The prevalence of obesity in the United States has doubled in the past two decades. Nearly one-third of adults are obese, that is, they have a body mass index (BMI ) of 30 or greater. One of the fastest growing segments of the population is that with a BMI ≥ 30 with – accompanying comorbidities. Over the last two decades, the prevalence of overweight among children and adolescents has increased substantially; it is estimated that as many as 16 percent of children and adolescents are overweight, representing a doubling of the rate among children and tripling of the rate among adolescents. A high prevalence of overweight and obesity is of great public health concern because excess body fat leads to a higher risk for premature death, type 2 diabetes, hypertension, dyslipidemia, cardiovascular disease, stroke, gall bladder disease, respiratory dysfunction, gout, osteoarthritis, and certain kinds of cancers.

Americans tend to be relatively inactive. In 2002, 25% of adult Americans did not participate in any leisure time physical activities in the past month, and in 2003, 38% of students in grades 9 to 12 viewed television 3 or more hours per day. Regular physical activity and physical fitness make important contributions to one’s health, sense of well-being, and maintenance of a healthy body weight. Physical activity is defined as any bodily movement produced by skeletal muscles resulting inenergy expenditure (http://www.cdc.gov/nccdphp/dnpa/physical/terms/index.htm). In contrast, physical fitness is a multi-component trait related to the ability to performphysical activity. Maintenance of good physical fitness enables one to meet the physical demands of work andleisure comfortably. People with higher levels of physical fitness are also at lower risk of developing chronic disease. Conversely, a sedentary lifestyle increases risk for overweight and obesity and many chronic diseases, including coronary artery disease, hypertension, type 2 diabetes, osteoporosis, and certain types of cancer. Overall, mortality rates from all causes of death are lower in physically active people than in sedentary people. Also, physical activity can aid in managing mild tomoderate depression and anxiety.

Increased intakes of fruits, vegetables, whole grains, and fat-free or low-fat milk and milk products are likely to have important health benefits for most Americans. While protein is an important macronutrient in the diet, most Americans are already currently consuming enough (AMDR = 10 to 35 percent of calories) and do not need to increase their intake. As such, protein consumption, while important for nutrient adequacy, is not a focus of this document. Although associations have been identified between specific food groups (e.g., fruits and vegetables) and reduced risk for chronic diseases, the effects are inter-related and the health benefits should be considered in the context of an overall healthy diet that does not exceed calorie needs. The strength of the evidence for the association between increased intake of fruits and vegetables and reduced risk of chronic diseases is variable and depends on the specific disease, but an array of evidence points to beneficial health effects.

Fats and oils are part of a healthful diet, but the type of fat makes a difference to heart health, and the totalamount of fat consumed is also important. High intake ofsaturated fats, transfats, and cholesterol increases the riskof unhealthy blood lipid levels, which, in turn, may increasethe risk of coronary heart disease. A high intake of fat(greater than 35 percent of calories) generally increasessaturated fat intake and makes it more difficult to avoidconsuming excess calories. A low intake of fats and oils(less than 20 percent of calories) increases the risk of inad-equate intakes of vitamin E and of essential fatty acids andmay contribute to unfavorable changes in high-densitylipoprotein (HDL) blood cholesterol and triglycerides.

Carbohydrates are part of a healthful diet. The AMDR for carbohydrates is 45 to 65 percent of total calories. Dietary fiber is composed of nondigestible carbohydrates and lignin intrinsic and intact in plants. Diets rich in dietary fiber have been shown to have a number of beneficial effects, including decreased risk of coronary heart disease and improvement in laxation. There is also interest in the potential relationship between diets containing fiber-rich foods and lower risk of type 2 diabetes. Sugars and starches supply energy to the body in the form of glucose, which is the only energy source for red blood cells and is the preferred energy source for the brain, central nervous system, placenta, and fetus. Sugars can be naturally present in foods (such as the fructose in fruit or the lactose in milk) or added to the food. Added sugars, also known as caloric sweeteners, are sugars and syrups that are added to foods at the table or during processing or preparation (such as high fructose corn syrup in sweetened beverages and baked products). Although the body’s response to sugars does not depend on whether they are naturally present in a food or added to the food, added sugars supply calories but few or no nutrients.