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What Is A Calorie?

Updated on March 29, 2014

Calories are amongst the most basic topics in nutrition. If somebody knows one thing about nutrition, chances are it's related to Calories. While Calories are certainly an important part of choosing healthy foods as part of an overall balanced diet, it is important to keep in mind that Calories are only aspect of food and they cannot be the sole determinant of what is healthy and what is not.

Calories just represent energy
Calories just represent energy | Source

Defining the Calorie

First, the technical scientific definitions

  • A calorie is the amount of energy required to raise 1 gram of water at a standard initial temperature 1 degree celsius at a pressure of 1 atmosphere.
  • A unit of energy-producing potential equal to this amount of heat that is contained in food and released upon oxidation by the body (from

The second definition is the more applicable one when discussing food, which is saying that the Calories in food are energy that is released when the body breaks them down. This second definition is more applicable when discussing Calories in the sense of food and nutrition.

The important aspect to note of these definitions is that Calories represent energy and nothing else. Calories are not nutrients, and they have no physical form, unlike a fatty acid or a carbohydrate which are actually molecules comprised of various atoms. This may seem a little confusing, how can nothing be something? Allow me to explain

Where do Calories come from?

Calories are technically stored in chemical bonds that hold together atoms. When your body digests food, it breaks these chemical bonds and the Calories contained in them are released as energy which the cells of your body use for a variety of processes. Calories are stored inside of Carbohydrates, Protein, Fat, and Alcohol. Each of these substances has different amounts of Calories stored in them, meaning that if you take an equal weight of carbs, fat, protein, and alcohol, there is a different amount of calories in them, see below:

  • Fat: 9 Calories per 1 gram
  • Alcohol: 7 Calories per 1 gram
  • Carbohydrates: 4 Calories per 1 gram
  • Protein: 4 Calories per 1 gram

Fat is the most Calorically dense energy source, alcohol is second, and protein and carbohydrates are tied with the lowest. All this tells us is that there is more energy in fat than anything else, and more energy in alcohol than in protein or carbohydrates. This does not make alcohol better than fat, carbohydrates equal to protein, or fat bad, it just tells us how much energy there is in these substances.

One important note: There is no difference between the Calories in one or another food. 100 Calories of Broccoli are the same as 100 Calories of Twinkies, they have the same energy value but are vastly different foods due to the nutrients in them. The fiber, vitamins, minerals, and phytochemicals (cancer protective compounds) in the broccoli makes it far better than the heavily processed Twinkie.

Energy Balance Diagram

When the Calories you eat equals the Calories you expend, weight stays constant
When the Calories you eat equals the Calories you expend, weight stays constant | Source

Why Are Calories Important?

Since Calories represent energy, they are important for maintaining weight. Maintaining a healthy weight is very important; being overweight, and especially obese, increases the risk for developing many health problems. Aside from the emotional and social problems that come with being overweight (which are not fun at all) physical issues such as high blood pressure, atherosclerosis (clogged arteries), heart disease, diabetes, cancer, and other diseases become very real problems when weight gets out of control.

Energy Balance

Maintaining weight is a result of maintaining energy. Energy comes into the body from food and is expended through basic metabolic processes (such as your heart beating, the muscles in your digestive tract contracting, your lungs expelling out air, your cells copying DNA and many more) exercise, and the thermic effect of food; the thermic effect of food is the extra energy your body needs to digest what you eat.

Energy balance ultimately determines whether you gain weight, lose weight, or stay at the same weight. "Calories In, Calories Out" is a popular phrase used to summarize the idea of energy balance in the diet and is the backbone of many diets, such as weight watchers. Tweaking energy balance can help your achieve your goals for seeing a certain number on the scale, and it is (in theory) quite simple:

  • Positive energy balance (eat more energy than you expend) = weight gain
  • Negative energy balance (eat less energy than you expend) = weight loss
  • Neutral energy balance (eat the same amount of energy you expend) = no change in weight

With this information, it may seem that Calories are the only part of nutrition worth thinking about. If you are thinking that than STOP! and think again! One very very very grave mistake many dieters make when they are exploring the idea of energy balance is that getting themselves into negative energy balance will cause them to lose fat. This is not how it works, unfortunately. Negative energy balance will certainly cause you to lose weight but that weight can come from a reduction in other parts of your body besides the fat, such as water, bone mass, or muscle (the last two don't sound so great to lose, do they?). Your body needs energy to keep you alive, and restricting your Caloric intake to an extreme degree can become dangerous, however, Calorie restriction is an important piece of any diet geared towards weight loss, it just cannot be the only piece of that diet.

Calories In the Context of A Healthy Diet

The real question, now that we know what Calories actually are and what they are used for, is how to use that knowledge to make healthier food choices. Here a few guidelines

  • Avoid foods that are energy dense and nutrient poor. Foods like soda, candy, white bread, sugary breakfast cereals offer lots of energy (Calories) but little nutrition (Vitamins, minerals, proteins, natural fats).
  • Read the nutrition facts label to find out how many Calories are in a serving of food and how many in the whole package (make sure to check the "number of servings" listed on the nutrition facts label in case there are more than 1 serving of food in the package).
  • Do not get tricked into thinking a food is healthy just because it is low in Calories: many reduced Calories ("diet" or "light" foods) have a lower Calorie count than the "regular" versions, but this does not mean they are healthy. It is easy enough for a food manufacturer to remove fat from a product and replace it with the less calorically dense sugar (sugar is a carbohydrate); this will reduce the overall Calories but does not make the food healthier.
  • Cut calories by choosing foods with less added sugar and refined grains (or none at all!), as well as unhealthy oils (vegetable oils like corn and soy).

While Calories are not the end all be all of health and nutrition, they are certainly a start. Replacing the low nutrient-high Calorie foods in your diet with foods of equal Caloric content and higher nutrient content OR replacing them with foods with less Calories and a similar nutrient content will likely benefit your diet.

Calorie Needs Chart Based on Age, Gender, and Physical Activity


How Many Calories Do I Need?

How many Calories you need depends on your age, activity level, gender, genetics, and other factors such as disease and menopause. You can use this Calorie calculator to get an idea of your needs.

The body has many well controlled mechanisms for regulating hunger and energy intake, however these systems can get easily manipulated by the sugar and salt laden world of processed foods we live in. As you acquaint your body to a diet consisting of more and more healthy (less processed and more natural) foods the systems in place for monitoring food intake will become stronger. Eventually, you should be able to "listen to your body" in the sense that if you are hungry, you eat and stop when you are full and do not start again until you feel hungry. This is the strategy I use for balancing my energy intake, I do not count Calories or track the food I eat or calculate my Calorie needs, I pick healthy foods (plenty of vegetables, fruits, natural meats from a local farm, wild seafood) and eat what I feel when I feel like it. I encourage you to try and do the same as your diet becomes filled with more and more healthy foods and your lifestyle includes more regular exercise. However, if you are having problems with your diet, are physically inactive, and struggling to achieve health, try using a Calorie counter first, and picking healthy foods that give you enough energy to get through the day, but not so much that you pack on extra pounds.

DO: Modify your Calorie intake to meet your weight loss goals

DO NOT: Reduce your Calorie intake by more than 500 Calories of what you need for weight maintenance (If you need 3,000 Calories a day, do not go below 2,500)

DO: Try tracking your food on an online journal such as, or

DO NOT: Obsess over your food journal to such an extent that you cannot enjoy life and food.

DO: Occasionally treat yourself if you feel you need to (if you are doing fine without the sweet stuff, no need to put it back in). It is true that you can have "Everything in Moderation" and be healthy, but be very careful to focus on the "Moderation" and not the "Everything." I suggest keeping junk food out of the house/workplace completely (or as much as you can based on your level of control) and picking up your favorite treat in a small (preferably single serving size) amount when you feel the need. Also, keep in mind that when holidays, parties, or events where unhealthy food is often serve come up, it is nice to be able to indulge will knowing you have been good for the last (insert amount of time here, make it the majority of the week if you can).

DO NOT: Sacrifice healthy foods for unhealthy foods for the sake of achieving negative energy balance (if you eat the candy bar, don't skip a balanced dinner).

For more help picking healthy foods, check out my basic guide to picking healthy foods


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    • nutritiondan profile imageAUTHOR

      Daniel Palenchar 

      5 years ago from SoCal

      Thank You, I appreciate the positive feedback and thanks for my first ever commment

    • My Cook Book profile image

      Dil Vil 

      5 years ago from India

      Very informative, i have gone through this subject very long back. Thank you for providing this information, now i have recollected everything again form your article. Good work, i voted your work UP useful and interesting.


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