Article: Science: The Calorie Counter

Andy

Andy

Retired committee member
"...

It’s another day in the Pontzer lab, where he and his students measure how much energy people expend when they are stressed, exercising, or mounting an immune response to a vaccine, among other states. By measuring the CO2 in Christina’s breath, he is finding out how much energy she has burned while coping with math anxiety.

At 44, Pontzer’s life’s work as a biological anthropologist is counting calories. It’s not to lose weight—at 1.85 meters tall and about 75 kilograms (6 feet 1 inch and 165 pounds), with a passion for running and rock climbing, he is “a skinny to normal size dude,” in the words of an online reviewer of Pontzer’s 2021 book Burn: New Research Blows the Lid Off How We Really Burn Calories, Lose Weight, and Stay Healthy.

Pontzer is happy to expound on weight loss on The Dr. Oz Show and NPR, but his real mission is to understand how, alone among great apes, humans manage to have it all, energetically speaking: We have big brains, lengthy childhoods, many children, and long lives. The energy budget needed to support those traits involves trade-offs he’s trying to unravel, between energy spent on exercise, reproduction, stress, illness, and vital functions."

.....

"Pontzer is now probing a mystery that emerged from his studies of athletes: There seems to be a hard limit on how many calories our bodies can burn per day, set by how fast we can digest food and turn it into energy. He calculates that the ceiling for an 85-kilogram man would be about 4650 calories per day.

Speakman thinks that limit is too low, noting that cyclists in the Tour de France in the 1980s and ’90s exceeded it. But they were injecting fat and glucose directly into their bloodstreams, a practice Pontzer thinks might have helped them bypass the physiological limits on converting food into energy. Elite athletes can push the limits for several months, as the study of marathoners showed, but can’t sustain it indefinitely, Pontzer says.

To understand how the body can fuel intense exercise or fight off disease without busting energy limits, Pontzer and his students are exploring how the body tamps down other activities. “I think we’re going to find these adjustments lower inflammation, lower our stress reaction. We do it to make the energy books balance.”

That’s why he wanted to know how much energy Christina burned while he grilled her in the lab. After the test, Christina said she “definitely was stressed.” As it went on her heart rate rose from 75 to 80 beats per minute to 115. And her energy use rose from 1.2 kilocalories per minute to as much as 1.7 kilocalories per minute.

“She burned 40% more energy per minute in the math test and 30% in the interview,” Pontzer says. “Think about any other process that boosts your energy by about 40%.”

He hopes data points like hers will help reveal the hidden cost of mental stress. Measuring how stress and immune reactions amp up energy use could help reveal how these invisible activities add up and are traded off in our daily energy budgets. Pontzer knows he’s got his work cut out for him. “Until we can show how the levers get pulled to make these adjustments in energy use, people will always be skeptical. It’s on us to do the next generation of experiments.”"

https://www.science.org/content/article/scientist-busts-myths-about-how-humans-burn-calories-and-why
 
Why is exertion framed as stress? It's well-known that the brain needs a lot of energy, no need to bring psychosocial woo. There is no free lunch, thinking requires energy, so of course it does.

What's amazing is that this is exactly what people who harp about "the mind and the body" should see as obvious, that the brain using energy should be no different than muscles. There is no special kind of energy that separates mechanical from electrochemical, since underneath the mechanical work of muscles it's all electrochemical anyway.

Of course they could be using stress to mean this, same as engineering talks about mechanical stress, but that only adds to the massive confusion of using different words to mean the same thing and using some words to have several unrelated meanings.

There seems to be a belief that intensely using muscles, exercising, is so much more demanding energy-wise than even a high level of concentration and must be special and different. Even though modern humans are literally capable of running (at a moderate pace) for most of a day. Muscles aren't that special, monkeys are too easily impressed by acrobatics.

Frankly most of what people think of stress is probably the cognitive equivalent of this phenomenon, overburdening the brain and probably hitting some heat dissipation limits, what with our huge brains and all. Again, no reason why cognitive exertion should be so completely separate from mechanical exertion, energy is energy, the universe doesn't care how it's used.
 
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I am a bit doubtful about this guy's facts. Mike Stroud and Randolph Fiennes knew how much food they had and how many calories they were burning on their way to the South Pole. My memory is that they found they were burning 7000+ when their sled only had enough for 6000 a day.

I am not sure about the stress idea either.
 
Rediscovered this article on social media. I do think these particular extracts are interesting,

"Pontzer still measures exhaled CO2 to get at calories burned in a particular activity, as he did with Christina’s stress test. But he found that physiologists had developed a better way to measure TEE [total energy expenditure] over a day: the doubly labeled water method, which measures TEE without asking a subject to breathe into a hood all day.

Physiologist Dale Schoeller, now at the University of Wisconsin, Madison, had adapted the method, first used in mice, to humans. People drink a harmless cocktail of labeled water, in which distinct isotopes of hydrogen and oxygen replace the common forms. Then researchers sample their urine several times over 1 week. The labeled hydrogen passes through the body into urine, sweat, and other fluids, but as a person burns calories, some of the labeled oxygen is exhaled as CO2. The ratio of labeled oxygen to labeled hydrogen in the urine thus serves as a measure of how much oxygen a person’s cells used on average in a day and therefore how many calories were burned. The method is the gold standard for total energy use, but it costs $600 per test and was out of reach for most evolutionary biologists."

This seems like something worth investigating in pwME using this method. It may or may not show a difference but given the relatively low impact on patients of the method it seems almost criminal not to do it in order to find out.


"That’s why he wanted to know how much energy Christina burned while he grilled her in the lab. After the test, Christina said she “definitely was stressed.” As it went on her heart rate rose from 75 to 80 beats per minute to 115. And her energy use rose from 1.2 kilocalories per minute to as much as 1.7 kilocalories per minute.

“She burned 40% more energy per minute in the math test and 30% in the interview,” Pontzer says. “Think about any other process that boosts your energy by about 40%.”

He hopes data points like hers will help reveal the hidden cost of mental stress. Measuring how stress and immune reactions amp up energy use could help reveal how these invisible activities add up and are traded off in our daily energy budgets. Pontzer knows he’s got his work cut out for him. “Until we can show how the levers get pulled to make these adjustments in energy use, people will always be skeptical. It’s on us to do the next generation of experiments.”"

This illustrates the impact that mental effort can have, though confounding that is the intentional effort to stress the participant. It would be interesting to see the results for 'non-stressful' mental activity.
 
I'm a bit shocked he would know about calculating energy use from exhaled CO2 but not about double labelled water, the latter is more common in dietary studies since it's easier (participants get the water, and then come back with urine samples throughout a time period, vs. being in a lab to have your CO2 measured).

Agree it should be done. Various forms of calorimetric chambers would also be interesting, either measuring heat expenditure or respiration.
 
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