In Ayurveda, the science of life and health, the word Dhatu is defined as a factor that supports the body. The accumulation of Amam (toxins) in the system vitiates the Tridhatus and causes their imbalance. Excess or deficiency of any one of the Dhatus disrupts their equilibrium. In their state of equilibrium, Vata, Pitta and Kapha are called Tridhatus.
The word Dhatu can also be used to mean body tissue. When used in this sense, there are seven and these are called Saptadhatus. These body tissues are formed from and nourished by the Aahara Rasa, the essence of food. Rasa (plasma), Rakta (blood), Mamsa (muscle), Meda (fat), Asthi (bone), Majja (bone-marrow) and Sukla (semen) are the seven such Dhatus. Each Dhatu is believed to be a metabolic refinement of the previous one.