Calories in Food and Exercise

Definition of Calories for Eating and Burning Them

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A calorie is a measure of energy expenditure and stored energy. The calories referred to in diet (calories eaten) and exercise (calories burned) are kilocalories (kcal).

One kilocalorie is equal to the amount of heat that will raise the temperature of one kilogram of water by one degree Celsius at sea level. One kilocalorie is equal to 4186.8 joules and 1000 calories (small calories) as referred to in science labs for heat energy.

Calories in Food

Calories in food are grouped as fats, alcohol, carbohydrates, and proteins. Different nutrients have more or fewer calories packed into the same weight (higher or lower calorie density). Nutrition labels in the U.S. use these rules of thumb:

  • 1 gram of fat has 9 calories (kcal)
  • 1 gram of alcohol has 7 calories (kcal)
  • 1 gram of protein has 4 calories (kcal)
  • 1 gram of carbohydrate (sugars and starches) has 4 calories (kcal)
  • While fiber is a carbohydrate, it is not easily digested by the body, so calories from fiber are estimated by the U.S. Food and Drug Administration to be 1.5 calories for 1 gram.

By checking the nutrition facts label on food you can see how many calories in a serving come from each of these sources.

Calories and Weight Loss

A pound of body fat stores 3500 calories (kcal). To lose a pound of fat in a week, you must eat approximately 500 fewer calories (kcal) per day than you expend in metabolism and exercise.

The number of calories that you burn in a day includes basal metabolic rate calories burned just to keep the body functioning, plus additional calories burned in physical activity. Your body will burn calories to maintain body temperature, breathe, circulate blood, digest food, eliminate wastes, build and repair cells and tissues, and maintain brain and nervous system activity.

The range of daily calorie burning is from 1600 calories (kcal) for a sedentary woman or an older person to 2800 calories (kcal) for active men, very active women, and teenage boys. You can check your calories burned per day with a calculator based on your height, weight, age, and activity level.

Using a fitness monitor and app to track calories eaten and calories burned can assist dieters who want to achieve a calorie deficit to lose weight. Tracking activity with a fitness monitor helps eliminate overestimates on the side of calories burned, while honest tracking of what is eaten can highlight where food calories are coming from.

Calories Burned in Physical Activity

Physical activity burns calories beyond the basal metabolic rate. Your muscles use both readily available and stored energy sources in your body.

The exercise calories burned during cardiovascular activities such as walking, running, swimming, and cycling depend on the intensity of the exercise, your body weight, and the amount of time you spend exercising. Moderate-intensity exercises such as brisk walking burn fewer calories per minute than more vigorous-intensity exercises such as running. For example, you can use a walking calorie chart to find out how many calories you can burn per mile based on your weight and speed. Walking burns approximately 90 calories per mile for a 160-pound person.

Depending on the duration and intensity of exercise, your body burns available blood sugar, glycogen stored in the muscles and liver, fat and, if required, even begins to burn muscle protein. If you want to burn body fat, aim for exercising at 60 to 70 percent of your maximum heart rate for at least 45 minutes. In that fat-burning zone, 85 percent of the calories you burn are from fat. But you must first expend the more easily-available energy sources before your body turns to the fat stores.

Fitness monitors and pedometers often estimate calories burned based on your weight, number of steps taken, speed, pace, and intensity. It is generally more accurate if the exercise intensity is measured by the heart rate during exercise. You may use handgrip pulse monitors on a treadmill or elliptical trainer for a more accurate estimate. More and more fitness bands and smartwatches have pulse detectors built in to monitor your exercise intensity. A chest strap heart rate monitor is considered the most accurate.

View Article Sources
  • Finding a Balance, Centers for Disease Control, Division of Nutrition, Physical Activity, and Obesity, National Center for Chronic Disease Prevention and Health Promotion.
  • Girard S. Endurance Sports Nutrition, Third Edition. Human Kinetics, 2014.
  • McArdle WD, Katch FI, Katch VL. Exercise Physiology: Nutrition, Energy, and Human Performance. 8th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2015.