Are all calories the same?

We have been told many times, that a calorie is a calorie. We've been told that on a macronutrient scale, it doesn't really matter where a calorie is coming from. We've also been told that eating too much calories will make us fat, while eating too few calories will make us loose weight.

I decided to write this post because I believe that what we've been told is not entirely correct. Yes, it is intuitive and it kind of fits the basic principles of physics. It is also very easy to understand. But is it the truth?

Recently, I found some information that made me thinking. On this blog, I've already been writing about Sam Feltham, who went through three 21-days long dietary experiments (or as he calls them: challenges). So think about this: same guy, same amount of calories, same period of time, same lifestyle. The only difference was his diet.

So what Sam did was the following. First experiment, he did a cca. 5.800kcal per day LCHF diet. Since he ate much more calories than he required, we would expect that he gained weight. Second, he did a cca. 5.800kcal per day high carb junk food diet. Again, we would expect him to gain even more weight, roundabout the same as on the first experiment, due to the fact that he ate the same amount of calories. And finally, he went to another LCHF diet where he ate exactly his daily caloric requirement. Under the assumptions that what we've all been told is true, we would expect him to maintain the weight that he gained during the previous two fattening experiments.

Below table shows that really happened. Sam tracked his weight and his waistline throughout all experiments.

Sam Feltham's 21-day dietary challenges	LCHF diet (to gain weight)	High carb diet (to gain weight)	LCHF diet (to maintain weight)
Daily caloric intake	cca. 5.800 kcal	cca. 5.800 kcal	cca. 3.600 kcal
Starting weight	85,6 kg	89,7 kg	96,0 kg
Ending weight	86,9 kg	96,8 kg	90,35kg
Difference	+1,3 kg	+7,1 kg	-5,65kg
Starting waistline	79,5 cm	79,5 cm	88,25 cm
Ending waistline	76,5 cm	88,75 cm	80,75cm
Difference	-3 cm	+9,25 cm	-7,5cm

Do you see something strange?

Sam Feltham during his third experiment, where
it would be expected he maintained his weight. But
in fact, he lost plenty of it.

On the first experiment, one would expect Sam to gain a significant amount of weight and waistline. But he only gained a little bit of weight and even lost a bit of his waistline. Then, on the second experiment, with the same amount of calories but on a different diet, Sam gained weight just as expected. And also quite a bit of waistline. Finally, on the third experiment, Sam should maintain his weight, but he didn't. He lost quite a bit of eat (almost as much as he gained on the second experiment) and he also lost plenty of waistline.

To me, Sam's data suggest that what we've been told is not entirely correct. It is obvious that effects of calories on his weight and waistline changed a lot when he switched between low carb-high fat and high carb-low fat diet.

You may say that uncontrolled N=1 experiments don't mean much, and you would be correct: they don't mean much! But what they do mean is that we should at least ask how can this be. So, is Sam Feltham just an exception to the rule that a calorie is a calorie, or is there something that we weren't told?

The first law of thermodynamics

Statement that a calorie is a calorie is in line with the first law of thermodynamics. This law is one of the most fundamental natural laws. It is so fundamental that in Slovenia and in many other countries, we teach children in primary school about it. It speaks about conservation of energy and it says that energy can not be created, nor can be destroyed. It can only be converted from one form to another, but total amount of energy is always the same. The first law of thermodynamics is universally correct, apart from nuclear physics, where it is replaced by another law - but since this is a blog about nutrition, not physics, I won't go into it any further. Especially because our bodies are not capable of nuclear reactions.

Another thing some people often forget is what exactly is a calorie. A calorie is a physical unit which represents amount of energy. Just like a meter is a measurement unit for length, so is a calore a measurement unit for energy.

The first law of thermodynamics in nutrition means that if Sam Feltham eats 5.800 calories of energy, this energy has to go somewhere. Sam didn't create any additional energy (nor any additional calories) and he also didn't destroy any. If Sam eats 5.800 calories, his body now contains 5,800 calories, no matter what kind of diet he is on. Since Sam's body obeys the first law of thermodynamics, we can ask: where did the energy (or "the calories") go in the first and where in the second experiment?

Where do calories go?

There are several different models which help us to analyze distribution of energy around different processes. I decided to use Dr. Peter Attia's model, because it is easy to understand and very intuitive.

Dr. Attia says that there are 4 major things for which we use energy, and this means that there are 4 major places where calories go:

Dr. Peter Attia before and during his LCHF lifestyle. Love
the second T shirt!

• digestion
• activities of daily living
• exercise
• resting metabolic rate

To Dr. Attia's model, I would like to add that some of the calories can also be stored (or retrieved from) the adipose tissue (aka "fat cells"), and some may be left in our poo. Our digestive system is extremely efficient and for this reason, we can neglect the calories that we flush down the toilet. On the other hand, the calories stored in our adipose tissue is the difference between the food we eat and the total sum of calories in the above four categories.

What does it mean for Sam and his first two experiments? Both times, he ate the same amount of calories, but the second time, he stored much more energy in the adipose tissue as the first time. This means that the total sum of caloric expenditure in the first experiment was larger than in the second one. So, let's analyse the categories to see where exactly could the differences take place.

Digestion. Digesting the food we eat requires some energy. There are plenty of muscles involved in digestion and there are complex chemical reactions going on which require heat. But overall, comparing to the amount of energy we eat, digestion uses only a small part of it. Of course, some foods take more than the others to digest and surely, there was some variety in Sam's usage of calories for digestion on different diets. But in the big picture, the differences are so small that they can be neglected. This is also logic from the evolutionary standpoint. If our digestion was very inefficient, we probably wouldn't exist in this world, since even in abundance of food we would end up with only a small portion of energy after digestion would have taken its toll.
Bottom line: changing your diet has very little effect on your energy requirements to digest food.

Activities of daily living. This is energy required to carry us around the world. It allows us to work and to think. Certainly, between people, there are big differences of how much energy the spend on activities of daily living. An office worker will burn much less than construction worker. The amount of energy depends on our lifestyle, habits and obligations. Theoretically, we could significantly influence the caloric requirements of activities of daily living by changing our lifestyle (and our job), but in reality, very few people do it. I mean, think about it: would you change your job to become a construction worker or a miner just to increase the caloric requirements in this category? I would assume that your answer is "no" and because of that, we may assume that energy expenditure on activities of daily living of an individual is pretty much constant. Furthermore, Sam Feltham deliberately followed his regular daily habits quite strictly, in order to keep the energy requirements constant.
Bottom line: changing the diet has no effect on energy expenditure on activities of daily living.

No doubt, a great poster. Too bad it's
a fairy tale. When it comes to being
lean, mind, heart and might don't
have much to do with it!

Exercise. This is by far the most popular category for controlling daily consumption. Again, this varies weekly caloric expenditure by about 2.000 calories. If this person was male, that would be roundabout 13% of his weekly caloric requirements. It is something, but not nearly as much as most people believe. And remember - the 13% difference is only if you went from a couch potato to a fitness fanatic. Every time you would skip a training session, this value would go down for a quarter. Anyway, back to Sam Feltham, who has been a very active person before and during his experiments, so his exercise expenditure in this category didn't change.
from person to person. We often hear something like: "Are you fat? Well, do more exercise!" So, let's take a look at the numbers. We could roughly estimate that a person can burn about 500 calories in a two-hour exercise. As you may know, it is not recommended (nor very practical) to exercise more frequently than 4 times per week. So I would say that someone who went from a total couch potato with no exercise to a full on fitness fanatic can increase his
Bottom line: it is possible to burn more calories with exercise, but in total energy expenditure, the amount is relatively small. Much smaller than most people would expect. It is also very sensitive to human error (i.e. skipping training sessions).

Resting metabolic rate. In the three caloric categories analysed so far, nothing has changed for Sam. So let's take a look at this last one. It is an important one too, since resting metabolic rate is the amount of calories we need for our body to function properly. We use it to breathe, to fuel our heart and internal organs, to think, to maintain our body temperature etc. It is the only of the four categories where we burn energy non-stop, 24 hours per day. Furthermore, resting metabolic rate takes plenty of calories, comparing to the other three categories. Dr. Peter Attia made and experiment on himself, when he switched from western to LCHF diet. He noticed that his resting metabolic rate more than doubled! This means that after he changed to LCHF, he burned more calories while sleeping, thinking, to pump his heart and to fuel all those important biochemical reactions in his body. Sam Feltham didn't measure his resting metabolic rate, but since he didn't change anything in the other three categories, we have a good reason to believe that there was a change in this category.
Bottom line: according to Dr. Peter Attia's measurements and Sam Feltham's experience, nutrition has a significant effect on resting metabolic rate. And since resting metabolic rate takes a big part of our caloric consumption, the effect of nutrition on our total caloric consumption is significant.

So, what happened to Sam Feltham? Let's summarize:

• no considerable changes in energy required for digestion;
• no changes in daily activities;
• no changes in exercise;
• LCHF diet seems to raise resting metabolic rate in comparison to a high carb diet;

Human body is not an internal combustion engine!

For an internal combustion engine, a calorie is a calorie. Think of your car. If you fill up your tank and go for a long lazy drive, you will do more miles. It wouldn't burn plenty of fuel (calories) per mile and hence do more. But if you would go for a sporty drive with lot's of accelerations and high revving, you would do less miles with the same amount of fuel.

If you would believe that your body and a combustion engine are based on a similar concept, you would say that all you need to do to loose weight is to put less fuel in your tank and drive around like crazy. Specifically: eat less - exercise more. But our body is not a combustion engine and even if it was, this would be a bad advice.

1. You would be hungry all the time, and that would have a bad impact on the quality of your life.
2. You would neglect three categories that a body has, but car doesn't (digestion, regular daily activities and resting metabolic rate).
3. You wouldn't change resting metabolic rate, unlike for a car, takes up the majority of calories. And, seems to be affected by the kind of food we eat.

The difference between calories

Sam Feltham's experiments are consistent in terms that in all three cases, he changed his diet, but not his lifestyle. Because of that, three categories of energy expenditures didn't change. The only thing that changed was resting metabolic rate, which seems to be considerably higher at high fat diets, comparing to low fat diets. This is the reason why high fat diets are very effective and do not require any exercise. Please note that I am not saying that you shouldn't exercise. Exercise brings many benefits, but weight loss isn't one of them (I borrowed this quote from Dr. Peter Attia).

I believe it is way easier and also much more effective to increase resting metabolic rate by eating a high fat diet, than working hard to exercise out the excess calories, while eating small portions. But if you choose a more popular diet that is very restrictive on saturated fats and more permissive on proteins and carbs (even if it permits low GI carbs only), cutting down calories and exercise will be your only options.

As a reward for going through another of my extensively long posts, I found an interesting video on Youtube, which illustrates how calories are measured. You will see the difference between toasted oats (high carb) and cheese puffs (high fat). You will see that cheese puffs have way more calories. Without Sam Feltham's experiments, one would easily draw a conclusion, that toasted oats are better. But remember: your body is NOT a combustion engine!

References

It wouldn't be possible to write this post without information generously provided by Sam Feltham, Peter Attia and Andreas Eenfeldt. They all have great websites with plenty of useful and down to earth information and if you have further interest in the subject, I recommend you to check them out.