A Calorie is a Calorie – Part II

By Jason Fung, MD

This is a continuation of our discussion of calories – click here for Calories part I.
A calorie is a calorie. This is obviously true. Just like a dog is a dog, a dollar is a dollar, or a desk is a desk. There are many different kinds of dogs and desks but the simple statement that a dog is a dog is true.

Are all calories equally likely to cause weight gain?

However, that is not really the question we are asking. The real question we are asking is “Are all calories equally likely to cause fat gain?”
A calorie is simply a unit of energy. It is the energy released when certain foods are burned in a laboratory. Certain foods contain more, and some less. It doesn’t matter whether these foods are protein, fat or carbohydrate. We can burn them in a laboratory (or in our bodies) and determine the amount of heat released.
Some people believe that only the total daily caloric intake matters to weight gain. It does not matter whether we eat salad or ice cream, in the end they can all be reduced to calories. Hence the saying “A calorie is a calorie”.
This is a relatively new belief. Back in our grandmothers day – say around 1900’s, it was ‘common knowledge’ that obesity was caused by sweets and starchy foods (refined carbohydrates). If you wanted to lose weight you cut those out and you lost weight. Nobody, they would argue, got fat eating broccoli.
In other words, they believed that calories were not all equally likely to cause weight gain. Some foods, like sweets and breads, would cause obesity but others would not. A calories is not a calorie. In fact, they likely did not even know what a calorie was. So who is correct?
Let’s look at this equation:
Fat = Calories in – Calories out
Let’s ask the question “Does ‘Calories in’ matter?”. First, we must assume that changing ‘Calories in’ does not change ‘Calories Out’. That is, they are independent of one another. We assume that what we eat has no effect on how much caloric energy is used. We will see later that this is completely false.
If we reduce all food simply to their caloric component, then we can compare what goes in (energy) to what goes out (energy expenditure).
Let’s look at an analogous situation. Let us think about dollars instead of calories. A dollar is a dollar.
Fat Wallet = Dollars in – Dollars out

Fat Wallet

Now let’s ask the question “Does ‘Dollars in’ matter?’
Let’s suppose that I run a cookie store. I buy cookies for $1 and sell them for $2. If I sell 10 cookies, I make $10. If I sell 20 cookies, I make $20. So, obviously, in this case the “Dollars in” is important. The higher the dollars in, the more fat my wallet.
However, let’s consider another case. I buy cookies from the bakery for $1 and sell them for $1. If I sell 10 cookies, I make $0. If I sell 20 cookies, I make $0. If I sell more cookies, I don’t make any more money. So, in this case, the “Dollars in” amount is completely irrelevant.
What if I buy cookies for $1 and sell them for $0.50. If I sell 10 cookies, I lose $5. If I sell 20 cookies, I lose $10. In this case the relationship is completely opposite. The more ‘Dollars in”, the more money I lose.
It is easy to see in this example that what is ultimately important is the margin, or the amount of profit per dollar of sales. It is vitally important to know what is happening to ‘Dollars Out”, because that determines profit. Knowing “Dollars in” without knowing “Dollars Out” is not relevant. Assuming that ‘Dollars Out’ stays constant is not correct.
Now let’s apply this to obesity:
Fat = Calories in – Calories out
One of the major assumptions of the Caloric Reduction as Primary (CRaP) theory is that “Calories Out” is independent of “Calories In”. However, that is actually quite untrue. If the ‘Calories In’ is matched by an equal rise in “Calories out” (the margin is zero), then no amount of excess “Calories in” will result in fat storage. If ‘Calories In’ decreases, but is matched with a decrease in ‘Calories Out’, then no amount of reduction in caloric intake will result in weight loss.
Put another way, if you were to eat an extra 1000 calories in, but this was matched by an extra 1000 calories of energy expended this would not result in weight gain. It is possible to expend this extra energy as exercise, but it is also possible this extra energy is expended as an increase in basal metabolic rate (body heat).
For example, would it be possible to eat 5,794 calories a day and still not gain any weight? That is the question that Sam Feltham set out to answer using himself as an experimental subject. The (not so) surprising answer is that it is certainly possible. How, you may ask? As he increased his caloric intake to 5,797 calories/day, his body increased his metabolism to burn 5,794 calories per day. In this scenario he would not gain any weight (which he did not).
On the other hand, suppose we decrease our caloric intake by 1000 calories. If this causes our body to reduce our energy expenditure by 1000 calories, then no weight will be lost.

How to measure energy expenditure

We spend obsessive amounts of time considering the ‘Calories In’ part of the equation without any consideration of the ‘Calories Out’. Why? That is very simple. It is much more difficult to measure ‘Calories Out’ and therefore we make the simple and erroneous assumption that it is constant.
How to measure energy expenditure
There are many metabolically active tissues (brain, kidneys, heart, liver) whose activity is simply very difficult to measure. For instance, suppose that your body decided to reduced the daily energy expenditure by reducing your body temperature from 36.5 to 36.0 C. How would we possibly measure that without fancy and expensive lab equipment and painstaking measurements?
What is crucial is not simply the “Calories in”, but the entire amount of “Calories in – Calories out”. How does changing one of these variables effect the other?
Furthermore, it is vitally important to know the breakdown of the ‘Calories Out’ or Energy Expenditure (EE). Is it voluntary exercise or involuntary resting metabolic rate?
If certain foods (what to eat) or dietary habits (when to eat) affect metabolic rate, then a calorie is not simply a calorie.
Are there food choices (what to eat) and food behaviors (when to eat) that will change Total Energy Expenditure (TEE)? The answer to this crucial question is yes but we have a lot of work to do before we can get to this answer.
Continue here for Calories Part III – Key Assumptions
Begin here with Calories I
Click here to watch the entire lecture: The Aetiology of Obesity 1/6 – A New Hope


By The Fasting Method

For many health reasons, losing weight is important. It can improve your blood sugars, blood pressure and metabolic health, lowering your risk of heart disease, stroke and cancer. But it’s not easy. That’s where we can help.

Jason Fung, MD

By Jason Fung, MD

Jason Fung, M.D., is a Toronto-based nephrologist (kidney specialist) and a world leading expert in intermittent fasting and low-carb diets.

Share this article with a friend

More articles you might enjoy…