The bathroom scale may not be the most reliable means of determining how much weight loss is needed, say experts, because body weight doesn't take into account the proportion of fat in the body, or where that fat is deposited. Instead, measuring tools such as skin-fold calipers, underwater or hydrostatic weighing devices, the waist-to-hip ratio, waist circumference and body mass index (BMI) may deliver a more accurate assessment of body fat versus muscle mass. Use this link to calculate your BMI.     

That said, most experts agree that each method has its limitations.  

“A person could have a normal BMI but still need to lose weight,” says exercise physiologist, Lauren McDonald, at Duke Health & Fitness Center, Durham, N.C.  “It's one of the inaccuracies of BMI measurements. It depends on where the weight is being carried. Carrying excess weight in the abdomen is riskier to your health than excess weight around the hips and thighs. Bottom line: BMI is a good screening tool but not a diagnostic tool."   

The American College of Sports Medicine reported similar findings in a study done by Michigan State University that measured the BMI of more than 400 college athletes and non-athletes. It was found that, in most cases, the student’s BMI did not accurately reflect his or her percentage of body fat. Their conclusion: BMI should be used cautiously when classifying fatness in college athletes and non-athletes, and study results support the need for different BMI classifications of what overweight means in these populations.  

“We aren't clear as to which metrics are the most accurate,” says Kevin Fontaine, PhD, associate professor of medicine at Johns Hopkins, division of rheumatology, Baltimore, Md. “BMI is useful, but it does not track perfectly. Too, you have to lose 15 to 20 pounds before you can see results. For that reason, we prefer measuring in terms of an overall percentage of weight loss." Science suggests that gradual weight loss – one-half to one pound a week – is the most effective at reducing body fat without losing muscle mass.

“The simpler the better,” says Missouri State University professor and exercise physiologist Barbara Bushman, PhD. “Most people can use the mirror test (gauging weight loss based on the appearance of body size and shape changes). But of the measuring devices commonly used, the added benefit of using BMI and waist circumference is that they are good indicators of cardiovascular risks, even more than waist-to-hip ratio measuring.”  

Regardless of the measurement tool used, any reductions in scale weight, BMI and waist circumference or waist-hip ratio ultimately each yield very similar results, says Robert H. Eckel, MD, and professor of medicine at the University of Colorado School of Medicine and past national president of the American Heart Association. “The real issue with all patients is compliance in regard to behavioral and dietary changes that need to include basic things like eating breakfast and including more dietary fiber, as well as using tools like record keeping to monitor calories and activity levels.”

McDonald agrees and stresses that the true focus of health and weight loss should be lifestyle changes, and that measuring devices should be used after a significant amount of time and progress.   

“Some people are encouraged and motivated by numbers and measurements, while others get discouraged and fail to realize the progress that isn't reflected on a scale, chart or measuring tape. I encourage my clients to shy away from obsessing over the scale and continuous measuring, and have them focus on how they feel, how they look, how their clothes feel. If you increase activity, eat a balanced diet, over time, you will see results.”