Yes, he would suffer serious malnutrition. However, he could supplement with one or two other cheap bulk crops (whole wheat, corn, and/or beans). Still, it would be efficient to raise small grass-eating animals for food, such as rabbit or even guinea pigs. Grass and weeds are abundant and free, far cheaper than meat.
Trace elements and minerals are fairly easy to get. Many of those same weeds you can feed to rabbits are chock-full of all kinds of good nutrition. A book on edible plants is recommended reading. Lichens and wild mushrooms (tread carefully!) are great sources of such nutrients.
For $10, you can buy a 50-pound bag of mineral supplement for livestock (chelated, highly bioavailble raw minerals -- pretty much mined from old lake/ocean beds and ground to a powder) that should last one person most of a lifetime. Much cheaper than a case of One A Day or Centrum tablets.