We are all familiar with the phrase, 'you are what you eat'. But clinical practitioners today are telling us to take this one -- or two -- steps further.
"The evidence that we have now is absolutely conclusive that, to a large extent, we are also what our mums and dads ate prior to and around our conception," Professor Chris O'Neill, Head Of the Human Reproductive Unit at the Kolling Institute of Medical Research, told The Huffington Post Australia.
"This is a huge issue that really does carry through to certainly the next -- and probably the next two -- generations."
We haven't really set up society to look after the next generation.
For many couples, going through the process of IVF is their only chance at having a baby. Whilst success rates in Australia are improving, the chances of falling pregnant, having a normal pregnancy and a healthy baby are significantly lessened by carrying extra weight.
With a PHD in embryology, O'Neill has been involved in pioneering in vitro fertilisation in Australia for decades. After being involved in initiating the IVF program at Royal North Shore Hospital in Sydney -- the first of its kind in NSW and among the first in Australia -- he now researches the effects of a range of stressors on gametes and embryos.
And he labels obesity a significant stressor.
"Being overweight is a continuous scale and there's no magic number to this. But when we are talking about obesity, we have to face up to the fact that it is a diseased state that has strong associations with subfertility," O'Neill said.
As Australia's obesity epidemic continues to impact a growing percentage of younger Australians, it is an association that is becoming increasingly relevant.
Obesity and subfertility: what's the link?
According to O'Neill, a major consequence of obesity is chronic inflammation.
"Obesity is the most common or widespread source of chronic inflammation, and we typically think of it as causing damage to cardiovascular tissue," O'Neill said.
"Gametes -- the eggs and the sperm -- are also particularly sensitive to inflammation and this can cause low-grade but measurable damage."
Whilst the association between body mass and inflammation is less understood, research strongly indicates that exposure to such inflammation can have secondary effects on both sperm and eggs.
For an optimally fertile couple, conception can usually occur in a relatively small number of cycles. When you consider partners who may be obese, that is going to be stretched out.
"An egg has large stores of lipid or fat-like material. It is clear that when people have poor diet and are overweight or obese, the nature of the lipids within their eggs is different and can cause abnormalities in their function," O'Neill said.
"The inflammatory stress generally results in sperm which are of poor quality and motility. Quite often, large potions of a man's sperm count are nonmotile when they are overweight or obese."
The common result of these effects is subfertility -- a form of reduced fertility with prolonged time of unwanted non-conception.
"For an optimally fertile couple, conception can usually occur in a relatively small number of cycles. When you consider partners who may be obese, that is going to be stretched out."
How does this impact conception?
According to O'Neill, this low-grade inflammation can pose a range of hurdles to conception.
"The first step is getting the gametes to fertilise," O'Neill said. Whether you fertilise naturally or in vitro -- where the chances of success are much more efficient in a test tube -- you are still starting off with poorer quality material."
"The next hurdle is getting the embryos to attach and implant in the uterus over the next four or five days. Then the challenge is ensuring that the attached embryo develops in a normal fashion."
According to O'Neill, the efficiency of each of these steps is lessened due to inflammatory damage.
Does weight loss help?
For bariatric surgeon and Kolling Institute researcher Dr Carolyn Jameson, the subfertile struggle is a cycle that she knows all too well.
"Patients may come in unable to conceive a child in the first place -- and then they become privy to the impact their weight poses. They'll lose a bit of weight, return to the IVF clinic and they may go through multiple unsuccessful cycles," Jameson told Huffpost Australia.
It becomes a cyclical problem.
"This then increases their stress and anxiety levels -- which are already more common among overweight or obese people -- which leads them to putting on more weight. It becomes a cyclical problem."
The key to improving fertility -- and busting the cycle -- involves removing traces of inflammation. And this can be achieved through weight loss.
"It's the inflammatory mediators that do the damage. As you reduce that inflammation, you reduce the damage," O'Neill said.
"It doesn't take very long after that inflammation has reduced to start producing sperm and eggs that have a lower damage profile."
When it comes to more severe cases, Jameson sees a number of patients who are referred for surgical management of their weight loss.
According to a recent study published in the Obesity Surgery journal, bariatic surgery improves factors that underlie fertility and pregnancy outcomes -- from body weight and type 2 diabetes to menstrual dysfunction and polycystic ovaries syndrome (PCOS).
With a reduction in all of those risks, their fertility levels increase.
"Losing weight regulates a person's hormones, improves malnourishment and associated comorbidities," Jameson said."With a reduction in all of these risks, their fertility levels increase."
She urges those considering falling pregnant to be aware of the impact of their weight.
"People need to understand that obesity significantly affects their chances of a successful pregnancy," she said.
What does all this mean?
For Jameson and O'Neill, this issue has broader implications related to not only lowering fertility rates but also rising obesity levels -- particularly in children.
If you are born with your metabolic programming set to be obese, it is a huge issue for those people to regain a normal weight.
"It is one thing that being obese is strongly associated with subfertility. But obese people do have babies and we know that the embryos they are producing are different," O'Neill said. "They contain within them information which is going to predispose that infant to obesity and all of its associated comorbidities."
Such 'embryonic programming' creates a 'double-barrel effect'.
"If you are born with your metabolic programming set to be obese, it is a huge issue for those people to regain a normal weight," O'Neill said.
"We haven't really set up society to look after the next generation," she said.
Click below to follow HuffPost Australia on Snapchat!