The Science of Energy Balance

aerobic exercise: An activity that uses the large muscles and involves increased breathing and heart rate over an extended period of time, usually a minimum of 20 minutes.

anorexia nervosa: A serious psychological disorder most often affecting young women and characterized by refusal to eat. Those affected exert extreme discipline over their eating habits and are usually obsessed about food. They carefully plan their meals and are fearful of overindulging.

appetite: A learned behavior and an emotional or mental desire for food that may be brought about by the sight or smell of food or by thinking of a pleasurable food or meal eaten in the past.

basal metabolic rate (BMR): A measure of the energy necessary for maintaining basic functions, such as breathing, heart rate, and digestion.

binge eating disorder: A condition characterized by frequent episodes of uncontrolled eating. The binge eater feels out of control, and episodes of overeating are followed by feelings of disgust, guilt, or depression. It is common for episodes of overeating to be followed by bulimic behavior, such as vomiting, using laxatives, or overexercising.

body mass index (BMI): A measure relating body weight to height. It is derived from a person’s weight (in kilograms) divided by their height (in meters) squared.

bulimia nervosa: An eating disorder aimed at averting weight gain. It is characterized by behaviors such as vomiting, taking laxatives, or over exercising after eating to rid the body of the calories consumed.

calorie: A unit of energy. In nutrition, calorie is used instead of the more precise scientific term kilocalorie. A kilocalorie is the amount of energy required to raise the temperature of a liter of water 1 ºC at sea level. The common usage of the word calorie is understood to refer to a kilocalorie when referring to food energy.

diabetes: A chronic disease associated with abnormally high concentrations of the sugar glucose in the blood. It may be due to inadequate production of insulin (a hormone made by the pancreas that lowers blood glucose) or inadequate sensitivity of body cells to the action of insulin. The major complications of diabetes include dangerously elevated blood sugar, abnormally low blood sugar due to diabetes medications, and disease of the blood vessels, which can damage the eyes, kidneys, nerves, and heart.

energy: As used in this curriculum supplement, it is the potential work value found in foods, measured in calories, and the work value found in animals after they eat foods.

energy balance: A condition determined by both energy intake and energy output. Energy balance is achieved when energy intake equals energy output. This is the desired condition for healthy adults.

hunger: The uneasy or painful sensation caused by lack of food. It may be defined as a consequence of a sequence of events that leads up to and follows a lack of adequate food intake.

hypothesis: A testable statement that predicts an outcome.

leptin: A protein produced by fat cells that appears to play an important role in how the body manages its supply of fat.

metabolism: The sum of all chemical reactions occurring in the body.

negative energy balance: A condition in which energy output exceeds energy intake. This condition results in weight loss.

nutrition: The process by which food is assimilated and used for growth and maintenance.

obesity: A chronic metabolic disease characterized by having a high amount of body fat. Individuals traditionally have been considered obese if they are more than 20 percent over their ideal weight. That ideal weight must take into account a person’s height, age, sex, and build. Obesity in adults (not children and adolescents) has been defined more precisely by the National Institutes of Health as having a BMI of 30 or higher (a BMI of 30 is about 30 pounds overweight for a woman who is 5’4” tall).

osteoarthritis: A type of arthritis caused by breakdown of cartilage with eventual loss of the cartilage of the joints. Arthritis is a joint disorder characterized by inflammation. Cartilage is a protein that serves as a “cushion” between the bones of the joints.

osteoporosis: A disease characterized by a reduction in bone mass due to depletion of calcium and bone protein.

ounce: A traditional unit of weight. The avoirdupois ounce, the unit commonly used in the United States, is 1/16 pound, or about 28 grams.

ounce, fluid: A traditional unit of liquid volume, called the fluid ounce to avoid confusion with the weight ounce. There are 16 fluid ounces in a pint, and each fluid ounce represents approximately 30 milliliters.

overweight: A condition in which one is too heavy for one’s height. The National Institutes of Health defines overweight in adults (not children and adolescents) as having a body mass index (BMI) of 25 to 29. Body weight comes from fat, muscle, bone, and body water. Overweight does not always mean “overfat.”

positive energy balance: A condition in which energy intake exceeds energy output for basal metabolic rate (BMR) and physical activities. Children, adolescents, and teenagers should be in positive energy balance. For these age groups, energy intake in excess of energy used for BMR and physical activities is used for growth or may be stored for use at a later time.

sleep apnea: A disorder in which breathing stops during sleep. It may be caused by blockage of the airways, cessation of respiration that is usually brain-related, or a combination of these two.

stroke: The sudden death of some brain cells due to a lack of oxygen when blood flow to the brain is impaired by blockage or rupture of an artery to the brain.

thermic effect of food: The energy needed to digest food.

undernutrition: Inadequate nutrition due to not enough or poor assimilation of food.