12.02.2013
by Salynn Boyles
Contributing Writer, MedPage Today

Metabolically healthy obese people have a long-term increased risk for death and cardiovascular events compared with their normal-weight counterparts, suggesting there is no such thing as benign obesity, according to a meta-analysis.

When studies with follow-ups of a decade or more were considered, obese people with no metabolic abnormalities had a 24% increased risk for these events compared with metabolically healthy, normal-weight people (relative risk 1.24; 95% CI 1.02-1.55), reported Caroline K. Kramer, MD, PhD, of Mount Sinai Hospital in Toronto, and colleagues.

All metabolically unhealthy people had a similar elevated risk for the events compared with metabolically healthy, normal-weight study participants, they wrote in the Annals of Internal Medicine, specifically an RR of 3.14 for normal weight (95% CI 2.36-3.93), 2.70 for overweight (95% CI 2.08-3.30), and 2.65 for obese (95% CI 2.18-3.12).

“Our results do not support this concept of ‘benign obesity’ and demonstrate that there is no ‘healthy’ pattern of obesity,” Kramer and colleagues wrote. “Even within the same category of metabolic status (healthy or unhealthy) we show that certain cardiovascular risk factors (blood pressure, waist circumference, low high-density lipoprotein cholesterol level, insulin resistance) progressively increase from normal weight to overweight to obese.”

It is well documented that substantial heterogeneity of metabolic features such as blood pressure, glucose tolerance, lipid profile, and waist circumference exists among people in the same weight category.

But studies designed to determine if people who are overweight or obese, but metabolically healthy, have an increased risk for adiposity-related disease or death have proven contradictory, the researchers wrote.

In an effort to better understand the effect of metabolic status on morbidity and mortality risk across body mass index categories, Kramer and colleagues conducted a systematic review and meta-analysis of eight observational studies involving 61,386 people.

The researchers compared all-cause mortality and the number of cardiovascular events in people who were metabolically healthy and overweight, metabolically healthy and obese, and metabolically unhealthy and normal weight, overweight, or obese with events in people who were metabolically healthy and normal weight.

In a pooled analysis of seven studies, the metabolically unhealthy, overweight group had an increased risk for all-cause mortality or cardiovascular events compared with the reference group (RR 2.70, 95% CI 2.08-3.30).

In a pooled analysis of all eight studies, the metabolically unhealthy, obese group had an increased risk for death or cardiovascular events compared with the reference group (RR 2.65, 95% CI 2.18-3.12), and all but one study reported a significant difference between the groups.

In a pooled analysis of all eight studies, metabolically healthy, obese people had a similar risk for all-cause mortality or cardiovascular events compared with metabolically healthy, normal-weight people (RR 1.19; 95% CI 0.98-1.38), but when the researchers analyzed only long-term studies with at least a decade of follow up, the metabolically healthy, obese people did have an increased risk for death and cardiovascular disease (RR 1.24; 95% CI 1.02-1.55; I² for heterogeneity=33.6%).

“This finding again argues against the notion that increased BMI can be harmless,” Kramer and colleagues wrote.