The material that remains undigested and unabsorbed passes into the large intestine. Unabsorbed dietary magnesium is excreted in feces; absorbed magnesium is excreted in urine and sweat. Unabsorbed drug is excreted in feces; absorbed drug is excreted rapidly in urine. Unabsorbed vitamin E is excreted via feces. Some patients compensate for fecal wastage of unabsorbed nutrients by significantly increasing their oral intake. If accidentally ingested, standard methods to remove unabsorbed drugs should be considered. Fermentation occurs when unabsorbed food residues may arrive in the colon. TPVs can be more efficient than PV systems owing to recycling of unabsorbed photons.