▶ Q&A by Dr. Herman Pontzer of Duke University
▶ “Exercise consumes more energy, but the body ultimately adjusts total calorie consumption on its own… “Exercise has the effect of reducing inflammation and stress response.”
Dr. Herman Pontzer, an evolutionary anthropologist at Duke University and author of Burn, a 2021 book on metabolic science, studied the metabolism of the Hadza tribe, a modern-day hunter-gatherer tribe in Tanzania, in 2012. At the time, Dr. Pontzer predicted they would be burning calories like a furnace. They were in almost constant motion, walking, running, dragging and lifting all day long. But when Dr. Pontzer and his colleagues compared the average daily energy consumption of the Hadja people, adjusted for body size, to that of a typical American office worker, the totals were virtually identical. “It was unexpected,” Dr. Pontzer said.
The results were so surprising that he developed a new theory of how we use calories, called the ‘limited total energy expenditure model’. This model proposes that, especially when we are active, the body and brain can rebalance calorie consumption within a narrow range by slowing or stopping some biological processes, keeping total calorie expenditure constant. “We studied really active people, for example people running across the United States, and we found that they actually burned the same number of calories,” said Dr. Pontzer. “This explains why exercise, while good for your health, has little effect on weight loss.”
This discovery is just one of many discoveries Dr. Pontzer and his colleagues have made in recent years that have challenged established ideas about our metabolism. Now, with the holiday season approaching, calorie and weight control has become an important topic, and Dr. Pontzer talks about the latest scientific facts about our metabolism, the effects of exercise on metabolism, the differences between men and women, and ‘boosting’ metabolism. We talked about whether we could do it. He also talked about why he thinks Thanksgiving is the most humane holiday. The following is a Q&A from the interview.
-I’ll start with questions that can be answered quickly yes/no. Is men’s metabolism faster than women’s?
▲No.
-Does metabolism slow down in middle age?
▲No.
-If you exercise more, will you burn more calories?
▲No, not overall.
-Then let’s ask a more basic question. What is metabolism
▲Metabolism refers to everything that all 37 trillion cells in our body do every day. The unit for measuring this work is the amount of energy required. So metabolism is measured in calories, and calories are a unit of measurement for energy.
-Most people think that metabolism is at its fastest when going through puberty and slows down drastically as one enters middle age. I also believe that men’s metabolism is faster than women’s. But isn’t that true?
▲Where should I start explaining? The main factor that determines how many calories you burn each day is how many cells are working. Larger people burn more calories. The type of cell is also important. Fat cells only burn a little energy, but not very much. So when comparing men and women, the reason men burn more calories than women is because men are usually slightly larger and have less fat. If you were to compare men and women with the same body size and same fat percentage, their daily energy expenditure would be exactly the same.
-So teenagers burn the most calories?
▲That’s right. The most total calories burned during one’s lifetime is probably late adolescence. But when compared to body weight, no one burns as many calories as a 3- to 4-year-old child. Their metabolism is at a fever pitch thanks to the enormous workload these cells perform during growth and development. However, because of their small size, their total calories are still quite low.
-So, does your metabolism slow down a lot as you reach middle age? It definitely feels that way.
▲I am in my late 40s, and I definitely feel that the way I react to food is different from when I ate it in my 20s. But surprisingly, this is not the case. So far, we have measured thousands of adults ranging from their 20s to their 50s and beyond. However, within this range, no difference is seen in metabolic rate after adjusting for body size. However, there appears to be a slight slowdown after the age of 60.
-But many people gain weight in middle age. If you can’t blame a slow metabolism, then what on earth is going on?
▲If it is not a problem in terms of calorie consumption, it may be a problem in terms of energy intake. Why does such a change occur? One reason is because we feel more stressed. At the same time, it becomes easy to develop unhealthy eating habits. Anyone who sees how people actually gain weight will relate. We usually gain a few pounds during the Thanksgiving and Christmas season and then make a New Year’s resolution to lose them. As we get older, we seem to become more accustomed to gaining weight and less concerned about losing it.
-Then where does exercise fit in? I run, and I like to think that the more I run, the more calories I burn and the more weight I lose. But no?
▲I thought so too. But it turns out it’s not that simple. If you exercise today, you will burn more energy today. However, if you significantly change your lifestyle and start exercising regularly and it becomes your new routine, your body will adjust and you will not burn more calories overall. Basically, if you expend more energy exercising, your body will find a way to reduce the energy it uses for other things. But there is good news. Reducing the body’s regulatory processes, such as inflammation and stress response, may also be a big reason why exercise is good for our health.
-Can metabolism be promoted through certain drugs or foods?
▲No, there is no way to accelerate metabolism by eating. There is no evidence that high-carb, low-carb, low-fat, or high-protein diets have a noticeable effect on the number of calories burned per day.
-Then, doesn’t thinking deeply burn more calories?
▲It would be great if just having meaningful conversations at the Thanksgiving table would help you burn off the calories from dessert or discuss chess strategy and help you lose weight. But that’s not the case. It is true that the brain consumes enormous amounts of energy. Basically, your brain uses up the same amount of energy as running 3 miles every day. It’s about 300 kilocalories. But it’s the same whether you’re thinking deeply or absentmindedly.
-Many people eat huge amounts of food on Thanksgiving. Will eating this way increase your metabolism and help you burn extra calories?
▲Thanks to the energy it takes to chew, digest, and process food in our cells, we burn about 10% of the calories we eat. But that is at a minimal level. Realistically, to avoid weight gain on Thanksgiving, you need to eat less. But as an anthropologist, let me tell you what is truly amazing about Thanksgiving. This is the act of sharing food. This is truly unique.
-How is it unique?
▲Other apes do not share food like we do. This is unusual in the natural world. But we did it every day. And whenever a special moment is celebrated, it is celebrated by sharing food. So Thanksgiving is, in my opinion, the ultimate celebration of human evolution. There is meat hunted, plants gathered, conversations held, and tools used. And we share this abundance with our extended family, friends, and kin groups. Is there any other festival that shows human evolution so well? Of course, you need to be conscious of health aspects. But let’s not overlook the fact that for humans, food is a social bond. Especially on Thanksgiving. Try to stop worrying about calories for a day and focus on that aspect. It’s okay to just enjoy the pie. really.
By Gretchen Reynolds>
