We all know that carrying too many extra kilos can up the risk of heart disease and Type 2 diabetes – so how come up to 30 per cent of us can be very overweight yet still have healthy hearts and healthy levels of blood glucose?
One possibility is the 'fit and fat' theory that suggests being physically active can protect us from chronic diseases even when we weigh too much. One effect of exercise, for instance is that it makes muscles use up more blood glucose for fuel – this can help ward off Type 2 diabetes by keeping blood glucose levels down.
" How come up to 30 per cent of us can be very overweight yet still have healthy hearts and healthy levels of blood glucose? "
But fitness isn't the whole story, says endocrinologist Dr Daniel Chen from Sydney's Garvan Institute of Medical Research.
"Studies also show that some obese people who aren't physically active are also unexpectedly free of problems like high blood pressure and high blood fats," he says.
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What's more, they're also insulin sensitive which means their body's insulin is doing a good job of keeping their blood glucose levels healthy - this is the opposite of insulin resistance, the common condition that means your insulin is struggling to keep the glucose in your blood under control and puts you in the running for diabetes.
"One of the differences that sets these healthier overweight people apart is whereabouts on the body they store their excess fat. In people whose insulin is working well fat is more likely to be carried around the hips and thighs rather than around the waist," explains Chen who's trying to find out why some obese people side step the insulin resistance that sets others up for diabetes.
The surplus fat that clings to hips and thighs is different to the fat that hugs the waistline. Called subcutaneous fat, it sits there under the skin doing nothing other than padding out your jeans. But fat around the waist is likely to be visceral fat which is bad news for two reasons, he says.
"One is that it secretes inflammatory chemicals that contribute to heart disease and diabetes, the other is that it releases fatty acids which can be harmful too – they end up being stored in the liver and muscles and this makes it harder for the body to keep blood glucose levels down," he says. "But overweight people whose insulin is working well tend to have less of this 'bad' fat. They might have a lot of fat around the arms, legs and hips but they're not storing it around the waist, so in terms of diabetes it's not a problem."
Having this visceral fat can give even a relatively slim person a higher risk of diabetes than someone who weighs more, but carries their extra kilos around the hips and thighs.
"People can be slim but still have this harmful fat around the waist – including some Asian people who tend to have a lower BMI yet still have visceral fat around the middle," Chen says.
But although some overweight people may be protected from diabetes and heart disease, they're not bulletproof – the extra weight is still going to increase the risk of osteoarthritis, for instance, by adding a burden to hips and knees, he adds.
"Whether there's less risk of cancer with healthier obese people isn't clear. So far we only know there's less diabetes and fewer deaths from heart disease – but we also know there's an increased risk of cancer from diabetes."
One possibility is the 'fit and fat' theory that suggests being physically active can protect us from chronic diseases even when we weigh too much. One effect of exercise, for instance is that it makes muscles use up more blood glucose for fuel – this can help ward off Type 2 diabetes by keeping blood glucose levels down.
" How come up to 30 per cent of us can be very overweight yet still have healthy hearts and healthy levels of blood glucose? "
But fitness isn't the whole story, says endocrinologist Dr Daniel Chen from Sydney's Garvan Institute of Medical Research.
"Studies also show that some obese people who aren't physically active are also unexpectedly free of problems like high blood pressure and high blood fats," he says.
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What's more, they're also insulin sensitive which means their body's insulin is doing a good job of keeping their blood glucose levels healthy - this is the opposite of insulin resistance, the common condition that means your insulin is struggling to keep the glucose in your blood under control and puts you in the running for diabetes.
"One of the differences that sets these healthier overweight people apart is whereabouts on the body they store their excess fat. In people whose insulin is working well fat is more likely to be carried around the hips and thighs rather than around the waist," explains Chen who's trying to find out why some obese people side step the insulin resistance that sets others up for diabetes.
The surplus fat that clings to hips and thighs is different to the fat that hugs the waistline. Called subcutaneous fat, it sits there under the skin doing nothing other than padding out your jeans. But fat around the waist is likely to be visceral fat which is bad news for two reasons, he says.
"One is that it secretes inflammatory chemicals that contribute to heart disease and diabetes, the other is that it releases fatty acids which can be harmful too – they end up being stored in the liver and muscles and this makes it harder for the body to keep blood glucose levels down," he says. "But overweight people whose insulin is working well tend to have less of this 'bad' fat. They might have a lot of fat around the arms, legs and hips but they're not storing it around the waist, so in terms of diabetes it's not a problem."
Having this visceral fat can give even a relatively slim person a higher risk of diabetes than someone who weighs more, but carries their extra kilos around the hips and thighs.
"People can be slim but still have this harmful fat around the waist – including some Asian people who tend to have a lower BMI yet still have visceral fat around the middle," Chen says.
But although some overweight people may be protected from diabetes and heart disease, they're not bulletproof – the extra weight is still going to increase the risk of osteoarthritis, for instance, by adding a burden to hips and knees, he adds.
"Whether there's less risk of cancer with healthier obese people isn't clear. So far we only know there's less diabetes and fewer deaths from heart disease – but we also know there's an increased risk of cancer from diabetes."
Researchers should look at the type of fat these people eat. If they are eating a lot of Omega 6 oils (which tends to get stored on hips and thighs), then their diet is what is helping to keep their blood fat levels down. It is also possible they are not eating diets with lots of refined sugar which helps their blood sugar levels stay normal. It's all about the food ultimately - a low saturated fat diet aka a predominantly vegan diets enables us to stay within the AMA guidelines of keeping saturated fat intake to around 7% of daily fat intake.
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