Body mass index (BMI) is a measure of your weight compared with your height. (You can find simple BMI calculators online.) The standard BMI categories are:
Underweight: BMI less than 18.5
Healthy weight: BMI between 18.5 and 24.9
Overweight: BMI between 25 and 29.9
Obese: BMI of 30 or more
People who are overweight or obese may be more likely to suffer from heart disease, diabetes, osteoarthritis, and some cancers. But recent research has found that overweight and moderately obese people with long-term illness, such as kidney disease, type 2 diabetes, and heart disease, often live longer than people of a healthy weight with the same illness. This finding has been called ‘the obesity paradox’. This is because of the paradox that the same condition that makes you ill (being overweight), also seems to help you live longer.
Studies on the obesity paradox have mainly looked at people with chronic (long-term) diseases. This new study looked at death from any cause and found that the paradox still held true.
The researchers found that overweight people were 6 percent less likely to die from any cause than people of a healthy weight. But obese people were 18 percent more likely to die from any cause when compared with people of a healthy weight.
However, when the researchers looked more closely at obesity, they found that moderately obese people (BMI between 30 and 34.9) were 5 percent less likely to die of any cause than people of a healthy weight. But very obese people (BMI of 35 or more) were 29 percent more likely to die from any cause when compared with people of a healthy weight.
Although this study did not try to explain why overweight and moderately obese people live longer, earlier studies on the obesity paradox have tried to give reasons. Some have suggested that overweight or moderately obese people may visit their doctor more often and may be treated more readily because of their weight. Others have suggested that overweight people have more energy reserves to draw on when ill or old. Another theory is that people with excess weight are better able to survive traumatic injury, such as falls or car crashes, because their excess tissue cushions their vital organs. These are just educated guesses. Nobody knows for sure why overweight and moderately obese people tend to live longer.
How reliable is the research?
This was a type of study called a systematic review, which looks at several smaller studies in order to get a bigger, more reliable picture than you would get from one study alone. In this case, the researchers combined the results from 97 smaller studies, covering 2.9 million people and more than 270,000 deaths.
Unfortunately, the study did not look at the causes of death or at how healthy people were during their lives. So it may be possible that, while overweight people may live longer, they may do so in poorer health.
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