Overweight and obesity have become an epidemic in many parts of the world threatening the health of over one billion people. In order to combat this epidemic effectively, it is desirable to develop new methods to monitor individual's food intake and provide quantitative information about the nutrients and calories consumed in people's daily life. We present an electronic photographic approach and associated image processing algorithms to estimate food portion size, which is then utilized to obtain the required information. Our experiments show that our approach is accurate, providing an effective tool for people to track their nutritional and energy intake.