Consider yourself fat, but fit? Sorry, new research suggests you can't be both.
Fat tissue samples taken from obese patients react the same to insulin and glucose, regardless of a person's heart rate or blood pressure, researchers in Sweden have found.
This means obese people who consider themselves fit are just as at risk from obesity-related health problems as those who aren't.
"The findings suggest that vigorous health interventions may be necessary for all obese individuals, even those previously considered to be metabolically healthy," says lead author Mikael Rydén of the Karolinska Institute in Stockholm.
Hundreds of millions of people are obese, and New Zealand is one of fattest countries in the world.
There has been growing evidence since the 1990s that some people while obese, have a relatively healthy cardiovascular profile - it's estimated around 30 percent of obese people fit this category. They typically have a higher sensitivity to insulin, which promotes cells' uptake of glucose, than those who are fat but not fit (insulin-resistant).
To test whether being obese is okay as long as you're fit, researchers tested fat tissue belonging to 50 obese people enrolled in a clinical study of gastric bypass surgery, as well as 15 patients of normal weight who have never been obese.
They took samples of fat from each person before and after an injection of insulin and glucose, measuring their glucose uptake and patterns of gene expression.
The results divided the subjects into two clear groups - the obese, and the never-obese.
"White fat tissue from insulin-sensitive and insulin-resistant obese individuals showed nearly identical patterns of gene expression in response to insulin stimulation," the study found.
"These abnormal gene expression patterns were not influenced by cardiovascular or metabolic risk factors such as waist-to-hip ratio, heart rate, or blood pressure. The findings show that obesity, rather than other common risk factors, is likely the primary factor determining metabolic health."
In short, obesity is bad whether you're fit or not.
"Since obesity is the major driver altering gene expression in fat tissue, we should continue to focus on preventing obesity," says Dr Rydén.
The research is published today in journal Cell Reports.