The body is alkaline by design, but can be acidic by function. It functions at its best when the pH of its internal biochemical environment, measured as a whole, is equal to 7.39, meaning slightly alkaline. The normal range of blood pH is very small, from a slightly more acidic reading of 7.36 to a more alkaline reading of 7.42. A reading of anything higher or lower than these figures indicates acidity (from 7 to 7.35) or alkalosis (7.42 to 7.8). If these limits are exceeded, the body can no longer function, and death results.

The zone of optimal blood health extends only from pH 7.36 to pH 7.42; illness will accompany any incidence of acidosis or alkalosis. Of these two, acidosis is by far the most common - more than half the population suffers from this condition.

The pH of the body's organic fluids and tissues varies from one part of the body to another. When we say the ideal pH of the body is 7.39, this refers primarily to the pH of the blood, and to a lesser extent that of the body's internal environment, meaning all organic fluids such as lymph and extra and intracellular serums (fluids surrounding or within the cells). Blood is indeed "a very particular sap" (Goethe) whose pH must remain extremely stable to maintain the life of the physical organism. Even the slightest change of blood pH is rapidly corrected by the body, which restores it to the ideal measurement of 7.39. When the body is unable to perform this task physical and mental disorders quickly appear.

The pH of the internal environment, the basic "ground" biochemical terrain, can tolerate more significant changes than that of the blood, but the pH of the internal environment should never go beyond 7.36 or 7.42 if good health is to be maintained.

Many individual organs and organic fluids, however, have a pH that is normally far above or below this ideal pH. The pH of urine, for example, may be 6, or even as low as 5 or 4.5. This is possible because urine is regularly eliminated and thus does not remain in the body for long. Areas of the body that are essentially acid include the colon (pH 6.8), the outer layers of the skin (pH 5.2), and the gastric region (pH 2). Others, in contrast, are quite alkaline: the inner layers of the skin (pH 7.35), the pancreatic juices (from pH 7.5 to 8.8), and the small intestine (pH 8).

These different values are all normal and correspond to precise needs of the body. For example, the extremely acidic nature of the gastric region is indispensable for protein digestion, and the high acidity of the skin helps it destroy microbes before they can enter the body. So restoring the acid-alkaline balance does not mean bringing the gastric region's pH 2 up to pH 7 - that would cause serious digestive problems - but rather restoring the pH of the basic internal biochemical terrain. The acidification of the internal terrain is in fact the source of all health troubles caused by acidity.