Obesity, Yet Fit – the Meaning of This Term

The concept of "Fat but fit" emerged in the 1990s. It refers to individuals who, despite being overweight, demonstrate high physical fitness. Some research suggests that high cardiorespiratory fitness (CRF) can mitigate the adverse effects of excess body weight. CRF is defined as the capacity of the cardiovascular and respiratory systems to efficiently deliver oxygen during prolonged exercise. In 2015, S. J. Dankel, J. P. Loenneke, and P. D. Loprinzi published an analysis of data from the NHANES program, involving over 11,000 participants aged 38 to 85. The researchers categorized the subjects based on body weight (overweight/obese/normal) and physical activity levels (active/inactive). The findings revealed that only physically inactive individuals had an increased risk of all-cause mortality. The authors emphasize the importance of focusing on physical fitness and advocate for routine assessments of patients' physical capacity.

Excessive body fat is a recognized risk factor for osteoporosis. Beyond the mechanical strain of increased body weight, pro-inflammatory cytokines released by adipocytes also adversely impact bone health. Conversely, physical activity exerts a beneficial effect on bone density. In light of this, A. Torres-Costoso and colleagues investigated whether individuals with excess body fat but high physical fitness (CRF) exhibit greater bone mineral density compared to those with low fitness. The study involved students aged 18–30 years. Researchers assessed body weight, body composition, and bone density. Additionally, muscle strength (via handgrip test) and cardiovascular fitness (using the multistage fitness test, or beep test) were evaluated. The beep test requires participants to run back and forth over a 20-meter distance between two signals, with increasing speed over time until exhaustion. Results were compared to standardized norms to evaluate aerobic endurance. The findings revealed that individuals with good fitness and stronger muscles, regardless of body fat percentage, demonstrated higher bone density than untrained individuals.

Scientific research indicates that consistent physical activity may significantly reduce the risk of mortality in individuals with coronary artery disease. In a study conducted by P. D. Loprinzi, 766 participants were divided into six groups: individuals with normal body weight, physically inactive; individuals with overweight, physically inactive; individuals with obesity, physically inactive; individuals with normal body weight, physically active; individuals with overweight, physically active; individuals with obesity, physically active. Over an 86-month observation period, 301 participants died. The data analysis revealed that regular physical activity enhances survival rates, regardless of body weight. Physically active individuals exhibited a statistically lower risk of mortality.

Research suggests that excess body weight may contribute to an increased risk of depression. Obesity is often accompanied by metabolic disorders such as diabetes and insulin resistance, which can negatively impact mental well-being. Additionally, societal pressure regarding physical appearance can lead to negative thoughts and lowered self-esteem. However, a study conducted by K. M. Beckofsky and colleagues found that low physical fitness is more strongly correlated with depression than fat content. Physical activity may influence neurotransmitter levels, such as serotonin and dopamine, and reduce stress by lowering cortisol levels.

Research indicates that it is possible to be overweight yet physically fit, though this phenomenon is relatively rare. G. E. Duncan examined data from the NHANES study involving over 4,500 individuals aged 20–49 years regarding body weight and physical fitness. He estimated that only 8.9% of adults in the United States meet the "fat but fit" criterion. Individuals with excess body fat face significantly greater challenges in achieving good physical fitness compared to those with normal body weight. As G. E. Duncan highlights, among obese individuals, 20% exhibited low CRF levels, while 80% achieved moderate to high levels. Among overweight individuals, 12.5% had low CRF levels, whereas 87.5% attained moderate to high levels. This suggests that even with excess weight, high physical fitness is attainable. However, excess body weight increases the risk of hypertension, cardiovascular diseases, and type 2 diabetes. Studies refer to the concept of MHO – metabolically healthy obese, describing individuals with normal insulin sensitivity and lipid profiles despite obesity. This term is not strictly defined. R. E. Brown and J. L. Kruk, in a review article, note that research on MHO is contradictory. Some studies indicate that the MHO phenotype carries a similar risk of cardiovascular diseases as normal-weight individuals. Others refute this, asserting that obesity, even without metabolic disturbances, increases the risk of heart disease and type 2 diabetes. It is estimated that MHO affects only 3–6% of obese individuals. Does being "fat but fit" truly protect against the consequences of overweight? There is no definitive answer. All studies are observational, meaning correlation does not necessarily imply causation. One certainty is that physical activity benefits health, regardless of initial body weight.