If your pants feel tighter than usual, you might begin to suspect that you've gained a couple of pounds. But at what point should you begin to worry that the weight gain is serious? Could you be one of the approximately two-thirds of American adults who are either overweight or obese, with an increased risk for conditions like diabetes and heart disease? While no single measurement is perfect, here are a few ways to size yourself up.
Step on the scale
Upside: Easy and handy. In a 2007 study published in the journal Obesity, researchers found that dieters who regularly and frequently weighed themselves appeared more likely to keep the weight off over time. Buying a scale for your bathroom to keep track of your weight won't break the bank, and your gym probably has one in the locker room.
Downside: You know how you can be skinny but out of shape? Or heavy and fit? Body weight doesn't take into account the proportion of fat in the body, or where that fat is deposited—factors that can point to health trouble. Also, experts say dieters often make the mistake of fixating on the number between their toes instead of focusing on changing the behavior that can improve it.
Body mass index
Upside: Your BMI provides a lot more information than your bathroom scale—specifically, a measure of body fat. "Fat is more important than weight," says Peter Katzmarzyk, associate executive director for population science at the Pennington Biomedical Research Center in Baton Rouge, La. "Excessive fatness is the definition of obesity, not excessive weight—and having too much fat can cause serious health problems."
This calculation uses a ratio of weight to height to estimate body fat and obesity.
- A BMI of less than 18.5 is underweight
- A BMI of 18.5–24.9 is normal
- A BMI of 25–29.9 is overweight
- A BMI of 30 or higher is obese
Downside: Since the BMI tool cannot distinguish between lean muscle mass and body fat, it has a tendency to overestimate the level of body fat in people who have a lot of muscle—say, Arnold Schwarzenegger—and underestimate the amount of body fat in people who have lost muscle mass, such as the elderly. Try to guess your favorite celebrities' BMIs. "If you are an Olympic body builder, it doesn't hold up so well," says Miriam Nelson, PhD, director of the John Hancock Center for Physical Activity and Nutrition at Tufts University's Friedman School of Nutrition Science and Policy, in Boston. Nelson notes that BMI still works well for the general population and estimates that it gives an inaccurate assessment in only 1% to 3% of people, despite its limitations.
And if you're looking to compare your BMI with other dieters, think again. Pretty much anyone can rattle off his weight, but only 20% of the population knows their BMI, suggests a National Consumers League survey conducted by Harris Interactive last year.
