What Can Weight Tell You About Your Metabolic Health?
The “obesity = dangerous” message is everywhere. Headline-making studies underscore the link between excess fat and more than 200 chronic diseases, and ads for the new wave of weight-loss agents—GLP-1 receptor agonist drugs—flood social media.
This idea is particularly embedded in discussions of metabolic health, as obesity increases the likelihood of insulin resistance, prediabetes, and metabolic syndrome, a cluster of conditions that elevate diabetes, stroke, and cardiovascular disease risk.
At the same time, some people with obesity never go on to develop these conditions, while some people at a “healthy” weight—and even those on the thinner end of the spectrum—do. So, to what degree is our weight really indicative of our metabolic health?
As you’ll learn below, the answer is complex. To connect the dots between weight and metabolic health, it helps to understand the current flaws in measuring obesity as well as what the research shows about this relationship. While it would be foolish to ignore our weight completely, this biomarker alone doesn’t provide the full picture of our health.
Defining a “healthy” weight isn’t simple
When we talk about weight and health, we’re most often talking about obesity. More than 40 percent of Americans live with obesity. Officially recognized as a disease by the American Medical Association since 2013, obesity is linked with medical conditions affecting nearly every part of the body, from head (dementia, stroke, depression) to toe (Type 2 diabetes, osteoarthritis, gout).
Historically, determining the cutoffs between healthy weight, overweight, and obesity has been based on a standardized body fat measurement known as body mass index (BMI). To calculate this, you divide your weight in kilograms by the square of your height in meters.
BMI = body weight (in kilograms) ÷ height (in meters) squared
≥30 = obesity
25.0 to ＜30 = overweight
18.5 to ＜25= healthy weight
＜18.5 = underweight
According to BMI, someone who is 5’3” and weighs 170 pounds has obesity (BMI = 30.1), as does someone standing 5’10” and weighing 210 pounds (BMI = 30.1).
When the Centers for Disease Control and Prevention says that as of 2020, an estimated 42 percent of U.S. adults have obesity and an additional 31 percent are overweight, those numbers are BMI-based.
The problems with BMI
BMI has long been used in obesity screening. Yet, it is also widely recognized as a flawed metric, especially when assessing metabolic health at the individual level.
First, BMI doesn’t measure body fat percentage. Instead, it relies on the number on the scale, which can’t distinguish fat from metabolically favorable muscle. (A heavily muscular professional athlete with an excellent cardiometabolic profile could easily fall into the obesity category.) Nor does it differentiate between subcutaneous and visceral fat or factor in body fat distribution, i.e., where one carries their weight.
These omissions are noteworthy, as body fat percentage and distribution are more accurate at assessing and predicting cardiometabolic risk than BMI.
Body fat distribution, in particular, is paramount. Fat accumulating at the waistline increases cardiometabolic risk far more than fat stored around the hips and legs. Doctors refer to people who carry most of their excess weight in the abdominal area as having “central obesity.” This is the more concerning pattern of body fat distribution, tightly correlated with insulin resistance, Type 2 diabetes, heart and liver disease, and other chronic conditions.