Recently, one of my patients, I’ll call him Joe, came in somewhat annoyed that a trainer at his gym used a traditional BMI (body mass index) test on him and deemed him overweight for his height. However, on visual inspection, Joe, a male over 40, looks to be quite fit, very muscular, very low body fat, weight trains and does aerobic exercise several times a week.
Conversely, I have a patient Helen, an over 50 female, mildly active, with a predominance of abdominal fat yet the BMI says she is within normal range weight for her height.
The above examples are exactly why the BMI can be misleading in determining if you are actually overly-fat or just weigh more. Fat is lighter than muscle yet takes up much more space on your body. Muscle mass weighs more yet takes up little space. A traditional BMI test can put many fit people in an “overweight” category and other unfit people in a normal category simply by using their height/weight ratio to calculate their overall mass.
The Problematic BMI
The BMI has been the “golden rule” of weight measurement for about the last 13 years. It was designed by the National Institute of Health to replace the old insurance height/weight charts as a method to determine a healthy weight.
According to National Institute of Health guidelines, anyone with a BMI over 30 is considered obese, and 25 to 29.9 is overweight, where my patient Joe falls. The problem with the BMI is that it cannot distinguish between fat mass and lean muscle mass – nor does it account for gender or age. In the BMI calculation, all mass is equal, and as a doctor, I know that is simply not true.
Helen, my patient I mentioned above, is over 50 and fairly sedentary. She has also lost a lot of muscle mass as she does not exercise enough and has more body fat than I would like her to have. Most of her weight is concentrated around her abdomen where a lot of women gain after menopause. As a doctor, I know that a predominance of abdominal fat can predispose you to diabetes and heart disease. However, the BMI says Helen’s weight is normal. If I went by BMI alone, I might neglect Helen’s higher risk of developing serious disease by not recommending that she decrease her abdominal fat and gain some muscle mass. Clearly, the BMI does not accurately assess everyone.
A Better Way To Determine Fit or Fat?
When I assess a patient for a healthy weight, I like to use a few things to determine how fit or fat they are. Here’s what I look at:
- Age – If someone is under age 40 and moderately active, I may use the BMI to get an initial calculation. However, at any age, if a person seems to be carrying predominantly abdominal fat, I want to know their waist measurement.
- Waist to Hip Ratio – The National Institute of Health has deemed that a waist greater than 40 inches for men and 35 for women determines if too much of their weight is concentrated in the abdomen. Weight concentrated in hip areas are associated with stronger bone mass and muscles and less of a risk for heart attack and diabetes.
- Muscle Mass – I’m less concerned with my patient Joe’s higher weight number than I am about Helen’s normal number yet high body/abdominal fat, with a waist circumference of 37. I would want a patient like Helen to increase muscle mass and decrease abdominal/body fat to reduce her risk of heart disease, stroke, and diabetes.
How To Turn Fat Into Fit
My over-40 patients, particularly menopausal women, who have too much abdominal fat are almost always insulin resistant, a condition in which your body excretes too much insulin from the over-eating of sweets and other simple carbohydrates. Too much insulin secretion causes you to store fat around your middle. Insulin resistance can be determined with a simple blood test.
Here’s what I recommend to my patient’s to improve insulin resistance, decrease abdominal fat, decrease their risk for serious disease, and get a better waist-to-hip ratio:
- Low sugar content diet: To get rid of belly, and other body fat, and normalize insulin secretion, try to stay within a daily 15-20 gram of sugar range. You must read labels where sugars are listed and get a good sugar/carb counting book.
- Limit overall carbohydrates: Try to stay between 75 and 100 grams of 0 to low sugar type carbohydrates a day to lose fat faster. For example, brown rice has no sugar in it, and has about 20 grams of carbohydrate per ½ cup serving. Also, watch portion sizes.
- Exercise: Regular aerobic activity for at least 30 minutes, but not more than 45 minutes at a time, will help burn body fat and normalize insulin. Over 45 minutes and you start to secrete cortisol, a stress hormone that can have the opposite effect on insulin.
- Resistance Training: Over age 40, both men and women lose muscle mass through slower metabolisms and lack of physical activity. You can, however, counteract this by upping your physical activity and weight train at least 3 times a week.
I think the BMI can be useful as an initial screening tool in determining a healthy weight. However, it’s pretty much one size fits all and is not sensitive enough for patients with special issues such as loss of muscle mass and predominance of belly fat.
A number on a scale only tells what your entire body weighs but not how much is muscle mass or fat weight. I recommend to my patients to simply use a plain old tape measure to decrease abdominal fat and track muscle growth. Get insulin levels under control with a low sugar/carb diet, aerobic exercise and weight training and you’ll be fit in no time!
Mark Rosenberg, M.D.
How Accurate is Body Mass Index? http://www.webmd.com/diet/features/how-accurate-body-mass-index-bmi?page=2
Calculate Your BMI, http://www.nhlbisupport.com/bmi/