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Calories Explained

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The most basic and fundamental law that governs whether you gain weight or lose weight is the first law of thermodynamics, which states that energy cannot be created or destroyed, it can only be transformed from one type to another. Although thermodynamics itself is generally not a simple subject, calories are explained quite easily according to its principles. Ultimately, your body weight is dependent only on the difference between the amount of calories that you consume versus the amount of calories that you burn (this is known as your caloric balance). Read the rest of this article to find out why.

What is a Calorie?

A calorie, as commonly referred to on food nutrition labels, is a unit of energy. More specifically, a calorie is the amount of energy needed to raise the temperature of 1 litre of water by 1 degree Celsius. When you eat food, you are consuming the energy that is stored within the protein, carbohydrate, and fat molecules of that food. The total amount of the energy stored in the food you are eating is represented by the calorie content of the food as indicated on its nutritional label.

How Does Your Body Use Calories?

a food nutrition label showing the amount of calories in a food product

Your body is capable of doing only two things with the calorie energy that it absorbs; it must either burn it or store it. This is how the effect of calories on our bodies can be explained according to the first law of thermodynamics. When we eat food the calories that are in it can never disappear or be destroyed, they can only change form. In their food form calories are stored as chemical energy in the bonds of the food molecules. When we eat them, calories do not disappear but rather are eventually transformed, or "burned," into the different types of energy that your body utilizes or produces each day, like heat energy, electrical energy, sound energy, and kinetic (movement) energy, OR, if they aren't burned, they are stored again as more chemical energy. Therefore, according to the first law of thermodynamics, any calories that you consume and do not burn must be stored on your body. And, unfortunately, the primary storage mechanism for the excess calories you consume is fat, rather than muscle.

Calorie Rules for Weight Loss and Weight Gain

What we've learned so far leads us to some very simple rules about calories by which weight loss and weight gain can be explained. These rules are absolutely fundamental to determining how much you weigh, and it is impossible to contravene them. They are the following:

  1. If you eat more calories than you burn you will gain weight.
  2. If you burn more calories than you eat you will lose weight.
  3. If you eat the same amount of calories that you burn your weight will not change.

To keep itself alive your body is always burning at least some minimum amount of calories that are used to support the function of vital organs like your heart, brain, nervous system, lungs, kidneys, liver, muscles, and skin. This rate of calorie burn is called your basal metabolic rate. If you want to accomplish anything beyond simply staying alive, such as moving your body for example, you will have to burn extra calories to do it. Therefore, on any given day the total number of calories you burn is the sum of your basal metabolic rate plus all the additional calories burned from the activities you do. Try our Daily Caloric Expenditure Calculator to estimate how many calories you burn each day. Once you know how many calories you burn in a day, you need to figure out how many calories you consume in a day. This is easy, all you have to do is know the calorie content of the food you eat and add it up. Click here to track the calories in the foods that you eat.

Once you know how many calories you burn in a day and how many calories you consume in a day it's easy to calculate if you are losing weight or gaining weight, and how quickly.

As an example, let's pretend that you've determined you burn 2,000 calories a day and eat 2,500 calories a day. Therefore, you are eating 500 calories more each day than you burn and you are gaining weight. How fast are you gaining weight? Well, since there are approximately 3,500 calories stored in one pound of fat, you are putting on fat at a rate of about 1 pound every seven days (since 3,500 calories/pound divided by 500 calories equals 7 days/pound).

For another example, let's pretend that you've calculated that you burn 2,000 calories a day and eat 1,800 calories a day. Therefore, you are burning 200 calories more each day than you eat and you are losing weight. In this scenario, you would be losing fat at a rate of about one pound every 17.5 days (since 3,500 calories/pound divided by 200 calories equals 17.5 days/pound).

Conclusions About Calories

So that's it. There is nothing more complicated to the theory of weight gain and weight loss than what you've read in this article. If you want to lose weight, all you need to do is make sure that you consume fewer calories each day than you burn and you will be GUARANTEED to lose weight. Of course, that being said, you want to make sure that you lose weight in a healthy manner. Although the concept of calories explained in this article reduces weight gain and weight loss to a simple formula, it is important to apply this knowledge safely. If you're trying to lose weight, the best approach is to exercise regularly, get your calories from nutritious sources, and maintain a healthy rate of weight loss. A healthy rate of weight loss is about 1 or 2 pounds each week (depending on how much fat you have available to lose). This corresponds to burning about 500 to 1,000 calories more than you consume each day. Read the Weight Loss Nutrition Tips article for some tips on how to modify your diet so that you consume less calories each day.

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