How much food does a colonist eat each Sol?
According to this article, it is 0.2 food per sol (so 1 food per 5 sols), seems about right to me. Also you can click the resources tab and see how much food was produced and eaten in your colony last sol. If you play for International Mars Initiative, each colonist arrives with 10 units of food - good for lengthy 50 sols (almost a life time supply), hence your domes will most likely be surrounded by piles of food and you will not need to worry much.