Many nutritional supplements on the market are made from substances that are better foods for plants than for humans. Dead minerals (dirt) are often included in nutritional supplements, but, although they can be absorbed into the bloodstream, they cannot be assimilated or used by your cells. Humans can only assimilate and use live organic whole foods like fruits, vegetables, whole grains, nuts, seeds, legumes, and herbs, and to a lesser degree meat, dairy, and other animal products (these are second hand nutrition and poorly suited to your body, although it can get some use out of them).
