New research has emerged which appears to indicate that Body Mass Index, (BMI) may not be a reliable way to measure total body fat. BMI is still a fair indicator of body fat for general purposes. It can be effectively used to indicate whether a person is healthy based on weight and height and it works for the vast majority of people. However, it is possible that two people of the same height and weight could get drastically divergent BMI numbers.
One reason for this is the simple fact that different people are built with different proportions. But the most important reason is that a person could be carrying around a given amount of body fat, while their height and weight counterpart has very little body fat and substantially more muscle. A 6 ft tall 200 lb athlete, for example, would have a lot of muscle contributing to his weight. At the same time, however, a 6 ft tall 200 lb couch potato, would have the same BMI as an athlete of the same height and weight. This is where BMI fails as a metric of health.
Professor of medical statistics at the University College of London Tim Cole, says, “You don’t see many bodybuilders but you do see plenty of overweight people. Lots of people get excited about that unnecessarily.” He explains that BMI is good for setting ordinary people into broad categories of health. For someone who is not an athlete and is visibly overweight, a BMI measurement may offer a helpful diagnostic guide for a physician. But for everyday use, it is less valuable.
Where BMI fails critically is in its inability to accurately appraise the difference between someone who carries some fat at the hips and someone who carries it at the waist and belly. That may not seem like a big difference, but health statistics show that those who carry their body fat at the waist are at higher risk for diabetes, stroke, and heart disease. This means measuring your waistline is a better way to gauge your health.
As a general rule, men should have a waste line no greater than 37 inches, and women should try to stay under 31.5 inches. These numbers hold true regardless of height.
So, BMI might be a good metric for doctors to use, but it is limited- in its usefulness for personal use as a fitness metric. So, our advice is to leave BMI to the doctors- and stick to measuring your waistline.