Some of the writings of Ayurveda have suggested that many psychosomatic illnesses have their origins in inappropriate behavior. With this possibility in mind, it is a reasonable approach to get a further understanding by looking at the yoga teaching on ethics.
The yams and niyams are the ethical practices that lay a foundation for yoga practice. Ha (sun) tha (moon) yoga proper includes four parts: Yams (-) don'ts, Niyams (+) do's, Postures, and Pranayama (the science of breath).
There are five yams: (1) harmlessness or non-violence to all living creatures; (2) living the truth, non-lying; (3) taking only what is honestly yours, non-theft; (4) avoidance of dissipation of life energy through excesses of all kinds, or non-indulgence; (5) not being chained to unnecessary things as 'needs' in life, or non-possessiveness.
The five niyams are: (1) keeping living quarters, clothes, body, food and thoughts as clean as possible, or cleanliness; (2) being happy with what life has provided, this is the underlying principle that nature always provides us with what we need (not necessarily what we want), or contentment; (3) being able to accept adversity (physical or emotional) without losing much balance. This can be considered an austerity when accepted with a certain attitude. There is no need to seek out austerity, as nature will provide ample emotional and/or physical unpleasantness to give us the opportunity to set the ego aside and endure the situation; (4) study of the world scriptures and writings of experienced mystics--examination and self study; (5) an understanding that there is a higher power both personal and in cosmic events, the energy of faith.
The number 84 is a classical number given to how many yoga postures there are. This is due to the fact that there are 84 lakhs (100,000 which = 8.4 million) species which include: 3,000,000 types of plants and trees, 2,700,000 types of reptiles and insects, 1,400,000 kinds of aquatic animals and birds, 900,000 varieties of mammals and 400,000 types of humans, gods, goddesses and disembodied spirits.
The names of the postures illustrate the universal principle of consciousness in different stages of evolution. By practicing the classical positions of man/woman and nature one helps to universalize consciousness.
This point also illustrates why the classic yogic diet has been lacto-vegetarian, not eating any meat, fish or eggs. Man/woman has all five elements active. With an active ether element one can reason, discriminate and perform actions that can promote an evolution in consciousness. Quadrupeds have four elements active, lacking the ether element and, as with all other creatures besides man, are in bog joni karma. This means they are reaping the effects of past karma but cannot perform actions that will give them realization of an ultimate reality in the form that they are presently in. Birds lack earth and ether elements. Reptiles only have two elements active, earth and fire. Vegetation and plants only have one element active which is water. The yogi, wanting to cause as little karma as possible, happily subsist on vegetables, grains, fruits, herbs and spices, and some dairy products.