Duke professor Herman Pontzer’s Burn (2021) is a must-read for anyone who cares about their weight and isn’t already familiar with Constrained energy expenditure. That’s probably most of us.
Still, we only give it three stars because we think the book suffers from poor organization and drags on longer than needed. Burn could have been three essays instead of a book – one a memoir of his work with the Hadza and his early research career; the second about constrained energy expenditure, diet, exercise, and health; the third his opinions about society and our use of energy in aggregate.
Herman Pontzer is an Associate Professor of Evolutionary Anthropology and Global Health at Duke University. His lab studies “evolutionary energetics and ecology”, or in other words “How did the human body evolve, and how does our species’ deep past shape our health and physiology today?”.
Burn is about his research on how human beings consume and use energy – that is, diet and metabolism.
Pontzer complements clear descriptions of our current best understanding of metabolism with vivid anecdotes from his field and lab research. You’ll read a story from his time working with a particular modern-day hunter-gatherer society, the Hadza, and then flip the page and learn the basics of how carbohydrates are turned into energy.
The stories Pontzer includes are entertaining and help readers understand the science in context, but they sometimes feel disjointed from what comes before and after.
In contrast, his explanations of physiological processes are coherent and expressed in simple terms. For example, “Metabolism is a broad term that covers all of the work your cells do. The vast majority of this work involves pumping molecules in or out of cell membranes and converting one kind of molecule into another.”
We’ll summarize a few key points from the book about energy and weight (there’s a lot we’re leaving out, so go read the book for yourself!):
Constrained energy expenditure
First, and most fundamental, how much you weigh is a function of how much energy you eat and how much energy you burn. If you ingest more than you use, your body stores that energy as fat.
“Constrained energy expenditure means that increasing daily activity through exercise or other programs will ultimately have little effect on the calories burned per day…Weight is fundamentally about energy balance: if we eat more calories than we burn, we gain weight; if we burn more than we eat, we lose weight.”
You might be able to burn more calories for a short period of time, but your body will quickly adjust and return to its normal burn rate. In Pontzer’s words, we need to think of our metabolism more like our body temperature – absent trauma, it’s not changing much.
Second, diet matters a lot. While we can’t change how much we burn, we can change how many calories we consume. From the perspective of weight, a calorie is a calorie. What matters most is how much you eat, not what you eat.
That’s not to say that what you eat is irrelevant. Eating foods that leave you feeling full makes it easier to reduce how many calories you eat in a day. If you reduce your caloric intake, your body will complain, making you hungry.
In today’s world of abundant, highly engineered food we encounter many options that don’t leave us feeling satiated, driving us to eat more. “Diets that work, including both low-carb and low-fat varieties, are effective because they cut out low-satiety foods and help us feel full on fewer calories.”
In general, foods with more fiber and protein will help you feel full sooner. The rule of avoiding the middle of the grocery store, where all the prepackaged food is kept, in favor of the perimeter where the produce, meat, and dairy is kept, seems like a good rule of thumb.
When it comes to diets, Pontzer is dismissive of the notion that there was a single “paleo” diet – what our ancestors ate varied wildly across climates, seasons, and societies. In fact, he emphasizes that “none of this advocates for or against any particular diet. If you find a diet that works for you, one that keeps you at a healthy weight and free from metabolic disease, keep with it…All diets work if you stick to them, because all diets reduce caloric intake.”
Additionally, there are times when you want to gain weight and you should eat more. The most important one is when a woman is pregnant. Also, if you’re trying to gain muscle by lifting a lot more.
Exercise still matters, just not how you think it does
Third, exercise still does matter. In fact, it matters a lot, and in ways most of us are ignorant of.
Because our bodies have a daily calorie budget, if we use calories to exercise, that means those calories can’t fuel some other activity. What our bodies choose to trade off against helps our overall health. For example, exercise limits how many calories go to our:
- Immune system, which for normal healthy people means less unnecessary inflammation and metabolic diseases
- Reproductive hormone production, which can reduce the likelihood of cancers in the reproductive systems.
- Stress response, which is one reason why exercising regularly improves our moods
Additionally, if you’ve lost a lot of weight, exercise will help you keep it off. This is the one major exception to the rule that exercise doesn’t directly help with weight loss.
What does this mean for people who work out at home?
Keep exercising! If anything, this book should reinforce your commitment to fitness.
If you’re trying to lose weight, consider what your current plan is and whether it still makes sense in light of the information in Burn.
Reflect on your diet and eating habits. Do you eat even when you already feel full? Do the foods you eat make you feel full or are they “empty calories”?