The benefits of exercise are numerous. Unfortunately, the thing that most people use exercise for is not one of them. we’re talking about weight loss.
The funny thing about exercise is that if it were a drug, we’d all be taking it. There is no better intervention for improving overall health than exercise. Although, weight loss may, which is why you have to control for weight loss in studies on health interventions. Even exercise.
While that may seem contradictory, it’s not. It only seems contradictory because of our skewed perception of how our metabolism works. In the most common paradigm we are exposed to, we are a simple engine that burns through what we ate through physical activity and stores what we don’t as body fat.
Furthermore, we believe we have strong control over the amount of energy we burn. Increasing physical activity increases our total daily energy expenditure, so if we eat too much we can just walk and exercise to take it off.
As it turns out, our metabolism is nothing like that at all. In fact, we have little control over the long term over how much energy we burn. If you start an exercise program today, within 5 months, you’ll burn the same number of calories as you did before you started exercising, even if you’re now running 40 miles a week.
Sounds crazy, huh?
A new book out by Dr. Herman Pontzer called Burn blows the lid off of our metabolism and how it works. Not only is it chock full of insanely good information, it’s a great read and written for anyone to understand.
Let’s dig into some of the bigger points!
Is calorie a calorie, and do calories matter?
I have to be honest, I used to be one of those “A calorie isn’t a calorie” guys. This was the result of getting most of my information from the blogosphere and podcasts. At the same time, I was passionately following the Darwinian/Evolutionary medicine stuff and fully bought into the idea that evolution has some fundamental answers to our health.
The truth is, a calorie is a calorie, it has to be. Just like a mile is a mile and a gram is a gram. Units of measurement, by definition, are consistent. Calories absolutely matter, and from the perspective of evolution, are incredibly important.
Dr. Pontzer summarizes this position so well when discussing his perspective: Evolution is about converting energy into babies. Can’t get more evolution-y than that.
Why calories absolutely matter
If we think about evolution in this light, calories are incredibly important. Calories are simply a unit of measurement for energy. Yes, there are no receptors for calories, but that’s because it’s a unit of measurement, not a physical thing. There are no receptors for grams, but that doesn’t mean low carbers shouldn’t measure grams.
Fundamentally, energy metabolism is after one thing. Whether it comes from carbohydrates, fats, protein, or creatine, our metabolic machinery is going to chop up what we eat to access one thing: the high energy phosphate bonds in our food.
Our metabolism converts this chemical energy into ATP through different pathways, which we use to power everything in our body. We can measure the energy contained within these bonds as calories(Actually kilocalories), or we could measure it as joules.
Regardless of the way you measure it, a calorie is a calorie and calories do matter. The pathways that access these calories change based on our habitual diet and behavioral patterns.
But fundamentally, there may be no more important measurement from an evolutionary perspective than calories. Dr. Pontzer does a fantastic job of laying this out in much greater detail and from a much better narrative style than I’ve ever read before.
Why would energy expenditure be randomly allocated?
I clearly remember reading Dr. Pontzer’s paper on energy expenditure and the Hadza back in 2015, showing that they burn the same amount of energy per unit mass as we do, despite walking 5 miles more a day. I was shocked, this was a complete paradigm shift!
This went against everything I believed about metabolism, and certainly put the kibosh on the idea that I would offset excess food intake with more exercise. But looking back, it makes so much sense after reading Burn that it almost seems silly to have believed it.
Evolutionary success is contingent on being able to extract more energy from the environment than it takes to acquire. Species that are more successful at this will thrive, those that can’t are doomed to fail. But allocation of this energy is equally important.
It makes no sense that this process would be completely random, and that evolution wouldn’t leave an imprint on how we manage our energy budget. In Burn, Dr. Pontzer details how our daily energy expenditure is mostly fixed, and our body fights to keep it that way.
Constrained energy theory
Sure, if you are completely sedentary and decide to walk 5 miles one day, you’ll burn more calories that day. But if you continue to do this for months, you’ll start pulling that energy from different systems that contribute to your metabolic rate. In the end, your body will adjust. This was one of the more clever findings of the Hadza data.
Sure we burn the same number of daily calories as they do, but the Hadza spend more of it on physical activity and less on basal metabolic rate. A sedentary Westerner experiences the opposite.
In this way, our daily energy expenditure is constrained to a specific amount. This happens in all species, and is likely an artifact of how successful we were in the past at procuring energy from the environment. This is known as constrained energy theory, and is a cornerstone of the book.
An average person burns approximately 3000 calories a day in total daily expenditure, split between basal metabolic rate, digestion, and physical activity. There also appears to be some sort of program that dictates where the resources from basal metabolic rate are partitioned, pulling first from non-essential tasks and, more than likely, making other essential tasks more efficient.
And herein lies where the benefits of exercise on health rear their head
The benefits of exercise: Divying up our daily energy budget
You have a daily energy budget that you are looking to spend to promote health. Over the course of evolution, the program that selects how much you burn and where it gets partitioned is determined.
This program was developed in an environment that demanded a good deal of that budget go to physical activity to acquire that energy. So our physiology would like to partition a good block of our daily energy budget to moving about finding food.
But what happens to that energy if we aren’t active? Clearly, from the Hadza data and constrained energy theory, it goes somewhere. Unfortunately, the answer isn’t good news for us. Dr. Pontzer discusses the theoretical basis in the book. One option is to turn up the immune system, which presents as chronic inflammation.
He also discusses several other deleterious effects that have some basis in the scientific literature such as making us more sensitive to stress. Put it this way, it’s no wonder we’re stressed, depressed, sick, and hungry all the time.
Obesity, popular diets, and constrained energy theory
It seems pretty clear based on the data that if your goal is to lose weight, exercise shouldn’t be your top line approach. This doesn’t mean that exercise is completely ineffective for weight loss, there are aspects of managing a healthy weight that exercise is effective for.
Over the long run, though, energy expenditure is fixed. So if you have weight to lose, you have to primarily address energy intake. Dr. Pontzer lays out perfectly why how you do this isn’t really all that important.
You can do low carb, low fat, Keto, Mediterranean, or anything of the like. The only consistent thing that matters is that energy expenditure exceeds energy intake.
Eating in a way that causes you to eat fewer calories than you expend is the key here. This differs from person to person and in no way suggests that you should count calories. In fact, Dr. Pontzer gives some excellent advice on this in the book that eschews over-complicating the matter. He also discusses what I believe to be the primary dietary driver of our obesity woes, but you’ll have to read the book to find out what it is. 🙂
I think this is the meat of the book that most people will find interesting, even those who still believe a calorie isn’t a calorie. Personally, I think that statement is essentially a way to deceive people into thinking the problem is more complex than it needs to be, or that what they’re being sold is the only effective way to lose weight.
It’s also a profoundly stupid statement that I’m glad I no longer utter. If evolution is about turning energy into babies, a measurement of energy is essential to that end.
The benefits of exercise to our health are numerous. In essence, optimal health and happiness are dependent on getting high levels of physical activity every day. This is an artifact of our evolutionary past.
Dr. Pontzer’s book Burn details how evolution has shaped our metabolism to be what it is. Whether you are a couch potato or a hunter gatherer, your body looks to burn the same amount of energy every day.
This is consistent among species, whether in the wild or in captivity. Getting adequate physical activity is essential to making our metabolic machinery partition resources towards health. It helps us be more immune to infection and resistant to stress.
If you want a deep understanding of how your metabolism works and how to leverage this information to improve your health, I can’t recommend this book enough.