Weight loss is one of the most common recommendations that doctors make. How do we know if a patient should lose weight? We usually use the Body Mass Index (BMI) which is a way to compare a patient’s weight to her height. (For all you math geeks, it’s the weight in kilograms divided by the height in meters squared. For all you physicists, I know the units make no sense.) A BMI of 18.5 to 25 is considered normal. A BMI of 25 to 30 is considered overweight, and over 30 is considered obese. (See the link below to calculate your BMI.)
An article in the health section of Tuesday’s Wall Street Journal reminds us that BMI may not be telling us the whole story. The article cites a study published in the European Heart Journal last year which followed over 6,000 adults with a normal BMI. They all had their body fat percentage measured and were followed for about 9 years.
Surprisingly, even in these adults with a “normal” weight, those with a high body fat content had a higher likelihood of high blood pressure, high cholesterol and cardiovascular disease.
This study is too small to be definitive, and it’s observational, not randomized. So we don’t know whether lowering body fat reverses any of these risk factors. I’m not suggesting we all run out to measure our body fat content. Still the article suggests a few tantalizing possibilities.
First, dieting may not be enough in improving cardiovascular health. It may decrease overall weight without decreasing percent body fat. Exercise is critical to burn fat and build muscle, thereby decreasing percent body fat.
Second, thin people who are inactive may have a high body fat percentage and may be falsely reassured by their “normal” weight. This is what the authors call “normal weight obesity”.
Finally, for those of you who are exercising and not losing weight, don’t despair. You may be losing inches from your waist, burning fat and building muscle, muscle while your weight stays the same. Going by the weight alone is a recipe for frustration when in reality your health is improving.
The Centers for Disease Control BMI calculator
Wall Street Journal article: The Scales Can Lie: Hidden Fat (only by subscription)
European Heart Journal article: Normal weight obesity: a risk factor for cardiometabolic dysregulation and cardiovascular mortality