You might want to shift a few kilos because your clothes are feeling a bit cozy, getting up the stairs seems harder than it used to, or perhaps the link between extra weight and diseases like diabetes, cardiovascular disease and certain cancers is top of mind. But many blokes might be less aware of the effect obesity or being overweight can have on their fertility and the health of their offspring.
Overweight men are 11% more likely than their normal-weight peers to produce low numbers of sperm and 39% more likely to produce no sperm at all1. Obese men are 42% more likely to have a low sperm count and 81% more likely to produce no sperm1.
However, a new clinical study has found obese men improved their semen quality if they lost weight with an eight-week, low-calorie diet, and maintained the weight loss2. The men involved in the research lost an average of 16.5kgs, which increased their sperm counts by 40%. This improvement was maintained for a year in the men who kept the weight off.
There’s often a strong focus on how women can improve their health to increase their chances of falling pregnant, but your health is also critical for conceiving, particularly when it comes to weight. Sperm count is just one of the factors that influence fertility (semen volume, sperm motility and motile sperm count were not changed by weight loss in this study) the results from the study are good encouragement to get in the best shape possible when you’re trying to grow your family.
How does being overweight affect male fertility?
Male infertility is caused by a problem with sperm production or the movement of sperm through the male reproductive system. These problems include azoospermia (when the semen doesn’t contain any sperm), oligospermia (low sperm count), abnormal shape (which affects the sperm’s ability to fertilise the egg) and poor motility (a problem with the sperm’s ability to swim).
There is a range of things that can cause male infertility including genetic conditions, abnormal hormonal function, and lifestyle factors, including your general health and weight.
Testosterone is a hormone needed for spermatogenesis — the production and development of mature sperm. Fat cells can reduce levels of testosterone directly, by turning it into a form of estrogen, or indirectly, through the production of leptin. As body fat increases, leptin production rises, which reduces testosterone production. This means that obese men with high leptin levels have low testosterone levels, which impair sperm production, sex drive and erectile function3.
Inflammation associated with obesity can also damage sperm, which can change the genes that are passed on from you to your child.
Sperm take around 70 days to develop, so reaching a healthier weight a couple of months before you start trying can improve the chance of conception.
How to lose weight
The study showed that medication, exercise or both were effective strategies for maintaining weight loss and improving sperm concentration and count. However, the participants were directed to eat 800 calories a day and while this might be effective for losing weight, it’s likely not sustainable and definitely not enjoyable.
“800 calories a day is far too low,” says Accredited Practising Dietitian, Joel Feren. “A toddler requires more calories than that. It’s a band-aid approach to achieving quick results. It may be effective in the short-term, but it isn’t sustainable.”
Changing your eating habits can help with weight loss but Feren says we need to move away from overhauling our entire diets and make small, lasting changes.
“It’s very likely we don’t need to throw the baby out with the bathwater, often it’s a case of making some minor incremental tweaks,” he says. “Perhaps it’s reducing the meat portion and increasing the veggies on the plate or limiting booze and going easy on the ‘extra’ foods like chocolate, sweet biscuits and chips.”
If you want to lose weight, chatting to your GP or an Accredited Practising Dietitian is a good place to start. Here are some general tips for weight loss.
- Avoid crash and fad diets as they’re unsustainable and can put you at risk of nutrient deficiencies
- Eat a wide variety of foods from the five food groups and choose 'whole', less-processed options. Find more information about these foods in the Australian Guide to Healthy Eating
- Add more vegetables to each meal — you’ll find you’re automatically eating less of the not-so-good foods when you fill up on fruit and veg, which are low in kilojoules and high in fibre
- Reduce your intake of foods that are high in added fat, saturated fat, sugar and salt
- Make soft drinks, lollies, snack foods and alcoholic drinks an occasional 'extra'
- Understand the recommended serving sizes of each food group to help you portion out your food groups appropriately when plating up a meal
- Practise mindful eating to help you stay present while consuming food, pay better attention to your hunger cues and cut down on overeating. Mindful eating strategies include plating up all meals (instead of eating snacks straight out of the box or bag), taking small bites, chewing slowly, focusing on the taste and texture of your food, and putting away screens to cut down on distraction.
- Have a regular pattern of eating and stick to it
- Drink plenty of water
- Aim to do some physical activity every day, a good goal is 30 minutes
- Each week, try to achieve 150 to 300 minutes (2½ to 5 hours) of moderate-intensity physical activity or 75 to 150 minutes (1¼ to 2½ hours) of vigorous-intensity physical activity, or an equivalent combination of both moderate and vigorous activities
- Reduce the amount of time you spend sitting or lying down for long periods and break it up with a bit of movement
“Men are very quick to make dietary changes [and] from my experience, they approach their newfound diets with gusto,” Joel says. “However, the shine is quick to rub off, and old habits die hard. The key is to make small changes along the way. This has been proven to create lasting change and is more likely to achieve long-term results.”
 Sermondade N, Faure C, Fezeu L, Lévy R, Czernichow S. 2012. Obesity-Fertility Collaborative Group AT. Obesity and Increased Risk for Oligozoospermia and Azoospermia. Arch Intern Med
 Emil Andersen, Christian R Juhl, Emma T Kjøller, Julie R Lundgren, Charlotte Janus, Yasmin Dehestani, Marte Saupstad, Lars R Ingerslev, Olivia M Duun, Simon B K Jensen, Jens J Holst, Bente M Stallknecht, Sten Madsbad, Signe S Torekov, Romain Barrès. 2022. Sperm count is increased by diet-induced weight loss and maintained by exercise or GLP-1 analogue treatment: a randomized controlled trial, Human Reproduction
 Khodamoradi et al., 2022. The role of leptin and low testosterone in obesity. International Journal of Impotence Research