Many people believe that our overweight and obesity epidemic is caused by a lack of activity – but is that really the case? While most Americans do not move enough to be healthy - decreased movement and activity is not the primary driver of weight gain and obesity!
A new study looking at 34 populations across six continents debunked the movement hypothesis.
Using the doubly labeled water method—the gold standard for measuring total energy expenditure—researchers examined 4,213 adults from 34 populations from hunter-gatherers to highly industrialized societies.
They found that absolute total energy expenditure (TEE), basal energy expenditure (BEE), and activity energy expenditure (AEE) were all higher in more economically developed locations—largely because bodies are bigger there. Importantly, activity energy expenditure and physical activity levels did not significantly change with development level of the population studied.
In other words, the common theory that modern populations burn fewer calories because they move less does not hold up when expenditure is measured with doubly labeled water and appropriately adjusted for important confounding factors.
When body size was accounted for physical activity levels and energy expenditure were very consistent across different populations.
Diet is the Key Factor in Weight Gain and Obesity!
Increased calorie intake – especially from ultraprocessed foods (UPF”s) – was estimated to be ten times more important than changes in activity level in driving modern obesity.
Why Ultra-Processed Foods Drive Overeating
Ultra-processed foods (UPF’s) now account for the majority of calories consumed in industrialized nations—nearly 60% of daily intake in the United States alone—and their link to obesity is becoming undeniable.
There are several other reasons why UPFs have such powerful effects on intake and adiposity:
They're hyper-palatable and highly rewarding. Foods that combine refined fats and carbohydrates (hallmarks of UPFs) hijack the brain’s reward systems in ways greater than the sum of their parts. This “engineered” appeal can drive persistent overconsumption.
UPFs are high in calories and sold in larger default portions. Reducing portion size alone can lower daily intake by ~140–230 calories.
We eat UPF’s faster and feel less satisfied. Beverages are particularly worrisome in this regard, and high intake of sugar-sweetened beverages is consistently associated with weight gain. "Don't drink your calories" is sound advice.
UPF’s are low in protein. To get enough protein to satisfy minimum biological requirements - people unconsciously eat more total calories, a concept known as the protein leverage hypothesis.
UPF’s are low in fiber and micronutrients.
UPF’s contain additives that alter the gut microbiome.
UPF’s are cheap and convenient. On a per-calorie basis, UPF’s are cheaper and more accessible than whole foods, reflecting a structural incentive toward UPF consumption, especially for lower-income families.
Final Thoughts
It is important to remember that population level averages and trends do not account for each person’s unique biology and psychology.. When it comes to weight loss or improving body composition, the most effective approach will be the one that aligns with your physiology, preferences, and lifestyle. This is why professional coaching with a knowledgeable trainer can be so helpful.
For some people, exercise is the easier lever to pull. Increasing calorie burn while maintaining a stable diet can be a sustainable and enjoyable path. Although critics often state that exercise causes increased hunger and compensatory eating, this is not universally true. In fact, research shows that high-intensity exercise—through mechanisms such as lactate production—can suppress appetite in the short term, meaning some individuals may actually eat less, not more, after a hard workout!
Others may find that a stronger focus on their diet is more feasible. It is, after all, often easier to avoid consuming 500 extra calories than to burn the same amount through physical activity. Adjusting the percentage of carbohydrates, fats, and proteins can also help control total caloric intake, satiety, nutrient partitioning, and even energy expenditure itself. For example protein enhances satiety and carries a higher thermic cost to digest, while the quality of carbohydrates and fats can dramatically influence downstream metabolic effects.
The reality is that neither diet nor physical activity is more important than the other. Both are indispensable, not just for weight management, but for optimizing longevity, metabolic resilience, and overall well-being. Obesity may be driven primarily by excess dietary intake at the population level, but for each individual, sustainable health will always require a mix of movement and nutrition.
