Feb 28, 2023 07:00:00

End of the 'obesity paradox'? Research results that contradict common sense that being a little overweight is OK are reported

Obesity is known to be the cause of various diseases, but mortality statistics show that overweight people tend to live longer, a phenomenon known as the '

obesity paradox .' However, a new study that analyzed weight trends over a period of about 30 years has shown that being overweight or obese is more dangerous than previously thought.

Sources and severity of bias in estimates of the BMI–mortality association: Population Studies: Vol 0, No 0
https://doi.org/10.1080/00324728.2023.2168035

Excess weight, obesity more deadly than previously believed | CU Boulder Today | University of Colorado Boulder
https://www.colorado.edu/today/2023/02/23/excess-weight-obesity-more-deadly-previously-believed

Many studies comparing body mass index (BMI) calculated from height and weight with risk of death have shown that while underweight (less than 18.5) and extremely obese (over 35) people have a higher risk of death, overweight (over 25 to under 30) people have a surprisingly low risk of death, and obese people (over 30 to under 35) do not have a significantly higher risk of death than healthy people (over 18.5 to under 25).

When this is graphed, it forms a U-shaped curve, so it has traditionally been thought that 'unless the BMI is extremely high, the risk of death does not increase, and being overweight has an advantage in terms of survival.'

by James Heilman, MD

Ryan K. Masters, an associate professor of sociology at the University of Colorado Boulder, has called a halt to this view. Masters cited the famous example of Tom Cruise, who is 5 feet 7 inches (170 cm) tall and weighed 201 pounds (91 kg) at one time, which is quite muscular, but if this were converted to a BMI of 31.5, he would be considered 'obese.' He went on to point out that the BMI that doctors often use as an indicator of health only looks at weight and height at a certain point in time, and does not take into account

body composition or the period of time a person was overweight.

To examine the impact of this 'BMI trap' on previous research, Masters used data from the National Health and Nutrition Examination Survey (NHANES) from 1988 to 2015, analyzing data from 17,784 individuals, including 4,468 deaths.

The results showed that a full 20% of people with a 'healthy' weight were in the 'overweight' or 'obese' group 10 years ago, and that these people had significantly poorer health than people whose weight had remained stable. Meanwhile, 37% of people with an 'overweight' BMI and 60% of people with an 'obese' BMI had a lower BMI 10 years ago, and those who had recently gained weight were also in good health.

These results suggest that previous studies have classified overweight people who became ill and lost a lot of weight as 'underweight,' which may have made thin people appear to be in poor health, or conversely, classified people who had recently gained weight as 'overweight,' which may have underestimated the health risks of obesity, Masters said.

In addition, this study also found that health conditions vary greatly depending on how fat is distributed, even if BMI is the same. When Masters recalculated after removing these BMI-related biases, the graph of mortality risk and BMI showed a straight upward line rather than a U-shape, and people with a low BMI between 18.5 and 22.5 had the lowest mortality risk. Also, unlike previous research results, there was no evidence that being 'underweight' significantly increased the risk of mortality.

'The impact of having a high BMI on health and mortality risk is not as clear-cut as flipping a switch,' Masters said. 'There is a growing body of evidence suggesting that these effects depend on the duration of time one has been overweight.'