It turns out that when it comes to fertility, size does matter – but maybe not in the way we all assumed.
Every day it feels like there’s some new advice for would-be dads about all the things they should be doing to protect their fertility. And every other day it seems like there’s a new warning about the dangers of obesity.
More and more research is showing that these two things are linked.
Fertility experts have discovered that a father’s weight actually affects a couple’s chance of conceiving – through changes in the sperm itself.
Does obesity cause infertility?
While everyone’s aware that obesity is bad for your heart, what’s less well known is that it can also be bad for your parts.
New research shows that obese men have a harder time having children, but it’s still unclear what exactly is going on.
In Australia’s obesogenic environment, more men are overweight or obese than ever. Despite the number of people facing this risk, not enough is known about the exact causes of obese men’s higher rate of infertility.
“This area needs a lot more focus and research to discover what’s actually occurring, and then to provide appropriate treatment recommendations” says Dr Andrew Peel, recipient of the Bellberry Fellowship in andrology from the University of Adelaide, and endocrinology registrar at the Mater Hospital in Brisbane.
“We know a lot about the effect of metabolic dysfunction on the female reproductive system, but on the male reproductive system we’re still trying to catch up.”
Sperm theory
Obesity affects women’s chances of becoming pregnant by disrupting hormone cycles and ovary function. It’s a different story for men, whose excess kilos have direct and indirect effects on their sperm.
Some studies have shown that obese men have fewer sperm or malformed sperm than smaller men, but it’s not the whole explanation.
One of the likely culprits of obesity-related male infertility is damage to the DNA carried by the sperm. In the same way a building can’t be constructed if the blueprint is jumbled, a baby can’t be conceived if the DNA carried by the sperm is damaged.
Dr Peel points out,“There have been a few studies that have shown that there is an increased level of DNA damage [in the sperm of obese men], though due to different study designs and confounders such as diabetes or metabolic syndrome, a direct linear relationship has not been established.”
But Dr Peel and his colleagues Dr. Nicole McPherson, Dr. David Jesudason and Professor Gary Wittert have been working on some theories.
Rounding up the suspects of obesity and infertility
The main players
Fat tissue actually creates its own hormones, which can have systemic effects on the male reproductive system and specific impacts on sperm.
One of these hormones is leptin. Leptin has a pretty straightforward relationship with obesity – more fat tissue leads to higher leptin levels. While high leptin affects various bodily functions, research in obese rats has shown that it can also be toxic to sperm. The chonky squeakers that were studied had fewer sperm, more deformed sperm, and the DNA in their sperm showed damage. Researchers believe similar effects might occur in humans.
Other hormones produced by fat tissue can cause inflammation throughout the body, including in the testicles. Inflammation occurs when the body perceives a threat, like a virus, and initiates a response to attack it. However, if there’s no actual threat, the attackers can go rogue, causing microscopic damage to the body’s own cells. Like leptin, the more fat tissue there is, the more severe the effect. The attackers cause damage through forming Reactive Oxidative Species (ROS), and are the reason doctors say we should all be eating lots of anti-oxidants, like those found in blueberries.
Fat tissue also affects a more familiar hormone – testosterone. Low testosterone reduces sperm’s ability to fight off oxidants like ROS, but can also promote weight gain, which can lead to a vicious cycle where weight continually creeps on as testosterone continually drops.
Finally, large men might be hot stuff, but when it comes to fertility, their higher body temperature can be a disadvantage. Testicles are sensitive to heat, and high temperatures can affect sperm production. This is also why men are advised to avoid hot baths when trying for a baby.
The less obvious culprits
Obesity is a risk factor for diabetes, and diabetes is also associated with infertility. The mechanisms behind this are still a bit unclear, which is why part of Dr Peel’s research (supported by the Freemasons Centre for Male Health and Wellbeing and Healthy Male) involves subjecting sperm to high levels of glucose byproducts. Through these experiments, he hopes to find exactly what goes on when sperm encounters high blood sugar levels.
While diet affects fertility, it’s a bit more nuanced than sausage sizzles resulting in sausage fizzles.
Western diets tend to be higher in a specific kind of fat called Omega 6, and lower in one called Omega 3. However, bodies work best when Omega 3 and Omega 6 levels are in a specific balance. This is especially important for fertility, since these kinds of fats actually help to construct sperm cells.
Obese men can also suffer from sleep apnoea, which can literally result in blue balls – that is, testicles not getting enough oxygen. While researchers aren’t quite settled on the details, this affects testosterone levels, and likely results in damage to sperm DNA.
Can infertility from obesity be reversed?
The good news is that big men don’t need to run a triathlon to the lettuce shop every day before they can think about becoming a father. Small lifestyle changes could make the difference between having a dad bod and becoming an actual dad. Evidence points towards a healthy diet and exercise routine being more important than the number of kilos lost.
“Bariatric surgery has significant benefits for people losing weight, but the studies checking fertility outcomes following bariatric surgery have actually not been too promising.” Dr Peel observes.
“But studies have pointed out that lifestyle interventions that may not result in a significant amount of weight loss are still beneficial, and so I [will be] trying to interrogate that relationship between lifestyle changes and fertility a bit further. We might be focusing too much on the weight loss and not enough on the healthy lifestyle.”
While more research is needed before doctors can give definite recommendations, Dr Peel is passionate about making sure men’s health isn’t ignored when it comes to obesity and infertility research.
“If you look at women, we’ve got clear recommendations from a pre-conception perspective. We should be maintaining a healthy diet and lifestyle, we should be a normal weight, and we’ve got folate replacement. For men, the recommendations are similar, but we don’t have enough evidence around time frame, nor the method or volume of weight loss.”
One of the reasons this area is under-researched is stigma – a lot of guys are ashamed to talk about weight and virility. Even though unhealthy convenience foods, stress, bad sleep and long hours at sedentary jobs make it extremely difficult to maintain a healthy weight, there’s still a perception that obesity is an individual problem.
Ultimately, Dr Peel wants to see more men involved in discussions around infertility.
“We have many recommendations for female health optimisation for fertility, but reproduction is a couple’s activity. We should be making sure that both sides of the couple are equally addressed, and equally optimised for the best health outcome for the offspring.”
