Sounds like you are probably iron deficient. Get your serum ferritin level checked, specifically. It doesn't matter how much steak you eat. You know how many hamburgers I ate in college, and my serum ferritin was only around 8 or so? Some people seem more prone to anemia than others. I was also a heavy coffee drinker, which may have had something to do with absorption interference. My biggest symptom was that I sucked -- my performances deteriorated and just weren't what they otherwise should have been. Legs were heavy. As soon as I started supplementing with prescription iron, I went from running 33:30 10ks to 29:30s within mere months. Magic.