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  • Writer's pictureSally Marchini, APD BND

Safety first when it comes to low-carb diets for fertility #PCOS

Updated: Jan 10, 2022

Know what you’re doing under competent guidance for best health outcomes. Dietary changes can boost your fertility by 69%, and it’s not all about weight loss.

In practice we see women who are planning pregnancies and are wanting personalised advice to improve their chances of falling pregnant and having a healthy pregnancy, birth and baby.

Bearing in mind we know that prenatal diet is very important in contributing to the development of the baby even before it’s conceived, both mentally and physically, there are several important safety factors to consider before taking on a low-carb diet for fertility. And does it even help towards fertility?

Do low carb diets help towards fertility?

Depending on the individual and their current circumstances, sometimes it can be advisable for some faster weight loss which as well as dealing with potential medical issues that may be preventing conception, inducing fast weight loss can be useful in breaking old habits and resetting new ones for moving forward meaning you’ll be providing the best nutrients to grow a healthy baby for during the pregnancy, the birth and well into their longer term health outcomes across life.

A 2016 systematic review found that a lower carbohydrate diet for obese or overweight women prior to pregnancy may reduce obesity-related pregnancy complications such as miscarriage, stillbirth and large for gestational age infants, however the authors recommend that the diet be undertaken in the earlier stages of conception planning instead of immediately before conception due to potential implications on oocyte health. In such cases a short term low-carb or ketogenic diet may be recommended, but we always ensure that the woman is returning to regular healthy eating at least 6 weeks prior to trying to conceive.

The dietitian’s role

When a new person visits us we put on our ‘dietitian detective’ hat and delve into what that person wants to achieve, whether their medical background may impact those goals, what their lifestyle can factor in and what’s going to be best for the person based on all options available. This process and decision making can take a whole hour. At the end of the first appointment there’s either some decision making to be made or we can get started with the plan we’ve agreed on.

If a low-carb or ketogenic diet is decided, our first job is to work out how much additional protein we need to supplement the shakes chosen for the role. This ensures that the person burns mostly fat in the ketogenic diet, rather than precious muscle and protein that can also be a focus. Depending on the size of the person too, we may need to adjust the prenatal supplements being taken as the regular doses may not be sufficient in the larger person.

We then lay everything out, provide a load of delicious veggie recipes and shopping lists, explain great methods to help people get through the often difficult and hungry first week before the ketosis sets in.

Important considerations

Safety is our prime driver.

As mentioned earlier it’s important that a plan is made and agreed to about when it will be safe to start trying to conceive. In the meantime contraception is an important consideration as ketones can cross the placental barrier and are thought to impact the baby’s brain development (2). Sussman et al explains this well in their paper: “Prenatal and early postnatal exposure to a ketogenic diet also results in significant alterations to neonatal brain structure, and results in retarded physiological growth. These alterations could be accompanied by functional and behavioural changes in later postnatal life.” So, although they’re only animal studies, we really wouldn’t recommend taking the risk.

Case study

One such case is a young woman who because of her size had stopped menstruating. She was keen to start her family sooner rather than later, so we discussed the benefits of an Optifast diet and she agreed that it was worth postponing the pregnancy for the best health outcomes for both herself and her yet unconceived child.

Under our guidance she was able to safely lose the weight that had caused her periods to disappear, and improved the quality of her usual diet. We got her back to a ‘normal’ healthy diet and she was able to safely fall pregnant. Having the nutrition training also means now that she’ll be able to nourish her family to minimise any unwanted health outcomes related to diet and lifestyle.

What’s your situation?

Call on 0249710770 for a free 10 minute discovery call with Sally to see if we’re a good fit for you.

Accredited Practising Dietitian Sally Marchini at Marchini Nutrition (Swansea and New Lambton Heights, NSW) is one of the specialist dietitians from the Australia-wide network Nutrition Plus who offer more than just nutrition advice - they offer experience, problem solving, understanding and most importantly compassion to assist you on your health journey in preconception, pregnancy, postnatally and for specific health concerns.

Sally can be contacted via her website, the Nutrition Plus website, by telephone on 0249710770, or by email at Telehealth consults are also available.


McGrice, M.; Porter, J. The Effect of Low Carbohydrate Diets on Fertility Hormones and Outcomes in Overweight and Obese Women: A Systematic Review. Nutrients 2017, 9, 204.

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