Nitrogen balance is a measurement of protein metabolism in the body. A negative nitrogen balance indicates muscle loss, as increased amounts of amino acids are being metabolized to produce energy. This increases the amount of nitrogen secreted from the body. Because the amount of nitrogen you are taking in is less than the amount of nitrogen you are secreting, you have a negative nitrogen balance.

This man is malnourished, edematous, cachetic, and has hypoalbuminemia. These clinical findings point to protein malnutrition (Kawashkior Disease), which causes edema due to decreased serum oncotic pressure. Low oncotic pressure in this case is due to protein loss, and hence a negative nitrogen balance.

Sources of nitrogen can be meat, eggs, and dairy product which he wasn't eating. The man had a low nitrogen intake but was still excreting nitrogen. Therefore, he had a negative nitrogen balance. A prolonged negative nitrogen balance may lead to a decrease in the plasma protein level, edema, anemia, lowered resistance to infection, increased susceptibility to certain toxic substances, the development of fatty liver or perhaps other serious sequel

Can someone please explain why it would not be glycogen depletion? I thought the question was talking about the Warburg phenomenon... so why not breakdown of glycogen to glucose?

I guess it would not explain the edema?