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The Science of Nutrition and Fertility

Updated: Mar 10

You can check out the corresponding YouTube video here.

You’ve landed on this page likely because you’re finally at a point in your life where you feel ready to have a baby, and you would like to optimize the process. Or, maybe you are just curious to know what food has anything to do with baby-making. It turns out that what you eat – and that goes for both my female and my male readers out there – impacts your sexual health in ways that may surprise you.


If you are trying to create one of these cute beings, making a few changes to your diet could make a big difference!

Before we get into the impact of diet on fertility, let’s start by defining fertility and infertility and looking at some key stats.


Fertility and Infertility


Fertility, defined simply, is the ability to conceive a child. According to the Centers for Disease Control and Prevention (CDC), “…infertility is defined as not being able to get pregnant (conceive) after one year (or longer) of unprotected sex.”


Data from the National Survey of Family Growth indicates that here in the US, 9% of men and 11% of women of reproductive age have fertility issues. In 1/3 cases, the problem lies with the male, in another 1/3 with the female, and in the final 1/3 of cases, both.


Fertility declines with age in both sexes, but the decline in fertility comes more rapidly for women. I’m sure you’re familiar with the notion of women having a biological clock that is forever ticking away. After age 35 years, there is an exponential decrease in fertility for women. For men, of course, having kids well into old age is much more probable. This may not be the case forever though.


Data from multiple studies across decades show that in the future, men may need to worry more about their ability to reproduce after they have a head full of gray hair - or no hair at all.

This is because sperm counts have been on a downward trend. Sperm count is a crucial indicator for male fertility. In this 2017 meta-analysis, which is a type of research study that combines data from multiple studies done on the same topic to get a unified picture of what is going on, it was found that between 1973 and 2011, there has been a 50-60% decline in sperm count. The results from this more recent paper support this conclusion, but the authors caution that these results are not generalizable to the entire global population – these findings apply to North America, Europe, Australia, and New Zealand. We don't really have data from Asian, African, and South American countries.


The silver lining is that it does not seem like sperm counts have decreased enough to have any noticeable impact on male fertility – not yet at least. Estimates of infertility in the US have actually been pretty steady for the past couple of decades.


Now, on to the big question: How does food affect fertility?


In this review paper published in 2021, researchers searched through evidence from over 100 research articles based on studies done around the world and found that diet pattern and intake of certain foods and nutrients can and does impact fertility.


I’m going to summarize all of this data under 10 topics.


1. Dietary Patterns


Dietary patterns give the most complete picture of what a person actually eats. The ones that most often came up in these studies are:

  • The Mediterranean Diet,

  • The Prudent Diet, and

  • The Western Diet.


In men, both the Mediterranean Diet and the Prudent Diet were associated with better sperm quality. Both of these diets are rich in fruits, vegetables, fish, poultry, legumes, and whole grains - the stuff that you know is good for you. The Prudent Diet in particular was linked to increased sperm concentration and higher levels of testosterone. Both this diet and the Mediterranean Diet were tied to a reduced sperm DNA fragmentation index – this means that the DNA of the sperm of the men following these diets had less mistakes. In women, the MedDi has been positively associated with fertility, pregnancy, and live birth.


So, guys, what you choose to eat daily literally affects the genes of your sperm cells.

Multiple studies showed that a Western Diet filled with sweets and snacks, refined grains, processed meat, especially processed red meat, and animal fat was associated with abnormal semen count, lower sperm motility, and abnormal sperm shape.


Now, let's look at specific foods and fertility.


2. Dairy


Dairy includes anything derived from cow’s milk. In men, a high intake of dairy products has been linked to lower levels of testosterone, follicle stimulating hormone, and luteinizing hormone – the last two being hormones that assist in sperm production.


This isn’t the full story though – the fat content of the milk appears to matter quite a bit, as do the hormones that tend to be mixed in with the milk fat. Dairy contains very small amounts of estrogen, and some studies show that for boys and men, consuming dairy and dairy products may lead to higher levels of female hormones and less testosterone. This is another tough one, because there is an almost equal number of studies both supporting and refuting this. Overall, the trend seems to be that full fat dairy products, not skim milk, are associated with poorer fertility measures.


In women, a high intake of dairy was associated with lower ovarian antral follicle counts (AFC) – a measure of how many eggs a woman has left, particularly among women with fertility issues. Results from the Nurses Health Study II – one of the largest studies ever done - suggest that dairy does not affect ovulatory infertility. However, anovulatory infertility was linked to low-fat dairy intake in this study. This means that people who consumed tons of low-fat dairy were more likely to have this particular type of fertility problem. The jury is out on this one though, because there is evidence from other cohort studies out of Denmark that suggest that low-fat dairy can actually increase fertility, and there are also studies saying that there is no association. Saying “no association” is boring, I know, but that’s honestly all we can conclude so far with the research that has been done.


3. Meat


Here, I’ll focus just on red meat and poultry. I’ll cover fish next. For men, hormones injected into meat to promote the growth of the animal may have a negative effect on sperm concentration. This applies to red processed meat especially. In women, animal protein was shown to have no effect on fertility in one study. In a different study, eating red meat and poultry was linked to reduced risk of infertility in women undergoing fertility treatment. Two studies is not a preponderance of evidence, so it would be great to see more studies done in this arena. It's likely that the type of meat, how it was prepared, what it was consumed with, and other factors would need to be considered.


4. Fish


In both sexes, fish intake has been associated with shorter time to pregnancy (TTP) and better fertility. One thing that I want to point out is that fish oil supplements did not have the same effect – you can’t take the “easy road” here, you have to actually eat the fish to enjoy the benefits. The difference is nothing small either – we’re talking up to 60% greater fertility after a year of eating fish every week.

Perhaps this is why some claim that salmon is an aphrodisiac.

If you are concerned about mercury, remember that the idea here is not to eat fish morning, noon, and night for nine months – just 3 servings of seafood per week is what the Food and Drug Administration (FDA) recommends. This is a case where the benefits can be said to outweigh the risks, but of course, you should take your own life circumstances into account and follow the advice of your medical team.


5. Soy


Soy is a great source of protein if you aren’t a fan of eating animals, but it also includes hormones that are very similar to estrogen. So you may guess that it benefits women and harms men – but the research isn’t that cut and dry. All in all, soy does not appear to have any effect on fertility for either sex.


Now, let's look at specific nutrients.


6. Fat


Fat is actually a pretty broad category, because there are many different types of fats – long chains, short chains, saturated chains, unsaturated chains, etc. The main ones that matter here are saturated fats, trans fats, omega-6s, and omega-3s. To make it really simple, saturated fats, trans fats, and omega-6s are all in the villain camp, and omega-3s are the heroes. Omega-3s are great because they may help with the regulation of hormones that are important for egg implantation and pregnancy.

Docosahexaenoic acid (DHA) is an example of an omega-3 polyunsaturated fat. Source.

Fat matters a lot for sperm health, because the type of fat that you eat is what ends up making up your sperm cells. Polyunsaturated fats (PUFAs), mainly DHA, accumulate in the sperm cell membrane, and more DHA here has been linked to greater sperm concentration and better sperm motility and shape. And yes, there are studies that show that eating foods rich in PUFAs like fish and walnuts help to improve these measures of sperm quality. Fish intake among men has also been associated with a shorter time to pregnancy and a reduced risk of infertility.


Omega-3s are also associated with greater testicular volume, which is positively correlated with sperm count, while omega-6s and trans fats are associated with smaller testicular volume. Trans fats are also related to negative measures like poor semen quality and lower sperm count. Artificial, lab-made trans fats were banned back in 2015 – that’s how bad they are, the government actually banned them.

You can check out this article for more details.

Nevertheless, trans fats can still be found in some corners of the food supply: they occur naturally in meat and dairy, and they form during high heat frying – so chicken wings, donuts, and any deep fried delicacy is likely to have trans fat, especially if the oil has been reused.


A higher intake of saturated fat has been linked to fewer mature eggs in women undergoing in-vitro fertilization (IVF). A high intake of trans fats and a low intake of omega-3s has also been linked to poorer fertility outcomes. On top of that, trans fats have been shown to increase the risk of metabolic disorders that negatively impact fertility, e.g. insulin resistance and inflammation.


7. Carbohydrates


For the purposes of this article, let's just say that we have two main categories of carbohydrates (carbs) – processed, refined carbs like bread, cupcakes, and soda, and unrefined, unprocessed carbs like apples, sweet potatoes, and beans.


In men a high overall intake of carbs has been associated with a greater prevalence of problems related to sperm motility. In other words, their swimmers don’t swim as well. In women, there is more evidence that the type of carb matters. Both total carb intake and intake of refined carbs have been linked to a higher likelihood of ovulatory infertility. There is also research showing that higher intake of whole grains is linked to a higher probability of live birth.


8. Alcohol


Now, let’s talk about alcohol. If you haven’t seen my video on the effects of alcohol on health in general, or read the article I wrote on the same topic, then you have some catching up to do!


On the topic of fertility, in men, daily alcohol consumption is tied to reduced semen volume and lower semen quality. Occasional intake did not have a significant negative effect, just daily intake. For women, occasional drinking also seems to have no impact on fertility.


9. Caffeine


There is no clear impact of caffeine on male or female fertility. Still, the general recommendation is to limit to 2-3 cups of coffee a day (equivalent to 200-300 mg caffeine). Up to 400 mg per day is safe for most people, according to the Food and Drug Administration (FDA). To be clear, I’m talking about coffee, not those sugar-laden Tik Tok inventions that we for some reason still call coffee.


I mean, where do we draw the line between coffee and dessert?

10. Sugary drinks


Lastly, let’s look at sugary drinks, or what we in the research community like to label as sugar-sweetened beverages (SSBs). In men, the intake of SSBs and sweet snacks has been linked to lower sperm concentration and quality. Women who drink SSBs, including energy drinks, are more likely to have poorer fertility compared to women who avoid those drinks altogether. This is because sugar may affect reproductive hormones, how eggs mature, and even the release of eggs from ovaries.


Let's look at some examples of popular drinks that are considered to be SSBs.


First, let's visit Starbucks. Use the arrows to scroll across and see the nutrition information for each of these examples. This grande frappucino has 59 grams of sugar. For those of you who do not frequent Starbucks, this is not even the largest drink that they sell.


Next, let's stop at a minimart and get some thirst quenchers. Thirsty AND running on 2 hours of sleep? You may pick up a Rockstar energy drink. That has 63 grams of added sugar in a can.


Maybe you have a small child with you, and they want a drink too. For a sweet treat that comes with unverified "facts," Snapple is the best choice, if you don't mind the 42 grams of added sugar per bottle.

For reference, the American Heart Association or AHA recommends a limit of 25 grams of added sugar per day for women and 36 grams for men. All of these drinks surpass that limit, showing how easy it is to overdo it with your added sugar intake.


11. Pesticides


Bonus item number 11 is pesticides. Fruits and vegetables are obviously good for you, but the pesticides that they are typically grown with aren’t. There is data showing that fruits and vegetables with low pesticide residues like avocados, beans, and onions are associated with healthier sperm, while intake of high-pesticide residue produce like strawberries, apples, and spinach is linked to poorer semen quality. If you have the money to buy organic, this may be one reason to do it. If you can’t, don’t worry – the whole planet is polluted anyway, so we’re all ingesting pesticides one way or another.




As a responsible scientist I want to add the following caveat – much of this wonderful research data is correlational, meaning that it came from observational studies, not intervention studies. This doesn’t mean that the data isn’t valid, it just means that there is the potential that other factors aside from diet may influence the reported outcomes. Also, with something as complex as nutrition, it’s really hard to isolate a person’s diet and perfectly control that single variable in a lab and then tie it to a single outcome – real life doesn’t work that way. The air we breathe, where we were born, how we make a living, and what unmeasured pollutants are in the water supply, are just a few of the innumerable factors that affect our health, so remember to keep a holistic view of these results.




References:


Fertility and Infertility Stats:




Chandra, A., Copen, C.E., & Stephen, E.H. (2013). Infertility and Impaired Fecundity in the United States, 1982-2010: Data From the National Survey of Family Growth. National Health Statistics Reports, 67, 1-19. Retrieved February 7, 2018, from https://www.cdc.gov/nchs/data/nhsr/nhsr067.pdf (PDF 328 KB)


Practice Committee of the American Society for Reproductive Medicine in collaboration with the Society for Reproductive Endocrinology and Infertility. (2013). Optimizing natural fertility: A committee opinion. Fertility and Sterility, 100(3), 631–637.


Hagai Levine, Niels Jørgensen, Anderson Martino-Andrade, Jaime Mendiola, Dan Weksler-Derri, Irina Mindlis, Rachel Pinotti, Shanna H Swan, Temporal trends in sperm count: a systematic review and meta-regression analysis, Human Reproduction Update, Volume 23, Issue 6, November-December 2017, Pages 646–659, https://doi.org/10.1093/humupd/dmx022


Auger, J., Eustache, F., Chevrier, C. et al. Spatiotemporal trends in human semen quality. Nat Rev Urol 19, 597–626 (2022). https://doi.org/10.1038/s41585-022-00626-w


Snow, M. Vranich TM, Perin, P, Trent, M. (2022). Estimates of infertility in the United States: 1995–2019. Fertility and Sterility, 118 (3), P560-567.


Food and fertility:


Aoun A, Khoury VE, Malakieh R. Can Nutrition Help in the Treatment of Infertility? Prev Nutr Food Sci. 2021 Jun 30;26(2):109-120. doi: 10.3746/pnf.2021.26.2.109. PMID: 34316476; PMCID: PMC8276703.


Nassan FL, Chavarro JE, Tanrikut C. Diet and men's fertility: does diet affect sperm quality? Fertil Steril. 2018 Sep;110(4):570-577. doi: 10.1016/j.fertnstert.2018.05.025. PMID: 30196939.


Gaskins AJ, Sundaram R, Buck Louis GM, Chavarro JE. Seafood in-take, sexual activity, and time to pregnancy. J Clin Endocrinol Metab. 2018. 103:2680-2688.


Ricci E, Al Beitawi S, Cipriani S, Candiani M, Chiaffarino F, Viganò P, Noli S, Parazzini F. Semen quality and alcohol intake: a systematic review and meta-analysis. Reprod Biomed Online. 2017 Jan;34(1):38-47. doi: 10.1016/j.rbmo.2016.09.012. Epub 2016 Oct 18. PMID: 28029592.


EFSA NDA Panel (EFSA Panel on Dietetic Products, Nutrition and Allergies), author Scientific opinion on the safety of caffeine. EFSA J. 2015;13:4102. doi: 10.2903/j.efsa.2015.4102.





Nutrition information for sugar-sweetened beverages mentioned in the video:


American Heart Association (AHA) recommendations for added sugar:

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