According to the ancient yogic teachings, all things in the universe are made up of energy particles; prana, the universal life force. Prana is in the environment in the form of our food, water, sun and air and the quality of the prana that we take in determines our energy levels. Eating good, high quality foods for example fresh fruit, vegetables, olive oil, fish and shellfish give us high levels of energy, whereas processed foods such as white flour, white sugar, margarine and alcohol give us little or no energy. 
The quality of the air we breathe also influences our energy levels. For example, going for a walk in the woods and breathing in lovely fresh air gives us more energy than sitting indoors breathing in stale air and of course, good quality water and sunshine are absolutely essential for our well-being.
It is also possible to increase and direct our own energy levels – our prana, by practising pranayama, (yogic breathing). This is a means of taking control of the breath – and by taking control of the breath we are also able to influence the mind. For the brain to be able to work properly it requires maximum prana and if it doesn’t get enough of it, we can start to feel ill, think negatively, feel depressed. By using yogic breathing to increase our prana levels we can also help to generate more positive thoughts.
The Hatha Yoga Pradipika (2:42) states:
‘The movement of the breath in the middle passage makes the mind still.
This steadiness of mind is the state of manonmani (devoid of thought)’
Normally only 1/10th of the brain is active because a very high level of prana is required for the brain to function simultaneously. Therefore when pranayama is practised regularly with concentration and dedication, the whole brain is awakened, and you become more aware of yourself, your thoughts, feelings and emotions. You can feel more alive and less likely to use those old negative thought patterns and knee jerk responses.
However, the benefits of pranayama are not instant, you do need to practise regularly over a period of time and I would advise anyone interested to find a good yoga teacher and attend a regular class – and keep on going to the class. The benefits are well worth the sustained effort.
 Swami Niranjanananda Saraswati, ‘Prana and Pranayama’ ISBN 978-81-86336-79-3