The expert: Fredrick vom Saal, PhD, an endocrinologist at the University of Missouri who studies bisphenol-A
The problem: The resin linings of tin cans contain bisphenol-A, a synthetic estrogen that has been linked to ailments ranging from reproductive problems to heart disease, diabetes, and obesity. Unfortunately, acidity (a prominent characteristic of tomatoes) causes BPA to leach into your food. Studies show that the BPA in most people's body exceeds the amount that suppresses sperm production or causes chromosomal damage to the eggs of animals. "You can get 50 mcg of BPA per liter out of a tomato can, and that's a level that is going to impact people, particularly the young," says vom Saal. "I won't go near canned tomatoes."