For weight loss, diet may matter more than exercise

Medical News Today

18-07-2025

The number of people with obesity has increased rapidly over the past 30 years, and numbers are still rising.Obesity results when energy intake from diet exceeds energy use over a prolonged period.People trying to lose weight are advised to increase their activity levels, but a new study has found that reducing the number of calories ingested may be more important than doing more exercise.While emphasizing the health benefits of regular exercise, the research suggests that cutting calories, particularly from ultra-processed foods, could be more effective in promoting weight loss. Obesity and overweight are global health concerns. The World Health Organization (WHO) states that carrying excess weight is associated with a number of health conditions, including cardiovascular diseases, diabetes, cancers, neurological disorders, chronic respiratory diseases, and digestive disorders. According to the WHO, in 2021, higher-than-optimal BMI — body mass index, a ratio of weight to height — caused an estimated 3.7 million deaths from these noncommunicable diseases.It has often been said that a sedentary lifestyle may lead to obesity. However, new research in a wide range of populations suggests that excessive energy intake, rather than a lack of activity, is the main driver of weight gain.A new study, is published in PNAS, suggests that the high rates of obesity associated with economic development are most likely caused by a high calorie diet containing a large proportion of ultra-processed foods.Thomas M. Holland MD, MS, a physician-scientist and assistant professor at the RUSH Institute for Healthy Aging, RUSH University, College of Health Sciences, Chicago, not involved in the study, told Medical News Today that:'This study underscores that while exercise remains vital for overall well-being, the growing obesity epidemic may be more closely tied to what, and how much, we eat. Importantly, it reveals that economic development brings with it both opportunities and risks: improved access to food, but also increased exposure to obesogenic diets.'Obesity: Is it driven by diet type or activity levels?For the 4,213 adults in their study, the researchers used two different measures of obesity — BMI and body fat percentage, which refers to the proportion of fat to total body weight.Participants were from 34 populations over six continents, and had a wide range of lifestyles. They included hunter-gatherers, farmers (both arable and pastoral), and people from industrialized populations.Researchers determined three types of energy expenditure:to estimate total energy expenditure (TEE) they used the doubly labeled water methodthey measured basal energy expenditure (BEE), the amount of energy used to sustain life while at rest, also called basal metabolic rate) using indirect calorimetry or, when no measures were available, estimated it from body sizethey estimated active energy expenditure (AEE) as 0.9 (TEE) – BEE (to assume that 10% of daily calories are expended on digesting and metabolizing food).Absolute body mass, body fat percentage, and BMI were greater, and obesity was more common, in more economically developed populations. However, total energy expenditure was also greater in these populations.Holland explained these findings. He told us that:'On the surface, one might expect that people in more traditional lifestyles would expend more energy due to physical labor. While that holds true in absolute terms, once adjustments were made for body size, the differences in energy expenditure (especially activity energy expenditure, or AEE) were not as stark as presumed.''The key takeaway,' he continued, 'and this is a very important consideration, is that industrialized populations are not necessarily less active, they often have larger bodies that require more energy. However, they also consume more calories, particularly from highly processed and energy-dense foods. This imbalance, higher intake relative to energy needs, appears to be the more critical factor in rising obesity levels.'Processed foods encourage overconsumptionHaving compared the patterns of energy expenditure in the widely varying populations, the researchers concluded that increased energy intake is the primary factor that links overweight and obesity to economic development.They suggest that differences in the quality and quantity of food may be key. Industrially produced foods common in developed countries may be more easily digested, reducing fecal energy loss and increasing the proportion of consumed calories that are absorbed.And they highlight the role of ultra-processed foods in driving obesity. These foods are energy dense, and designed to encourage overconsumption. Processing also increases the percentage of the energy consumed that can be absorbed by the body.In their study, the percentage of ultra-processed foods in the diet was positively correlated with body fat percentage.Holland told MNT that, 'while physical activity has undeniable health benefits, including mental and cardiovascular health, its role in weight regulation may be overstated.''The study suggests that excessive calorie intake, particularly from ultra-processed foods, which are designed to be hyper-palatable (tastier and essentially irresistible) and easy to overconsume by reducing satiety (fullness), is more strongly associated with higher body fat percentage and BMI than low levels of physical activity,' he told us.Reduce calorie intake, particularly from processed foods, to shift weightCommenting on the findings, Mir Ali, MD, a board-certified general surgeon, bariatric surgeon and medical director of MemorialCare Surgical Weight Loss Center at Orange Coast Medical Center in Fountain Valley, CA, not involved in the study, noted that:'If someone is trying to lose weight it is more about what they are eating than about how active they are. I do encourage my patients to exercise to preserve muscle and help burn calories, but I emphasize that if they do not eat the right foods, they will see little weight loss.'Holland advised that, 'ultimately, this study reinforces that health isn't just about 'calories in versus calories out,' but also about the quality of the calories we consume, emphasizing that what we eat may be just as important, if not more so, than how many calories we take in or burn.'He suggested that policy changes could help people lead healthier lives.'Governments can play a pivotal role in shaping food environments and public health outcomes,' said Holland. 'Policies that subsidize healthy food production (e.g., fruits, vegetables, legumes), restrict the marketing of junk food to children, and improve food labeling can help guide healthier choices. Investments in infrastructure, such as safe parks, pedestrian-friendly streets, and community centers, can also promote physical activity.''Furthermore,' he added, 'preventive health programs and equitable access to primary care are crucial for identifying and addressing obesity early, particularly in underserved populations. Public policy is a powerful lever to make the healthier choice the easier one.'