Vegetarianism can be a challenging part of my practice. I've been mostly vegetarian, with the exception of fish, for more than twenty years. Even so, I have to work to maintain my protein, iron and energy levels in keeping with an Aryuvedic Vata profile.
After studying with Simon Borg-Olivier for several years, I have improved focus on pranayama to try to address some of these aspects of my constitution. In short, breathing less and including retentions, increases levels of carbon dioxide (CO2) in the body. Increased CO2 results in greater systemic acidity and more oxygen being sent to the brain. This is due to something called the Bohr effect where cells release oxygen to haemoglobin only in the presence of CO2. When we are too alkaline due to over-breathing in practice or an alkaline vegetarian diet, we actually get less oxygen to the brain.
Slowing the breath and even practicing gentle retentions in pranayama is a powerful tool. It can calm the post-practice high, reduce our appetite and improve our focus in readiness for meditation.