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Overweight patients with type 2 diabetes were less likely to die in a decade-long study than otherwise similar normal-weight patients.
The counterintuitive results form a paradox, according to the authors: There is a survival advantage for diabetes patients that comes with a little extra weight. But diabetes and diet experts warn that it's not quite time to reach for that extra doughnut -- it's an incomplete picture of diabetes, they contend, and, in fact, there's no paradox at all.
In the study, researchers led by Pierluigi Costanzo, MD, at Hull York Medical School in England, looked at body mass index (BMI) in more than 10,000 patients with type 2 diabetes. Those classified as overweight (BMI 25-29.9) had lower mortality risk than did the normal-weight group (18.5-24.9) with a hazard ratio for death during follow-up of 0.87 (95% CI 0.79-0.95; P<0.01); mortality in obese patients (BMI 30 and higher) was virtually identical to that seen with normal weight.
Underweight patients (BMI <18.5) fared the worst (HR 2.84, 95% CI 1.97-4.10; P<0.001), according to the researchers.
But overweight and obese patients did not entirely escape worse outcomes than normal-weight individuals: they had a higher rate of cardiac events.
"Our study suggests that type 2 diabetes induced by the metabolic stress of obesity may fundamentally differ from that which develops in the absence of obesity," wrote Costanzo and colleagues. "[But] whether weight loss can reduce mortality risk is still unclear."
They published their results on May 4 in Annals of Internal Medicine.
The 10,568 patients (54% male) were followed for an average of 10.6 years. Median BMI at baseline was 29.0 (interquartile range 26.0-32.0) and median age was 63 (IQR 55-71). They all had a known type 2 diabetes diagnosis and had visited the clinic at Kingston upon Hull from 1995 to 2005.
Nearly all patients (99%) had no known history of cardiovascular disease. Data on age, diabetes duration, smoking history, height, weight, and blood pressure were collected. But data on exercise and medications were not.
Some 9% of patients were admitted to the hospital for acute coronary syndrome, 7% for cerebrovascular accident, and 6% for heart failure. Overall mortality during follow-up was 35%.
Costanzo and colleagues noted that 16 previous studies examined the relationship between obesity and mortality, with varying results. Most found a U-shaped risk curve: participants with lower-than-normal and above-normal BMI had greater mortality risk than those with normal weight.
But four of the studies found that being overweight or obese was associated with better survival rates. Costanzo and colleagues suggested the inconsistent findings could be due to poor study design.
The results of the new study are "unsettling," according to Keith Ayoob, EdD, RD, at Albert Einstein College of Medicine in New York City, because they run contrary to expectations. "The results end up producing more questions than they answer," said Ayoob in an email to MedPage Today. "You'd expect to see a higher risk of cardiovascular problems as degree of obesity increases."
But Ayoob added that there were a lot of unknowns. And other experts have questioned the study's finding that there is a paradox.
The Paradox That Isn't
"There is no paradox -- this is a misunderstanding," said Joel Zonszein, MD, who is also at the Albert Einstein College of Medicine. Viewing it as a paradox is a very "crude way of looking at it," said Zonszein in an interview with MedPage Today.
Perry Wilson, MD, at Yale School of Medicine said in a video for MedPage Today that there are two explanations for the finding that the overweight group lived longer than the normal weight group, "and neither one of them is a paradox."
The first is that BMI was only measured once -- trends after the baseline exam were unknown. The other is that diabetes is at least partly caused by excess body weight. "Put simply, an otherwise healthy diabetic is an overweight diabetic," he said.
Additionally, as Elizabeth Kitchin, RD, PhD, from the University of Alabama at Birmingham, pointed out to MedPage Today in an email, the average age of the participants in the study was over 60. "There is some data that suggests that a little extra weight in older people may be protective," she wrote.
She said that there was a crucial data point that wasn't included in the findings: medications.
"The study showed that overweight and obese people with type 2 diabetes were more likely to be hospitalized for cardiovascular events -- so the people in the overweight/obese group were 'sicker,'" she wrote. "This could mean that they were more likely to be put on meds like statins which would likely have the effect of lowering their risk of death from heart disease."
"These types of studies -- observational with a lot of important factors missing -- need to be very carefully interpreted and their results not exaggerated," said Kitchin. "I don't think we should be making any clinical decisions based off of this study."
Ayoob and Kitchin both pointed out another missing element of the findings: cause of death. "Knowing what they died from would have really helped to clarify the results," said Kitchin.
"Modern medicine is far better at keeping people alive than keeping them healthy, so this may merely indicate the expected impact of modern medical treatment among those intact enough to respond to it," wrote David Katz, MD, at Yale University, in an email to MedPage Today.
He added that it's possible a little extra weight confers a survival advantage. "Overall, though, I think the issue is one of reverse causation: it's not that overweight confers a survival advantage, but that salient survival advantages related to overall health and social circumstance are associated with keeping on the extra weight that caused the type 2 diabetes in the first place, whereas adverse social and health circumstances are apt to be the reasons that weight starts to fall off," he wrote in an email to MedPage Today.
Yet another limitation of the study was that development and treatment of type 2 diabetes may influence body weight, Costanzo and colleagues noted. And, they wrote, "The results could also represent a higher mortality risk among patients with lower BMI who were already ill for reasons unrelated to diabetes."
Kitchin said that much more work needs to be done. "The next step is a well-done randomized, controlled trial in which overweight and obese patients with diabetes are randomized to a weight-loss group (and they lose weight!) and to a group that maintains their weight and then evaluate over time their likelihood of having a heart event and their risk of death -- not an easy study to do," she wrote.
John Cleland, a co-author, disclosed receiving grants and personal fees from Novartis, Amgen, Philips, and Servier.
- Reviewed by Henry A. Solomon, MD, FACP, FACC Clinical Associate Professor, Weill Cornell Medical College and Dorothy Caputo, MA, BSN, RN, Nurse Planner
Annals of Internal MedicineSource Reference: Costanzo P, et al "THe obesity paradox in type 2 diabetes mellitus: Relationship of body mass index to prognosis" Ann Intern Med 2015; 162: 610-618.