Written by: Jon Zhang ‘24
Edited by: Meehir Dixit ‘24
Obesity has emerged as a worldwide public health issue. According to the WHO, over 1.9 billion adults were overweight or obese in 2016, almost tripling since 1975 . The rise in obesity stems largely from industrialization and urbanization, as individuals around the globe consume more calorie-rich foods and lead less active lifestyles.
Many people want to get in shape and desire quick solutions to lose weight. Nevertheless, the only tried and true way to lose weight is to run a caloric deficit, which means spending more calories than you consume per day–simple to understand, yet difficult in practice.
To help individuals achieve their weight-loss goals, two schools of thought have emerged: one focused on minimizing caloric intake with a healthy and balanced diet and another involving exercise to maximize calories expended. While both undoubtedly contribute to a healthy lifestyle, researchers and those looking to get in shape have been left wondering which area to prioritize to lose weight most effectively.
One scholar set out to address this mystery; Dr. Herman Pontzer and his team studied the Hadza people in Tanzania and analyzed their physical activity. Lacking modern conveniences such as vehicles and mechanized tools, the Hadza people rely on walking and performing tasks like hunting and foraging completely by hand. The researchers wondered if the participants would use more calories compared to Westerners due to their more active lifestyles .
These researchers studied energy expenditure for 30 Hadza adults using the doubly-labeled water method. In this approach, participants drank water enriched with two different isotopes of hydrogen and oxygen. The researchers later measured the concentration of these isotopes in the participants’ urine samples. This correlates with the body’s daily rate of carbon dioxide production, which is, in turn, proportional to one’s daily energy usage. Pontzer and his team then compared these calculations with data pertaining to populations living in industrialized nations .
The findings showed that Hadza men expended an average of 2,649 calories/day, roughly 200 more than the average man living in an industrialized nation. However, this larger value still fell within the standard error distribution of ± 395 cal/day, indicating that this was not a significant increase. For women, the difference was even less prominent. The average Hadza woman burned about 1,877 calories per day, closely matching the 1,864 daily calories expended by Western women .
Pontzer’s work in the field doesn’t end there. Following his study on the Hadza, Pontzer participated in the Modeling the Epidemiological Transition Study, a large analysis examining physical activity and energy expenditure. Out of 332 participants, calories spent plateaued among the higher range of activity levels compared to the lower end. In other words, while active individuals burned more calories than those leading sedentary lifestyles, the most active participants burned similar levels of calories as the moderately active participants .
The research challenges the assumption that physical activity leads to significantly more calories burned. If physically active individuals do not, in fact, expend more calories than less active individuals, then limiting caloric intake holds the key to determining one’s weight.
“Exercise is actually a crappy tool for weight loss,” Pontzer proclaims, because “you’re never going to run off your Krispy Kremes” .
Comparing Hadza society to industrialized nations also provides historical insight. The Hadza lifestyle embodies a traditional, hunter-gatherer culture, while Western life represents a culture shaped by modernization. Individuals living in both societies used roughly the same amount of calories per day. Pontzer’s findings suggest that the historical transition to less active lifestyles as a result of industrialization did not lead to fewer calories burned.
“If daily energy expenditure has not changed over the course of human history, the primary culprit in the modern obesity pandemic must be the calories consumed,” Pontzer writes . Therefore, consumption of more calories, not a lack of exercise, must have contributed to the rise in obesity levels witnessed in many modern countries today.
So why did the Hadza participants expend roughly the same amount of calories as Westerners? Pontzer believes that the human body adapts to the cost of increased physical activity by reducing the number of calories spent on unseen yet crucial physiological responses. For example, exercise modulates the immune system and can reduce inflammation. By using fewer calories on these housekeeping tasks, the body can accommodate a larger number of calories burnt through exercise .
Contrary to popular belief, exercise’s role in achieving weight loss may be limited. While working out has a vast array of other benefits, focusing on diet may present a more effective weight-loss strategy. All in all, these findings provide greater insight and understanding into human physiology and can help individuals make better-informed, healthful decisions.
 World Health Organization. Obesity and overweight [Internet] [Cited 2021 March 16]. Available from: https://www.who.int/news-room/fact-sheets/detail/obesity-and-overweight
 Pontzer H, Raichlen DA, Wood BM, Thompson ME, Racette SB, Mabulla AZP, et. al. Energy expenditure and activity among Hadza hunter‐gatherers. American Journal of Human Biology [Internet]. 2015 [Cited 2021 March 16]; 27(5), 628-637. DOI: https://doi.org/10.1002/ajhb.22711
 Pontzer H, Durazo-Arvizu R, Dugas L, Plange-Rhule J, Bovet P, Forrester TE, et. al. Constrained Total Energy Expenditure and Metabolic Adaptation to Physical Activity in Adult Humans. Current Biology [Internet]. 2016 [Cited 2021 March 16]; 26(3), 410-417. DOI: https://doi.org/10.1016/j.cub.2015.12.046
 Smith RA. Living like a caveman won’t make you thin. But it might make you healthy [Internet] [Cited 2021 March 16]. Available from: https://today.duke.edu/2019/01/living-caveman-won%E2%80%99t-make-you-thin-it-might-make-you-healthy
 Pontzer H. The Exercise Paradox [Internet] [Cited 2021 March 16]. Available from: https://www.scientificamerican.com/article/the-exercise-paradox/
[Image Citation] Paley M. The Evolution of Diet [Internet] [Cited 2021 March 17]. Available from: https://www.nationalgeographic.com/foodfeatures/evolution-of-diet/