The human body is the microcosm of the universe, made of five substances, ie the properties of akash (space), vayu (air), tejas or agni (fire), jala (water) and prithvi (earth).
Akash has the loosest bonds and the most space between molecules. Prithvi has mass, is tangible, dense matter, but we must remember that all properties are present in all cells and everything that exists. Cells consist of space, chemicals, processes of transformation and matter.
According to Vaisesika, like increases like, opposites decrease and we can only absorb what is like us. While nothing that exists in nature can be completely alien to us, food which is more similar to us, eg meat, proteins and fats, is better absorbed. Vegetables don't help us grow so much or build so much muscle, though they can replace what is lost and give energy (carbohydrates) fibre and micronutrients.
The Charaka concept is that ''there is nothing in this world which is not medicine'' so everything is useful when used at the right time. In diarrhoea, for example, liquids are lost, so must be replaced, ie whatever is lacking must be built up. When one is overheated, cooling foods must be used to reduce the excess.
Coca cola is considered to be made of air and ether (therefore a ´vayu´ food) and affects bones and teeth badly by leaching calcium and other minerals from them. It could not be considered suitable from a nutritional point of view, but even coca cola could save a life in the case of dehydration. Although not optimum nutrition, in the absence of good food even processed food may be better than nothing, at least giving enough energy to allow the body to function.
Food is categorised as having the same five properties.
Akasha (ether) is present in all the spaces and lumens in our bodies, mouths, noses, the digestive tract, hollow organs (i.e., lungs, bladder and stomach) and the respiratory tract. You can't see it, only through it, ie it's what there is between denser matter, though it does usually contain a mixture of chemicals in the form of gases. It has the most air between molecules and a quality of nothingness.
Psychologically, ether represents expansiveness and freedom but is also associated with isolation, emptiness and fear. It is subtle, light and helps mobility (sukshma, laghu, sara)
Vayu (air) represents movement and communication in the body. Heartbeats, the movement of blood in our veins, breathing, blinking,the movement of enzymes and hormones, the digestion of food, etc. all require air. Air has a lot of space between molecules.
Psychologically, air is the flow of our thoughts and desires (messages, communication) but is also associated with anxiety, nervousness and fear. Air is subtle, mobile and light, penetrative, active (sukshma, sara, laghu and tikshna)
Agni (fire) represents heat and movement and is responsible for metabolism and body temperature. This means digestion of food as well as information, sensory experiences and emotions. Fire is present in our digestive tracts as hydrochloric acid, agnis, the function of our brains where information is processed and is present in our eyes where we perceive light. Visible fire, has hydrogen like property, heat, for example sun is made of hydrogen.
Psychologically, fire is the light of intelligence but is also anger, hatred, criticism and competitiveness. Fire is hot, sharp and spreading (ushna, tikshna, sara-chala)
Jala (water) is present in all liquids in the body. Blood, mucous, perspiration, saliva, plasma and other secretions are mostly made of the water element. The fire element is also present (as hydrogen). Water is cool, heavy, liquid (shita, guru, drava)and it is also cohesive, ie it is what joins matter together, and it has strong bonds. Waterdrops naturally run together and it is difficult to separate water into droplets for example.
Psychologically, water is love and compassion but is also slow and lethargic.
Prithvi (earth) is what makes our bones and muscles strong, giving them stability and solidity. The minerals in our bodies are made of the earth element. Earth has the least space between molecules, ie it is the most dense and its bonds are stronger and harder to break.
Psychologically, earth is support and grounding but is also greed, attachment and stubbornness. Earth is heavy, stable, dense and hard (guru, sthira, sandra, kathina) Compared to ether and air, it is gross (sthoola).
Akash (ether) and Prithvi (earth) are unchanging, whereas Vayu, Agni and Jal are unstable. This is crucial to our understanding of what ´doshas´ are (literally ´that which goes out of balance´)
It should be remembered that in talking about panchabhutas, we are talking about the properties of the physical universe (prakriti, matter) which forms, transforms and dissolves. However mind and soul, along with time and direction, do not consist of panchabhutas, but of purusha, ie the indestructible and the eternal. Together the nine gunas, mind, soul, time, direction, ether, air, fire, water and earth make up everything in the universe.