One of the most important and abundant of the carotenes, a portion of which the liver converts to vitamin A. It should be noted, however, that while excess vitamin A can be toxic to the body, residual beta carotene is quickly eliminated. Scientists now believe that beta carotene is a powerful antioxidant with properties that can contribute to reducing cancer and heart disease. It's found in vegetables like carrots, broccoli, squash, spinach and sweet potatoes. Beta carotene's orange-yellow pigment is also used as a coloring in foods like butter and margarine.