Citrus fruits, especially lemon and lime, have the highest content of citric acid. Citric acid is an organic acid that is not required in the diet. However, it is beneficial for people with kidney stones.It inhibits stone formation and breaks up small stones that are beginning to form in the kidneys. The more citric acid in your urine, the more protected you are against formation of new kidney stones. Eating citrus fruits and drinking an eight-ounce glass of orange juice daily may help prevent the painful disease that strikes most men aged 40 to 65. Individuals with a history of kidney stones should avoid highly processed foods and dairy products. Do consume at least two quarts (or more) of water daily.