For years, it’s been widely accepted that exercise plays a crucial role in weight loss. It increases metabolism and helps burn calories. Nevertheless, recent discussions, including those popularized by evolutionary anthropologist Herman Pontzer, have questioned this view. Pontzer’s hypothesis gained traction in his 2021 book Burn. It suggests that humans burn calories within a narrow range of about 3,000 calories a day. This occurs regardless of physical activity levels. But is this theory truly backed by evidence?
Pontzer’s theory posits that we may increase energy expenditure through physical activity. Yet, our bodies adapt by reducing energy expenditure elsewhere. This reduction occurs particularly through resting metabolism. This, he suggests, means that increasing activity won’t necessarily lead to higher overall calorie burn due to the body’s exercise-induced adaptations.
Pontzer used a pivotal study to support his hypothesis. This study examined the Hadza tribe, a group of hunter-gatherers in Africa. Despite their active lifestyle, the research showed that the Hadza burned no more calories than the average Westerner. This led Pontzer to claim that we burn calories within a fixed range, regardless of activity level. His findings have implications for understanding how exercise impacts our daily calorie expenditure.
Nonetheless, a review of this theory in 2023 found its conclusions to be less convincing. The evidence supporting the theory is largely observational, meaning it observes patterns without establishing cause and effect. The Hadza study was intriguing. However, data from different populations and age groups shows considerable variability in daily energy expenditure, suggesting exercise does play a role.
THE EVIDENCE: DOES EXERCISE INCREASE ENERGY EXPENDITURE?
Unlike observational studies, randomized controlled trials (RCTs) prove cause and effect, making them the gold standard in scientific research. These trials give clearer insights into the impact of exercise on daily energy expenditure.
Several RCTs have shown that structured exercise programs lead to an increase in daily energy expenditure. These programs need to be followed consistently, up to five days a week for six to ten months. Both young and middle-aged men and women have shown increased calorie burn after completing exercise regimens. This evidence directly contradicts Pontzer’s claim that activity levels have little impact on energy expenditure. Commitment to regular exercise is key.
WHY THE INCREASE IN ENERGY EXPENDITURE MAY BE MODEST
While the evidence shows that exercise increases energy expenditure, the increase might not always match expectations. For example, burning 600 calories during a workout doesn’t automatically mean that your total daily energy expenditure will rise by 600 calories. The total daily increase is usually smaller.
Several factors explain why exercise doesn’t have as large an impact on energy expenditure as some may hope:
- Physical Activity Substitution: Sometimes, the exercise you do replaces other activities. These activities are ones you would have done during the day. This results in only a small increase in total calories burned.
- Behavioral Compensation: After exercising, you might naturally reduce your activity levels later in the day. This leads to fewer additional calories burned.
Additionally, it’s important to recognize that exercise is only a small fraction of our waking hours. Spending five hours a week exercising accounts for around 4% of your waking time. It can only have a modest effect on overall calorie burn, yet exercise remains essential for overall health.
UNREALISTIC EXPECTATIONS AND THE ROLE OF EXERCISE IN WEIGHT LOSS
Part of the misunderstanding about exercise and energy expenditure comes from unrealistic expectations about how many calories we burn during workouts. It’s easy to assume that intense workouts should result in significant calorie burn. However, the science shows that while exercise does increase energy expenditure, the effect is not as dramatic as many people expect.
