In Andy Weir’s novel The Martian, a stranded Mark Watney must survive on Mars for several months. Since his prepackaged food supplies will run out before he is rescued, Mark grows and only eats potatoes for several weeks.
A botanist by trade, our fictional Mark uses Martian soil, his limited water supply, and some self-produced fertilizer to grow his potatoes. According to the novel, he “[has] plenty of vitamins; over double what [he needs],” plus an ample supply of protein in the pre-packaged NASA meals. Potatoes are just calories to Mark.
The question is: could humans survive with potatoes and milk as their only sustenance? Mark Watney had vitamins and protein to round out his nutritional needs, but could we do without?
Potato Nutrition 101
According to Potatoes USA, one 5.3 ounce potato with skin on has 110 calories, 26 grams of carbohydrates (9% DV), three grams of protein, and no fats, sodium, or cholesterol. They’re a great source of potassium, and one single potato has almost half a day’s requirement of Vitamin C: 27 milligrams.
While potatoes supply three of the most important macro-molecules for life (carbohydrates, protein, and nucleic acid), they miss the fourth: lipids, aka fat. This is where milk comes in.
Despite what certain diets tell you, your body needs healthy fats. Certain vitamins (A, D, E, and K) are fat-soluble, so our bodies can’t absorb them without fat or oil. In Mark Watney’s case, depending on what was in his NASA meal supplements, he might’ve been lacking those fat-soluble nutrients.
Whole cow’s milk would provide fat for a strictly potato diet as well as other nutrients potatoes lack, like certain amino acids. Varying your protein sources ensures that you get all the right proteins for your body.
The Expert Opinion
For our potatoes and milk diet, I asked registered dietitian and K-State professor Kathleen Hoss-Cruz about its feasibility.
“There’s basically three components to a healthy diet: balance, variety, and moderation. If you eat a variety of whole foods, you’ll get all the nutrients you need for [good] health. One food does not contain all the nutrients that you need.”
Professor Hoss-Cruz further explained, “the problem with potatoes is you’d get enough calories, but when you only eat one food source—especially one plant food source—you won’t get all the protein you need.” She said potatoes and milk would provide a complete set of protein, but a person would still run short on other nutrients like fiber.
Here’s the lowdown: a potato and milk diet seems wholesome in theory, but a person can’t stay healthy and balanced on a restrictive diet like that, even if they took a multivitamin too. According to Hoss-Cruz, a healthy diet has lots of variety.
Mark Watney ate what was available, and I doubt he’d endorse this potato diet. Hoss-Cruz and I don’t either. The concept of switching to a limited yet wholesome diet is interesting, and some products like Soylent make that a little more possible. In practice, however, a varied, moderated diet is the best way to go.