Excess iron causes diabetes. If people have more iron than they need, removing it makes it easier to process sugar.
Blood letting in high-ferritin type 2 diabetes
https://diabetesjournals.org/diabetes/article/51/4/1000/34602/Blood-Letting-in-High-Ferritin-Type-2-Diabetes
If you consume meat and have more iron than you need, bloodletting reduces iron and it’s beneficial. You can use blood ferritin to estimate how much stored iron you have. If blood ferritin is more than 100 ng/ml, the person usually has more iron than they need and would benefit from donating blood or bloodletting.
If a person’s blood ferritin is less than 70 ng/ml, the person has an iron deficiency.
Interesting. I do take iron supplements & B12 after I donate power reds but usually only for a week or so. I’ll look into that as we do eat a lot of red meat.