While the body has enough calories to support its energy needs you will hold enough nitrogen to store the protein you eat. (fitnessandpower.com)
As a 2003 study published in the same Science journal put it, «there will not be enough nitrogen available to sustain the high carbon uptake scenarios.» (co2coalition.org)
Its greatest challenge is to obtain enough nitrogen and carbon while conserving water. (newscientist.com)