The Caloric Balance Hypothesis: Its Basis in the 1st Law of Thermodynamics

The calorie counting idea -- technically known as the Caloric Balance Hypothesis -- comes from one of the most fundamental principles of physics, the 1st law of thermodynamics. This is also known as the Law of Energy Conservation. It tells us that the energy put into a system must equal the energy coming out of it. (For more details about how the first law works, click here.)

So how does this all relate back to calorie counting? Well, a calorie is a unit of energy. Technically speaking, it’s the energy required to heat up a gram of water by 1 degree Celsius. The calories on nutrition labels are technically 'kilocalories' because they're equal to a thousand thermodynamic calories. If this confuses you at all, click here to find out more about what a calorie is.

Calorie counting is done by an instrument known as a calorimeter. Foodstuffs get incinerated, and the amount of energy they release as heat is measured. Different foods have different "caloric values." Fat is more "energy dense" than either carbohydrates or proteins. Proteins and carbs each have around 4 calories per gram. Fats have 9 calories per gram. In other words, a gram of fat is over twice as caloric as a gram of either protein or carbohydrate!

So how do these two ideas we've discussed -- the 1st law of thermodynamics and the concept of calorie counting -- go together? And how does this all relate back to how and why we get fat?

Gary Taubes sums this idea up nicely on page 293 of Good Calories, Bad Calories[1]:

"The calories we consume will either be stored, expended, or excreted. This in turn implies that any change in body weight must equal the difference between the calories we consume and the calories we expend."

He then presents the energy balance equation, which looks like this:

Change in energy stores = energy intake - energy expenditure

Another (although perhaps somewhat less accurate) way of phrasing this equation is:

Change in the Amount of Fat You Have = Calories In - Calories Out

The Caloric Balance Hypothesis rests on two key assumptions:

1) "Calories In" and "Calories Out" drive fat accumulation. In other words, the right side of the equation is "in charge."

2) "Calories In" and "Calories Out" are 'independent variables' as opposed to 'dependent variables.' You can adjust one of these factors without affecting the other. (learn more about the difference between independent and dependent variables here.)

Supporters of the Caloric Balance Hypothesis appear to include:

Here are some choice quotes from public health authorities about the Caloric Balance Hypothesis.

The Department of Health and Human Services website supports the calorie counting theory[2]:

"We’ve been talking a lot about calories. Why? Because the number of calories you eat and drink, and use up through daily activities, is closely associated with your weight. Does it matter what types of foods the calories come from? Yes and no. When it comes to calories and managing your weight, the answer is no. A calorie is a calorie is a calorie."

The USDA's website supports the Caloric Balance Hypothesis[3]:

"Reaching and maintaining a healthier weight is important for your overall health and wellbeing. If you are significantly overweight, you have a greater risk of developing many diseases including high blood pressure, type II diabetes, stroke and some forms of cancer. For obese adults even losing a few pounds or preventing further weight gain has health benefits. How can I move toward a healthier weight? Reaching a healthier weight is a balancing act. The secret is learning how to balance your 'energy in' and 'energy out' over the long run."

The National Cancer Institute's website also argues for the Caloric Balance Hypothesis[4]:

"We know that balancing 'energy in/energy out' -- the calories eaten versus those burnt each day -- is imperative to avoid gaining weight. For many Americans who are overweight and sedentary, eating fewer calories and increasing physical activity is necessary to reach a healthy weight."

And the National Institutes of Health website is a fan of the Caloric Balance Hypothesis[5]:

"Energy is another word for 'calories.' What you eat and drink is energy in. What you burn through physical activity is energy out. ... it’s the balance over time that determines whether you can maintain a healthy weight in the long run."

This is from The American Diatetic Organization[6]:

"Eating right equals calories in minus calories out. Diet trends often focus on one food or one nutrient, promising it will be the magic bullet for losing weight and keeping it off forever. But when registered dietitians analyze a weight loss plan, inevitably it turns out the key is reducing your intake of calories. Budget your diet just like you budget your finances. If you overspend in the calorie department one day, try to make up for it in the exercise department the next."

Obviously these organizations -- The Department of Health and Human Services, The National Institutes of Health, The American Dietetic Organization, The National Cancer Institute, and the USDA -- are not exactly lightweights. So they must be right, right? Case closed? The Caloric Balance Hypothesis is proven?

Not necessarily.

As Gary Taubes puts it (GCBC page 293):

"this faith [in the idea that 'a calorie is a calorie'] is founded on two misinterpretations of thermodynamic law, and not in the law itself. When these misconceptions are corrected, they alter our perceptions of weight regulation and the forces at work."

To read about the theory that Taubes espouses and that this website argues is likely correct, click here.

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Return to main page on the Caloric Balance Hypothesis


1. Taubes, Gary (2007). "Good Calories, Bad Calories." New York: Knopf.

2. "Chapter 5. A Calorie Is a Calorie, or Is It?" "" (2005)

3. "Steps to a Healthier Weight" (April 15 2009) "Energy Balance: The Complex Interaction of Diet, Physical Activity, and Genetics in Cancer Prevention and Control" (Jan 20 2004)

5. "Healthy Weight Basics"

6. "Eating Right = Calories In - Calories Out" (March 31 2009)

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