Fertility and diet - a research update

Fertility and diet is something relevant to many of our readers as they navigate their conception journey. Luckily, here at eat for baby, we know just the person to offer a research update in this area. Dr Jessica Grieger, PhD, Research Fellow at The University of Adelaide is the author of  “Preconception, diet, fertility, and later health in pregnancy”. This peer reviewed manuscript was recently published in Current Opinions in Obstetrics and Gynecology.

Our Founder, Dr Hayley Dickinson, PhD sat down with Jess to talk all things fertility and diet.

Read more for the interview in full.

Hayley: Jess, thanks so much for sharing your expertise and time with us. We got pretty excited when we saw your latest paper come out. It's obviously an area that is really important to the eat for baby community. We’d love to ask you a few questions and understand more about the research world of diet and fertility vs what we might all see in our instagram feeds!

Jess: Ha! Yes, let’s do it. It’s great to talk to you Hayley. 

Hayley: In the introduction of your review you make the statement “....key dietary factors in relation to optimising fertility are nonexistent.” I think this would be surprising to lots of people given the huge offering of fertility diet plans and advice around what to eat during this time. What leads you to that statement? 

Jess: You’re exactly right, it would come as a surprise because there seems to be a lot of information out there on supplements and ‘best foods for fertility’ but what we don’t have is the hard evidence. We don’t have consistent, large studies actually demonstrating which foods or nutrients optimise fertility, and which consistently show a shorter time to conceive or better fertility outcomes. This is really what we need, studies that are well designed, and that consistently show which foods are key. I don’t think we are there yet with this sort of evidence but we do know that a healthy diet in general is a good place to start.

Hayley: What are some of the reasons we don’t have that evidence yet?

Jess: We have the Australian Guide to Healthy Eating which is a great resource for an overall healthy diet and there are some great suggestions on foods to increase during pregnancy, as well as foods to avoid, like alcohol, foods high in saturated fat and foods that are at risk for containing listeria.
In the preconception period however, we really don’t have this sort of information. Part of the challenge here is that it is difficult to capture women who are ‘planning a pregnancy’, particularly if couples get pregnant quickly, or if a pregnancy is not planned.
When we do these research studies, women are already pregnant, so we ask them to think back on their diets so we can relate that to their fertility, or we look at these factors in couples requiring ART (assisted reproductive technologies). These men and women however may have already changed their diet and lifestyle habits because it already has taken them some time to achieve a pregnancy. So those reasons make it difficult because of the diversity in study populations. Additionally, the consistency across the studies is lacking, sometimes there are only a couple studies looking at certain foods, for example fast foods on fertility, so we can’t draw robust conclusions on this small amount of evidence. We also need to have a better understanding of the mechanisms that contribute to how foods and nutrients impact fertility.

Hayley: Looking at the evidence we do have, you discuss a study of 598 women undergoing ART for infertility treatment that looked at a range of foods and the likelihood of a live birth. If I summarise this again and ignore all the things that didn’t appear to impact ART outcomes - eating more fish increases the probability of a live birth. What is it about eating fish that improves ART outcomes and does it matter what sort of fish?

Jess: Fish contain a range of nutrients as well as omega 3 fatty acids. In particular, oily fish like salmon, trout and sardines, are even higher in omega 3 fatty acids. From that particular study, we don’t know specifically what it is about fish that was associated with higher live birth rates, as their study also showed that red meat, high in zinc and iron, but higher in omega 6 fatty acids, also associated with higher live birth rates. Fish oil supplements, which are made up of omega 3 fatty acids, were not associated with higher live birth rates. This points to the need for further studies to look at diet as a whole, but also to further examine the mechanisms that play a role in supporting fertility outcomes.

Hayley: Interesting that fish oil supplements didn’t improve outcomes, but the whole food did. It tells us that there are potentially lots of interactions happening in our bodies when we eat a whole food, vs just one specific nutrient that we would get from supplements.
You also report that women with higher intakes of beta carotene from orange and red vegetables, or lutein and zeaxanthin from green leafy vegetables had lower chances of a live birth compared to women with lower intakes. Am I reading this right, because it seems counterintuitive.
Does the research suggest that women should eat fewer orange/red vegetables and green leafy vegetables to increase their chance of a live birth? 

Jess: This is a good example of why we need to look at research as a whole and sum up all the available evidence rather than making up our minds just from one study. The results are in fact correct, and the results are not what you would expect; however, they are in line with other work that showed no benefit of antioxidant supplementation for females requiring ART.

Hayley: Do we know if these vegetables were organic? You refer later to lower intake of high-pesticide fruits and vegetables being associated with increased odds of a live birth. Could something else be going on with these results?

Jess: It is not stated whether the foods were organic or sprayed with pesticides, but rather than suggesting these antioxidants cause harm, the results from this single study suggest that these antioxidants are not beneficial.

Hayley: I think many of us are starting to understand that there is not one thing that helps us achieve our pregnancy goals. There are lots of factors that contribute to our overall health, and our fertility. How does the research separate out dietary factors from other lifestyle and wellbeing measures such as stress levels, environmental exposures and so on? How can we assess all of these things and come up with a holistic lifestyle plan for couples TTC?

Jess: In good quality research studies, scientists make decisions as to what other factors might also contribute to the variables that are being examined. For example, when looking at diet and fertility, scientists decide whether something like age or social class might link to both diet and fertility. If so, they include these variables in their analysis, so that any relationship that is found between diet and fertility, the other important factors have already been accounted for.
We really need more research identifying key dietary factors that relate to fertility, both at a population level, but also how to use this information at an individual level. Each couple has a unique fertility journey, so taking an individual approach, incorporating their diet and other characteristics, might be the way forward. 

Hayley: I really like this idea of dietary patterns, rather than individual foods, so I want to come back to that. I think what we are saying, is the overall diet, the sum of all of our food choices, is what really matters. When you looked at the research, it looked like the more fruit, vegetables, legumes, fish and olive oil consumed, the classic mediterranean diet, is associated with higher rates of clinical pregnancy and live births in women attempting to conceive and in women undergoing ART. Is this an appropriate conclusion to draw?

Jess: At this stage, and based on the recent but limited evidence I reviewed, these are foods that do seem to optimise fertility. While the research in this area needs to be supported by further studies, an overall healthy diet, that typically contains Mediterranean characteristics, appears beneficial.

Hayley: You refer to a study that looked at the ‘pro fertility diet’. What is the pro fertility diet? 

Jess: The pro fertility diet has been coined from the dietary information obtained from a series of smaller studies in couples undergoing ART. Participants received scores depending on their intakes of supplemental folic acid, vitamin B12, vitamin D, low-pesticide fruits and vegetables, whole grains, seafood, dairy, and soy foods. Scores were lowered for higher intakes of high pesticide fruits and vegetables. Overall, higher scores for the diet were associated with higher rates of implantation, clinical pregnancy, and live birth. 

Hayley: Is it accurate to say that if women eat more fruit while they are trying to conceive (more than 3 pieces per day), they might expect to fall pregnant more quickly, than if they don’t eat a lot of fruit (less than 3 pieces per month)? What about everybody in the middle?

Jess: This was actually a study that I published using a large cohort of women in which we were the first to report on a relationship between fruit intake and time to pregnancy. Again, this is just one study and we need more of these to support our results. A higher intake of fruit, of at least 3 pieces per day, had the greatest effect on time to conceive compared to those who consumed basically none, but there was still a small effect of those in the middle. Having more fruit than none at all was helpful for fertility. Exactly how many pieces of fruit each day a woman should eat, is still an area that needs to be investigated, but 3 pieces a day is a great start.

Hayley: I think many of us are starting to get the message that sweetened beverages are a bit of a no no, but it may not be clear that they can negatively affect your fertility too. You report on a study that compared people who have no sweetened beverages to people who have at least 7 sweetened beverages per week. Those who drank the sweetened beverages had a longer time to pregnancy. What are sweetened beverages doing to the body to have this effect on fertility?

Jess: Definitely, we are becoming more aware of the impact that sugar sweetened beverages can have on our overall health. In terms of fertility, the sugar these drinks contain may cause insulin resistance, which is when your body doesn’t respond so well to insulin, making it difficult to take up glucose (sugar) from your blood. This can lead to higher levels of inflammation and oxidative stress, leading to cell and tissue damage. Inflammation and oxidative stress can impact both egg and sperm quality, potentially making it more difficult to get pregnant. Additionally, the caffeine in some of these drinks may also affect fertility but mechanisms for how this might happen are currently limited.

Hayley: Overall, would you say that there are foods we really must include in our diets to optimise our fertility, or is it more the case, that there are some foods that we need to avoid in our diets?

Jess: Population data from the Australian Health Survey show that in adult women, only 7% consumed the right number of fruits and vegetables. However, calorie intake from discretionary foods, those that are higher in salt, fat and sugar, contributed to one third of daily energy intake. Clearly the balance here is not right, and we all have work to do in increasing healthier foods and reducing unhealthy food choices.
This also goes for fertility, and when planning a pregnancy. Including as many healthy foods as possible, like fruits, vegetables, dairy, lean meats and fish, and good quality carbohydrates, is much more likely to have a beneficial effect on fertility than having a diet including lots of unhealthy food choices like sugar sweetened beverages and take away foods. Further studies on key amounts and types of foods that really optimise fertility are needed, but again, aiming for improving diet quality is a good place to start.

Hayley: Jess, thank you, this has been incredibly valuable for us and our community. What would be the one message you want the eat for baby community to take away from your latest research?

Jess: It’s never too late to start eating a healthier diet.

Hayley: You also talk about diet and PCOS, diet and gestational diabetes and the diet of the male partner in this review. Can we talk to you again and cover these important topics too?

Jess: Absolutely, I look forward to it.