A new Lancet study challenges how we define obesity — and, in doing so, exposes the failure of decades of efforts to combat it.
The study recommends looking beyond body mass index (BMI) to metrics of body composition, such as waist-to-hip and waist-to-height ratios, that better capture where and how fat is stored in the body. When that broader lens is applied, analyses estimate that the share of Americans who qualify as obese rises from 42% to roughly 68%.
This definitional shift highlights BMI’s limitations as a measure of metabolic health. Unlike body composition metrics, BMI obscures the true extent of metabolic dysfunction and cannot distinguish between muscle and fat — or between superficial fat and the visceral fat that drives diabetes, heart disease and other chronic conditions.
That’s likely one main reason why public health guidance built around BMI — urging Americans to “eat less and move more,” to count calories and cut fat — has failed to curb, and has possibly even fueled, the chronic disease crisis.
Even now, as the crisis worsens with the new definition of obesity, the reflex is to reach for prescription drugs to “solve” the problem. But this moment shouldn’t trigger more medication — it should prompt a reckoning with the dogma that got us here.
Understanding metabolism requires rethinking the conventional “calories in, calories out” model, which assumes that all calories are equal — that 100 calories of refined carbohydrates and 100 calories of salmon or meat affect the body in the same way. They don’t.
Processed and refined carbohydrates are rapidly converted into glucose, rapidly increasing blood sugar and driving a large release of insulin — the hormone that signals the body to take up glucose and store the extra as fat. When insulin remains chronically elevated, fat becomes locked inside cells and can’t be used for energy, leading to continued weight gain. Naturally occurring protein- and fat-based foods, by contrast, are metabolized more slowly, promote satiety and help preserve lean muscle mass.
The solution isn’t ever-tighter calorie restriction but rather restoring metabolic balance. Nutritional strategies that promote satiety and lower insulin — such as low-carbohydrate and particularly ketogenic diets — enable the body to use fat as its primary fuel source, thereby improving insulin sensitivity and overall metabolic health.
A growing body of research supports this approach. In a 2020 study, participants who followed a ketogenic diet experienced significant reductions in waist and hip circumference and total body fat percentage, without reducing their calorie intake. Another 12-week randomized trial found that a low-carbohydrate diet was more effective at reducing body fat and waist size than a traditional calorie-restricted plan.
The takeaway is clear: Lasting health depends not on losing weight by any means, but on metabolically directed weight loss that improves body composition.
As a cardiologist, I’ve seen this firsthand. Patients who spent years cycling through calorie restriction and medication without metabolic success have reversed obesity, diabetes and hypertension by focusing on low-carbohydrate nutrition that stabilizes blood sugar and rebuilds muscle.
Yet public health guidance still lags decades behind the science. For too long, official recommendations have prioritized calorie counting, low-fat nutrition and weight loss at any cost instead of metabolic function and nutrient quality. The newly released 2025-2030 Dietary Guidelines for Americans, which influence meals at schools, VA hospitals and more, correctly emphasize the importance of whole, nutrient-dense foods. While there’s much more work to be done, these guidelines represent a move toward the promotion of metabolic health through real, whole foods.
GLP-1 drugs will undoubtedly have a role in combating the obesity epidemic, but they also are the latest expression of that flawed approach if we expect them to be the ultimate “solution.” The right path forward isn’t broader prescription medication use — it’s addressing the root of metabolic health.
By focusing on insulin control and body composition with metabolically focused nutrition — like ketogenic diets — we can finally begin to reverse an obesity crisis that decades of conventional advice have helped create.
Scher, M.D., is a board-certified San Diego cardiologist and lipidologist and the founding medical director of the Coalition for Metabolic Health.