धातु शब्द शरीर में धारण एवं पोषण अर्थ में प्रयुक्त होता है अत: शरीर का धारण एवं पोषण करने वाली रचनाओं के लिए प्रयुक्त किया जाता है।
धातुओं की संख्या सात होती है, यथा रस, रक्त, मांस, मेद, अस्थि, मज्जा, शुक्र। इन सातों में धारण और पोषण कार्य की समानता होने से, इन्हें धातु कहा जाता है।
रसाऽसृङ् माँसमेदोऽस्थिमज्ज शुक्राणि धातव: सप्त दूष्या… (अ.हृ.सू.1/13)
इन्हें ‘दूष्य’ भी कहते है, क्योंकि ये दोषों से दूषित होती है।
धातुओं की संख्या सात ही क्यों है? इसका सीधा सा उत्तर यही है कि धारण एवं पोषण केवल सात धातुओं के द्वारा ही होता है। प्रत्येक धातु अपने से अग्रिम धातु का पोषण करती है। रस से रक्त तथा रक्त से मांस का पोषण होता है। इसी प्रकार पूर्व धातु अपर धातु का पोषण करता है। आचार्य चरक के अनुसार रस से रक्त, रक्त से मांस, मांस से मेद, मेद से अस्थि, अस्थि से मज्जा, मज्जा से शुक्र, शुक्र के प्रसाद से गर्भ की उत्पत्ति होती है।
रसाद्रक्तं ततो मांसं मांसान्मेदस्ततोस्थि च।
अस्थ्नो मज्जा तत: शुक्रात् गर्भ: प्रसादज:।। (च.चि. 15/16)
पोषण एवं धारण कर्म दोनों ही स्थलों पर रसादि छ: के धातुत्व की पुष्टि हो जाने पर भी शुक्र के धातुत्व की पुष्टि में संशय रह जाता है, क्योंकि प्रत्येक समय गर्भ को शुक्र का प्रसाद रूप में मानना शुक्र द्वारा पोषण क्रम को स्पष्ट नहीं करता है। केवल प्रजा उत्पादन काल मे ही शुक्र द्वारा गर्भ का पोषण होता है तो क्या शुक्र प्रजोत्पादन काल मे ही धातु होती है अन्य समय नही? इसका समाधान ये हो सकता है, कि शुक्र से भी धातुओं के अन्त में बनने से प्रसाद रूप ओज का निर्माण और पोषण होता है। यह शुक्र ही तो है जो सम्पूर्ण शरीर में रहता हुआ शरीर को बल प्रदान करता है। यह बल रुपी ओज का पोषण करता है, अत: हम कह सकते कि शुक्र के धातुत्व सिद्दिकरण में धारण और पोषण दोनों कार्यो की उपस्थिति कारणभूत है।
In spite of the many meanings of the word Dhatu, it is mainly used for these seven Dhatus, namely Rasa, Rakta, Mansa, Meda, Asthi, Majja and Sukra in Ayurvedic Physiology.
The word Dhatu is used in the sense of Dharan (supporting) and Poshan (nourishing) the body, hence it is used for the creations that hold and nourish the body.
The number of Dhatu is seven, i.e. Rasa, Rakta, Mansa, Meda, Asthi, Majja, Shukra. These seven having similarity of Dharan (holding) and Poshan (nurturing) function, they are called Dhatus.
रसाऽसृङ् माँसमेदोऽस्थिमज्ज शुक्राणि धातव: सप्त दूष्या… (अ.हृ.सू.1/13)
They are also called 'Dushya', because they are contaminated with defects.
Why are Dhatu only seven in number? The simple answer to this is that Dharan (holding) and Poshan (nourishment) is done only by the seven Dhatus. Each Dhatu nourishes its next Dhatu. The Rakta Dhatu is nourished by Rasa Dhatu and Mansa by Rakta Dhatu. Similarly, every Dhatu nourishes next Dhatu.
रसाद्रक्तं ततो मांसं मांसान्मेदस्ततोस्थि च।
अस्थ्नो मज्जा तत: शुक्रात् गर्भ: प्रसादज:।। (च.चि. 15/16)
Due to both Poshan (nurturing) and Dharana (holding) actions, the Dhatutva of the six Dhatu is confirmed, but still there remains a doubt in the confirmation of the Dhatutva of Shukra Dhatu. Treating the womb as the Prasad of Shukra does not explain the nutritional sequence every time. Its solution can be that Shukra is a Prasad due to the formation of all the Dhatu at the end. This Shukra Dhatu, residing in the whole body, provides Bala (strength) to the body and this Bala (strength) is known as Oja. Oja is nourished by Shukra Dhatu. With this, both the Dharana (holding) and Poshan (nurturing) functions of Shukra Dhatu are expressed. And this proves the Dhatutva of Shukra.
Dhatu Poshan Nyaya:
In Sanskrit, the term "Dhatu" refers to the constituents or fundamental tissues of the body, while "Nyaya" means a logical principle, system, or theory.
Dhatu Poshan Nyaya is the Ayurvedic hypothesis that explains the formation, nourishment, and maintenance of the body's tissues (Dhatus) throughout life. It offers a systematic understanding of how nutrients derived from digested food are progressively transformed and assimilated into the seven dhatus—Rasa (circulating fluid), Rakta (red blood cells), Mamsa (muscle), Meda (fat), Asthi (bone), Majja (marrow), and Shukra (reproductive tissue).
It uses logical metaphors (nyayas) drawn from everyday life to describe biological and physiological processes, particularly nutrient transformation and distribution.
Four main Nyayas describe how digested food essence (Ahara Rasa) nourishes the dhatus:
- Ksheera-Dadhi Nyaya (Milk-to-Curd theory or law of transformation)
- Analogy: Milk gradually turns into curd, then butter, and ghee.
- Explanation: Each dhatu is sequentially formed from the previous one, with progressive refinement. This is applied as it for first time formation of dhatu after fertilization. It is also important to understand the Sequential nutrition of Seven Dhatu by previous Sukhsm Dhatu. Better understanding make through Sukhsm and sthool Dhatu types in this theory ( commentary by Dhalhanon on ksheera- Dadhi Nyaya).
- Modern Parallel: Differentiation of stem cells into progressively specialized tissues, or conversion of nutrients into various biochemical forms.
- Kedari-Kulya Nyaya (law of irrigation or Field-and-Canal theory)
- Analogy: Water is distributed from a main source to fields through smaller and smaller canals.
- Explanation: Nutrients are transported through progressively smaller channels (Srotas) to reach each Dhatu.
- Modern Parallel: The vascular system, where large arteries branch into capillaries to nourish every cell.
- Khale-Kapot Nyaya (Law of selectivity or Pigeon-Picking Grain theory)
- Analogy: Just as pigeons pick specific grains from a threshing floor…
- Explanation: Each dhatu selectively absorbs what it needs from the circulating nutrient pool.
- Modern Parallel: Receptor-mediated uptake, like how cells selectively absorb glucose, amino acids, or hormones.
- Eka-Kala Dhatu Poshana Nyaya (Simultaneous Nourishment theory)
- Analogy: Rain falls and all plants absorb water simultaneously according to their capacity.
- Explanation: All Dhatus are nourished at the same time, based on their state and needs.
- Modern Parallel: Systemic nutrient distribution, where all tissues receive blood simultaneously but extract only what they need.
🔄 Table
| Nyaya | Core Idea | Analogy | Biological Parallel | ||
| Ksheera-Dadhi | Sequential transformation | Milk to curd to ghee | Biochemical differentiation | ||
| Kedari-Kulya | Nutrient delivery through channels | Water through canals to fields | Vascular circulation and nutrient transport | ||
| Khale-Kapot | Selective nutrient uptake | Pigeons picking grains | Receptor-based cellular absorption | ||
| Eka-Kala Dhatu Poshana | Simultaneous, need-based nutrition | Rain to all plants | Systemic distribution with selective uptake | ||
These Nyayas are not mutually exclusive; they reflect different dimensions of the same process—how nutrition moves from food to cells, how tissues form, and how the body maintains balance.