Calories are a way of keeping track of the body's energy budget. A healthy balance is when we put in a similar amount of energy as we burn. If we consistently put more energy into our bodies than we use, the excess will gradually be stored in our cells as fat. That is when we'll gain weight. However, if we burn more energy than we put in, we'll lose weight. A calorie is a measurement we use to count the energy we consume.

Understanding calories

One large calorie is defined as the amount of energy it would take to raise the temperature of one kilogram of water by one degree Celsius.  Everything we consume has a calorie count - a measure of how much energy the item stores in its chemical bonds. For example, an apple has about 52 calories, and the average slice of pizza has 272 calories.

How to measure a calorie

Energy is released during digestion and stored in other molecules. It is then broken down to provide fuel to the body when needed. Energy is used in three ways:<ul><li>Roughly 10% enables digestion</li><li>About 20% fuels physical activity</li><li>Around 70% support the basic functions of our organs and tissues. </li></ul>

How a body's energy is used 

BMR is the number of calories you would need to survive.  The official guidelines for how many calories the average person requires each day are based on only the body's most basic functions. The MBR for women are 2000 calories and for men 2500 calories.  It is based on average weight, physical activity and muscle mass.  If you are doing activities such as cycling the Tour de France, your body could use up to 9000 calories per day.  Pregnancy requires only slightly more calories than usual, and elderly people need fewer calories as they typically burn energy more gradually.

Basal metabolic rate (BMR)

<ul><li>The calorie counts on nutrition labels measure how much energy the food contains, not how much energy you can actually get out of it.</li><li>Fibrous foods like whole-wheat take more energy to digest, meaning you'll get less energy from eating a 100 calorie serving than a 100 calorie serving of potato chips. </li><li>Different people might not get the same number of calories from eating the exact same food. It can vary based on enzyme levels, gut bacteria and intestine length.</li></ul>

Before you start counting calories

View full lesson: http://ed.ted.com/lessons/what-is-a-calorie-emma-bryce We hear about calories all the time: How many calories are in this cookie? How many are burned by doing 100 jumping jacks, or long-distance running, or fidgeting? But what is a calorie, really? And how many of them do we actually need? Emma Bryce explains how a few different factors should go into determining the recommended amount for each person. Lesson by Emma Bryce, animation by Qa'ed Mai.

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View full lesson: http://ed.ted.com/lessons/what-is-a-calorie-emma-bryce

We hear about calories all the time: How many calories are in this cookie? How many are burned by doing 100 jumping jacks, or long-distance running, or fidgeting? But what is a calorie, really? And how many of them do we actually need? Emma Bryce explains how a few different factors should go into determining the recommended amount for each person.

Lesson by Emma Bryce, animation by  Qa'ed Mai.

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