The question of whether a person could survive long-term on a single food item is a fascinating thought experiment rooted in nutritional science. To “live off of” a food means it must supply every nutrient the human body requires, not just calories, for an indefinite period. This analysis reveals that no single food naturally exists that is truly complete, forcing us to examine the complexity of human nutritional needs and what “completeness” truly demands from a diet.
Essential Requirements for a Complete Diet
A food capable of sustaining life must first provide sufficient energy through macronutrients: carbohydrates, fats, and protein. The protein must supply all nine essential amino acids, which the body cannot synthesize, and the fats must include essential fatty acids. Failure to meet these macro requirements results in muscle wasting or organ damage.
The micronutrient profile is where most single foods fail, as a complete diet requires all 13 essential vitamins and all 16 essential minerals. Plant-based candidates, such as grains or tubers, are often inadequate due to the lack of Vitamin B12 and an incomplete amino acid profile. Conversely, most animal-based foods, while rich in protein and B12, contain no dietary fiber and frequently lack Vitamin C, which is necessary to prevent scurvy.
Evaluating the Most Common Single Food Candidates
Potatoes
Potatoes are often cited as a survival food because they are nutrient-dense, offering complex carbohydrates, Vitamin C, and potassium. However, relying solely on potatoes would quickly lead to significant deficiencies in fat-soluble vitamins A, D, E, and K, and Vitamin B12, which is non-existent in plant matter. Furthermore, the protein content is disproportionately low and lacks a complete profile of essential amino acids.
Whole Milk
Whole milk comes closer to a complete food, providing an excellent balance of protein, fat, carbohydrates, and is a strong source of calcium, phosphorus, and B vitamins, including B12 and often Vitamin D. However, the major nutritional gaps for an adult are a near-total absence of non-heme iron and fiber, and a low level of Vitamin C. The lack of iron would eventually lead to severe anemia, while the absence of fiber would cause significant digestive dysfunction.
Eggs
Eggs are another commonly suggested candidate, boasting high-quality protein that contains all essential amino acids and a good balance of fats and fat-soluble vitamins, including A, D, and various B vitamins. Like milk, however, eggs contain no fiber and are a poor source of both Vitamin C and calcium. Relying solely on eggs would rapidly lead to specific micronutrient deficiencies.
Addressing Critical Vitamin and Mineral Deficiencies
To fill the most pronounced gaps in common diets, we must look to foods high in difficult-to-obtain nutrients. Organ meats, specifically liver, are a micronutrient powerhouse, offering high levels of Vitamin B12, Vitamin A, and highly bioavailable heme iron. Fatty fish like salmon and mackerel are also exceptional sources of Vitamin D, essential omega-3 fatty acids, and B12. While these animal products address deficiencies common in plant-based foods, they contain zero dietary fiber and negligible amounts of Vitamin C, making them incomplete on their own.
Why Monodiets Are Not Sustainable
Even if a single food could theoretically tick every nutritional box, a monodiet cannot be sustained due to biological and psychological limits. The extreme concentration of certain nutrients can quickly lead to toxicity, such as the risk of hypervitaminosis A from excessive liver consumption. Furthermore, the human digestive system relies on varied sources of fiber, which are necessary to support a diverse and healthy gut microbiome. A lack of diversity in fiber leads to digestive distress and compromised nutrient absorption. Beyond the physical effects, eating the exact same food repeatedly causes sensory-specific satiety, where the desire for that food rapidly diminishes.