Short version of this post - the experiments done about whether chickens will balance their own diets when offered all of the ingredients of a balanced diet was done with people (babies) too. With similar results - they do.
Long version -
About a third of the way in, he tells of Clara Davis, a pediatrician who was concerned about what the medical establishment was pushing in the 1920s:
"No one can satisfactorily prescribe food for an infant who does not have knowledge of the composition of that food." quote of an article in the journal of the American Medical Association. American mothers were routinely given eating lessons based on the latest nutritional science. But the children didn't seem to care about the data and refused to eat the food. It became such a problem that the majority of visits to pediatricians during the 1920s were about fussy eating. The profession advised parents to let children go hungry and be firm... an example is telling parents with children who vomited (willfully or not) that "force is necessary... Give such a child a small amount of the food. If he vomits, give him more until he keeps that food down."
Not from the book but my oldest child was born, my grandmother told me the doctor told her to feed my mother every four hours. Grandma told him that the baby gets hungry at three hours. He insisted it was important to get the baby on a schedule. So, my mother cried the last hour nearly every time. Fifty years later, Grandma still looked haunted as she told me; she said: I couldn't understand what was wrong with a 3-hour schedule but he was the doctor and was so sure. It is good you are feeding her when she is hungry.
Anyway,
Davis knew there was no evidence for such an approach from history and that wild animals seemed to be able to maintain their health without being told what to eat by scientists. She was worried about the modern food. In one paper she describes "the poor nutrition of infants that were weaned onto the pastries, preserves, gravies, white bread, sugar, and canned foods that are commonly found on the adult table" she thought such foods were incomplete and altered and noted that they "formed no considerable part of the diet a hundred years ago"
She persuaded a number of mothers (a dozen or so) to place their children in her laboratory for months at a time, in one case for more than four years, in that is the longest running clinical trial of eating that has ever been conducted.
She let the infants choose their own food and then measured if they could be as healthy as the infants who were fed prescribed diets using the best nutritional advise of the time.
Her hypothesis is that since the body has internal regulatory mechanisms for water and oxygen intake, heart rate, blood pressure, body temperature and every other physiological variable, the same thing should be true for body composition and nutrient intake.
Wow! This going to be too much to put here. He gives a LOT of detail. Incidently, I see why the mothers may have been willing to let the children stay in the lab. The first baby (Earl) was nine months old when he came and showing signs of severe rickets and (maybe) other signs of malnutrition. His mother also did.
Thirty-two foods (named), at least ten at each meal, all what I would call "whole" foods, if any were finished at one meal then a larger quantity of that food was offered at the next, nurses instructions (designed to not influence the choices the children made), how health was measured, how the children acted during meals, and so on.
They "throve" (Davis' word)... many details and descriptions given.
One example: Earl had the option of a small glass of cod liver oil at each meal. He drank from it often but irregularly and in varying amounts until his blood calcium and phosphorus levels reached normal levels and his xrays showed his rickets were healed. At which point he stopped drinking it entirely.
All the children followed this pattern for whatever health problem they had, not necessarily rickets.
Davis was clear that her experiment should not be misinterpreted. She did not believe children should eat anything they wanted. She thought it important for adults to teach children what is good to eat to avoid poisoning and so forth . But they should allow that children should be learning to self regulate their eating in response to what they need.
Edit to add: under the long version has a lot that is semi-quoted from the book Ultra-Processed People
