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
While diets avoiding meat, poultry, cheese, and grains can be used in order to make the urine more alkaline (higher pH), difficulties in effectively predicting the effects of these diets have led to medications, rather than diet modification, as the preferred method of changing urine pH. The "acid-ash" hypothesis was once considered a risk factor for osteoporosis, though the current weight of scientific evidence does not support this hypothesis.