Calories in Food and Exercise

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.

Understanding 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:

• Alcohol: 1 gram of alcohol has 7 calories (kcal)
• Carbohydrate: 1 gram of carbohydrate (sugars and starches) has 4 calories (kcal)
• Fat: 1 gram of fat has 9 calories (kcal)
• Protein: 1 gram of protein has 4 calories (kcal)

Although 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 roughly 3500 calories (kcal) although this number is an estimate. To lose a pound of fat in a week, a general guidelines is to reduce your calorie intake by approximately 500 fewer calories (kcal) per day than you expend in metabolism and exercise. However, it is important to take this guide with a grain of salt. There are other factors (in addition to the simple calories in/calories out equation) that can influence weight loss.

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.

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.

The "fat-burning" zone is more tolerable for many people and might allow you to exercise for a longer period of time. But if you work out for a shorter period of time, a higher intensity session will help you to burn more calories

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 hand grip 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.