Overnight, 70% of Americans Became Obese

In January 2025, a global commission of 58 experts did something extraordinary: they rewrote the definition of obesity. And with the stroke of a pen, the percentage of Americans classified as obese jumped from 43% to 70%.

That's not a typo. Under the new criteria—endorsed by 76 major medical organizations including the American Heart Association and The Obesity Society—seven out of ten American adults now meet the definition of obesity.

Your first reaction might be: "This is ridiculous. Did everyone suddenly get fatter overnight?"

No. But here's the uncomfortable truth: those extra 27% of people were always at serious health risk. BMI just couldn't see it. And that invisibility was killing them.

A Mass General Brigham study published in October 2025 found that people newly classified as obese under the expanded definition—people who would've been told they were "normal weight" under the old BMI-only system—had significantly higher risks of diabetes, cardiovascular disease, and early death compared to truly healthy individuals.

The new definition didn't create more obesity. It revealed the obesity that was already there, hiding in plain sight.

What Changed: The Lancet Commission's Revolutionary Framework

The Lancet Diabetes & Endocrinology Commission spent years developing a radically different approach to diagnosing obesity. Published on January 14, 2025, their framework makes two fundamental shifts:

Shift #1: BMI + Body Fat Distribution

Instead of relying solely on BMI (which only considers weight and height), the new definition requires direct measures of body fat or anthropometric criteria that account for where fat is stored.

You now have obesity if:

Waist circumference
Waist-to-height ratio
Waist-to-hip ratio
Direct body fat measurement

This is called "BMI-plus-anthropometric obesity"

Two or more of the above anthropometric criteria showing excess fat

This is called "anthropometric-only obesity"—the hidden obesity BMI completely missed

Shift #2: Preclinical vs. Clinical Obesity

The Commission introduced two categories based on whether obesity is currently causing harm:

Excess body fat confirmed by measurements
Normal organ function (no dysfunction yet)
Increased risk of developing clinical obesity, diabetes, cardiovascular disease, and cancer
Think of it like pre-diabetes or pre-hypertension—not sick yet, but at elevated risk

Excess body fat confirmed by measurements
PLUS evidence of organ dysfunction, impairment, or limitations in daily activities directly caused by obesity
Examples: obesity-related heart failure, sleep apnea, joint pain limiting mobility, shortness of breath, type 2 diabetes, fatty liver disease

"Clinical obesity can lead to severe end-organ damage, causing life-altering and potentially life-threatening complications like heart attack, stroke, and renal failure," the Commission stated.

The "Anthropometric-Only Obesity" Problem

Here's the shocking part: The entire 43% to 70% increase came from people with "anthropometric-only obesity"—individuals BMI labeled "normal weight" but who actually had dangerous levels of body fat.

The Mass General Brigham study analyzed over 300,000 Americans in the NIH's All of Us Research Program. Here's what they found:

By Old Definition (BMI only): 42.9% had obesity

By New Definition (BMI + body fat distribution): 68.6% had obesity

Nearly 80% of adults over age 70 had obesity

Higher risk of type 2 diabetes than people without obesity
Higher risk of cardiovascular disease than people without obesity
Higher mortality risk than people without obesity
About 50% met criteria for clinical obesity with actual organ dysfunction

Dr. Lindsay Fourman, lead author and endocrinologist at Mass General Brigham, called the findings "astounding."

"We already thought we had an obesity epidemic, but this is astounding. With potentially 70% of the adult population now considered to have excess fat, we need to better understand what treatment approaches to prioritize."

Why BMI Missed So Many People

BMI = weight (kg) ÷ height (m²). That's it. No information about:

Where fat is stored – Visceral belly fat is deadly; subcutaneous hip fat is relatively benign
Muscle mass – A muscular person and sedentary person at the same weight look identical to BMI
Body composition changes with age – Older adults lose muscle (sarcopenia) while gaining fat, maintaining "normal" BMI despite obesity
Sex differences – Women naturally carry more body fat than men at the same BMI
Ethnic variations – Asian populations show metabolic disease at lower BMI thresholds

This creates the phenomenon of "normal weight obesity" or "skinny fat"—people with BMI in the "normal" range (18.5-24.9) but excessive body fat percentage, particularly dangerous visceral fat around organs.

2-3x higher cardiovascular mortality than truly healthy normal-weight people
Metabolic syndrome prevalence similar to people with BMI-defined obesity
Increased inflammation and insulin resistance despite "healthy" BMI

BMI's blindness to body fat distribution has been letting millions of at-risk people slip through the cracks for decades.

How to Know If You're in the Hidden 27%

The new definition means you might have obesity even if your BMI says you're "normal weight" or just "overweight." Here's how to check:

Step 1: Calculate Your BMI

BMI = weight (kg) ÷ height (m)²

Or use an online calculator.

Underweight: <18.5
Normal: 18.5-24.9
Overweight: 25-29.9
Obese: ≥30

Step 2: Measure Your Waist Circumference

Stand up straight, exhale normally
Place measuring tape around your waist at navel level (belly button)
Keep tape parallel to floor, snug but not compressing skin
Record measurement

Men: >40 inches (>102 cm) — or >35 inches (>90 cm) for Asian men
Women: >35 inches (>88 cm) — or >31 inches (>80 cm) for Asian women

Step 3: Calculate Waist-to-Height Ratio

Divide your waist circumference by your height (use same units).

Healthy threshold: <0.5

Your waist should be less than half your height. If it's ≥0.5, you have elevated health risk.

Height: 5'8" (68 inches)
Waist: 35 inches
Ratio: 35 ÷ 68 = 0.51 (elevated risk)

Step 4: Calculate Waist-to-Hip Ratio (optional)

Measure hips at widest point, then divide waist by hip measurement.

Men: >0.90
Women: >0.85

Step 5: Assess for Obesity

You have obesity under the new definition if:

Scenario A: BMI ≥30 AND at least 1 elevated measure (waist, waist-to-height ratio, or waist-to-hip ratio)

Scenario B: BMI 18.5-29.9 (normal or overweight) BUT at least 2 elevated measures

If you meet the criteria, determine whether it's preclinical or clinical:

Preclinical obesity: You have the measurements above but no organ dysfunction or physical limitations
Clinical obesity: You have the measurements PLUS health conditions caused by obesity (type 2 diabetes, high blood pressure from obesity, joint pain limiting mobility, sleep apnea, shortness of breath, fatty liver disease, etc.)

Why This Definition Could Save Your Life

The old BMI-only system had two fatal flaws:

Underdiagnosis: Missing people at serious health risk (the hidden 27%)
Overdiagnosis: Labeling healthy, muscular people as "obese"

The new system fixes both problems.

Catching Hidden Risk Early

Diabetes
Cardiovascular disease
All-cause mortality

Evidence-based health counseling
Monitoring over time
Preventive interventions appropriate to their risk level
Lifestyle modification programs
Earlier access to medications if needed

Dr. Robert Kushner, Commission member and professor at Northwestern University Feinberg School of Medicine, explained:

"Two children may share the same body fat, the same BMI, but one is at much higher risk than the other. You can have obesity and yet be very healthy and you may never develop a medical problem. But we called it 'preclinical obesity' because even in that situation, we know from other studies that if you wait long enough, there is a higher risk of developing medical problems."

Distinguishing Risk from Disease

The preclinical vs. clinical distinction is crucial. It prevents two extremes:

Extreme 1: Treating everyone with excess body fat as "diseased" and needing aggressive medical intervention
Extreme 2: Ignoring excess body fat until it causes catastrophic organ failure

"Obesity is a spectrum," said Prof. Francesco Rubino, Commission Chair and expert at King's College London. "Some individuals manage to live healthy lives with excess body fat, while others experience severe health challenges. This new framework allows us to better assess and address the needs of each patient."

Who Benefits Most from the New Definition

Older Adults

The Mass General Brigham study found obesity prevalence skyrocketed to nearly 80% in adults over age 70 under the new definition.

This makes sense: aging causes sarcopenia (muscle loss), meaning older adults can maintain "normal" BMI while body fat percentage climbs dangerously high. The new definition catches this sarcopenic obesity—a particularly deadly combination linked to disability, falls, and mortality.

Women

Women naturally carry 6-11% more body fat than men at equivalent BMI. The new definition's inclusion of waist measurements and body fat distribution helps identify women at risk despite "healthy" BMI scores.

Asian Populations

Research consistently shows Asian populations develop metabolic disease at lower BMI thresholds. The Commission explicitly calls for "cutoff points appropriate to age, gender, and ethnicity." Asian-specific thresholds for waist circumference are already incorporated.

Normal-Weight Individuals with Belly Fat

Perhaps most importantly, the new definition identifies the "skinny fat" population—people who look slim but carry dangerous visceral fat around organs. These individuals face cardiovascular risk comparable to BMI-defined obesity but would never have been diagnosed under the old system.

The Policy Implications Are Massive

With 70% of American adults now meeting obesity criteria, the implications ripple across healthcare, insurance, and public health:

1. Insurance Coverage

The Commission recommends health insurers cover evidence-based obesity treatments (including GLP-1 medications like Ozempic and Wegovy) for clinical obesity as a standalone condition.

Currently, many insurers require an additional diagnosis like diabetes to cover these drugs. The new framework could expand access significantly—but also raises questions about cost and resource allocation when 70% of the population qualifies.

2. Treatment Prioritization

Dr. Fourman's question is critical: "With potentially 70% of the adult population now considered to have excess fat, we need to better understand what treatment approaches to prioritize."

Clinical obesity: Needs timely, evidence-based medical treatment
Preclinical obesity: Needs health counseling, monitoring, and risk-appropriate interventions

3. Reducing Stigma

By defining obesity as a "chronic, systemic illness" with "multifactorial causes still incompletely understood," the Commission shifts away from blaming individuals.

"Public health strategies to reduce the incidence and prevalence of obesity at population levels must be based on current scientific evidence, rather than unproven assumptions that blame individual responsibility for the development of obesity," the Commission stated.

"Weight-based bias and stigma are major obstacles in efforts to effectively prevent and treat obesity."

4. Public Health Resources

If 70% of adults have obesity, traditional public health approaches need radical rethinking. The Commission achieved 90-100% consensus on all recommendations—an extraordinary level of agreement among 58 global experts.

American Heart Association
The Obesity Society
Chinese Diabetes Society
World Obesity Federation
European Association for the Study of Obesity

This isn't fringe science. This is the global medical establishment acknowledging that our current approach to obesity diagnosis is fundamentally broken.

What to Do If You're Newly "Obese"

If you fall into the anthropometric-only obesity category (normal BMI but elevated waist measurements), don't panic—but don't ignore it either.

1. Get a Comprehensive Assessment

Waist circumference, waist-to-height ratio, waist-to-hip ratio
Body fat percentage (via BIA or DEXA scan if available)
Blood biomarkers: fasting glucose, HbA1c, lipid panel, liver enzymes
Blood pressure
Assessment of organ function

2. Determine Preclinical vs. Clinical

Type 2 diabetes or prediabetes
High blood pressure (obesity-related)
Fatty liver disease
Sleep apnea
Joint pain limiting daily activities
Shortness of breath affecting mobility
Urinary incontinence

If yes, you have clinical obesity and should discuss evidence-based treatments including lifestyle modification, medications, or surgery depending on severity.

If no, you have preclinical obesity—increased risk but no current illness. Focus on prevention.

3. Evidence-Based Interventions

Nutrition: Reduce ultra-processed foods, increase protein and fiber
Exercise: Combine cardio (150+ min/week) with strength training (2x/week minimum)
Sleep: 7-9 hours nightly
Stress management: Chronic stress elevates cortisol, promoting visceral fat storage
Monitoring: Regular check-ins to ensure you're not progressing to clinical obesity

All of the above PLUS consideration of medications (GLP-1 agonists, etc.) or bariatric surgery for severe cases with organ dysfunction

4. Focus on Waist Circumference

The easiest actionable target: get your waist-to-height ratio below 0.5.

Visceral belly fat is metabolically active, inflammatory, and directly linked to cardiovascular disease and type 2 diabetes. Reducing waist circumference—even without major weight loss—improves metabolic health.

The Bottom Line

The 2025 Lancet Commission didn't make more people obese. It revealed that millions of people have been walking around with dangerous levels of body fat that BMI was completely blind to.

Yes, 70% of Americans now meet obesity criteria. But that 27% increase represents real people with real health risks who were being told they were fine.

The 55-year-old woman with BMI 24 ("normal") but a waist-to-height ratio of 0.58 and prediabetes—anthropometric-only obesity, clinical
The 68-year-old man with BMI 26 ("overweight") but 32% body fat, sleep apnea, and high blood pressure—anthropometric-only obesity, clinical
The 40-year-old with BMI 28 and waist circumference of 38 inches but no symptoms yet—anthropometric-only obesity, preclinical

Under the old system, none of these people would have been classified as obese. Under the new system, they get the monitoring, counseling, and treatment they need before organ damage becomes irreversible.

The new definition isn't inflating an epidemic. It's finally measuring what actually matters: body fat distribution and its impact on health.

And for the hidden 27%, that diagnostic accuracy could be the difference between prevention and catastrophe.

Scientific References

Rubino F, Cummings DE, Eckel RH, et al. Definition and diagnostic criteria of clinical obesity. The Lancet Diabetes & Endocrinology. 2025;13(3):221-262. doi:10.1016/S2213-8587(24)00316-4

Fourman LT, Siddiqui S, Ankers E, et al. Implications of a New Obesity Definition Among the All of Us Research Program. JAMA Network Open. 2025;7(10):e2438835. doi:10.1001/jamanetworkopen.2024.38835

Mass General Brigham. Study Indicates Dramatic Increase in Percentage of U.S. Adults Who Meet New Definition of Obesity. Press release. October 14, 2025. Available at: https://www.massgeneralbrigham.org/en/about/newsroom/press-releases/dramatic-increase-in-adults-who-meet-new-definition-of-obesity

The Lancet Diabetes & Endocrinology Commission. Redefining obesity: advancing care for better lives [Editorial]. The Lancet Diabetes & Endocrinology. 2025;13(2):75. doi:10.1016/S2213-8587(25)00004-X

King's Health Partners. The Lancet Diabetes & Endocrinology Commission on Clinical Obesity. Available at: https://www.kingshealthpartners.org/our-work/clinical-academic-integration/diabetes-endocrinology-and-obesity/lancet-diabetes-and-endocrinology-commission-clinical-obesity

Iacobucci G. Define obesity as clinical or pre-clinical for more accurate diagnosis, says global commission. BMJ. 2025;388:r78. doi:10.1136/bmj.r78

Northwestern University. A better definition of obesity: New guidelines use more than just body mass index to diagnose obesity. January 14, 2025. Available at: https://news.northwestern.edu/stories/2025/01/redefining-obesity-with-new-global-guidelines

Fourman LT, Grinspoon S, et al. Researchers report 'astounding' obesity surge in U.S. Harvard Gazette. October 14, 2025. Available at: https://news.harvard.edu/gazette/story/2025/10/researchers-report-astounding-obesity-surge-in-u-s/

Brouwer S. Beyond BMI: Experts propose 'preclinical' and 'clinical' obesity. STAT News. January 13, 2025. Available at: https://www.statnews.com/2025/01/14/bmi-lancet-report-obesity-as-disease-spectrum-urges-body-fat-measurements/

Else H. New obesity definition sidelines BMI to focus on health. Nature. 2025;637:28-29. doi:10.1038/d41586-025-00123-1

World Obesity Federation. The Lancet launches new framework for redefining obesity as a chronic disease. January 14, 2025. Available at: https://www.worldobesity.org/news/the-lancet-launches-new-framework-for-redefining-obesity-as-a-chronic-disease

Przybyłowski A, et al. Redefining Obesity: A Narrative Review of Diagnostic Criteria Evolution. Journal of Clinical Medicine. 2025;14(16). doi:10.3390/jcm14165267

The New Obesity Definition Just Made 70% of Americans Fat (And That Might Save Your Life)