[diveoceanos]

I am writing a course outline for free diving, and during my search for information on nutrition for free divers I came across this thread. I have read a lot of interesting things on the above discussion and frankly some of them created a wow effect as they came in conflict with what I was knowing. As far as I remember myself I was always looking for a proof to buy an information. My background is School of Health Sciences - department of Pharmacy in Patras Greece. I have the sense that a lot of the information in this thread are inexact science or the interpretations some of the pals are offering are at least incomplete.

Just to clear up a few things I would like to invite every1 to read some chapters about the regulation of body fluids pH in a Human Physiology textbook, like the one of A Guyton MD.

The bottom line is that the human body and specifically the chemosensitive area of the breathing control center in the brain develops adapatation to progressively lower pH in a way that the onset of contractions regulated by the breathing control center is delayed in well trained individuals compared with beginners. This phenomenon is well established and known among the free diving community as the development of tolerance to higher CO2 with training. But gee, one may not affect his or her blood pH more effectivelly by eating anything than by regulating it with respiration!

The normal pH of arterial blood is 7,4 and the normal pH for venous blood is 7,35. Even the slightest change in these values may alter the rate of biochemical reactions that occur inside our cells. Therefore the human body possess many effective mechanisms and buffer systems in order to maintain its pH within relatively close limits. Otherwise it would be a disaster.

These mechanisms which I am not intending to elaborate on include buffer systems that are present in all body fluids (bicarbonate system, phosphate system, protein system), control by increasing or decreasing the respiration rate, and finally the most effective system is the renal system that produces either alkaline or acidic urine accordingly to maintain the body pH within the close normal values.

The minimum you can achieve by eating acidic foods and overdo it is to achieve a pathologic state called "metabolic acidosis" where the blood pH goes below 7,35. Whether that contributes to the development of faster adaptation to more acidic blood and thus delay in the initial contactions during apnea remains to be proved. Also whether one may affect its fluid pH by eating lemons before apnea towards a more alkaline one and thus delay the onset of the first contraction is doubtful and remains to be proved by proper research. As far as the supplements are concerned please be aware that the most of the time the so called claimed "miraclelous phenomena" by their marketing campaigns are purely hoax. The theories about the source of human desease are numerous. Some of them are take the cake though like the one of attributing every bad thing to body pH. For your information there are bacteria than can leave in very acidic environment and some that can leave in alcohol or they can develop resistance to human body defenses. Don't tell me than cancer can be cured by controlling ones pH. To make the long story short, IMO nothing can increase your fitness significantly more than a balanced diet, weight control, a healthy lifestyle and a lot of excercise. The rest is philology!

But what is all this discussion about? What creates that much interest in altering ones pH by applying all these tricks, anyway? You probably know that on repetitive exposure to apnea conditions your chemosensitive area of the breathing control center in your brain becomes less sensitive to H3O+. The higher the concentration of H3O+ the less is the pH (which is BTW a negative logarithm of H3O+ ions concentration). During apnea or breath-hold the CO2 concentration increases in the body fluids and then it reacts with water to give H3O+ and HCO3- (bicarbonate). Progressively the body adopts to gradually higher levels of H3O+ and the onset of the first contraction is being delayed making apnea less troublesome. One more thing that you might need to know about pH is that as it drops it might reach the zone of 7.0, under which condition the CNS is supressed so much that the individual looses conciousness. The mechanisms are far much more complicated as I am describing them right here but just to give you an other point of view.