Debunking the ‘obesity paradox’: Can fat be fit?

Fat does not have a protective effect on the risk for cardiovascular disease (CVD), and any misconceptions about being “fat but fit” should be erased posthaste, according to recent research.

The obesity paradox stems from several studies in which researchers previously suggested that being overweight or obese, especially in the elderly, may not be deleterious at all, but instead, protective, with no effects on CVD and all-cause mortality.

But researchers of three recent studies have debunked the idea that fat may be protective in any way—especially with respect to cardiovascular health—and have done so in large cohorts with long follow-up periods. As evidence mounts debunking the obesity paradox, let’s take a look at the three latest studies to do so. 

The first of these is a large study conducted in the United Kingdom, which was published in the European Heart Journal. Researchers from the University of Glasgow compared CVD outcomes in overweight vs healthy-weight individuals. They included 296,535 participants from the UK Biobank study (all of white European descent; 57.8% women). Using five measures of adiposity, they determined the incidence of fatal and non-fatal CVD events.

In all, 3.3% of women and 5.7% of men had a cardiovascular event. Those with a healthy BMI of 22-23 kg/m² had the lowest risk of CVD, after which increasing BMI was associated with an increasing risk of CVD.

BMI increases by one standard deviation above the average (5.2 kg/m² for women; 4.3 kg/m² for men) was associated with a 13% increased risk of CVD events, including stroke (HR: 1.13, 95% CI: 1.10-1.17). Researchers saw similar increase in risk as well for one standard deviation increase in waist circumference, waist-to-hip ratio, waist-to height ratio, and percentage body fat.

Participants with a BMI ≤ 18.5 kg/m², which is considered underweight, also had a higher risk of cardiovascular events.

In another study published in The Lancet, researchers used data from 90,257 women in the Nurses’ Health Study, who were followed for up to 30 years.

In women who were obese but metabolically healthy, CVD risk was increased compared with those who were metabolically healthy but of a healthy weight (HR: 1.39; 95% CI: 1.15–1.68). And, like the researchers of the previous study, these researchers found that CVD risk was not only higher in women who were overweight (HR: 2.61; 95% CI: 2.36–2.89) and obese (HR: 3.15, 95% CI: 2.83–3·50), but also in those with metabolically unhealthy normal weight (HR: 2.43; 95% CI: 2.19–2·68).

In a third study published over the past year in JAMA Cardiology, researchers used data from 190,672 in-person exams, pooled from 10 large US prospective cohorts, who were followed from 1964 to 2015. They found that lifetime risks for CVD were higher in middle-aged adults who were overweight and obese compared with normal-weight adults, despite similar longevity. Higher BMI had the strongest association with heart failure.

But while the message is clear that obesity is a strong risk factor for CVD and other chronic diseases, it is also clear that exercise and diet can go a long way to getting to a healthy weight and reducing risk of CVD and other diseases.

"Even within the normal BMI category of between 18.5-25 kg/m², the risk of CVD increases beyond a BMI of 22-23 kg/m². The other adiposity measures show that the leaner the person the lower the risk of CVD, and this must be a public message, that healthy individuals should maintain a lean physique to minimize their risk of CVD," said Dr. Stamatina Iliodromiti, clinical lecturer, Obstetrics and Gynecology, and MRC Fellow, University of Glasgow, Scotland, UK, lead author of the study published in the European Heart Journal.

Her co-author, Professor Naveed Sattar, Metabolic Medicine, University of Glasgow, agreed: "We know many cannot get to such low BMIs so the message is, whatever your BMI, especially when in the overweight or obese range, losing a few kilograms or more if possible, will only improve your health. There are no downsides to losing weight intentionally and the health professions needs to get better at helping people lose weight."

The study from the University of Glasgow was funded by the BHF Centre of Research Excellence; the European Federation of Pharmaceutical Industries Associations (EFPIA), Innovative Medicines Initiative Joint Undertaking, European Medical Information Framework; and the Medical Research Council Skills Development Fellowship.The second study was funded by the US National Institutes of Health, German Federal Ministry of Education and Research. This study was supported by grants from the National Heart, Lung, and Blood Institute.