Gastric acid
The highest concentration that gastric acid reaches in the stomach is 160 mM in the canaliculi. This is about 3 million times that of arterial blood, but almost exactly isotonic with other bodily fluids. The lowest pH of the secreted acid is 0.8, but the acid is diluted in the stomach lumen to a pH between 1 and 3.
Alkaline diet
Advocates propose that since the normal pH of the blood is slightly alkaline, the goal of diet should be to mirror this by eating a diet that is alkaline producing as well. These advocates propose that diets high in acid-producing elements will generally lead the body to become acidic and thereby foster disease. This proposed mechanism, in which the diet can significantly change the acidity of the blood, goes against "everything we know about the chemistry of the human body" and has been called a "myth" in a statement by the American Institute for Cancer Research because it is "virtually impossible" to create a less acidic environment in the body. While a selectively alkaline diet may change the pH level in the urine, it has not been shown to elicit a sustained change in blood pH levels, nor to provide the clinical benefits claimed by its proponents. Because of the body's natural regulatory mechanisms, which do not require a special diet to work, eating an alkaline diet can, at most, change the blood pH minimally and transiently.