Blood type O: No wheat at all, *very* few of other types of low gluten grains. NO MILK! Perhaps a tiny bit of mozerella cheese every now and then. Ghee would be better for you than butter. Avoid caffeine. If you drink de-caf and must lighten it, you are better off with heavy cream rather than half-and-half. If you have arthritis, cut out the nightshade veggies. If you have a thyroid problem, avoid the cruciferous veggies, except kale. Eat red meat at least twice a week. Some soy is OK, but don't overdo it. There are other small do's and don't, but that's it in a nutshell for O's. Frankly, low carbing is IDEAL for O's, who generally have a higher protein requirement than the other blood types.