Jutians are a group that have abilities that includes utilizing blood magic. Which requires the expenditure of their own blood as "fuel" for the magic.
Assume they are 100% biologically human except when it is pointed otherwise.
To them it is not much magic and just a thing they are born with.
So the way they can use it is very close to how a human moves their body.
You can move your hand, and think about moving your hand.
Now to the actual magic and the part that concerns is it is as following:
Once the person decided to do something magical they have to give away a measure of their blood. The amount changes based on the required effect, also can be called spell, so the bigger the effect the more blood is required.
The "size" aspect is not so complicated. For example lighting 2 meters on fire is easier than 10 meters.
The blood is then magically focused on one part of the body, usually the palm of the hand, then that parts opens and the required amount of blood is expelled from that point and the spell happens.
Basically think of it as a wound or donating blood.
The better and more experienced the Jutian the more they can utilize the amount of blood they use and get better results.
Now such a system means that the theoretical maximum amount of blood they can use is roughly the same amount of blood we have which is around 5 liters, a quick google search gives 4.5-5.6 liters, but that is not reasonable as that would mean instant death.
Anyway most of the time the amount of blood magic is few millimeters and expending a full liter is problematic as they will suffer as much as as humans would.
Anyway google again supplies me with an answer of how much blood people can replace in a day with numbers in a range of 40-70 ml per day.
To simplify things lets take an average of 55 ml per day. But since those people always had this blood magic thing I though to up their numbers as their bodies are constantly having to reproduce blood to replenish the lost blood. So say an average of 25% of 55 so around 68 ml per day.
Anyway I'm not sure if it related but I just thought to provide it.
And there are actual limitations on their magic.
They can't get a random bucket of blood to use as fuel, it has to be their own magic from their own veins. They can't just drink a lot of blood to use it. They can't try to store their blood in a container. DNA matching or blood type matching is not a thing. This is magic. Anemia or other medical conditions are not a problem. Blood is still blood. And since this is pre blood transfusion setting they can't use blood packs or get transfusion. No magic means can increase their blood or enhance their recharging.
Lastly blood here is the dictionary definition of blood. No plasma complication.
So all they have is their bodies and their natural body's ability to recharge the blood.
So what can they do to quickly replenish their blood and enhance their recharging abilities?
Like what food? What exercise?
I know that for example red meat, beans, dried fruits...etc are good for people who suffer from anemia but honestly my medical knowledge is awful so will that translate to overall blood recharging or just improving the quality of the blood?
It is not purely medical thought as I'm also interested in knowing what is the general tricks and overall methods would such a race use to always be full of blood.
This is important as if you just used a lot of blood you want to recharge it quickly but not concerned with the quality of the blood so the type of food you look for can be different.
They are not idiots and trial and error insures that even without access to our advanced medical knowledge they can still figure out foods and other things that helps them.
So that's why the question is here I'd say. I mean you can replace the blood magic part with just someone just someone who wants to know the science behind it and it would remain the same. I just provided the context.
Without modern medicine or supplements what can they do to always be replenishing blood as fast as possible assuming their are human, like I detailed before, and have no technology or medical knowledge above the renaissance period.
Edit: I don't get the close votes. This is just a medical question with magic for context. Like just what would a human do in that situation. Human biology and knowledge of the time applies. Just that.
It's like asking how can this guy build a pyramid about 147 meters high with a base of 230 meters in 2580 BC.
The whole plasma and blood components and transfusion thing is simply off limits because of the scientific limitation of the time.
They don't have knowledge about plasma and so they themselves don't know exactly what part of their blood is consumed in magic.
Even if I decide the it is iron in the blood that is consumed, then it is pretty much useless as they don't know that.
Bringing 2020 medical knowledge to a setting roughly equaling 1600 just seems absurd in the context of the world. I know you are scientifically right but those people simply don't know that much like our actual ancestors.
Even if they attempt transfusion without know about blood types of the dangers of diseases in the blood. So again they fail.
I appreciate the input but when dealing with worlds with less science things are complicated.