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🚀The Book in 3 Sentences

• Your daily activity level has little to no bearing on the number of calories you burn each day
• Your metabolism adapts to fit into a constrained daily energy expenditure by regulating where energy is allocated based on what you do in a day.
• Human's rise to the top of the food chain can be explained as a result of the invention of fire and our propensity for sharing.

🎨 Impressions

• Burn is a fascinating book because it flies in the face of everything the exercise industry tells you. Everyone is told if they want to lose weight they should increase exercise and reduce.
• I wish he didn't put so many anecdotes of the Hadza tribe in the book. The book could have been half as long. It was entertaining to read these anecdotes but some of them had nothing to do with the book as a whole.

📖Who Should Read It?

• People interested in the nuances of exercise and metabolism
• Those frustrated with their past attempts at dieting and exercising to lose weight
• People interested in Nutrition Science

☘️ How the Book Changed Me

• I no longer excuse myself to eat massive amounts of food just because I moved a lot in a day. For example, on my long run days of 8.5 miles, I don't eat a massive amount of food just because I moved a lot.
• I realize even more how much diet should be individual. The best diet is the one that works for you.

✍️ My Top 3 Quotes

• "Energy is the currency of life; without it, you’re dead. Your body is made up of roughly 37 trillion cells, each humming along like microscopic factories, every second of every day. Together, they burn enough energy every twenty-four hours to bring eight gallons (about thirty liters) of ice water to a raging boil."
• "The bottom line is that your daily activity level has almost no bearing on the number of calories you burn each day."
• "The brain and liver share the title of “costliest organ.” Your brain weighs a little less than 3 pounds but burns about 300 kcal per day, accounting for 20 percent of BMR."

Main Points

In this fascinating book, Burn, Pontzer changes the way that we should think about metabolism. He defines not only the history of metabolism, what it is, but also how we can change our behavior with a better understanding of how it works.

Much of Pontzer's research for the book came from studying a contemporary hunter gatherer tribe called the Hadza. This tribe gave him insight into the ways our hunter gatherer ancestors used to live before modern industrialization.

❤️‍🔥The History of metabolism

Pontzer believes the story of humanity is a story of energy balance. Our brains take an average of 300 calories to maintain per day even though it only takes up around 3 pounds. The only way we can support them is by evolving incredibly elaborate and beautiful methods of energy metabolism.

🔥Fire

Fire was the major milestone in human evolution. Our brains are incredibly energy intensive. Once humans invented fire we could get vastly more energy out of food we were already eating and also had access to much more foods from other sources.

🤝Sharing

But another thing that makes humans unique to other animals is our capacity for sharing. Unlike our ape ancestors, we regularly share food with others in our tribe. Sharing a meal with someone is one of the most sacred acts of bonding there is.

Getting meat requires a great deal of physical activity to do. Our ancestors needed to be sure if they went out on a meat search and came back empty handed, they wouldn't go hungry. By having the women stay back and forage for food they could share with everyone, men could risk going out and looking for meat. Plus, if they did find a big catch, everyone in the tribe could feast.

This is one of the reasons I believe humans crave social interaction like we crave food. Humans don't function well when they don't feel they are being understood by another human being.

🍴You are what you eat

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You are literally what you eat. The fat, proteins, and carbohydrates you eat provide the kilocalories you require to function on the daily. Through glycolysis, ketosis, gluconeogensis, the aerobic, and anaerobic respiration your food becomes energy for the body.

Because of the incredible diversity of available food, humans have evolved to be incredibly adaptable to the food you through at it. We can thrive on practically any diet. While the details differ, one thing is clear about what we have evolved to eat: humans are evolved to be opportunistic omnivores. We eat whatever is available which is almost always a mix of plants and animals (and honey).

In fact, the only diet that has scientifically been proven to be terrible for us is The Western Diet which has many of its problems detailed in Michael Pollan's book, In Defense of Food.

This is why I believe the best diet is the one that works for you. I personally find|fasting is the best diet for me but if you find the keto diet or vegetarian diet is the most sustainable for you, than by all means stick with that. As long as it's not the Western diet you will probably be fine.

What makes up your metabolism?

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Your metabolism is made up of three things: Basal Metabolic Rate (BMR)--the amount of energy you spend merely existing--accounting for around 60-75% of energy expenditure and further comprised of Nonactivity Exercise Thermogenesis (NEAT)--the energy you spend doing everything outside of exercising and sleeping like hand gesturing and walking, thermic effect of food--the calories it takes to bring your food up to body temp to digest--accounting for around 5-10% of energy expenditure, and finally physical activity--the calories from all of your moving around all day--accounting for around 15-30% of energy expenditure.

⚖️Why I recommend weighing yourself

Even knowing these four parts of metabolism, it's incredibly difficult to calculate for certain how much you burn in a given day. Aside from direct calorimetry which works by measuring the CO2 levels you excrete (this corresponds directly with energy expenditure because CO2 is produced in every reaction producing ATP for energy expenditure), you can use one of the many equations available online to estimate it. However, this estimate could easily be 200 to 500 calories off. When I calculated my BMR it came out to 1636 calories.

This is why I recommend you weigh yourself every morning. This provides an objective source of measurement and gives you an idea for if you are overconsuming or underconsuming calories. I personally find this much easier than trying to count calories and it saves me lots of time as well.

Everyone's metabolism is different. This is why I so adamantly believe that Health is individual. Some people can eat tons of food and not get fat while others can't eat much without having. Generally, the older one gets the slower their metabolism gets.

🔁How your metabolism is regulated

⚡Calories in Calories Out

CICO or Calories in Calories Out is still, Pontzer argues, the main method through which we lose or gain weight. If we burn more energy than we consume, we will lose weight. If we burn less calories than we consume, we will gain weight. Simple as that.

Mark Haub, a professor at Kansas State University, followed a junk food diet for ten weeks to make the point that calories are all that really matter for weight, and tracked his progress on Facebook for the world to see. He ate a Twinkie every three hours instead of normal meals, and rounded out the diet with chips, sugar-rich cereal, and cookies. But he limited himself to 1800 calories per day. At the end of ten weeks, he had lost twenty-seven pounds, went from an “overweight” BMI of 28.8 to a “normal” 24.9, and lowered his cholesterol and triglycerides.

Despite these results, I still believe eating a healthy well-balanced diet is crucial to a good life. Losing weight with a diet doesn't matter if the diet isn't sustainable. I also believe the way you lose weight matters. From the research I have done, I believe Fasting doesn't put you in starvation mode like calorie restriction does.

🍌Diet matters more than exercise for weight loss

In his studies, Pontzer found that Hadza men who were walking on average 10 to 15 miles a day had the same average metabolism as a normal American male who lounges on the couch all day.

What is going on?

One of the major points in Pontzer's book is that your daily activity level has little to no bearing on the number of calories you burn each day. The body seems to want to maintain daily energy expenditure in some narrow window. Pontzer calls this phenomenon constrained daily energy expenditure. This is why increasing exercise is a misguided way of losing weight and it's why Hadza men still burn on average the same amount of calories per day as the average American.

As the old saying goes, "You can't outrun a bad diet."

Apparently, your metabolism responds to long periods of exercise by downregulating other areas of your metabolism to offset the increased calories burned through exercise. It does this through four main ways:

1. Reproduction hormones decrease. I have personally felt this. The more I have exercised ironically the less sexually hungry I am. Sure, I still would like to find a girlfriend but not nearly as much as when I was 30 pounds heavier and more inactive.
2. Stress hormones decrease. Your body stops releasing chronic levels of cortisol. This is one of the reasons for exercises beneficial effects on stress.
3. Your body lowers levels of inflammation. Chronic inflammation which is one of the major precursors to diabetes.
4. Your body increases hunger levels. If you exercise more, you become more hungry. Your brain, particularly your Hypothalamus the master brain hormone regulator, is incredibly good at communicating with other parts of the brain and the endocrine glands to regulate hunger levels from increased exercise. This makes you more likely to eat more in response to your increased exercise offsetting the calories you burned through exercising.

👟Exercise is still great for you

So the message is to stop exercising entirely? No! Exercise is still great for so many other reasons. Exercise might not change the number of calories you burn over time but it does influence the way those calories are spent in the body.

As seen earlier, exercise can help with anxiety and depression by influencing cortisol levels; it can help reduce inflammation and has a whole other bunch of positive effects.

Pontzer believes exercise won't help you lose weight but it will help you maintain it.

My Big Complaint About The Book

One thing that I wish was talked about is the degree to which exercise does have an effect on metabolism. Pontzer talks about elite athletes needing much more calories than the average person but he never gives insight into how lesser athletes (like me) will be affected by significantly above-average exercise.

Other than that, however, the book is absolutely fantastic! Get it for yourself using my Amazon affiliate link.

Thanks to Astrid Helfant for the conversations which fueled this blog post.