Answer provided by Nadia B. Pietrzykowska, MD, FACP
The BMI is a formula expressed as a person’s weight in kilograms divided by the square of a person’s height in meters. It is used to classify individuals as having normal weight, less weight than normal or excessive weight.
The BMI is a formula that was first invented in the early 1800’s by Lambert Adolphe Jacques Quetelet (1796-1874), a Belgian mathematician, statistician, astronomer and sociologist. Later on, it was used by the Metropolitan Life Insurance Company to analyze and classify their policy-holder population according to medical risk.
It certainly is a good starting point. Providers can use this easy calculator to assess their patient’s weight without any equipment other than a scale and a height rod. Unfortunately, it does have limitations and this “one size fits all” approach can be flawed. This is because BMI does not take into account body composition and does not give a good estimate of body fat, muscle mass and other tissues.
Here are some examples showing why relying on BMI alone may result in inaccurate conclusions:
While it is a very simple measurement, waist circumference can provide useful information. In general, excessive fat tissue located in the abdomen is considered to be harmful. To decrease cardiometabolic risk (the risk of developing certain diseases such as heart disease, stroke, diabetes, high cholesterol, etc.), an optimal waist circumference should be below 35 inches in women and 40 inches in men. When it’s higher than these values, waist circumference can contribute to Metabolic Syndrome. This is a constellation of physical and laboratory findings that increases one’s risk of developing cardiometabolic diseases like the ones mentioned earlier. Measuring weight circumference can supply valuable information that will help healthcare providers treat their patients appropriately.
In addition to a waist measurement, a hip width measurement should be made. When the circumference of the waist is divided by the circumference of the hips, a ratio will result. A ratio of less than 0.9 for men and less than 0.8 for women is considered healthy. Higher ratios predispose to many cardiometabolic diseases as described earlier. For example, an apple-shaped woman (higher waist/hip ratio and more fat tissue in the abdomen) with a BMI of 40 may be at a higher risk of developing diabetes than a pear-shaped woman (lower waist/hip ratio and more fat tissue in the hip area) with the same BMI.
As a result, a person with excessive weight and an apple-shaped body may have to be more concerned about their weight than someone with a pear-shaped body, despite them both having the same BMI.
Body fat and body composition measurements:
There are several ways to estimate or measure body fat. Skin calipers that measure skin folds can help determine body fat content and provide helpful information regarding the need for weight-loss. More complex measures can also be achieved by machines that determine body composition. Some of them may be available in your health provider’s office, and others are mostly used by scientists for research. These machines can, with varying accuracy, estimate ad measure body composition and the proportion of tissues: fat tissue, musculature, other lean tissues and water. They can be helpful during weight-loss to guide treatment and build a program with an adequate diet and exercise regimen.
These additional tools provide useful information that helps determine whether an individual is at a healthy weight or if weight-loss is needed.
Other Factors to Consider When Determining Weight-loss Goals
In addition to these factors, two more should be taken into consideration when trying to determine weight-loss goals:
In summary, it is important to understand that weight-loss goals should not be exclusively determined by a number on a scale. In this article, several different factors were described that can affect and guide one’s weight-loss goals.
It’s also important to add that several other factors will determine how much weight someone cannot only lose, but maintain as well. Complex processes involving the brain, several body systems, hormones and behavioral factors will determine the extent of weight-loss and long-term weight maintenance. Although much is still to be researched and understood, this information should not go underestimated.
About the Author:
Nadia B. Pietrzykowska, MD, FACP, is a Board Certified Obesity Medicine Specialist, Nutrition Physician Specialist and Health Coach with a primary specialty in Internal Medicine. She is the Founder and Medical Director of “Weight & Life MD,” a Center for medical weight management located in Ewing, NJ. She promotes the use of evidence-based methods for obesity treatment as well as cutting edge science intertwined with a holistic approach. She contributes to the Education Committee of the OAC and writes for its publications.
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