-chain carbon that has been proven to provide medicinal support to those people who suffer from chronic fatigue, fybromyaglia and lack of energy.
5-10 grams 3x weekly seems to be the most widely accepted dose for this supplement.
Food does not actuallydoes not actually contain D-Ribose so I can understand that this would be an addition to a great diet.
Consider whether it would be more advantageous to supply the body with a more organic/natural form of carbohydrate such as beans/quinoa/brown rice/legumes/potatoes, or take a substance such as D-Ribose to replace the absence of carbohydrates to keep the ketogenic state of the body.