BMI R.I.P.
For experts in metabolism, we have long worried about the over-emphasis on the use of body mass index (BMI) as the arbiter of a "healthy" weight. It is one of those measurements that is in some senses too easy, and the results are deceiving. I regularly see people claim that a certain BMI will "predict" the risk that someone will develop cardiovascular disease or diabetes. The truth is very diferent.
There are two ways to calculate your BMI:
1. Metric system – Kilograms and Metres
[Your weight] divided by [Your height squared]
2. Imperial System – Pounds and Inches
[You weight] divided by [Your height squared] times 703.5
A person is said to be healthy if his or her BMI is between 18.5 and 24.9.
The trouble with this is that the calculation lumps together fat and muscle: a muscular six foot tall football player weighing 300 pounds and with 3% body fat, would have an "unhealthy" BMI of 26.3. That is clearly absurd, and one of the reasons that most experts use BMI only as one part of an evaluation of health.
Our scepticism has been confirmed by an important study from the Mayo Clinic in Rochester, Minnesota, and published in this week’s issue of the medical journal The Lancet.
The researchers looked at 40 studies involving 250,152 patients. Their analysis revealed that people with a BMI of 30-35 were at lower risk of cardiovascular disease than those whose BMI was below 20.
BMI does not correlate well with fat. A better way to distinguish between fat and muscle is to take a cross-sectional view of the abdomen, and to focus on the waist-hip ratio.
A separate study by researchers at the London School of Hygiene and Tropical Medicine of 14,833 people over the age of 75 was published in the American Journal of Clinical Nutrition. They also came to the conclusion that BMI is a poor indicator of health in both men and women in this age group. These researchers also agreed that waste-hip ratio was a better indicator of mortality risk.
This is all music to my ears. For almost three decades we have been teaching about the importance of different stores of fat and the limitations of the BMI calculation. It has been known since the 1940s that gaining weight on the hips, or developing "lover’s handles" are only very weak predictors of diabetes and vascular disease: it is the intra-abdominal fat that is the problem.
There are particular problems with using BMI in the elderly and in some ethnic groups, especially people from the Indian sub-continent and Japan.
The bottom line?
BMI is misleading, and in some age groups and races, grossly misleading.
Much better to use weight and waist-hip ratio.
And BMI only if there is a space on the medical forms where they still need to have it filled in.
Dr. Richard G. Petty, MD is a world-renowned authority on the brain, and his revolutionary work on human energy systems has been acclaimed around the globe.
He is also an accredited specialist in internal and metabolic medicine, endocrinology, psychiatry, acupuncture and homeopathy. He has been an innovator and leader of the human potential movement for over thirty years and is also an active researcher, teacher, writer, professional speaker and broadcaster. He is the author of five books, including the groundbreaking and best selling CD series Healing, Meaning and Purpose. He has taught in over 45 countries and 48 states in the last ten years, but spends as much time as possible on his horse farm in Georgia.
