Over the past 2 months, a patient was on a nonscientific fad diet for weight loss which excluded all meats, eggs, legumes, nuts, and seeds. She takes a protein powder supplement, but not a vitamin supplement. Which one of the following will be greatly impaired in this patient?

The excluded foods are all great dietary sources of vitamin B6 (pyridoxine). Vitamin B6 is water soluble so is easily excreted from the human body and is poorly stored by the body. At this time, the patient would have developed a B6 deficiency. B6 is essential in the production of PLP, which is the cofactor for the transamination reactions. Low PLP would greatly impair transamination, along with glycogen phosphorylase activity. A lack of B6 would have no effect on absorption of amino acids, membrane-transport systems, or uric acid production. Ammonia is produced by bacteria in the gut in a B6 -independent mechanism. The protein powder supplement will not provide B6 in sufficient quantity for the body's needs.