Obesity may not be a risk factor for all diseases
Being overweight or obese doesn’t mean that you’re at risk for every disease; on the contrary, the people who are obese are more likely to develop specific medical conditions. But a diagnosis doesn’t necessarily mean that a person’s health problems are under control.
BMI, the Body Mass Index, is a measure of body fat based on height and weight, which is determined by taking a person’s weight in kilograms and dividing it by the square of his or her height in meters. BMI is often used to categorize individuals as overweight or obese, and can provide a tool for measuring how much weight someone needs to lose.
Overweight, for example, puts a person at a higher risk for type 2 diabetes, heart disease, high blood pressure, and some cancers. Obese individuals have a greater risk for type 2 diabetes, cardiovascular disease, high blood pressure, and some cancers.
In addition, there are some very specific health conditions for which being overweight or obese is considered a risk factor. To meet the CDC guidelines, a person must have a BMI of 25 to 29.9. If a person is considered overweight or obese, his BMI should be between 25 and 29.9. If the person is categorized as obese, his BMI should be 30 or higher.
The lack of accuracy of the BMI, however, has led to an increasing body of evidence that BMI cannot tell us whether someone is at risk for all diseases, or whether he’s at higher risk for a disease.
A clinical study of more than 88,000 individuals found that BMI could not distinguish between men and women with the same number of BMI points. Researchers found that when BMI was used as a screening tool for obesity, it was no better than a self-reported measure of body fat, the Body Mass Index (BMI).
In a separate study, 3,877 men and women were randomized to one of three treatment groups: medication (sedative) or behavioral therapy (home obesity control). The individuals in the study had BMIs from 25 to 54, and on average, they were at higher risk for Type 2 diabetes than those who were treated. For men, the weight they were not achieving was more important in determining risk for diabetes than the number of BMI points they had. In women, lower BMI points alone were a better predictor of health status than BMI.
Interestingly, the study also found that overweight and obese patients had a lower chance of being diagnosed with hypertension, diabetes, or high cholesterol. In the study, BMI points were not related to cancer diagnoses. Among the men in the study, those with BMIs of 25 to 34.9 had lower cancer rates than those with BMIs of 35 to 44.9, and those with BMIs of 45 to 54.9 had lower cancer rates than those with BMIs of 55 to 74.9.
These results do not support the idea that BMI is a definitive measure of health. There are many factors that may contribute to the development of certain conditions, and a BMI that does not accurately distinguish between overweight and obese patients may inadvertently increase their risk for one disease but not another. For that reason, physicians need to make sure that patients with a high BMI are taking the appropriate measures to lose weight and/or engage in a healthy lifestyle.
Hopefully, as BMI becomes less of a means for diagnosing or misdiagnosing weight gain, more of these recommendations for “what not to do” will become more widely available.
Chris D. Madaleno, M.D., Ph.D., is assistant professor of internal medicine and pediatrics in the division of adolescent medicine and adolescent health at the University of Maryland School of Medicine, Baltimore. He is also a board-certified sleep specialist and a member of the American Academy of Sleep Medicine.
