A medical article described a British patient who was rushed to the hospital after eating primarily chicken nuggets for the last 15 years. The patient had an occasional bag of chips or toast, but otherwise had only eaten chicken nuggets. The patient had collapsed, and had to be admitted. She improved, but was advised to change her diet.
Is there a single food that you can live on without any problems? Unfortunately the answer is no. There is no single food (other than breast milk for infants) that can sustain all of our nutritional needs.
Surprisingly, the potato actually comes closest to a perfect single food. Potatoes have an unusual amount of protein and wide variety of nutrients. However if potatoes were the only thing eaten, a human would still have nutritional deficiencies. Recently, an Australian man ate only potatoes for one year. He included sweet potatoes to get more vitamins A and E, iron, and calcium. He did reasonably well for one year and lost weight. However researchers note that this diet would not prove enough B vitamins and zinc.