Foods and fertility: how dietary patterns can influence fertility

What we eat is increasingly recognised as an important element in influencing fertility. With almost one in six couples experiencing fertility problems, knowing more about lifestyle factors such as diet that can alter this has major consequences. Most research in this area has focused on specific nutrients or food groups. But we don’t eat foods or nutrients - we eat whole diets which are described as dietary patterns. In this podcast episode, I profile new research into the area of dietary patterns and fertility to see what clues it can give to an optimal ‘fertility diet’.

Links referred to in the podcast

• Dietary patterns and fertility in two large cohorts https://ajcn.nutrition.org/article/S0002-9165(23)03668-7/fulltext

Episode transcript
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Transcript

What we eat is increasingly recognised as an important element in influencing fertility. With almost one in six couples experiencing fertility problems, knowing more about lifestyle factors such as diet that can alter this has major consequences. Most research in this area has focused on specific nutrients or food groups. But we don’t eat foods or nutrients - we eat whole diets which are described as dietary patterns. In this podcast episode, I profile new research into the area of dietary patterns and fertility to see what clues it can give to an optimal ‘fertility diet’.

Infertility - defined as the inability to achieve pregnancy after 12 months of unprotected sex - is common, affecting between 10 and 15 percent of couples. Causes of infertility vary and include PCOS, endometriosis, poor egg condition, age, excessive weight or being underweight. But one factor linked to it is diet quality – in both men and women.

Previous research has linked different types of nutrients and diets to fertility. And a summary of this is that it seems for women trying to become pregnant naturally, it is folic acid, vitamin B12, omega-3 fatty acids, and an overall healthy diet (such as the Mediterranean diet) that have a positive link. On the negative side, trans fats and unhealthy diets (defined as one high in red and processed meats, added sugars and many highly processed foods) are linked to a greater chance of infertility.

For men, it is not too a dissimilar story with healthy diets linked to improved sperm quality while the opposite has been linked to diets high in saturated fat or trans fat.

Considering the cost of assisted reproductive technologies, it is not surprising that the question: “How can I change my diet to improve my fertility?” is one of the most common fertility-related questions asked to health professionals and Google. So, what do we know about diet and fertility?

Several studies have looked at associations between individual nutrients or specific foods and the ability to conceive, but it is difficult to translate these findings into dietary guidelines for couples. And even when there is a case for a specific nutrient helping with fertility, it is hard to know how solid the evidence is because nutrients are found in foods, and foods contain a whole range of nutrients. So, looking at overall dietary patterns can give more practical insights when it comes to knowing what a healthy diet for fertility looks like.

And that was the subject of a just-published research paper in the American Journal of Clinical Nutrition. It set out to give greater depth to our knowledge of diet, and by diet here I mean dietary patterns, and fertility defined as the chance of a woman conceiving in any given reproductive cycle.

The four dietary patterns looked at were the Mediterranean Diet, the Healthy Eating Index 2010 (which is a measure of diet quality used to assess how well a set of foods aligns with Dietary Guidelines), the Danish Dietary Guidelines Index, and the Dietary Inflammatory Index. And of course, there was a lot of overlap between the different dietary patterns, but each had some unique features. More about that shortly.

The study groups were two large North American and Danish cohorts composed of women who were trying to conceive. The degree of adherence to the different types of dietary patterns was tracked in the women along with their pregnancy and live birth success. Importantly, the study groups were trying for pregnancy naturally, so the study excluded women on fertility treatments such as IVF. And I’ll link to the study in the show notes. https://ajcn.nutrition.org/article/S0002-9165(23)03668-7/fulltext

 So, what did the study find? The more a person adhered to any of the dietary patterns, the higher their chance of becoming pregnant. So, that was good news all around. But the magnitude of association was modest and was not always consistent across cohorts – meaning that diet wasn’t the defining factor in affecting fertility.

The one surprise from the study was the dietary pattern with the most consistent and strongest effect on fertility was the Dietary Inflammatory Index. This dietary pattern is designed to minimise inflammation and doesn’t directly align with a specific diet or government dietary recommendation. This suggests that standard ‘healthy-eating’ advice, which tends to revolve around dietary guideline recommendations, or a Mediterranean-style diet might not always be optimal advice when it comes to women trying to conceive.

Inflammation plays a major role in the development of insulin resistance, an important determinant of ovulatory function, so this could be an important link to understanding the results of the study. As an example, PCOS is often (but not always) driven by high insulin and inflammation in the body – both of which are affected by diet.

So, what components of the Dietary Inflammatory Index pattern made it stand out above and beyond the others? The top anti-inflammatory contributors to this diet include fibre; magnesium; beta-carotene; vitamins A, B, C, D, and E; and polyunsaturated fatty acids. Noticeable also is the lower amount of nutrients considered to be pro-inflammatory and that includes trans and saturated fats.

I’ve already done a whole podcast episode on the topic of inflammation and the influence of diet so check out episode 61 titled: Inflammation: the good, the bad and the ugly

The research study also observed that the beneficial effects of adherence to a healthy diet, particularly the dietary inflammatory index, on fertility were stronger among women who were overweight and obese and among older women. These groups of women certainly are known to have greater difficulty conceiving so it suggests that dietary changes could have a more pronounced effect on them.

Mediterranean diet and fertility
Now it may be surprising to hear that the Mediterranean diet didn’t come out on top. Firstly, all the dietary patterns studied showed a benefit on the chances of becoming pregnant. And there is a lot of overlap between the foods eaten on each. Prior studies have found associations between Mediterranean-style dietary patterns and pregnancy with three out of 4 studies finding that greater adherence to a Mediterranean-style diet was associated with an increased probability of clinical pregnancy. But the study group is almost always in couples undergoing IVF while the study I’m profiling in this podcast was in women who were trying to conceive naturally so this could be a defining difference.

The benefit of a Mediterranean diet doesn’t just sit with a woman though. Another study, this time involving the male partners of women undergoing IVF, found improved semen quality was linked to following a Mediterranean diet.

So, let’s wrap all this up. Clearly, more work is needed to improve our understanding of the ideal combination of foods and nutrients to optimise fertility in women (and men), but the findings from this latest research, which I should stress are purely observational, are an important step forward that can help guide future research. It also gives some clues as to what an optimal fertility diet could look like.

So that’s it for today’s show. You can find the show notes either in the app you’re listening to this podcast on if it supports it, or else head over to my webpage www.thinkingnutrition.com.au and click on the podcast section to find this episode to read the show notes.

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I’m Tim Crowe and you’ve been listening to Thinking Nutrition.