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Mortality risks associated with being overweight may be worse than thought

Harold Mandel's picture
A fattening meal

There has been a growing awareness of the evolving obesity epidemic. It appears that more people than ever are overweight or obese. This problem seems to be primarily associated with poor diets and sedentary lifestyles. It has been known for awhile that being overweight or obese is associated with increased mortality. A new study shows that the mortality risks from such weight problems are worse than previously thought.

It has been observed that the high prevalence of disease and associated weight loss which occurs at older ages decreases the validity of prospective cohort studies aimed at examining the association which exists between body mass index (BMI) and mortality, reports Population Health Metrics. Andrew Stokes, a researcher at the University of Pennsylvania, examined mortality which is associated with excess weight using maximum BMI in order to avoid confounding findings due to illness-induced weight loss.

Stokes found that the percentage of mortality which was attributable to overweight and obesity among adults who never smoked between the ages 50-84 was 33 percent when an assessment was made using maximum BMI. The comparable figure which was obtained using BMI at time of the original survey was significantly smaller at 5 percent.

The discrepancy which was seen in the estimates has been explained by the fact that when using BMI at time of survey, the normal category uses a combination low-risk stable-weight individuals and high-risk individuals who have experienced weight loss. When using maximum BMI only the low-risk stable-weight group is categorized as normal weight. The use of maximum BMI has revealed that estimates which are based on BMI at the time of survey may significantly underestimate the mortality burden which is associated with excess weight in the United States.

Penn researcher Stokes has found the mortality risks of being overweight or obese are underestimated, reports the University of Pennsylvania on April 7, 2014, in a review of this study. Stokes is a doctoral student in demography and sociology in the School of Arts and Sciences at the University of Pennsylvania. His study suggests that many obesity studies have substantially underestimated the mortality risks which are associated with excess weight in the United States.

Stokes has commented, “The scholarly community is divided over a large meta-analysis that found that overweight is the optimal BMI category and that there are no increased risks associated with obese class 1.” BMI is broken down as follows:

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1: Normal weight is BMI of 18.5-24.9 kg/m2

2: Overweight is a BMI of 25.0-29.9 kg/m2

3: Obese class 1 is a BMI of 30.0-34.9 kg/m2

4: Obese class 2 is a BMI of 35.0 kg/m2 and above

It has been argued by skeptics of this meta-analysis that the findings may be driven by biases, particularly by illness-induced weight loss. Stokes says, “Using BMI at the time of the survey to assess the mortality risks of overweight and obesity is problematic, especially in older populations, because slimness can be a marker of illness.”

Stokes has explained that a considerable fraction of individuals who were classified as normal weight using BMI at the time of survey were previously overweight or obese. This group experienced substantially increased mortality rates in comparison to individuals that were consistently at a normal weight throughout their lives. This suggests that for many of these people the weight loss was associated with an illness. He has come to the conclusion that the prior literature underestimates the impact which obesity has on levels of mortality in the U.S.

Clearly, overweight and obesity has become a tragic problem for more people than ever across the United States and worldwide. The quick availability of high fat, high calorie, low nutrient junk food coupled with sedentary lifestyles appears to be the primary culprits. In spite of an increased public awareness of this serious health problem it persists.

The finding that the mortality risks associated with obesity may be significantly higher than previously thought are not surprising in view of the association of excess weight with serious illnesses such as cancer, hypertension, heart disease and diabetes. Primary care physicians should be encouraged to spend more time counseling their patients about the importance of maintaining a healthy weight and how to do so.