Food Metabolism

"The amount of energy that is needed or ingested per day is measured in calories. A calorie is the amount of heat it takes to raise 1 g of water by 1 °C. On average, a person needs 1500 to 2000 calories per day to sustain daily activities. The total number of calories needed by one person is dependent on body mass, age, height, gender, activity level, and the amount of exercise per day. If exercise is a regular part of one’s day, more calories are required. As a rule, people underestimate the number of calories ingested and overestimate the amount they burn through exercise. This can lead to ingestion of too many calories per day. The accumulation of an extra 3500 calories adds one pound of weight. If an excess of 200 calories per day is ingested, one extra pound of body weight will be gained every 18 days. At that rate, an extra 20 pounds can be gained over the course of a year. Of course, this increase in calories could be offset by increased exercise. Running or jogging one mile burns almost 100 calories. The type of food ingested also affects the body’s metabolic rate. Processing of carbohydrates requires less energy than processing of proteins. In fact, the breakdown of carbohydrates requires the least amount of energy, whereas the processing of proteins demands the most energy. In general, the amount of calories ingested and the amount of calories burned determines the overall weight. To lose weight, the number of calories burned per day must exceed the number ingested. Calories are in almost everything one ingests, so when considering calorie intake, beverages must also be considered. Metabolic rates and calorie requirements will be discussed in further detail in the weight management chapter. To help provide guidelines regarding the types and quantities of food that should be eaten every day, the U.S. Department of Agriculture updated its food guidelines from MyPyramid to MyPlate. MyPlate categorizes food into six food groups: fruits, vegetables, grains, protein foods, dairy, and oils. The guidelines recommend making half the plate fruits and vegetables. The other half is grains and protein, with a slightly higher quantity of grains than protein. Dairy products are represented by a drink, but the quantity can be applied to other dairy products as well. ChooseMyPlate.gov provides online resources for planning a healthy diet and lifestyle, including weight management tips and recommendations for physical activity. It also includes the SuperTracker, a web-based application to help analyze one’s diet and physical activity. Obesity in the United States is an epidemic. In 2010, the U.S. Centers for Disease Control and Prevention reported that nearly 36 percent of adults over 20 years old were obese and an additional 33 percent were overweight, leaving only about 30 percent of the population at a healthy weight. Research has shown that losing weight can help reduce or reverse the complications associated with obesity."