Fruits, vegetables, legumes and nuts tend to be alkaline, which means they have a relatively high pH. Some diets may prohibit meat because it is believed to be "acid-forming," increasing the acid level and therefore the pH of a person's blood, but meat and poultry themselves also are alkaline.
Cantaloupe and watermelon are particularly alkaline fruits. Some legumes and vegetables with especially low acid are garbanzo beans, lima beans, mushrooms, asparagus and cooked broccoli.
So-called alkaline diets are not promoted by mainstream medicine because the human body works to maintain the pH level of the blood -- for example, by excreting excess acid in urine -- and the diets may lower consumption of important substances. As of 2015, there is little or no evidence for the specific health claims of alkaline-forming diets. Most doctors do not believe that an alkaline diet can change a person's pH enough to be less hospitable to cancer, for instance.