Excessive calories from sugar can contribute to weight problems,and sugar is also well known for its ability to promote teeth __1__ decay.Too many calories from fat have also taken their toll from the __2__ public's health. In 1988, the U.S surgeon general issued a report linking high level of fat intake to an increased risk for obesity.Obesity is a risk factor for high bloody pressure, stroke, and __3__ diabetes. Research has also shown a relationship between high levels of fat in the diet and cancer. In addiction, scientists have linked some types of fat to high blood cholesterol level,which must lead to heart disease. Such reports have prompted __4__ health experts and nutritionists to recommend that adults and children over age 2 not only watch their sugar intake but also to limit their fat intake to a maximum of 30% of their __5__ complete calories. This has encouraged many people to turn __6__ to products made with fat and sugar substitutes.Low-calorie sugar substitutes have been around for decades,but the recent trend in eating "light" has created a boom in this branch of food-technology research. Today, food chemists are seeking for better substitutes by modifying existing foods, __7__ searching for new compounds in nature, and concoct entirely __8__ new substances. But the research process is complicated by our incomplete understanding of how the human body interacts with the chemicals we eat.For example, scientists do not already know exactly why some __9__ substances taste sweet. Other questions involve the safe and __10__ usefulness of artificial fats and sweeteners.