BMI vs Body Composition
The American Medical Association has been reviewing the concept of using body mass index (BMI) to define whether someone actually has obesity or should we pay more attention to a person’s body adiposity or body fat? The BMI is a height/weight (kg/m2) equation and does not take into account someone’s actual adiposity vs lean muscle mass. Using body composition testing to determine someone’s actual adiposity or body fat percentage may be a better way to define obesity. People who have a lot of lean muscle mass may show a BMI over 30 (obesity range) but have a body fat percentage in a healthy range. Conversely, someone with a BMI of 24 (normal) with low lean muscle mass, may have an elevated body fat percentage and fall into the overweight (preobesity) or obesity diagnostic category.
Body composition testing can be done with skin calipers, bioimpedence, DXA scans or underwater weighing. Skin calipers can be less accurate unless an experienced person is doing the measuring. The bioimpedence machines are more accurate and seem more available at doctors’ offices or at the gym and easier to use (though not as accurate as DXA). Some scales you can get for home use include bioimpedence reading of body fat percentage. The body composition test also includes information about how much lean muscle mass you have which is great to know! Especially if you are embarking on a new physical activity routine and deciding how much time to spend on strength training and which muscle groups to focus on.
BMI is a good tool for screening populations but falls short as a way to make an accurate diagnosis of excess adiposity for an individual. Some ethnic groups such as Asian people can have obesity at a lower BMI than the general population (>27). It is someone’s adiposity that determines risk for metabolic disease, especially visceral fat or excess adipose tissue in the abdomen. A waist circumference to hip circumference ratio can give you an idea of excess visceral adiposity (apple shape). Divide waist by hip measurement and ideally for men a W:H ratio is <1.0 and for women <.9 for lower risk.
We have a new bioimpedance body composition testing machine at Weigh to Wellness Denver, InBody 570. It improves on our old machine by giving an estimate of visceral fat vs what is stored in extremities. We can put your phone number into the machine and it will send you a copy of your test to your phone. Each time you repeat an InBody test (with us or elsewhere), you will get results to your phone and can track your progress.
