There's a problem with overweight and obesity that has nothing to do with body image or dress size. It's the rise in the most common gynaecological cancer – endometrial cancer which develops in the lining of the uterus.
It's also the gynaecological issue most strongly linked to obesity, says Associate Professor Pamela Pollock of the School of Biomedical Sciences at Queensland University of Technology. Yet this connection between body weight and endometrial cancer isn't high on our radar.
But it should be. Rates of this cancer have increased over the last two decades in western countries like Australia, the US and Britain because of the rise in obesity. This same rise in obesity is also driving an increase in the numbers of younger women under 40 affected by the disease according to Professor Andreas Obermair, director of research at the Queensland Centre for Gynaecological Research at the University of Queensland.
"A BMI of 18.5 to 25 is considered normal, a BMI between 25 and 29.9 is overweight and BMIs between 30 to 34.9, 35 to 39.9 and over 40 are categorised as obese, severely obese and morbidly obese respectively," he explains. "For every five BMI units above the normal range the risk of endometrial cancer doubles so that while an overweight woman has a two-fold increased risk of developing the disease, a woman with a BMI above 35 has an eight-fold increased risk. Having polycystic ovary syndrome also increases the risk."
We need more awareness of the link between body weight and endometrial cancer – if we could get more overweight and obese women to drop their BMI by five points we could save more lives, adds Dr Pollock.
"I've dropped my own BMI down almost four points by dropping 10 kilos – it's difficult but do-able.
"While we should accept people for the size they are we need to encourage them to be healthy, too. A number of studies have shown that incorporating exercise into your lifestyle, no matter what your size, can reduce your cancer risk," she says.
"We can accept that someone is obese but there also needs to be a message that says 'your health is at risk but if you can reduce your weight you'll lower that risk.' No one needs to be model-thin to be healthy."
What is it about carrying extra fat that drives some, but not all, types of this cancer? The general consensus is that too high levels of oestrogen are an important factor, says Dr Pollock. Fatty tissue produces some of the body's oestrogen and too much surplus weight can create excess oestrogen.
"But research is also underway to find out if inflammation caused by carrying too much abdominal fat is also having an effect," she says.
The good news about endometrial cancer is that in its early stages it's very curable – but treatment involves surgery to remove the uterus and often the ovaries, spelling the end of fertility in younger women.
This is why Queensland researchers are trialling a new approach to see if it can treat endometrial cancer in its early stages without the need for surgery. Called the feMMe trial, it compares three different approaches using the IUD Mirena which delivers the hormone progesterone to the lining of the uterus. Some women will use the IUD alone, others will use the IUD with a dose of the anti-diabetes drug Metformin, and a third will use the IUD and a weight loss program.
"The use of progestin helps rebalance hormone levels and Metformin is used because it's been found to have an anti-cancer effect in some studies and reduces levels of blood glucose," says Professor Obermair, who's running the trial, a world first, with Queensland University of Technology's School of Public Health.
"Regaining a lower weight closer to the normal range requires behaviour change, but it's associated with better chances of fertility for young women," says QUT's Professor Monika Janda who's leading the lifestyle component of the trial.
The main symptom of endometrial cancer? Unusual vaginal bleeding either before or after menopause – although it's also a symptom which can be due to other less serious causes.
It's so important for women not to ignore symptoms, stresses Dr Pollock.
"A lot of women don't want to talk about 'down there' but I'm hoping that a new campaign – Save the Box – launched last year will lift this taboo, increase awareness of all gynaecological cancers and get women talking to their GP, " she says.