Exercise is an Inefficient Method of Weight Loss

By Jason Fung, MD

  • Most people today are about as active as in the past
  • Most people compensate for vigorous exercise by being less active the rest of the day
  • Increasing exercise has little effect on weight loss
By Jason Fung, M.D., Co-founder of The Fasting Method


Diet and exercise, common strategies for reducing calories for weight loss, are usually treated as equally important. Many people also believe that the lack of daily movement plays a large role in today’s obesity epidemic and that primitive societies moved more, and therefore had less obesity problems. This is sometimes called the “Cars” hypothesis. Prior generations used to walk everywhere and now we drive. They burned off a lot of calories and avoided widespread obesity with all this inadvertent exercise.

Like any good deception, this one sounds pretty reasonable at first, but it is just not true. Researcher Herman Pontzer found one such modern day hunter gatherer society – the Hadza in Tanzania.  Many days they will travel 15-20 miles to gather food.  With all that walking, you might think that you burn way more calories than a modern-day office worker. Wrong.  In the New York Times “Debunking the Hunter-Gatherer Workout” he discusses the surprising results.


We found that despite all this physical activity, the number of calories that the Hadza burned per day was indistinguishable from that of typical adults in Europe and the United States. We ran a number of statistical tests, accounting for body mass, lean body mass, age, sex and fat mass, and still found no difference in daily energy expenditure between the Hadza and their Western counterparts.

What was that again?  There is no difference in daily calories burned between the walking-all-day Hadza hunter gatherers and my own lazy, car-sitting ass?  Yes. Oui. Ja. How can this be? The reason overall daily activity stays relatively constant is called compensation.  The Hadza, who were walking all day, reduced their physical activity when not necessary.  Those North Americans who were sitting all day, on the other hand, likely increased their activity when they had a chance.

Think about it this way.  If you have been walking all day gathering roots and bugs to eat, the last thing you want to do in your spare time is to go for a 10 km run.  On the other hand, if you have been sitting in a meeting all day, then a 10 km run after work sounds pretty good.

Exercise or lack of?

What about this idea that we are so much lazier than we used to be and that is why we got fat? Well we can compare modern day humans, not only to prior generations, but also to other wild mammals – lions, tigers, and bears, oh my. Let’s look at this article entitled “Physical activity energy expenditure has not declined since the 1980s and matches energy expenditures of wild mammals”

Energy Expenditure Over Time

Physical activity energy expenditure was measured using doubly labeled water for the period from the mid-1980′s to the mid 2000′s (see above graph). Contrary to the ‘Cars’ hypothesis, physical activity has NOT decreased since the 1980′s but actually increased. This means that people, in general, were more active than before. But the authors went even further, calculating the predicted energy expenditure for wild mammals which is predominantly based on body mass and ambient temperature.

Compared to wild mammals, humans in 2020 are not less physically active than its wild mammal cousins such as the vigorous appearing cougar, fox and caribou.  Here’s the researcher’s conclusions.

“As physical activity expenditure has not declined over the same period that obesity rates have increased dramatically, and daily energy expenditure of modern man is in line with energy expenditure in wild mammals, it is unlikely that decreased expenditure has fueled the obesity epidemic.”



Exercise is not nearly as effective for weight loss as we think because of compensatory mechanisms. We tend to compensate for vigorous activity (eg. exercise) by reducing activity in ‘spare’ time so that overall activity is unchanged. In this study “Physical activity, total and regional obesity: dose-response considerations.” There was no effect of exercise on weight loss in most long-term studies.

There is significant variability in the studies. Some showed strong benefits and others showed none at all. When you consider them all together, there is no indication that increasing exercise increases weight loss, just as there is no indication that calorie restriction increases weight loss. Here’s the bottom line.  There is no measurable association between obesity and physical activity.  I’m not saying exercise is not good for you.  It just doesn’t work that well for weight loss.

We only believe that exercise is effective for weight loss because it has been drilled into our heads since primary school. Basal energy expenditure (BEE) is estimated to be roughly 12-15 calories per pound.  In the bed bound state (lying in bed all day), caloric needs are estimated to be 1.2 times BEE.  So, for a 140-pound person, the estimated daily caloric needs are 2200 – 2500 calories per day.

If we now start to exercise by walking at a moderate pace (2 miles/hour) for 45 minutes every day, that would burn roughly 104 calories.  In other words, that will not even consume 4% of the BEE.  And that is assuming you do this every day.

The immutable fact remains that the vast, vast, vast majority (96%) of caloric intake is used to heat the body and other metabolic housekeeping (keep the heart beating, breathing, digestion, brain function, liver and kidney function, etc.).

Exercise is good for you.  There are many benefits to regular exercise – better muscle tone, increased insulin sensitivity of muscles, increased strength and increased bone density.  So, I am not suggesting that you should not exercise. YOU SHOULD GET REGULAR EXERCISE.  Just don’t expect that you will lose weight.

In the end, the well described phenomenon of compensation can be summed up in one photo:

That is – yeah, we’ll do the exercise, but we’ll take the escalator to the step classes that we paid for.

We need to focus our attention on the 95% portion of the equation.  That means that while exercise is important for overall health, when we are talking weight loss and diabetes, we need to focus on the diet part.


For more, see The Obesity Code.

Learn more about Pique Fasting Tea.

For fasting education, support and community, go to The Fasting Method.


Jason Fung, MD

By Jason Fung, MD

Jason Fung, M.D., is a Toronto-based nephrologist (kidney specialist) and a world leading expert in intermittent fasting and low-carb diets.

Share this article with a friend

More articles you might enjoy…