THERE’S NO ARGUING THAT AMERICA is the most obese country in the world. But there’s plenty of debate about why. It’s a riddle we haven’t been able to solve for thirty years or more, no matter the latest fad diet, workout craze, or superfood on the market. The American Medical Association (AMA), back in 1999, officially described rates of obesity in the United States as having reached epidemic proportions, noting how “rarely do chronic conditions such as obesity spread with the speed and dispersion characteristic of a communicable disease epidemic.” The AMA was so alarmed and serious about the subject that they devoted an entire issue of the Journal to it.

Their concern was justified: prevalence of obesity had taken a sharp upturn in less than a decade, from 12% of the population in 1991 to 18% in 1998. Despite continual research and awareness, that escalating trend hasn’t changed. Today, nearly 33% of American adults are obese, and another 33% are overweight.

The clinical difference between being overweight and obese is defined using the Body Mass Index (BMI) height-to-weight ratio. To calculate your BMI, first multiply your weight in pounds by a conversion factor of 703, and then divide by your height (in inches) squared. So, for example, a five-foot-nine-inch person weighing 150 pounds would have a BMI of 22, which falls within the healthy range. A BMI ratio over 25 is considered overweight; a BMI of 30 or more is considered obese. The formula, as everyone will acknowledge, isn’t perfect because it doesn’t directly measure body fat; a body builder, for instance, will likely have a very high weight-to-height ratio because of muscles, not fat — but in general, the BMI is a useful tool in gauging health at a glance, even if no two bodies are alike.

There’s nothing wrong with being overweight or obese in and of itself; it’s the health risks that correlate highly with excess weight that are the issue. Even so, many people might be surprised to learn that obesity is not a prescription or even a necessary precursor for metabolic disease: approximately 30% of clinically obese people have none of the risk factors associated with metabolic syndrome. And as many as 40% of people in the normal-weight range actually have risk factors for metabolic syndrome.

The obesity epidemic remains such a hot-button issue in American society because excess weight is so highly linked with the other diseases of metabolic syndrome — and because it’s the most outwardly visible symptom of possibly ill health (but again, only possibly). You don’t necessarily have to go to the doctor to find out if you’re overweight, the way you might have to in order to check your blood glucose levels or blood pressure. Appearances aside, the fact is that obesity and even being moderately overweight is associated with three to four times the risk for developing type 2 diabetes, as well as a greater risk for hypertension, high cholesterol, heart disease, and the overall chance of morbidity stemming from any one of these illnesses.

Yet in many cases of obesity, even a 5% reduction in body mass can prevent, delay, or even reverse symptoms and diseases of metabolic syndrome.