Beyond the Burn: Unraveling the Exercise Paradox — Why Physical Activity Fails in Weight Loss

Science Claims: Your workouts burn fewer calories than you think!

That I could buy. But when science said walking 5 miles burned the same energy as walking 3 miles, I had a problem.

How can walking two additional miles not burn more energy? Where does that energy go? This statement not only defied the laws of logic but appeared to defy the fundamental laws of nature.

This article is going to show the science behind two things:

1. Exercise is even more important for our health than we thought, and

2. Although exercise is critical to maintain weight loss, it’s next to useless to achieve weight loss.

The Background

With the advent of the doubly labelled water method in the 1980s, data began to question the caloric expenditure of physical activity.

In a study published in 2008, Amy Luke, a researcher in public health at Loyola University Chicago, compared energy expenditure and physical activity in rural Nigerian women with African-American women in Chicago. To her astonishment, there were no differences in daily energy expenditure despite significant differences in activity levels.

Following up on that work, Lara Dugas, along with Luke and others, analyzed data from 98 studies around the globe and showed that populations with all the modern conveniences of the developed world have similar energy expenditures to those in less developed countries, with more physically demanding lives.

In 2012, anthropologist Herman Pontzer went to Tanzania to live with the Hadza, one of the few remaining hunter-gatherer tribes.

For 11 days, Pontzer and his team tracked the movements and energy expenditure of 13 men and 17 women ages 18 to 75, using a doubly labelled water technique — the best-known way to measure the carbon dioxide we expel throughout the day.

The results were astonishing. While the hunter-gatherers were physically active and lean, the lab results showed that they burned the same number of calories as the average American or European, even after the researchers controlled for body size.

As Pontzer said, “We looked at the data in every way imaginable, accounting for effects of body size, fat percentage, age and gender. No difference.”

How was it possible? What were we missing? What else were we getting wrong about human biology and evolution? How could hunting and foraging Hadza burn the same energy as sedentary Westerners?

In search of answers.

Following the Hadza study, Pontzer wanted to account for the Exercise Paradox.

So he piloted a large collaborative effort to measure daily energy expenditure among primates: monkeys, apes, lemurs, and humans. He found that captive primates living in labs and zoos expend the same number of calories each day as those in the wild despite apparent differences in physical activity.

In 2013, Australian researchers found similar energy expenditures in sheep and kangaroos kept penned or allowed to roam free.

But Pontzer went even further. He wanted to compare individuals instead of population averages.

In a classic, multiyear analysis known as the Modeling the Epidemiological Transition Study (METS), Pontzer et al. recruited more than 300 participants who wore accelerometers (similar to a Fitbit) 24 hours a day for an entire week while their daily energy expenditure was measured with doubly labelled water.

The study found that daily physical activity was only weakly related to metabolism. On average, couch potatoes tend to spend about 200 fewer calories each day than moderately active people: the kind of folks who get some exercise during the week and make a point to take the stairs. But more importantly, energy expenditure plateaued at higher activity levels: intensely active people burned the same number of calories each day as moderately active ones.

Even when people push things to the extreme, like ultra-marathon runners or Tour de France participants, they burn more energy, but their overall energy expenditure isn’t near what we would predict. In fact, the evidence suggests that over a long enough period, their bodies would adjust to bring them back to a lower “normal” metabolic range.

The Explanation … “Speculation!”

How does the body adjust to higher activity levels and still keep daily energy expenditure in check?

Although the data is irrefutable, scientists like Pontzer admit that they are unsure why the activity cost isn’t directly correlated with the amount of activity.

The speculation is that people with high activity levels change their behaviour in subtle ways that save energy, like sitting rather than standing or sleeping more soundly.

But then, Pontzer adds, “the data suggests that although these behavioural changes might contribute, they are not sufficient to account for the constancy seen in daily energy expenditure.”

Another possibility is that the body makes room for the cost of additional activity by reducing the calories spent on the many unseen tasks that take up most of our daily energy budget: the housekeeping work that our cells and organs need to keep us alive. Saving energy on these processes could make room in our daily energy budget, allowing us to spend more on physical activity without increasing the total calories spent daily.


In a recent Harvard Podcast Interview with Pontzer, he noted that the Hadza don’t get heart disease, Type 2 diabetes, or reproductive cancers at the levels we see in the US.

There seems to be a sort of energy compensation, a re-juggling of the energy budget, which is one of the big reasons they’re so healthy compared to us in terms of those non-communicable diseases.

All this explains why exercise is so critical to our health while at the same time being a pretty poor tool for weight loss.

According to Pontzer; “When it comes to exercise, if you push it as hard as you can for as long as you can, you might see some weight loss, at least initially, but eventually your body kind of rights the ship. The long-term expected weight loss from exercise alone is about 2 kilograms … less than five pounds.”

All of the above can be reduced to a well-known phrase: 

“You Can’t Out Run a Bad Diet.”

Although I still have a hard time accepting it … now I know why.