Meda Dhatu (मेद धातु)
According to Ayurveda, Meda dhatu (Samskrit: मेद धातुः) is one of the 7 dhatus (धातु) present in sharira (शरीरम्). It is that body component which indicates fat or adipose tissue in general. According to Ayurveda the function of oleation (स्नेहनम्) and lubrication at all levels in the body is performed by meda dhatu. Thus Meda dhatu itself is unctuous, heavy, soft in nature and present everywhere in the body.
मेद धातु उत्पत्तिः ॥ Meda dhatu utpatti
The meda dhatu is formed from its predecessor mansa dhatu (मांस धातु). When mansa dhatu is subjected to the process of micro-transformation (सूक्ष्मपचनम्), one processed part of it is specifically utilized to provide nourishment to the next dhatu in order i.e. Meda Dhatu (मेद धातु). This part is responsible for development and nourishment of meda dhatu in body. Transformation of this solid form of mansa dhatu into fluid  form of meda dhatu happens due to action of Teja (तेजः), jala (जलम्) mahabhutas (महाभूतानि). This process generates excess unctuousness in the processed part. Excess unctuousness and fluidity are therefore the distinguishing features of meda dhatu from all other dhatus.
मेद धातु स्थानम्॥ Location of Meda Dhatu
Like all other dhatus Meda is also present everywhere in the body. However, abdomen (उदरम्), buttocks (स्फिक्), Chest (स्तन) are few sites where it is predominantly present. Vrkka (वॄक्कम् | body organs equivalent to kidneys) , Vapavahanam (वपावहनम् | body organs equivalent to omentum & misentry) and Kati (कटी | low back and loin region) are known as the chief sites of medovaha srotas (मेदोवह स्रोतसम् | channel of transportation and transformation of meda dhatu). Thus at and around these sites, meda is found in abundance.   A specific type of meda dhatu which is present in a compound form along with rakta dhatu (रक्त धातु) is believed to be present in small bones (अण्वस्थि) according to Sushruta samhita.
मेद धातोः पांचभौतिकत्वम्॥ Panchabhautika constitution
Meda dhatu is fluid, unctuous and heavy in nature. Also Meda is the site of location for kapha dosha. Thus it is clear that it has Jala (जलम्) and Prithvi (पृथ्वि) mahabhuta dominance. Also, considering the process of its generation and transformation, considerable amount of Teja maahabhuta (तेज महाभूतम्) is required for its maintenance in fluid state. Therefore Prithvi, jala and teja mahabhutas are predominant elements in meda dhatu.
मेद धातोः उपधातवः॥ Upadhatus of meda dhatu
Meda dhatu when subjected to the process of micro-transformation (सूक्ष्मपचनम्), it generates 1 more entity which is known as Upadhatu (उपधातु Metabolic by-product) of Meda dhatu. Snayu (Equivalent to ligament) is known to be that upadhatu of meda dhatu. 
मेद धातोः मलाः॥ Malas of meda dhatu
During the micro-transformation of Meda dhatu inside body and formation of upadhatus (उपधातु), one liquid form of substance is generated as a waste byproduct and it is called as ‘Sweda’ (स्वेदः). Sweda is one of the 3 malas (मलाः) of body. It performs the function of balancing the hydration and temperature of body. The excess water in the body which is in the form of waste accumulated inside body is timely excreted out by the sweat.
मेद सारता लक्षणानि॥ Characteristics of best quality of meda dhatu
Those who have supreme quality of meda dhatu in a body are identified by some characteristic features. These features are called as meda-sarata features (मेदसारता लक्षणानि). Most of these features are manifested on various external body parts. Thus one can identify the quality of meda dhatu by assessing presence or absence of following signs in person.
वर्णस्वरनेत्रकेशलोमनखदन्तौष्ठमूत्रपुरीषेषु विशेषतः स्नेहो मेदःसाराणाम्|
सा सारता वित्तैश्वर्यसुखोपभोगप्रदानान्यार्जवं सुकुमारोपचारतां चा चष्टे॥ (Char. Samh. 8.106)
varṇasvaranetrakeśalomanakhadantauṣṭhamūtrapurīṣeṣu viśeṣataḥ sneho medaḥsārāṇām|
sā sāratā vittaiśvaryasukhopabhogapradānānyārjavaṁ sukumāropacāratāṁ cā caṣṭe||106|| (Char. Samh. 8.106)
Meaning: The person endowed with best quality of meda dhatu has significant unctuousness (wetness and softness) specifically in complexion, voice, eyes, hair, skin hair, nails, teeth, lips, urine and feces. This indicates wealth, power, happiness, enjoyment, charity, simplicity and delicacy in dealings.
मेद धातोः कार्याणि॥ Functions of meda dhatu
Meda dhatu performs various function in body. It is chiefly responsible for maintaining the lubrication in all systems for their uninhibited smooth functioning and preservation of energy.
The various function of meda dhatu are listed below 
- Snehanam (स्नेहनम् | lubrication) - Maintains hydration, softness and oil balance in the body
- Swedanam (स्वेदनम् | Sweating)- It controls sweat formation and thus indirectly participate in temperature control of the body
- Drudhatvam (दृढत्वम् | stability)- It protects body from excess cold or hot climate and at the same time provides strength support to other body organs to work smoothly by preventing friction and heat generation.
- Asthipushti (अस्थिपुष्टि | nourishment of bone tissue)
- Proper nourishment of Meda Dhatu gives proper shape to the body. If excess meda is formed it accumulates in various body parts and leads to obesity related signs.
मेदधातुदुष्टिलक्षणानि॥ Vitiating factors
Diet and lifestyle related some factors directly and adversely affect meda dhatu. Acharya Charaka explained few such factors as below,
अव्यायामाद्दिवास्वप्नान्मेद्यानां चातिभक्षणात्| मेदोवाहीनि दुष्यन्ति वारुण्याश्चातिसेवनात् ॥ (Char. Samh. 5.16)
avyāyāmāddivāsvapnānmedyānāṁ cātibhakṣaṇāt| medovāhīni duṣyanti vāruṇyāścātisevanāt ॥ (Char. Samh. 5.16)
Meaning: The channels of transportation and transformation of meda dhatu are affected by the sedentary lifestyle including lack of physical exercise, daytime sleep, excessive consumption of fatty food, and alcoholic drinks. 
Thus following factors adversely affect meda dhatu balance in body and lead to development of meda dhatu related diseases.
- Lack of exercise and sedentary lifestyle (अव्यायामात्)
- Daytime sleep (दिवास्वप्नात्)
- Excessive consumption of substances that increase meda i.e. heavy to digest, fatty, oily, sweet substances. (मेद्यानां च अति भक्षणात्)
- Excess consumption of alcoholic drinks (वारुणी अतिसेवनम्)
Some of these are also the common causes of obesity known in these days. Therefore one needs to prevent indulging in the habits mentioned above so as to keep meda dhatu in balanced form and prevent obesity.
मेदस्य स्वास्थ्यरक्षणे उपयोगिता॥ Importance of meda dhatu in the preservation of health and well-being
A normal human being performs various activities daily to survive. All these activities can be performed smoothly only when optimum level of moisture, lubrication and unctuousness is present in the body. This helps in protection and preservation of body systems and their efficiency. Thus all this can be achieved when sufficient amount of meda dhatu is present in the body. Snayu which are supposed to be metabolic byproducts of meda and thus are invariably related to meda play significant function of holding asthi (bones) together. Thus this can be achieved and locomotor movements can be performed smoothly only when meda dhatu in body is in good state.
Meda dhatu also controls thermo-regulation of body. A human body maintains a specific temperature inside the body in order to carry out all vital functions optimally. If this temperature is disturbed, attempts are made to normalize and stabilize the previous normal temperature which is usually achieved by sweating as seen in the cases of fever. Normally sweat performs the function of hydration of skin and adjacent tissues and whenever required participate in the process of temperature control. Thus maintaining the texture of skin and temperature control are few other important functions governed by Meda making it one of the important component for preserving health and well-being. Thus Meda dhatu is integral part of homeostatic mechanism of body and without optimum amount and quality of meda one can not function well.
- Charaka Samhita (Chiktisasthanam Adhyaya 15 Sutram 24-30)
- Charaka Samhita (Vimanasthanam Adhyaya 5 Sutra 8)
- Sushruta Samhita (Sharirasthanam Adhyaya 9 Sutra 12)
- Sushruta Samhita (Sharirasthanam Adhyaya 4 Sutra 13)
- Ashtanga Hrudayam (Sutrasthanam Adhyaya 12 Sutra 3)
- Charaka SAmhita (Chikitsasthanam Adhyaya 15 Sutra 17)
- Charaka Samhita (chikitsasthanam Adhyaya 15 Sutra 18-20)
- Charaka Samhita (Vimanasthanam Adhyaya 8 Sutra 106)
- Sushruta Samhita (Sutrasthanam Adhyaya 15 Sutra 5)
- Charaka Samhita (Vimanasthanam Adhyaya 5 Sutram 16)
- Available from charakasamhitaonline.com