A recent article in the International Journal of Epidemiology has featured in much of the news and media for dispelling the myth that people can be ‘fat but fit’. However, what did the study actually show and what does this mean?
Firstly, this was a cohort observational study. What this means in this circumstance is that the authors enrolled a huge number of people (1.3 million young men in the military in Sweden) and monitored them over a ~30-year period and measured their mortality status. The benefits of these studies is that they can show links between risk factors (in this case activity levels and weight) against a parameter (in this case premature death).
What the study found:
Despite all the media attention, the studies biggest find was that exercise was associated with reduced risk of premature death relating to alcohol or substance abuse (80%) and suicide (60%). This is quite significant and links in with the body of evidence associating the benefits of exercise and mood already.
However, what has caught the attention of the media was that the risk of death was 30% higher in obese men that were classed as fit in comparison to men that were of normal weight and unfit. Meaning obese men who exercise are more likely to die prematurely than those who do little exercise who aren’t obese. This challenges the current evidence (including systematic reviews and meta-analysis) despite being obese individuals can still be healthy; ‘fat but fit’.
- Huge sample size and long follow up period.
- Not all factors considered, for example smoking and mental health.
- This is only relevant to young (~18 years old) men in Sweden that were in the military. This cannot be compared to women, older men and the wider civilian population.
- Physical fitness was only assessed during recruitment to the study – therefore a person’s fitness could have changed throughout the ~30-year period.
- BMI is not always a good indicator of body composition.
- Observational study: many samples were lost during follow up.
- The study is not yet peer reviewed, which reduces the validity of the results.
Important points to keep in mind
This doesn’t mean that exercise does not affect your health; the study still showed that men of normal weight who had the greatest fitness had a reduced risk of death compared to those who had the lowest fitness by 50%.
This study doesn’t explain why there was a correlation between being fit and obese with an increased risk of premature death. It is worth noting the main cause of death was trauma.
This does not mean that someone cannot be overweight and healthy, just that being obese will increase the risk of premature death.
Being a healthy weight is likely to reduce your risk of developing heart disease.
Health is multi-factorial and focusing only on one aspect of your health will not necessarily reduce all risks of death.
The study has shown a link between weight and risk of premature death, highlighting that being obese can increase the risk of premature death despite the person’s fitness level. However, the validity and strength of this study is not enough to change recommendations – it still remains extremely important to exercise and be a healthy body weight.
Hogstrom, G., Nordstrom, A. & Nordstrom, P. 2016. Aerobic fitness in late adolescence and the risk of early death: a prospective cohort study of 1.3 million Swedish men, International Journal of Epidemiology, 1159-1168.