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Medical Author:

Gayle M Galletta, MD

Medical Editor:

Jerry R. Balentine, DO, FACEP

Jerry R. Balentine, DO, FACEP

Dr. Balentine received his undergraduate degree from McDaniel College in Westminster, Maryland. He attended medical school at the Philadelphia College of Osteopathic Medicine graduating in1983. He completed his internship at St. Joseph's Hospital in Philadelphia and his Emergency Medicine residency at Lincoln Medical and Mental Health Center in the Bronx, where he served as chief resident.

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Weight gain is caused by consuming more calories than the body uses.

• The average person uses as many as 2,500 calories daily, or 17,500 calories per week.
• If you eat the amount your body needs, you will maintain your weight. It takes 3,500 extra calories to gain 1 pound.
• To lose weight, you must consume fewer calories than your body uses. You must eat 3,500 calories less than you need, say 500 calories per day for one week, to lose 1 pound.

Calories count. It's important to understand where calories come from and how to make the smartest food selections. Here are some basics:

• Foods are composed of the following three substances, in varying amounts:
• Carbohydrates (four Calories per gram): Examples include grains, cereal, pasta, sugar, fruits, and vegetables.
• Protein (four Calories per gram): Examples include legumes (beans, dried peas, lentils), seafood, low-fat dairy, lean meats, and soy products such as tofu.
• Fats (nine Calories per gram): Examples include whole-fat dairy products, butter, oils, and nuts.

Alcohol is a separate fourth group (seven calories per gram).

A calorie is the amount of energy (heat) needed to raise the temperature of 1 gram of water by 1 degree Celsius. A kilocalorie (or Calorie with a capital C) is the amount of energy needed to raise the temperature of 1 kilogram of water by 1 degree Celsius.

• The energy contained in food is measured in kilocalories but is commonly referred to on food packages and elsewhere as calories.
• Most people underestimate the number of calories they consume by about 30%.
• Calculate the number of calories you should consume each day to keep your weight the same.
• If you are moderately active, multiply your weight in pounds by 15.
• If you are sedentary, multiply by 13 instead.
• To lose weight, you need to eat less than this number.

Excess calories from any source (even fat-free foods) will turn into body fat.

• Any carbohydrate not immediately used for energy will be stored in the liver as glycogen for short-term use. The body has only a limited number of liver cells to store the glycogen. Whatever is left over will be converted to fat.
• Excess protein and fat in the diet are also stored as fat.

Fat cells are no longer thought to be responsible only for energy storage and release.

• They synthesize the hormone leptin, which travels to the hypothalamus in the brain and regulates appetite, body weight, and the storage of fat.
• Leptin was first discovered in 1994. The exact way it works is not yet fully understood.
• Disorders of leptin account for only a few cases of obesity, usually morbid (extreme) obesity.

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