"Volunteers," by which we mean prisoners, were deprived of nutrients and then given the bare minimum they needed to be restored to health.
My Tuesday question from student readers of NYU's Washington Square News:
Question: How can we determine our individual caloric, vitamin, carbohydrates, fats and other intake requirements per day based on our own individual weight, height and lifestyle?
Answer: You can't. You will have to be satisfied with estimates based on measurements performed years ago on a small number of study subjects.
We require calories and nutrients -- 40 to 50 separate substances that our bodies cannot make, we must get from food. Because these interact, studying one at a time gives results that may well be misleading.
Early nutrition scientists got "volunteers"-- in quotes because study subjects often were prisoners -- to consume diets depleted in vitamin C, for example. They waited until the subjects began to develop scurvy, a sign of vitamin C deficiency. Then they fed the subjects the smallest amount of vitamin C that would eliminate symptoms.
Because individuals vary in nutrient requirements, scientists used this data to estimate the range of nutrient intake that would meet the needs of practically everyone.