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Where does science sit in this age-old debate of fitness vs fatness?

There’s no question that obesity is inextricably linked with poor health outcomes. So, too, are low fitness levels and the integral part they play in the causal chain leading to T2DM and heart disease. Somewhere in the mix is the ‘Fit but Fat’ theory, arguing that cardiovascular fitness attenuates the risk of disease and premature mortality independent of BMI.
Put simply, being overweight or obese doesn’t really matter as long as you perform regular exercise. Or so the story goes.
Fit but Fat, popularised in the late 1990s, is based on evidence from large cohort studies showing that, after adjusting for other risk factors, the ‘health benefits’ of being lean are limited to fit men and that a general level of fitness may also reduce the inherent hazards linked with being obese.201610-twins-healthy-fat
More recent studies have provided compelling evidence that disputes this argument. In late 2016 a group of Swedish researchers using data from 1.3m men revealing that unfit, normal-weight men had a 30% lower risk of early death from any cause compared with ‘fit and fat’ individuals. Fit and fat debunked!
Another study examined the associations between physical activity and all-cause mortality and asked the question slightly differently – does fatness modify these associations? The participants were followed for 12 years and the findings revealed that if obesity were avoided, the number of deaths would be reduced by 3.66%.
There are, of course, ongoing issues with how we measure obesity. Body Mass? BMI? Waist Circumference? Percentage Body Fat? Nonetheless, what is crucially important is the distribution of fat on the body.
It is now generally accepted that central, abdominal obesity is linked with a constellation of metabolic abnormalities. It’s also important to appreciate the importance of lean muscle mass because it is increasingly evident that changes in the metabolic function of muscle plays a direct role in the development of insulin resistance.
There has been research at UWA for more than a decade looking at the benefits of exercise for individuals with, or at risk of developing, cardio-metabolic disease. Results consistently show that exercise training confers cardiovascular and metabolic benefits, independent of changes in total body weight. We can confidently say that exercise confers critically important benefits.
We now also know that these improvements are beyond the manipulation of the traditional risk factors linked with CV and metabolic disease, with evidence suggesting that a large proportion (~40%) of the benefit of exercise cannot be attributed to changes in traditional risk factors alone.
Regular exercise increases lean muscle mass, reduces the risk of developing cancer, CVD, improves metabolic health and directly impacts the vascular system. It’s also linked with improved ageing, improves bone health, general mood and reduces the risk of dementia and Alzheimer’s disease.
There are many benefits linked with regular physical activity. One of them is, hopefully, avoiding becoming an obesity statistic because the Fat but Fit argument isn’t looking all that attractive anymore.


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