Obesity: Study suggests there is no such thing as being "fat but fit"

There is no such thing as being 'fat but fit' according to a new study.

Although up to one in five obese people appear relatively healthy they still have a far higher risk of diabetes and heart disease. German researchers exploring the concept of metabolically healthy obesity (MHO) - more commonly referenced as fat but fit - showed that obese people with favourable health were still 50 per cent more likely to develop coronary heart disease.

The study concluded that though people considered to have MHO have not been prioritised in the past, weight loss is still important for all people with obesity - even those currently without health complications. The researcher team, led by Professor Matthias Blüher of the University of Leipzig and the Helmholtz Center in Munich, Germany, set out to explore MHO and ask whether it can truly be described as healthy or 'fit'.

"Some 15 to 20 per cent of people living with obesity have none of the metabolic complications we associate with the condition," Dr Blüher said. "Namely abnormal blood sugar control and blood fats, high blood pressure, type 2 diabetes and other signs of cardiovascular disease."

Estimates suggest that women living with obesity are more likely to have MHO (7-28 per cent) than men (2-19 per cent). Around half of all people living with obesity are believed to have at least two complications due to their weight. But Dr Blüher insists it's how the adipose tissue behaves in people with obesity, rather than their BMI, that determines whether or not their obesity can be classified as MHO.

People with adipocytes, or fat-storing cells, that are a normal size are less likely to display the complications of obesity. Whereas those with enlarged adipocytes and inflamed adipose tissue are more likely to experience traits like insulin resistance, which can lead to metabolic complications. The way we store fat, says Dr Blüher, is likely to be key in whether or not obesity is described as MHO - or 'fit but fat' - or not.

“When people with obesity have fat stored viscerally, or internally around their organs, such as in the liver, the data show that these people are much more likely to develop type 2 diabetes than those who store fat more evenly around their body," Dr Blüher said.

He adds that in people with adipose tissue dysfunction, this can lead to damaged tissue, fibrosis, secretion of proinflammatory and adipogenic molecules that subsequently contribute to end-organ damage. Fat-released hormones adipokines, for example, may act directly on cells of the vascular system and lead to atherosclerosis or furring of arteries; and metabolites such as fatty acids may impair the function of the liver or insulin-producing cells in the pancreas.

On the key question of whether or not those said to have MHO can be genuinely described as being healthy, Dr Blüher and his team rubbished the long-held theory.

He explained that, compared with people of normal weight with no metabolic comorbidities - conditions associated with obesity such as diabetes or high blood pressure - people living with obesity with no similar conditions still have a 50 per cent increased risk of coronary heart disease. The research team therefore concluded that, though there are people with obesity who do not exhibit cardio-metabolic complications, describing obese people as having metabolically healthy obesity can be misleading.

Those described as having MHO have, in the past, been given lower priorities for obesity treatment due to their favourable health status. But Dr Blüher says treatment and weight loss should still be encouraged in people with MHO.

“There is still a residual increased risk for those people living with obesity, even with what we would call metabolically healthy obesity,” he said.

“Even in the absence of other cardiometabolic risk factors, increased fat mass and adipose tissue dysfunction contribute to a higher risk of type 2 diabetes and cardiovascular diseases.

"Therefore, weight management and recommendations for weight loss are still important for people living with metabolically healthy obesity."