Is “Calories in Versus Calories Out” True?
Weight loss and weight gain are complex, but at its core weight is based on caloric balance; calories stored as fat vs. calories used.
This means the old adage that “weight is calories in versus calories out” is only true with a few disclaimers:
- Calories must be stored as fat to equate to weight gain. Many calories are used as energy. Learn about metabolism.
- Not every type of macronutrient (protein, carbohydrates, or fats) is equal. See “is a calorie just a calorie?“
- And generally, an individual’s ability to gain or lose weight is influenced by a number of other factors including what they eat, how they exercise, sex, age, body type, conditions, nutrition, metabolism, and more.
Below we explain the ways weight is based on caloric balance and what that means.
A People love to present calories-in calories-out as a myth… This is a sort of odd trend that is focused on showing that there is more to weight loss and weight gain than caloric balance. This is true, but it doesn’t affect the fundamental truth that weight is based on calories stored versus calories burned, it just expands on it.
FACT: We are saying that weight loss and weight gain is “calories in versus calories out”. When we pair this with the knowledge that “calories on the label isn’t equal to the calories we store“, we get a clear picture of how weight loss works in regards to food (exercise is another matter).
What is a Calorie?
- Small calorie: the energy needed to raise the temperature of 1 gram of water through 1 °C (now usually defined as 4.1868 joules).
- Large calorie: the energy needed to raise the temperature of 1 kilogram of water through 1 °C, equal to one thousand small calories and often used to measure the energy value of foods.
Small Calories Versus Large Calories
What we think of “calories” are large calories. 1 large calorie (1kcal) = 1,000 small calories.
According to CDC.gov calories count:
- A calorie is defined as a unit of energy supplied by food. A calorie is a calorie regardless of its source. Whether you’re eating carbohydrates, fats, sugars, or proteins, all of them contain calories. 
- Caloric balance is like a scale. To remain in balance and maintain your body weight, the calories consumed (from foods) must be balanced by the calories used (in normal body functions, daily activities, and exercise). 
How Does the Body Store Calories?
If you eat excess calories, your body stores the energy as glycogen or fat to use at a later time. These compounds are stored in your liver, muscles, and fat cells. Over time, continually eating excess calories causes your body fat stores to expand, resulting in weight gain. 
Your body also has temporary stores where calories can “hang out” until they are needed to be converted to energy or to be stored in your body. When this storage is full extra calories are stored, or simply flushed from the body.
On the same note, if you create a caloric deficit rather than a surplus your body will burn more calories than it stores, resulting in weight loss over time.
How Many Calories in a Pound?
According to the Mayo Clinic one pound equals about 3,500 calories. In order to gain a pound a person must store an excess of about 3,500 more calories than they burn. It’s worth noting that this is a estimate of how many calories it takes to gain or lose a pound of fat, not an exact number applicable to every person. It should also be noted that only calories burned from fat result in the loss of fat calories, in other words burning calories in temporary storage or burning calories stored in muscle can result in weight loss, but not the ideal weight loss most people would be striving toward.
Get the truth about calories from this great documentary on calories.
How Does the Body Burn Calories? How Does Metabolism Work?
Metabolism is the process by which your body converts what you eat and drink into energy. Or rather, it uses a complex biological process to convert energy (calories) stored in the body (either temporarily or in fat cells or even muscle) into energy used for everything from basic functions like breathing, circulation, repairing cells, and regulating body temperature, to processing food (thermogenesis) to physical activity.
How your body burns calories, and where it takes those calories from is a complex issue involving biology, physiology, nutrition, and the methods and speed at which one tries to lose weight.
Why Do Calories Seem to Affect Different People Differently?
There is a wide range of factors that affects a person’s ability to convert and store energy. This has to do with how active a person is, how much they eat, what they eat, if they have a condition that affects their metabolism, how any given person’s body uses energy, and a number of other factors.
Are All Calories Created Equal? When is Calories-in Versus Calories-out Not True?
Protein doesn’t metabolize the same way fat does, carbs are different too. Each food has it’s own nutritional value and may be more or less filling than other food. Your body may have an easier time with one food or food group than another.
If you generalize calories-in versus calories-out too much, you could be left with a misleading view on calories. A calorie is a calorie only in the general sense, your body is going to get a lot more out of an avocado than a tub of lard and you’ll lose more fat from losing weight slowly and lose more muscle from doing it too quick.
This isn’t a simple issue, but the fundamental truth that weight is calories burned versus calories stored is unaffected by details and semantics. There is a great difference between nutritional whole foods and junk foods, or unhealthy diet and exercise habits versus good ones.