I’ve practiced Buteyko breathing for a few years, and I believe that there are some benefits. However, I think that the dietary rules prescribed by *some* Buteyko instructors are mistaken.
Personally, I have found the most improvement through a combination of eating enough without restrictions, sleeping enough, de-stressing through other means, and breath retraining inspired by Buyteko. And I don’t find that CP is always a good indicator of health.
I have made the mistake of suggesting CP as a good measure of health in some of my own writing previously, but now that I have a better understanding of breathing biology I don’t believe that it is the best indicator.
Consider that one way to artificially extend CP is to hyperventilate. That is because one of the things (actually, the primary thing) that triggers air hunger is carbon dioxide build-up. Hyperventilation expels carbon dioxide. That is a problem in terms of health. But it can artificially extend the CP. That is just one example of how CP is not the most reliable indicator of health.
HOW YOU FEEL is the best indicator. Of course that too can be hijacked. Stimulants of various sorts can make you feel well even if your health is compromised. But increasing metabolic health through whatever means, including eating enough, tends to lead to sustained health improvements.
Keep in mind that carbon dioxide is one of the products of metabolism. Increases in metabolic rate will produce more carbon dioxide. That will naturally trigger air hunger more rapidly. That doesn’t mean that health is being compromised. It just means that the metabolic rate is increased.
My own experience is that my breathing has dramatically improved as a result of eating more. I am not terribly concerned about my CP. Although it is not a terrible indicator, it’s not the most reliable in my opinion. Whether my CP is high or low, what I have noticed is that my resting respiratory rate is now about 8 breaths per minute, and when I give attention to it I can easily reduce it to 6 breaths per minute. My chest, neck, shoulders, and abdominal muscles are entirely relaxed. The exhalation is passive and long. I feel good.
I believe that the Buteyko system has a lot of merit, but it’s not perfect. Like so many things, many people involved become zealous and start promoting ideas that aren’t necessary or even beneficial for everyone.
In fairness, some Buteyko instructors offer what I believe is sensible advice. For example, Artour Rakhimov of normalbreathing.com typically suggests that diet, sleep habits, and interest in stimulants and other drugs will naturally change as CP increases. He does not prescribe a diet that I know of. And that approach seems sensible to me. In my humble opinion it is a mistake to suggest that one who is already likely calorie deificient and hypometabolic should apply a restrictive diet.
By the way, I don’t believe that it is necessary to take the advice to practice breathing exercises on an empty stomach too far. I regularly practice reduced breathing immediately after eating. It would be difficult, of course, to get good results if one has eaten too much. But I have no problems. I normally eat 3000+ calories a day. I eat lots of sugar, dairy, meat, starch, and salt. This has helped to improve my breathing.
In my opinion, do what works for you. What I find is that for me and for most people that I communicate with eating enough and sleeping enough are usually most important. Sometimes environmental factors are also very important. Once those are squared away then it can be helpful to look at breathing, exercise, etc.
Don’t restrict food if it is helping you feel better just because you’re afraid of a temporary lowering of CP. My two cents.
Hope that helps.