The Myth of a Normal BMI
According to the most recent National Health and Nutrition Examination Survey two out of every three adults in the United States are overweight. A third are classified as obese. You have probably read or heard that an obesity epidemic occurred in the United States in the latter part of the twentieth century. The percentage of people classified as overweight or obese increased by 31 percent between 1976 and 1991 and by another 24 percent between 1994 and 2000. The change since that time has been negligible.
Why did the “obesity epidemic” occur when it did? It resulted primarily from a change in the definition of obesity, not because people were suddenly becoming fatter.
Historically, obesity was defined by the percentage of body fat present. Accurately determining body fat percentage is difficult, however. To simplify the process of determining obesity, a ratio of body weight to height called the Body Mass Index (BMI) was adopted by the World Health Organization in 1980. It has subsequently become the standard by which weight is judged by medical organizations and governmental agencies in the United States.
The reported increase in obesity between 1976 and 1991 was due largely to the introduction of the BMI definition of obesity. The supposed increase between 1994 and 2000 occurred because the cutoff for normal weight by BMI was lowered from 27.8 to 25 in 1998.
While they may be convenient, BMI measurements are notoriously unreliable in assessing an individual’s health. People who are defined as “overweight” by BMI are routinely told that they must lose weight to be healthy, but this is not the case. The National Center for Health Statistics reported in 2005 that while individuals who are classified as underweight or obese by BMI are more likely to die earlier than those in the “normal” weight category, people who are considered “overweight” are less likely to die prematurely than those considered normal by BMI.
Additional studies have found that people who are defined as overweight by BMI are less likely to die from heart attacks than those of “normal” weight. As people age the BMI definition of overweight becomes even less reliable as a means of determining health risk.
Carrying excess body fat does predispose an individual to health risks such as diabetes, high blood pressure, and atherosclerosis, but the BMI standard that has been chosen to define a “normal” physique is far too stringent to serve a useful purpose for most people.
Just as people have different eye and hair color, they have different body types. Some are thin, some are plump, and some are in between. Something is seriously wrong when two out of every three people are told that they must achieve a weight that is impossibly low if they want to be healthy.
Labeling one person healthy and another sick solely on the basis of his or her body type does a disservice to both of them. The person who is naturally thin has no incentive to be physically active or choose foods that support long-term health. Conversely, the one who is naturally plump is given the message that a future of disability and an early death await no matter what path is chosen.
A much more reliable measure of body fat is the waist to hip ratio. This is determined by dividing the waist circumference at the navel by that at the hips. The result should be less than 1 in men and less than 0.85 in women. Individuals with the lowest waist to hip ratios are much less likely to develop diabetes and atherosclerosis than those with the highest ratios.
If you want to improve your chances of living a long and healthy life don’t go on crash diets in an attempt to achieve a “normal” BMI. Instead, strive to maintain a good waist to hip ratio. It is a much better indicator of a healthy weight.
Dr. Dale Peterson is a graduate of the University of Minnesota College of Medicine. He completed his residency in FamilyMedicine at the University of Oklahoma. He is a past president of the Oklahoma Academy of Family Physicians. He had a full-time family practice in Edmond, Oklahoma, for over 20 years and was a Chief of Staff of the Edmond Hospital. He was active in teachingfor many years as a Clinical Professor of Family Medicine through the Oklahoma University Health Sciences Center.
Dr. Peterson left his full-time family practice in 1999 to consult with individuals who are seeking ways to restore and maintain their health through improved nutrition and other lifestyle changes. He founded the Wellness Clubs of America to give people access to credible information on supporting and maintaining their health. His monthly wellness letter, Health by Design, and his Health by Design E-Newsletter provide helpful information to individuals interested in preventing and conquering health challenges. He is the author of Building Health by Design: Adding Life to Your Years and Years to Your Life .
Dr. Peterson speaks regularly on subjects related to health and nutrition. He hosted a weekly radio program,Your Health Matters, on KTOK in Oklahoma City for five years. For the past nine years he has addressed questions from across the nation on his Your Health Matters weekly teleconference.He offers a free video LifeXtension course at www.drdalepeterson.com.