Blaming a burgeoning waistline on ‘big bones’ is seen by most people as a laughable excuse.
But scientists are increasingly realising it could contain a grain of truth — our bones may affect how much fat we store in our body and even our risk of type 2 diabetes.
This may also help to explain why we develop middle-age spread.
It seems bones produce a type of hormone that affects fat and insulin levels in the body.
As a leading expert, Thomas Clemens, professor of orthopaedic surgery at John Hopkins University, explains: ‘For a long time this hormone was a mystery — no one really knew what it did.
'Now we’re just beginning to realise the effect it has on the whole body.’
Early studies on animals showed that low levels of the hormone, known as osteocalcin, are linked to high blood sugar levels and high fat levels.
Now research involving humans has found the same link. A study published in the journal Obesity in 2013 found that overweight people with lower osteocalcin had more fat around their organs.
This visceral fat squeezes organs such as the liver and pancreas and stops them functioning properly, increasing the risk of conditions such as heart disease and type 2 diabetes.
Some people seem to have naturally lower osteocalcin levels, though it’s not clear why.
Interestingly, the study also suggested osteocalcin levels may affect levels of another hormone, leptin, which controls appetite.
Meanwhile, an Australian study published last year found that men with higher osteocalcin levels had a lower risk of diabetes.
But how does this bone hormone make us slimmer and healthier? And what can you do to boost your levels?
Experts believe osteocalcin helps keep our levels of insulin, the hormone that mops up sugar from the blood, steady.
Osteocalcin stimulates the release of insulin, but, crucially, it makes all cells across the body more sensitive to it.
‘It also seems to affect how we accumulate fat, though we are still unclear how exactly it does this,’ says Dr Celia Gregson, a consultant senior lecturer in musculoskeletal medicine at the University of Bristol.
The problem is that as we age, we seem to produce less osteocalcin. The hormone is made from a type of cell that builds bones.
As we get older, these cells become sluggish. This is why our risk of crumbly bones — osteoporosis — increases.
Another effect of these cells ageing is that less osteocalcin is released into the body.
This may be a factor in middle-age spread, and also increase the risk of diabetes.
That’s why exercise is so important — and why it may be the key to staying slim and healthy.
It triggers the bone-building cells to become more active, and so releases more osteocalcin.
Some experts suggest this may be a factor in why exercise helps the body eliminate fat and reduces the risk of diabetes.
This new understanding may have implications if you’re taking medication for osteoporosis.
Dr Gregson is investigating whether these drugs can affect fat levels and diabetes risk.
In a new one-year study, 60 people with osteoporosis who are taking medication for the condition will have their body fat, insulin and blood sugar levels monitored.
The participants will be taking one of three osteoporosis drugs — zoledronate (a so-called bisophosphonate), denosumab or teriparatide.
The first two drugs stop cells being broken down, to preserve what bone people have left, but they also slow down the bone-building cells.
The third drug, teriparatide, boosts activity of the bone-building cells and so may increase osteocalcin levels — and possibly reduce fat and diabetes risk.
But Dr Gregson cautions it is too early to draw any conclusions.
‘There is no evidence at the moment to say osteoporosis drugs make you fat — and we have had no anecdotal reports to even suggest that.’
But while the relationship between our bones, fat and diabetes is still a source of much debate and intense research, one point on which most people agree is the potential of this work.
‘Drug companies are thinking: “What if we can design a drug that’s good for your bones and good for weight — a drug that will make you lean and strong?” ’ says Professor Clemens.
‘Or wouldn’t it be wonderful to have a drug that treated both diabetes and osteoporosis? It may be a way off, but that’s where we’re headed.’
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