This breathing technique was created by Marc David in his book, "The Slow Down Diet." He has a great way of breaking down things into very usable steps. Check it out.
At every meal or snack, and any time food is about to pass across your lips, ask yourself “Am I about to eat under stress? Is my mind in high gear?” If the answer is yes, pause. Then take ten long, slow deep breaths. Ideally, your deep-breathing exercise would follow this sequence:
Sit in a comfortable position with spine straight, feet flat on the floor.
Eyes can be open or closed.
Deeply inhale, filling your lungs to approximately two-thirds capacity.
Hold your breath for several seconds.
Exhale fully.
Repeat this cycle ten times.
This simple practice can shortcut the stress response in as little as one minute, depending on the intensity of your flight-or-fight condition. Even if you’re in a situation in which breathing is socially unacceptable, such as a business luncheon with tough-minded associates who have little regard for oxygen, you can still use this technique. Simply remain focused on your breathing while you continue to look at others and monitor the conversation at the table. They’ll think you’re listening to them attentively, but what you are doing is stimulating parasympathetic dominance. It’s really quite exciting.
By holding in the breath for several seconds the carotid bodies, tiny clumps of nerve tissue containing specialized chemical receptors and located along the carotid arteries, are fooled into thinking that blood pressure is rising. The carotid bodies will then signal a message for blood vessels to dilate, which causes an overall drop in blood pressure and hence a diminishment of the stress response.
By breathing in to only two-thirds of your lung capacity, you ensure that blood pressure won’t go up from the sheer exertion of forcing the lungs to maximize expansion. By breathing out more fully than you breathe in, you help move stale air out from the lungs. Slow deep breathing has also been shown to increase endorphin release in the body, producing a sense of relaxation and well-being.
With basic deep breathing it’s preferable to breathe in and out through the nose. Air entering through the nasal passages is quickly warmed to body temperature because lungs work most efficiently with warm air. Step outside on a cold winter day, breathe in through your mouth, and you’ll prove this to yourself quite easily as the cold air causes the lungs to tense. Nasal breathing also has a potent effect on the central nervous system because nerve receptors in the nose reach directly to the brain. If your sinuses are clogged and nasal breathing is difficult, breathing through the mouth will still work sufficiently.
A useful variation on this technique is to place a hand on your belly, or even one hand atop the other over your abdomen. This may help you focus more clearly on your gut and relax more deeply.
