Is “fit but fat” simply a myth?

Exercising and eating at the same time
December 2015

We report on a study which says that being a healthy weight is more important than being physically fit when it comes to premature death.

Obese people who exercise regularly are 30 per cent more likely to die prematurely than healthy-weight people who do little exercise, according to a study published in the International Journal of Epidemiology

Researchers from Umea University, Sweden, monitored 1.3 million men of various body types over a 30-year period. They found the top fifth in terms of fitness when they were 18 were 51 per cent less likely to die prematurely; however, the benefits of exercise were cancelled out when the men were significantly overweight. The study found there was an increased risk of heart disease in obese men, even if they exercised, and even bigger increases in some other causes of death, including alcohol or drug abuse, and suicide.

These results suggest low Body Mass Index (BMI) early in life is more important than high physical fitness with regard to reducing the risk of early death

Professor Peter Nordstrom

Professor Peter Nordstrom, who led the study, said: “These results suggest low Body Mass Index (BMI) early in life is more important than high physical fitness with regard to reducing the risk of early death.”

How the story was covered

This story was covered widely, including in the Telegraph, Mirror, Daily Mail, and others. However, the headlines, such as “Fat but fit counts for nothing”, could be taken to mean that physical fitness and exercise in general are not beneficial to the health, which is not what the study found.  Additionally,  some articles use the terms ‘fat’ and ‘obese’ interchangeably, which could lead to the misinterpretation that even a small weight excess could cut life expectancy.

The study did show benefits to being fit – for normal-weight men, those in the upper half of aerobic fitness had 34 per cent lower risk of death than did those in the lower half.

The strengths of the study include that the complete data, and that a large number of test subjects (more than 1.3 million men) were monitored over a long time period. In terms of its limitations, the findings were based on information on teenagers from the Swedish Military Conscription Registry, who were 18 when their fitness was tested, and do not include data from other age groups or women – so we don’t know whether they would be applicable to these groups.

The study reveals a correlation between being ‘physically fit and obese’ and being at risk of premature death; but it does not prove cause and effect. This is highlighted by the fact that the most common cause of death was ‘accident or trauma’, which is unlikely to be related to fitness or weight levels.

The BHF view

Our Senior Dietitian, Victoria Taylor, said: “Cardiovascular disease is a multi-factorial condition and both physical inactivity and being obese are factors that can affect our risk. There were limitations to this study in that it only assessed physical activity at the start of the study and didn’t look at other important risk factors like smoking. But, nonetheless, it’s a good reminder that addressing one risk factor does not necessarily cancel another one out.  We need to look at our lifestyle as a whole to fully address our overall risk.”

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