Obesity is a complex medical condition marked by excessive body fat that increases the risk of serious health problems such as heart disease, diabetes, high blood pressure, and certain cancers. While it’s often believed that lack of exercise is the primary cause of obesity, a groundbreaking study published in PNAS challenges this assumption. Researchers found that people in both industrialised and developing societies burn a similar number of calories daily, regardless of how active they are. This suggests that physical inactivity may not be the main driver of the obesity epidemic. Instead, the study points to diet, particularly the overconsumption of ultra-processed foods as the leading cause.
What is obesity, and its causes
Obesity is a complex health condition characterized by excessive body fat. It’s not merely a cosmetic issue, it’s a serious medical concern that significantly raises the risk of various diseases. Obesity doesn’t have a single cause. It usually results from a combination of factors, including:
- Genetics: Family history can predispose individuals to obesity.
- Hormonal and metabolic factors: Hormonal imbalances and slowed metabolism play a role.
- Lifestyle habits: High-calorie diets, especially rich in ultra-processed foods, are a major contributor.
- Physical inactivity: Although not the sole cause, sedentary lifestyles can worsen weight gain.
- Environmental factors: Limited access to healthy foods, poor sleep, and stress can also contribute.
- Medications: Certain drugs (e.g., antidepressants, corticosteroids) can lead to weight gain.
“Constrained Total Energy Expenditure” model of the study
Researchers measured total energy expenditure among over 4,200 individuals across 34 countries with lifestyles ranging from hunter-gatherers to city dwellers using the gold standard “doubly labeled water” method. Surprisingly, when adjusted for body size, daily calorie burn was almost identical regardless of lifestyle, debunking the idea that less activity equals fewer calories burned This finding supports the constrained total energy expenditure model, which suggests our bodies regulate energy use within a fixed range, even with increased activity. According to lead author Herman Pontzer, overeating, especially ultra-processed foods, is nearly ten times more responsible for obesity than decreased calorie burn.
Is exercising still important to manage obesity?
The study does not suggest abandoning exercise. While exercise may not significantly influence weight loss on its own, it plays a crucial role in:
- Maintaining weight after loss
- Improving cardiovascular and metabolic health
- Enhancing mood and mental clarity
- Building muscle and bone strength
- Increasing lifespan
Exercise is essential for overall well-being, but controlling calorie intake is more effective for managing obesity.
Health complications of obesity
Unchecked obesity can lead to life-threatening complications, including:
- Insulin resistance and type 2 diabetes
- Heart attacks and strokes
- Liver damage and gallbladder disease
- Reproductive issues and infertility
- Increased risk of surgical and anesthetic complications
- Poor mental health: depression, anxiety, low self-esteem
- Certain types of cancer (Breast, Colon)
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