Prakriti or the material nature is said to be made up of three primary qualities or ‘gunas’. These three gunas exist simultaneously in varyig degrees in everything, in our mind and in our nature. SATTVA (tranquility, purity & balance); RAJAS (restlessness & disturbances) and TAMAS (dullness & lethargy) are the three gunas. They are present in every object, gross or subtle, including mind, intellect and ego, operating on physical, mental and emotional levels. 
SATTVA Sattva manifests as purity and knowledge, balance and vitality. It promotes health and equanimity. Pranayama or breathing exercises oxygenate every cell in our body and bring purity and balance. The proportion of sattva also increases through proper diet such as fresh and organic fruits and vegetables. It is important to eating only that much that is essential for good digestion and eating with appreciation. A sattvic mind is always steady, finds delight internally, achieving inspiration for oneself and to offer encouragement and motivation to others. Bondage still exists towards happiness.
RAJAS Rajas manifests as restlessness and motion. It promotes stimulation to constantly search for new variety, new activity and hence disturbs the mind and body, leading to numerous ailments. Yoga postures allow settling down of this restlessness. Rajas is often increased by consumption of highly stimulating foods such as onions, garlic, chilly, pungent spices or over spiced food. Bondage still exists in fine attachment to activity.
TAMAS Tamas manifests as inertia, laziness and dullness. It promotes depression, anger amongst several other chronic diseases. Consumption of alcohol, drugs, stored canned food, processed and overcooked foods highly increases the tamasic quality in the body and mind. Tamas binds a man with an attachment to delusion.
Yoga represents the approach to the attainment of truth beyond all the above three gunas or qualities. Although sattva is the purest quality, one is still bound to the idea of tranquility. Once this is transcended, total freedom is achieved.