Obesity is not associated with early death unless it is accompanied by other metabolic risk factors, such as high blood pressure, type 2 diabetes or high cholesterol, reports a study published last week in the journal Clinical Obesity.
“We found that a person of normal weight with no other metabolic risk factors is just as likely to die as the person with obesity and no other risk factors,” said Jennifer Kuk, the study’s lead author and a professor of kinesiology and health science at York University in Toronto, in a released statement.
“This means that hundreds of thousands of people in North America alone with metabolically healthy obesity will be told to lose weight when it’s questionable how much benefit they’ll actually receive,” she added.
About 1 in 17 people who are obese have no other metabolic risk factors, according to the study’s findings.
This research is the latest foray into the ongoing debate about whether obesity (usually defined as having a body mass index, or BMI, of 30 or higher) can be healthy. Just last month, for example, an American study found that older women who are obese but otherwise metabolically healthy are significantly more likely to have a heart attack or stroke than metabolically healthy older women who are not obese.
In 2017, a large European study involving both men and women came to a similar conclusion.
An unresolved issue
In the current study, Kuk and her colleagues looked at whether obesity in the absence of other metabolic risk factors is associated with an increased risk of dying early from any cause.
As they point out in their paper, current health guidelines recommend that all people who are obese lose weight. That advice stems from the assumption that being obese, even without other metabolic risk factors, increases the likelihood of chronic diseases and premature death.
It’s an assumption based on the evidence of previous research. But a major limitation of those earlier studies, say Kuk and her co-authors, is that obese people with one or more metabolic risk factors were still considered healthy. “Allowing individuals with risk factors to be included in the definition of healthy may have incorrectly inflated the mortality risk associated with this group,” they write.
Looking at obesity on its own
For the current study, Kuk and her colleagues used data collected from 54,089 men and women who had participated in five different cohort studies — ones in which groups of people are followed over time to see if any factors identified at the start of the study might explain later health outcomes. The participants in these five cohort studies were followed for an average of almost 13 years.
The researchers found that 16.7 percent of the participants were not obese and were free of three specific metabolic risk factors: high blood pressure, type 2 diabetes and dyslipidemia (abnormal blood levels of cholesterol, triglycerides or other lipids).
Among the people who were obese, only 5.8 percent had none of those three metabolic risk factors.
During the follow-up periods of the five studies, 4,864 participants (9 percent) died. The researchers then compared the premature death risk for people with and without obesity and with and without the three metabolic risk factors.
They found that obesity, on its own, did not increase the risk of premature death. By contrast, type 2 diabetes increased the risk by 94 percent, high blood pressure by 64 percent and dyslipidemia by 17 percent.
Obesity was associated with a higher risk of early death only when it was accompanied by at least one of the other metabolic risk factors.
The findings held when obesity was defined by waist circumference rather than by BMI. Some experts believe abdominal fat is a better indicator of unhealthy weight than BMI.
Limitations and implications
The current study has its limitations, as all studies do. For example, the five cohort studies on which it is based were not consistent in capturing demographic and health-behavior information about their participants, such as socioeconomic status, medication use, physical activity levels and diet.
As a result, “it is unclear whether individuals with metabolically healthy obesity also had better lifestyle factors, high socioeconomic status, better medical care or other factors that may have confounded the results,” Kuk and her colleagues write.
In addition, the current study looked only at the association between obesity and deaths from all causes. An association might exist for death from cardiovascular disease, the researchers acknowledge.
Still, Kuk and her colleagues believe their findings are robust enough to raise questions about whether all people who are obese should be counseled to lose weight.
“It is unclear whether these individuals with metabolically healthy obesity would benefit from weight loss,” they write. “Furthermore, given the low success rates for obesity reduction and the stigma and bias experienced by those struggling with obesity, it may be particularly important to confirm whether obesity itself is associated with increased morbidity and mortality risk or reduced qualify of life outcomes.”
As already noted, however, this study found that less than 6 percent of obese people are free of all metabolic risk factors, and other studies have indicated the figure may be closer to 4 percent.
So, the vast majority of people who are obese — up to at least 94 percent — would likely benefit from shedding excess pounds.
In addition, people who are obese are at an increased risk of becoming metabolically unhealthy over time.
In the American study published last month, for example, 84 percent of the participants who were obese went on to develop high blood pressure, high cholesterol or type 2 diabetes compared to 68 percent of the non-overweight participants. If the goal is to keep people metabolically healthy, then efforts to prevent obesity need to continue.
This issue is far from being resolved. Stay tuned.