For more than 30 years, WDDTY has been advocating a diet rich in fruits and vegetables—the best approach for most people most of the time. But a small minority of us suffer from a chronic health problem even when we are eating a healthy diet. When this happens, the very healthiest of foods could be doing us harm. Some vegetables, fruits and nuts contain oxalates, compounds that can cause kidney stones plus other issues, and this could be the unsuspected cause of a chronic health problem.