Ash left from the burning of foods can directly affect the acidity or alkalinity of your body. The pH value is a measure of how acidic or alkaline something is.
Simply put, eating a diet that produces a more acidic pH systemically is conducive to promoting a disease state, while eating a diet that produces a more alkaline or base pH is more likely to help prevent disease.
In examining the U.S. diet, researchers found that contemporary net acid-producing diets (i.e., high in animal protein with a relatively low intake of fruits and vegetables) characteristically produce a low-grade systemic metabolic acidosis in otherwise healthy adult subjects, and that the degree of acidosis increases with age, in relation to the normally occurring age-related decline in renal functional capacity.
REFERENCES
Potential renal acid load of foods and its influence on urine pH. Remer T, Manz F. J Am Diet Assoc. 1995 Jul;95(7):791-7.
Acid-Alkaline Balance & Health: An Examination of the Data. Supplement Science. 34-39.
Bruno, G., MS, MHS. (2013, April).