A groundbreaking international study has toppled one of the most persistent beliefs about obesity: the idea that sedentary lifestyles in wealthy countries are chiefly to blame for the global epidemic of excess weight. Instead, new research published this week in the prestigious Proceedings of the National Academy of Sciences (PNAS) points squarely at what we eat—particularly the prevalence of ultra-processed foods—as the dominant cause of rising obesity rates around the world (Washington Post).
For decades, both public health campaigns and popular wisdom have portrayed modern societies, with their technology-driven office jobs and reliance on motorized transport, as burning far fewer calories than their counterparts in rural or less developed settings. In Thailand, where urbanisation and Western dietary trends have accelerated in recent decades, this narrative has often shaped both government messaging and family habits. But the latest findings force a major rethink, with profound implications for individuals and policymakers alike.
The international team of researchers, led by a professor of evolutionary anthropology and global health at Duke University, compiled data from more than 4,000 men and women representing 34 nations and diverse cultural groups. Their methodology is notable for its rigour: using “doubly labelled water”—an advanced technique that precisely measures metabolic rates—they tracked how many calories people actually burn in their daily lives. The study included hunter-gatherers, forager-farmers, herders, office workers, and city dwellers, encompassing a full spectrum of lifestyles and economic backgrounds.
The results upend expectations. After adjusting for body size—since people in developed countries often have larger bodies, which naturally burn more calories—the researchers found virtually no difference in the total daily energy expenditure between people in industrialised nations and those leading physically demanding traditional lifestyles. For example, the Hadza hunter-gatherers of Tanzania and white-collar professionals in Norway expend about the same number of calories each day once differences in body mass are accounted for. This challenges the notion that populations in modern societies burn fewer calories due to inactivity or that simply exercising more would reverse the obesity tide.
The explanation, according to this study, lies elsewhere—overwhelmingly in diet. A key insight emerging from the research is the so-called “constrained total energy expenditure model.” This theory suggests the human body tightly regulates its daily calorie burn within a narrow range, regardless of physical activity levels. When individuals repeatedly engage in strenuous movement—such as foraging, farming, or training for a marathon—the body compensates by downregulating other biological processes, such as growth and immune response, keeping the total calorie expenditure constant.
“Our analyses suggest that increased energy intake has been roughly ten times more important than declining total energy expenditure in driving the modern obesity crisis,” the study authors conclude. The main culprit: the growing dominance of ultra-processed foods. These industrial products—defined as “formulations of five or more ingredients”—now form a substantial proportion of daily calories in developed societies, with a strong statistical link to higher body fat percentages, even when total calorie burn remains unchanged.
Some of the world’s leading experts have praised the research. An obesity authority from the University of North Carolina at Chapel Hill called it “a well-done study” confirming long-held suspicions about dietary drivers of obesity. The director of the Food is Medicine Institute at Tufts University reinforced this view, stating, “It’s clear from this important new research and other studies that changes to our food, not our activity, are the dominant drivers of obesity.”
What does this mean for Thailand, where over one-third of adults are now considered overweight or obese, according to the National Health Examination Survey? The rise in waistlines has mirrored increased urbanisation, the spread of Western fast food chains, and a shift away from home-cooked traditional meals to pre-packaged convenience foods. Many Thais, just like their Western counterparts, have tried to battle weight gain with vigorous exercise regimens, jogging in Lumpini Park, joining gyms, or taking part in workplace wellness programmes—often with frustrating results. This study suggests such efforts, while valuable for overall health, will be insufficient unless paired with dietary reform.
However, this is not a green light to give up on movement. The study’s lead researcher emphasised, “We know that exercise is essential for health. This study doesn’t change that.” Physical activity offers a host of benefits, from cardiovascular wellness to mental health and disease prevention. But in the fight against obesity, focusing exclusively on boosting activity levels misses the real threat: the proliferation of energy-dense, processed foods, many of which are high in sugar, unhealthy fats, and artificial additives.
In Thailand, deeply rooted cultural practices—such as communal home-cooked meals, the use of fresh herbs and spices, and the popularity of street-side fruit vendors—could become powerful assets in curbing the obesity epidemic. Yet these traditions are under increasing threat from convenience foods and aggressive marketing by multinational corporations. For example, a Bangkok-based public health official noted in an interview with a local news network that “the traditional Thai diet, rich in vegetables and lean proteins, is being edged out by processed snacks and sugary drinks, especially among younger generations.”
Historical data reinforces the message. In the 1980s and 1990s, Thailand experienced rapid economic growth and urbanization, accompanied by transformations in work and food environments. The once-dominant rice-vegetable-fish meals of rural communities were gradually replaced, in city centers, by fast food, instant noodles, and factory-made bakery items. Public health campaigns continued to encourage exercise, sometimes at the expense of addressing dietary risks. The new findings suggest that a recalibration is needed.
Looking ahead, experts say Thailand must urgently pivot toward strategies that prioritize “food environment” reform. This could mean implementing clearer front-of-package labels on processed foods, taxing sugary beverages (as Mexico and several European countries have done, with positive early results), and promoting access to affordable, healthy foods in schools and workplaces. A leading nutrition expert at Thailand’s Ministry of Public Health has advocated for restrictions on junk food advertising targeted at children, noting that “early exposure to processed foods shapes lifelong preferences and eating habits.” These proposals are supported by mounting evidence that the marketing and availability of unhealthy foods play a critical role in dietary patterns and, by extension, obesity.
Globally, the findings are likely to generate intense discussion among public health authorities, healthcare providers, and the food industry. Within the World Health Organization and Asia-Pacific health forums, calls are already mounting for an overhaul of both school lunch programmes and urban planning policies that make healthy eating easier. Some local governments in Thailand have begun pilot projects to reintegrate fresh produce from local farmers into school meals, while district hospitals are ramping up nutrition counselling services.
The Thai government, for its part, faces tough decisions. On the one hand, efforts to curb obesity through dietary reform confront resistance from industry groups and questions of economic impact. On the other, the mounting costs of obesity-related illnesses—ranging from diabetes to heart disease and cancer—are a growing burden on the national healthcare system. A senior official at the Bureau of Nutrition has highlighted the urgency: “Without decisive action to address diet quality, not just quantity or physical activity, Thailand risks significant setbacks in public health and productivity.”
For individual Thais and their families, this research offers both a wake-up call and a roadmap. It’s not the number of hours spent at the gym or on the football pitch that will ultimately determine the nation’s health, but rather the choices being made at the market, the restaurant, and the family table. Experts recommend practical steps such as:
- Limiting ultra-processed foods and snacks
- Preparing more home-cooked meals using fresh ingredients
- Being mindful of portion sizes and added sugars
- Supporting local food markets that offer unprocessed fruits, vegetables, fish, and meats
- Encouraging schools and community centers to provide nutrition education and healthy meal options
In conclusion, while exercise remains vital for physical and mental well-being, tackling obesity head-on in Thailand demands a shift in focus—away from caloric “output” toward the quality and quantity of what’s on our plates. Public health messaging, school curricula, and policy incentives alike must rise to this new reality. As evidence mounts, the time is ripe for a return to the fundamentals of the Thai kitchen, reinforcing dietary traditions that may hold the key to a healthier future.
Sources: Washington Post, Proceedings of the National Academy of Sciences, Thai National Health Examination Survey Report, WHO Obesity Factsheet