They knew it, somehow, though at that time any scientific or medical knowledge about it had not been shared or even established yet.
Simply say, it is danger to give a person, who is in starvation state, well-nourished food. That is refeeding syndrome.
And it poses a degree of risk on life if a person who shows hypothermia is given heat directly. Often the person shows a kind of shock and dies.
In Japan, during samurai era, some samurai warrior might have possibly known refeeding syndrome, guessing from their diary.
Also in Japan, there is a recode around late 18s about large scale tragedy of a marine accident with more than 100 fishermen died and just a few survived. The survived were saved by people in a tiny island and then the people knew something of how to treat hypothermia and how to avoid refeeding syndrome although in that era in Japan any knowledge about those medical issues did not exist at all. Maybe they attained experiential knowledge throughout their own history of saving life.
I read a nonfiction novel about 33 men trapped in copper mine in Chile. In the story, prevention measure of refeeding syndrome was being described. I remember slightly a short explanation about the knowledge of refeeding syndrome. It states that the knowledge was officially acknowledged through experiences on medical treatment for POW during WWII. (US army officers and soldiers captured and maltreated by Japanese army…… I must admit it.)
Anyway, here what I want to make remark on is the fact that some people had already known it well before the knowledge is well established in scientific manner.
You see of course some kind of knowledge can be obtained through experiences especially in case the knowledge is quite tangible but for refeeding syndrome normally people who try to save the life of starved person will obviously tend to give the person nourishing food as simple conclusion.
How can a person be aware of the risk? There in their hand is the food that normally gives human the power of survival! They would think, “Yes! You can eat it now and gain a strength!”
As for hypothermia as well, how can a person be aware of the risk in providing heat from such source as bonfire. The person simply sees the necessity of giving warmth to the patient’s body. And then if the patient has died, the person would think that it would have been too late simply rather than having doubt of the way of giving warmth.
In that incident of fishermen in Japan, the people in that tiny island found some fishermen who drifted on the coast. And the islanders brought the fishermen in their shacks, there their wives and grown daughters, naked, laid their body contacted to the fishermen’s body so that their natural and biological heat transferred to the fishermen’s body then after all hypothermia is avoided. They didn’t apply the heat of their bonfire though actually at that time they had bonfire to get their shack warmed. Instead, they used voluntarily their body heat, though the people whom they were trying to save were all unidentified strangers.
When the islanders found the fishermen keeping their strength, if not fully being recovering, they gave them warm water with red clay soil dissolved, though the fishermen’s urge for food. Then a few days later, they started giving them light food, a kind of soup.
How could they know the way?
Assuming that long time ago before they attained the knowledge, they would have found some persons on the coast, what would have happened have been leading to that knowledges?
Since each family would have lived in very small shack, they would have decided that one family would taken one person to its shack. Some family would have been able to afford having bonfire while others not. At that time such islanders would have been suffered from a condition somewhat close to poverty, if not being died of it. So, some family would have used their bonfire, others, since at that time they had used to sleep every night with family members all together huddled to share their warmth instead of bonfire, would have applied their body to give the persons warmth.
Then the next morning they would have found a fact that some persons survived and others not. Therefore they would have found a fact that all survived were ones taken to a family who did not use bonfire.
In case of refeeding syndrome, assuming that some family did not afford any food, what would ——-, no, that is impossible. The family alive that means they have food.
So, —–, how about this;
Some applied nourishing food, some applied minimal light food, some gave the patient only water served in wood tray, some provided it in a tray improvised with red clay soil.
Now a days, scientists often undertake so called control experiment. For instance, when the objective of a science research is to verify the existence of photosynthesis, they carry out multiple experiments. In one, they would leave a leaf of tree as it is, in another they cover a leaf with non-transparent sheet. Then after a period of time, they put some chemicals on these leaves. The chemical of course as you know can detect the existence of starch. The result is apparent.
I am not sure of this kind of story, especially of the reason why the islanders came to know that. Anyway, as far as their behavior is concerned, it can be valued as power of humanity and therefore now, entering such an era of technology, any scientific and technological activities should always be started and established from and with humanity, otherwise anything comes from the activities will be of life threatening.
How about this. If peaceful families from another countries worldwide moved in Ukraine and lived there next to next with Ukrainians and then helped them with daily life, production as raising wheat, with revival activity for war torn area instead of giving them weapons even though Russian offensive continued (but perceiving the war as a kind of natural disaster so once offensive has started, they all would take refuge to shelters), then even with the targets not only their enemy but also peaceful families from the world would Russians further continue their offensive? I mean, this kind of behavior can be a parallel of those islanders who lay next to fishermen to give them biological warmth. No! No! No! How can on earth peaceful families move in such a dangerous war zone and consider the war as natural disaster?
IMPOSSIBLE!
Or perhaps people who actually need to be saved with such way of salvation could be Russians.
科学好きの独り言 Science Monologue 
