If you're confused about what a "healthy weight" really means, you're not alone. According to data from the National Health and Nutrition Examination Survey, two out of three Americans are considered to be overweight or obese, but only half of those people actually think they have a weight problem. In fact, the gap between how overweight we think we are and how overweight we really are is the widest it's ever been.
Herein lies the problem. We know that even small-scale weight loss — just five to 10 percent of total body weight — can substantially reduce the risk of weight-related medical conditions such as high blood pressure and diabetes. But if you don't have a clear picture of how healthy your weight is, you're less likely to make small but high-yield lifestyle changes to improve your health.
Because height and body composition vary widely among women, a healthy weight for one person may be completely unhealthy for someone else. To identify where you fall on the healthy weight spectrum, you'll need to understand your BMI and waist circumference — not just the number on the scale.
BMI, or Body Mass Index, is the most commonly used tool to screen if someone's overweight and obese. The calculation is simple: your weight in kilograms, divided by height in meters squared. There are plenty of online calculators, like this one, that will do the work for you. A normal BMI is between 18.5 and 24.9. A BMI of 25 to 29.9 is considered overweight and above 30 is considered obese. A BMI that falls under 18.5 is considered underweight, which has its own attendant health risks, such as osteoporosis, fertility issues, and malnutrition.
Though an important first step, BMI isn't quite sufficient to fully assess your risk for weight-related health issues. The current cutoffs underestimate the risk associated with obesity in Asian and South Asian populations and overestimate the risk in black populations. Plus, because BMI doesn't differentiate between muscle mass and fat mass, it's particularly inaccurate for people who are very athletic, since the high degree of muscle mass can land them in the overweight category even if body-fat percentage is low. To get a more comprehensive picture of your risk profile, you'll also need to measure your waist circumference.
Because abdominal obesity is an independent risk factor for diabetes, high blood pressure, high cholesterol, and liver disease, measuring your waist circumference provides key information about your risk profile. Though it's not entirely clear why abdominal fat, or visceral fat, is more dangerous than the subcutaneous fat that accumulates elsewhere in the body, scientists think this may be related to the pro-inflammatory properties of visceral fat, or the fact that these visceral fat cells release their metabolic byproducts directly into the circulatory pathway to the liver, where they can lodge and accumulate.
To measure your waist circumference, use a flexible tape measure placed just above your iliac crest (aka the top of your hip bones) then bring the tape measure all the way around your body, level with your belly button. A waist measurement of 35 inches or more in women (or 40 inches or more in men) is considered high and is associated with increased weight-related health risks.
If your BMI and waist circumference fall within normal range, your current shape is probably perfectly healthy, and there is no evidence that losing weight will improve your health in any meaningful way. But if your numbers exceed the normal cutoffs, guidelines recommend that you take steps to lose body fat in order to improve your cardiometabolic risk profile.
Remember, changes don't have to be big to make a difference — just a five to 10 percent reduction in body weight, achieved through small, sustainable lifestyle modifications, can have a major impact on your overall health.