Prevalence of excess adiposity and clinical obesity in a Mexican nationally representative survey
A nationally representative study of Mexican adults reveals that relying solely on Body Mass Index (BMI) underestimates clinically relevant obesity, as nearly a quarter of individuals with clinical obesity have a BMI below 30 kg/m², highlighting the need to incorporate waist-based measurements for more accurate identification of excess adiposity and metabolic risk.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
For decades, doctors and public health officials have relied on a single, simple number to decide if a person carries too much body fat: the body mass index, or BMI. This calculation compares a person's weight to their height. While it is a quick tool for sorting large groups of people, it has a blind spot. It cannot tell the difference between heavy muscle and heavy fat, and more importantly, it cannot see where that fat is stored. Fat tucked deep inside the belly, wrapping around vital organs, is far more dangerous to heart health and metabolism than fat stored under the skin or around the hips. Because of this limitation, a person could have a BMI that looks normal on paper while harboring a dangerous amount of internal fat, leading to a false sense of security about their health risks.
A team of researchers in Mexico set out to see how often this blind spot misses the mark in a real-world population. They turned to a massive, nationally representative survey of Mexican adults conducted between 2018 and 2019, which included measurements from over 13,000 people. Instead of just looking at the standard BMI number, the researchers applied a newer, more rigorous definition of obesity proposed by a global commission of medical experts. This new definition requires two things to be present: confirmed excess body fat, measured not just by weight but by waist size and other body proportions, and evidence that this fat is causing harm to the body's organs, such as high blood sugar, high blood pressure, or unhealthy cholesterol levels. By using this stricter, more complete checklist, the team could compare the old way of counting obesity against the new way to see who was being left out.
The results revealed that relying on the old method significantly underestimates the true scale of the problem. When the researchers counted only those with a BMI of 30 or higher, they found that about 34.5 percent of Mexican adults had obesity. However, when they added the requirement for excess fat distribution and organ damage, the picture changed. About 30.9 percent of adults met the criteria for what is now called "clinical obesity." While these overall numbers are close, the composition of the group was surprisingly different. The study found that one in four people who met the criteria for clinical obesity actually had a BMI below 30. These individuals were not heavy enough to trigger the old alarm, yet they carried dangerous amounts of fat around their organs and showed signs of metabolic strain.
This hidden group was not evenly distributed across the population. The researchers discovered that the phenomenon of having excess fat despite a lower weight was much more common in older adults. Among those aged 60 and older, 60.3 percent showed signs of elevated central fat, a rate significantly higher than in younger age groups. In contrast, this pattern was less frequent in younger adults. The study also highlighted a gender difference in how these conditions appeared. While men had a higher rate of obesity based on weight alone, men and women had nearly identical rates of clinical obesity when the stricter definition was applied. This suggests that women, who often carry more fat around the hips and thighs, were just as likely as men to have the dangerous, organ-wrapping fat that the new definition catches, even if their overall weight was lower.
The data also showed that where a person lives and their level of education played a role. Clinical obesity was slightly more common in urban areas than in rural ones. Furthermore, the prevalence of this condition was highest among adults with a primary or secondary education (34.0%) and lowest among those with a college degree or higher (24.7%). Income levels showed a different trend, with the highest rates of clinical obesity appearing in the wealthiest quartile of the population (36.9%), though the differences across income groups were less dramatic than those seen with education.
The researchers concluded that the traditional focus on weight alone is insufficient for understanding health risks in Mexico. They noted that half of all adults with a BMI under 30 showed signs of increased central fat, a finding that underscores the limitations of the current standard. The study does not claim that the old method is useless, but it clearly demonstrates that it misses a significant portion of the population who are at risk. By incorporating simple measurements of waist size and checking for metabolic issues, doctors and health officials could identify these individuals much earlier. The authors suggest that adding these extra steps to routine health checks would provide a clearer, more accurate picture of who truly needs help, ensuring that people with dangerous fat levels are not overlooked simply because their weight appears normal.
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