Different but the same
Herman Pontzer is an anthropologist at Hunter College. He studies energy expenditure in humans and great apes to test hypotheses about the evolution of human physiology and anatomy. In a February 2017 article published in Scientific American, he explained how we know this to be true and why it happens.
Working with the Hadza hunter-gatherers in northern Tanzania, he meticulously measured their daily energy expenditure.
Most Hadza burned between 1,500 and 3,000 calories per day, with an average of 1,900 for women and 2,700 for men.
The same measurement of North American and European people showed most burn between 1,800 and 3,500 calories per day.
Western women burn on average the same number of calories per day as Hadza women, while Western men burn about 200 more (2,900). For both populations, the more the individuals weighed, the more energy they burned.
This study shows that hunter-gatherers burn as many or fewer calories than Western populations. The energy paradox accounts for the discrepancy.
Energy paradox under the microscope
So you may be thinking: “That’s the average American lard! I am a trail runner! I am a calorie burning machine!”
To examine whether individual fitness fundis and couch potatoes in the same population had different energy expenditure, Herman Pontzer fitted 300 participants with fitness trackers. They found that on average, an inactive person used only 200 calories fewer than an active person.
Another important finding was that a person who deliberately takes the stairs and works out a couple times a week has roughly the same energy expenditure as people with intensely active daily lives.
“Our data indicate that, contrary to received wisdom, humans tend to burn the same number of calories regardless of how physically active they are.” Herman Pontzer, anthropologist
Capetonian registered dietitian Jessica Kotlowitz is skeptical that elite athletes will have the same energy expenditure as their active peers. “Conditioning is very important when considering energy requirements,” says Jessica. “Our bodies adapt to what we do all day.
“It is uncertain whether these results would be found in high-level athletes, or those training at high intensities.
“In fact, laboratory isotope studies in athletes have found very high energy expenditures, and certainly in practice we see that high-level athletes require high energy intakes.
“Intensity of physical activity also affects the fuel your body uses for energy (fat vs. carbs) which would affect the changes in body composition in response to this activity. Something often not considered in the old-fashioned calories in versus calories out approach.”
Diet vs exercise
Jessica explains weight management: “The body of evidence regarding exercise and weight management definitely points to the fact that exercise has a limited role to play in weight management and is largely ineffective at inducing weight loss.
“Most health professionals know this and most of the emphasis on increasing activity for weight loss is a push from Big Food. (Why give up McDonalds when you can just go for a run and burn it all off?)
“This may be due to the fact that we have adaptive mechanisms (as the Scientific American article explains) which limit energy expenditure in response to energy output or it may also partly be due to compensatory overeating (exercise increases appetite so you are likely to make up for your calorie burn by eating more).”
Do our bodies use energy differently?
The researcher theorised that our bodies allocate less energy to background functions to free up calories for activity.
In lab animals, increasing daily exercise didn’t increase energy used, but it did slow down tissue repair and reproduction cycles. It’s possible humans save energy in a similar way.
“If our bodies have adaptive mechanisms which shunt energy away from less important biological functions, towards activity outputs in order to maintain a set energy balance, what are the consequences of not replacing this energy?” asks dietitian Jessica.
“For example, in athletes who have huge energy outputs, and who are only eating a standard energy input, what will happen to the biological functions that are being compromised in order to conserve energy for activity? Will they stop menstruating or become infertile? Will their muscle recovery or immunity be compromised?
“Athletes who don’t eat sufficient calories and carbohydrates to replace energy expenditure have reduced recovery. Although the body manages to maintain energy equilibrium by relying on fat stores and shunting energy away from less important jobs, the long term effects of doing so will be detrimental to our health. This is more of a short-term survival strategy (thanks evolution!) than a longevity and disease prevention strategy and probably has limited application in athletic populations.
“But recreational athletes should be made aware that exercise will not induce weight loss and that nutrition is the most important factor in weight reduction.
Don’t stop running.
The obsession with being lean has taken precedence over being healthy. Exercise may not help you lose weight, but it does help you live a longer, more fulfilling life. But only if you eat healthily. Because as we all know, you can’t outrun a bad diet.
If you have a balanced diet, and are active, there’s no reason to create imbalance by under-eating or overexercising. Forget the scale, focus on the trail.
The Energy Paradox article was originally published in TRAIL 25.