Something of a misnomer, the Optimized Digestive System replaces much of the augmented individual's jaw, as well as the entire esophagus, stomach, and intestinal tract with a system that converts virtually any ingested matter into material that can be used as fuel for the body.
If they still have their own skin, individuals with the ODS tend to develop a curious pigmentation as they ingest far more transitional materials and metals than they do carbon. Breath scenting of the sea or motor oil is not uncommon.