Obesity Paradox: Fat Not Risky
Heavier Folks Live Longer—Analysis Startles Many
The new study seems to fly in the face of old health adages. Can it be that heavier people live longer? Researchers at Northwestern University found they did, or at least, putting it a different way, overweight people had less risk of death in one group of people.
The Study
The study looked at over 2,000 people who were referred for exercise stress tests because they were at risk of having heart disease. They were not known to actually have any heart disease at the time of the examination. Information collected included all the usual heart risk factors—the characteristics associated with coronary heart disease. The exercise stress tests provided scores of physical fitness. Over the study period, about eight years, the subjects’ names were checked against Social Security’s Death Master File.
Some of the other risk factors tabulated were presence of diabetes, high blood pressure, abnormal blood lipids (cholesterol, triglycerides), family history, smoking, and results of the stress test. Body mass index (BMI) was calculated for each subject (BMI goes up with body weight). BMI is determined by the formula, weight in kilograms / (height in meters)squared.
The Analysis
The outcome of interest was death within the study time period. Subjects were divided into four groups for analysis according to their BMI. Physical fitness was determined by number of exercise minutes completed during the stress test. Researchers adjusted for the effects of the other risk factors.
Results
As expected, those who were more physically fit were less likely to die. But BMI was also negatively associated with death—higher BMI meant less deaths, in this analysis.
The extremes highlight this finding. In the group with the lowest BMI (less than 25), those who had the lowest physical fitness had an almost 30% mortality rate. But their heavier colleagues, those in the highest BMI category with the same level of physical fitness, had a mortality rate of only about 10%.
How Is This?
It’s important to note that these findings were after adjusting for other risk factors. Without this adjustment, there was no significant relation between BMI and mortality. Diabetes and high blood pressure, both associated with heavier weight, increased the risk of death across all categories. It was only after these and other risks were accounted for that the BMI “protective effect” was seen.
The researchers could not explain the paradox. They suggested that perhaps heavy weight was not the same as abdominal fat, which is probably more dangerous. Also, eight years may not be long enough to see the negative effects of obesity.
It’s also true that these results were in people without known heart disease. Opposite findings have been repeatedly reported in people with coronary heart disease. Other questions about the statistics may also be raised.
This study was reported in the American Journal of Cardiology, October 2008, pages 1028-1033. The principal author is Dr. Nils Johnson.
What do you think about this article?
More in Health & Wellness
Latest Articles