A groundbreaking study published in JAMA Network Open is challenging everything we thought we knew about obesity, revealing that the condition affects far more Americans than previously recognized. Using a new framework that looks beyond the traditional bathroom scale, researchers found that nearly 70% of adults in a major U.S. health study meet criteria for obesity, compared to just 43% under the old definition.
The findings carry profound implications for millions of Americans, potentially reshaping who gets treatment, how doctors screen for health risks, and what Medicare and insurance companies will cover in the coming years.
Beyond the BMI
For decades, obesity has been defined almost exclusively by body mass index, or BMI, a simple calculation based on height and weight. If your BMI hits 30 or above, you’ve traditionally been classified as having obesity. But scientists have long recognized a critical flaw in this approach: BMI tells you nothing about where fat is stored in your body, and location matters enormously.
A new definition proposed by an international commission of experts and endorsed by 76 professional organizations takes a more nuanced approach. It incorporates measurements like waist circumference, waist-to-hip ratio, and waist-to-height ratio alongside BMI. The reasoning is straightforward: excess fat around your midsection poses different health risks than fat distributed elsewhere on your body.
To understand what this change means in practice, researchers at Massachusetts General Hospital applied the new definition to more than 301,000 participants in the All of Us research program, a diverse cohort designed to represent the American population. What they found was striking.
The Discovery of Anthropometric-Only Obesity
The study revealed a previously unrecognized group: people with what researchers call “anthropometric-only obesity.” These are individuals whose BMI falls in the normal or overweight range, but who carry excess fat around their abdomen based on waist measurements.
This group turned out to be substantial. More than 78,000 participants, representing about one in four people in the study, fell into this category. Even more surprising, roughly one in four of these individuals had BMI in the traditionally “normal” range, meaning they would never have been identified as having obesity under the old definition.
These aren’t just statistical curiosities. People with anthropometric-only obesity faced real health consequences. They were 76% more likely to experience organ dysfunction and had more than double the risk of developing diabetes compared to people without obesity. Their risk of cardiovascular events like heart attacks and strokes was also elevated by 55%.
“These findings support the new definition of obesity by identifying individuals with anthropometric-only obesity as having a heightened risk of adverse health outcomes,” the researchers wrote. The discovery suggests that millions of Americans walking around with “normal” BMI scores may actually be at elevated health risk.
The Wide-Ranging Health Toll of Obesity
The reason the new definition matters so much becomes clear when you understand the sheer breadth of health conditions linked to excess body fat. Obesity isn’t just about one or two diseases. It affects virtually every organ system in the body, often in ways that compound each other.
The study tracked a comprehensive list of obesity-related complications. Among the most common were hypertension, or high blood pressure, which affects blood vessels throughout the body and forces the heart to work harder. Close behind was obstructive sleep apnea, a condition where excess tissue in the throat repeatedly blocks breathing during sleep, leading to fragmented rest, daytime fatigue, and increased cardiovascular strain.
But the list extends far beyond these well-known conditions. The cardiovascular system takes a particularly heavy hit. Beyond hypertension, obesity increases the risk of heart failure, where the heart can no longer pump blood effectively. It raises the likelihood of atrial fibrillation, an irregular heart rhythm that can lead to stroke. Blood clots and thrombosis become more common, as do the most devastating cardiovascular events: heart attacks and strokes.
The metabolic consequences are equally serious. Type 2 diabetes emerged as one of the strongest associations in the study, with people having clinical obesity facing more than six times the risk of developing the disease compared to those without obesity or organ dysfunction. Even preclinical obesity, where no complications have yet appeared, more than tripled diabetes risk. The condition develops when the body becomes resistant to insulin, the hormone that regulates blood sugar, and the pancreas can no longer keep up with demand. Obesity also frequently leads to dyslipidemia, abnormal levels of cholesterol and triglycerides that further increase cardiovascular risk.
The liver, a metabolic workhorse that processes nutrients and filters toxins, becomes infiltrated with fat in many people with obesity. This can progress from simple fat accumulation to inflammation and scarring, potentially leading to cirrhosis. The kidneys also suffer, with obesity increasing the risk of chronic kidney disease that can eventually require dialysis.
Breathing problems extend beyond sleep apnea. Some people with severe obesity develop hypoventilation, where they can’t breathe deeply enough to properly exchange oxygen and carbon dioxide. Pulmonary hypertension, or high blood pressure in the lungs, can develop and strain the right side of the heart.
The musculoskeletal system bears the literal weight of excess body mass. Osteoarthritis becomes more common as joints wear down under increased load. Back pain, joint pain, and physical limitations that interfere with daily activities like climbing stairs or walking distances become increasingly prevalent. The study found that physical limitations were among the most common manifestations of clinical obesity, affecting people’s quality of life and independence.
Reproductive health is affected in both women and men. Women with obesity face increased risks of irregular menstrual periods, polycystic ovary syndrome, fertility problems, and pregnancy complications. Men may experience erectile dysfunction and reduced testosterone levels. The researchers documented distinct patterns of reproductive dysfunction associated with obesity in both sexes.
Even the lymphatic system, which helps fight infection and maintain fluid balance, can be overwhelmed, leading to lymphedema where fluid accumulates and causes swelling, typically in the legs.
The brain and nervous system are not spared from obesity’s reach. The study documented central nervous system effects among people with clinical obesity. Research has increasingly linked obesity to cognitive decline and elevated risk of neurodegenerative diseases, including Alzheimer’s disease and other forms of dementia. The mechanisms appear complex, involving chronic inflammation, insulin resistance in the brain, and vascular damage that affects blood flow to brain tissue. Some scientists now refer to Alzheimer’s as “type 3 diabetes” because of the strong metabolic connections. Obesity during midlife appears particularly risky for later cognitive problems, suggesting that the duration of exposure to excess body fat matters.
Cancer represents another sobering dimension of obesity’s health impact. According to the CDC’s 2017 analysis, 40% of all cancers diagnosed in the United States are associated with overweight and obesity, affecting approximately 631,000 Americans annually. Excess body fat has been linked to at least 13 different types of cancer, including some of the most common and deadly forms. These include breast cancer (particularly after menopause), colorectal cancer, endometrial cancer, kidney cancer, pancreatic cancer, liver cancer, esophageal cancer, ovarian cancer, gallbladder cancer, stomach cancer, thyroid cancer, multiple myeloma, and meningioma (a type of brain tumor). The burden falls disproportionately on women, with 55% of female cancers being obesity-associated compared to 24% in men. The mechanisms vary but often involve chronic inflammation, altered hormone levels (particularly estrogen and insulin), and changes in how cells grow and divide. While this study didn’t track cancer as a primary outcome, the connection between obesity and cancer risk is well established and represents a critical part of why identifying and treating obesity matters for long-term health.
Urinary problems, including incontinence and increased frequency, become more common with obesity. The additional abdominal weight puts pressure on the bladder, while metabolic changes can affect nerve function.
What makes obesity particularly insidious is how these conditions interact and amplify each other. High blood pressure and diabetes together dramatically increase cardiovascular risk. Sleep apnea worsens blood pressure control. Physical limitations make it harder to exercise, which worsens metabolic health. Inflammation driven by excess fat tissue may accelerate both cardiovascular disease and neurodegeneration. This cascade of interconnected problems helps explain why the study found that organ dysfunction itself, even in people without obesity, carried substantial health risks, suggesting that once complications develop, they take on a life of their own.
The Age Factor
Perhaps the most striking finding emerged when researchers looked at older adults. Among participants 70 years and older, nearly 80% met criteria for obesity under the new definition, more than double the rate identified by BMI alone. More than half of people in this age group had what the new framework calls “clinical obesity,” meaning obesity accompanied by organ dysfunction or physical limitations.
The pattern makes biological sense. As people age, they tend to lose muscle mass and accumulate fat around their midsection, even if their weight stays relatively stable. A 70-year-old and a 30-year-old might have the same BMI, but vastly different body compositions and health risks.
For older adults, this isn’t just academic. The study found that clinical obesity conferred similarly elevated risks of diabetes, cardiovascular disease, and death across all age groups, providing a rationale for treatment even in older populations who might have been overlooked under the traditional definition. The cognitive implications are particularly relevant for aging populations, as obesity-related neurodegeneration and dementia risk compound the challenges of maintaining independence and quality of life in later years.
The implications for healthcare costs are staggering. With an aging population and obesity rates approaching 80% in older adults, the burden of obesity-related conditions like heart failure, diabetes, kidney disease, joint problems, dementia, and cancer will place enormous strain on Medicare and the healthcare system.
Clinical Versus Preclinical Obesity
The new framework introduces another crucial distinction: clinical obesity versus preclinical obesity. Clinical obesity means you have both excess body fat and at least one obesity-related health problem, such as high blood pressure, diabetes, sleep apnea, heart disease, or physical limitations. Preclinical obesity means you have excess fat but no apparent complications yet.
In the study, about 36% of all participants had clinical obesity. These individuals faced the highest risks, with more than six times the likelihood of developing diabetes, nearly six times the risk of cardiovascular events including heart attacks and strokes, and nearly three times the mortality risk compared to people without obesity or organ dysfunction.
But even preclinical obesity wasn’t benign. People in this category had more than three times the diabetes risk and 40% higher cardiovascular risk compared to those without obesity. This suggests that preclinical obesity may be a window of opportunity for prevention before complications like hypertension, metabolic syndrome, fatty liver disease, or the cellular changes that can lead to cancer develop.
The most common health problems associated with clinical obesity were high blood pressure, which affected the majority of people in this group, followed by physical limitations that interfered with daily activities, and obstructive sleep apnea. However, the full spectrum of complications, from liver disease to joint problems to reproductive dysfunction, appeared throughout the cohort.
Who Gets Treatment?
One of the most immediate practical impacts of the new definition involves medications. A new generation of highly effective obesity drugs, including semaglutide (Wegovy) and tirzepatide (Zepbound), have transformed treatment options. But who should receive them?
Currently, these medications are approved for people with a BMI of 30 or higher, or a BMI of 27 or higher plus at least one weight-related health condition like high blood pressure, high cholesterol, sleep apnea, or cardiovascular disease. About 45% of participants in the All of Us study met these criteria.
Under the new framework, which recommends treatment for all people with clinical obesity and some with preclinical obesity, the treatment-eligible population would shift dramatically. Roughly 22% of people with clinical obesity by the new definition, people who already have conditions like diabetes, hypertension, or heart disease alongside their obesity, wouldn’t meet current medication criteria. Conversely, about half of people currently eligible for these drugs don’t have clinical obesity by the new definition.
Consider two hypothetical patients. One is a 55-year-old woman with a BMI of 34 and no health problems. She currently qualifies for obesity medication. The other is a 62-year-old man with a BMI of 24 (traditionally “normal”), significant abdominal fat, high blood pressure, elevated cholesterol, and prediabetes. He doesn’t qualify for treatment under current rules, despite having clinical obesity by the new definition and facing elevated risks of heart attack, stroke, progression to full diabetes, and potentially cancer and cognitive decline in the years ahead.
The new framework would flip these scenarios, potentially denying treatment to the first patient while making the second patient a priority for intervention. This reflects a fundamental shift toward treating obesity based on health risk rather than weight alone.
Racial and Gender Patterns
The research revealed important differences across demographic groups. While overall obesity rates were similar between men and women under the new definition, men were significantly more likely to have anthropometric-only obesity. Nearly one in three men fell into this category, compared to about one in five women.
The pattern reflects known biological differences. Men tend to accumulate fat around their abdomen (the “apple” shape), while women more often store it in their hips and thighs (the “pear” shape). Abdominal fat is metabolically active and more strongly linked to health problems like diabetes, heart disease, and fatty liver disease.
Across racial groups, the new definition led to the largest relative increase in obesity prevalence among Asian individuals, with rates jumping 90%. This aligns with research showing that Asian populations face elevated health risks at lower BMI levels, leading to lower BMI thresholds for obesity in Asian populations.
Black or African American participants showed high rates of clinical obesity, with particularly high prevalence of hypertension and cardiovascular complications. Meanwhile, metabolic dysfunction including diabetes and fatty liver disease was particularly prominent among Asian individuals with clinical obesity. These patterns underscore the importance of considering race and ethnicity in obesity assessment and treatment, as different populations may be prone to different patterns of organ dysfunction.
The Organ Dysfunction Puzzle
One of the study’s more intriguing findings involved organ dysfunction itself. People who had conditions like hypertension, diabetes, heart failure, or kidney disease but didn’t meet obesity criteria still faced substantially elevated health risks. Their likelihood of cardiovascular events was nearly as high as people with clinical obesity, and their mortality risk was actually slightly higher.
This pattern suggests a complex relationship between obesity and disease. In some cases, obesity may contribute to organ dysfunction, which then takes on a life of its own even if weight normalizes. In other cases, factors beyond obesity, such as genetics, aging, or other medical conditions, may drive organ dysfunction independently.
The finding raises an important question: if someone with obesity loses weight and their blood pressure normalizes or their diabetes goes into remission, has their clinical obesity been “cured,” or do they remain at elevated risk? The study couldn’t definitively answer this, but the results suggest that reversing organ dysfunction through weight loss could potentially reduce long-term health risks, including risks of cardiovascular disease, kidney failure, and potentially even cancer and neurodegeneration, providing additional motivation for treatment beyond cosmetic concerns.
Questions and Challenges
The new framework isn’t without complications. It’s more complex and time-consuming than simply calculating BMI. Doctors need to measure waist and hip circumference, calculate ratios, assess for the presence of hypertension, diabetes, sleep apnea, heart disease, liver dysfunction, kidney disease, reproductive problems, musculoskeletal limitations, and other conditions. Smart tools integrated into electronic health records could help, but implementation will require significant effort and resources.
There’s also the challenge of determining whether health problems are truly caused by obesity. The researchers classified anyone with both obesity and organ dysfunction as having clinical obesity, reflecting how the definition will likely be applied in practice, since establishing causality is difficult. But some people may have conditions like hypertension or diabetes driven primarily by genetics or other factors, not their body fat distribution.
Perhaps most fundamentally, the study raises questions about millions of people with anthropometric-only obesity and preclinical obesity, groups that haven’t been well studied. Traditional weight-loss approaches developed for people with elevated BMI may not work the same way for someone with normal BMI but excess abdominal fat. Exercise programs and medications that specifically target visceral fat, the deep abdominal fat that surrounds organs and drives metabolic dysfunction, may be more appropriate for this population.
Similarly, for people with preclinical obesity who haven’t yet developed hypertension, diabetes, sleep apnea, or other complications, the optimal intervention strategy remains unclear. Should they receive intensive treatment to prevent disease, or can lifestyle modifications alone suffice? The answers will require dedicated clinical trials.
Looking Ahead
The researchers emphasize that their findings should not cause alarm but rather inform better care. The new definition appears to effectively identify people at highest risk for serious health problems, from diabetes and heart disease to kidney failure, cancer, cognitive decline, and premature death, which is ultimately the goal of any diagnostic framework.
For individuals, the message is clear: the number on the scale doesn’t tell the whole story. Waist circumference and overall health matter just as much, if not more. A “normal” BMI doesn’t necessarily mean you’re in the clear, particularly as you age. Getting your blood pressure, blood sugar, cholesterol, and liver function checked regularly becomes crucial, as these markers of organ dysfunction often appear before symptoms do. Being aware of cancer screening recommendations and cognitive health as you age adds further dimensions to comprehensive health monitoring.
For the healthcare system, the implications are profound. Obesity prevalence approaching 70% of adults and 80% of older adults, coupled with the enormous disease burden from diabetes, heart disease, stroke, kidney failure, cancer, dementia, and other complications, represents a massive public health challenge. The estimated costs of expanded treatment, particularly with expensive new medications, will put pressure on insurers and government programs like Medicare.
At the same time, the new framework offers hope for better targeting of interventions. By distinguishing between people who already have hypertension, diabetes, or heart disease and face immediate health risks versus those who might benefit from less intensive approaches, it could allow more nuanced, personalized care. Someone with preclinical obesity might focus on exercise and dietary changes to prevent metabolic dysfunction, while someone with clinical obesity and multiple organ systems affected might warrant more aggressive medical or surgical intervention.
The study’s authors call for urgent research into optimal prevention and treatment strategies for the newly identified groups, particularly people with anthropometric-only obesity. As one of the largest and most comprehensive analyses of the new obesity definition to date, this work sets the stage for a fundamental rethinking of how we understand, diagnose, and treat one of the most pressing health challenges of our time.
The era of relying solely on BMI appears to be coming to an end. What replaces it promises to be more accurate, capturing the true health risks from a condition that touches nearly every organ system and increases the likelihood of dozens of serious diseases, from heart attacks and diabetes to cancer and dementia. But it will also be more complex, with implications rippling through medicine, public health policy, and the lives of millions of Americans for years to come.
