Question: After 400 days, the stranded astronaut's original, on-board, food ran out. After that, he lived on just potatoes for two or three more years (or something like that). He says, himself, "I have to grow three years' worth of food." The only food he grew was potatoes. Starch only - no lipids and no protein. For two or three years, to live on just potatoes? Is that even physically possible?
Answer: The book explains it a bit more in depth. He had vitamins, minerals and supplements for six people, and NASA supplied enough for each person for a year, just in case some were damaged or spoiled... so he had plenty of vitamins. However, you can't live on just vitamins; you still have to have food... namely the potatoes.
Answer: I've seen the movie a few times, but did some additional Internet research. Watney was spreading out his 400 days of rations with the potatoes. I seem to recall him opening a small packet of a powdery substance and putting it on his food. Presumably it was vitamins, minerals, or other supplements. Of course, he was still severely malnourished when rescued.
raywest ★