I can't give any general advice that is proven to aid everyone, but I can share with you my personal experiences. When I have drastically reduced my intake of carbohydrates and sugar, I have seen a significant slowdown in the rise of my hematocrit. Eating breads, grains, and processed foods I generally require a phlebotomy every 4 weeks. When I am in a state of nutritional ketosis, I find that I can go three to four months between phlebotomies. Your mileage may very, but this is what I have experienced over the past three years.