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Meat, Poultry, Fish, Tofu: Which Protein is Best and Which One is Worst for Your Fertility?

by Katelyn

In the second part of my Foods for Fertility series I’ll try to answer this question: depending on the type of protein I eat, does it help or hurt my chances of getting pregnant? And as always, I give you my thoughts on the facts as backed by science.

Part 1. The Ultimate Fertility Diet: What To Eat When Trying to Conceive
Part 2. Meat, Poultry, Fish, Tofu: Which Protein is Best and Which is Worst for Fertility?
Part 3. Definitive Guide to Fats That HELP Fertility: Omega-3 and Other Fatty Acids
Part 4. Definitive Guide to Fats That HURT Fertility: Saturated Fats and Other Fats

 

Why protein is important for your fertility

Protein is an important part of a well-rounded diet. Your body needs protein for growth, maintenance, and energy. Protein is an important building block of bones, muscles, and skin, it’s needed to create enzymes and hormones, and it’s crucial for tissue repair. In other words, in order to function properly, your body needs protein.

And I’m not just talking about protein being important to you! Getting enough protein is also really important for your future baby as well. For example, feeding rats a protein-restricted diet results in impaired embryo implantation and way fewer baby rats being born.1,2

So yeah, I think we’ve established that protein is really important 😉

But does it matter what you eat? Chicken or fish? Pork or beef? Soy or Turkey? Beans or Yogurt?

For most of us, these are our main sources of protein. A lot of research has focused on dairy, so I’ll talk about that in its own separate post. Let’s start off with meats!

 

Beef? Pork? Chicken? Fish?

Meat and fertility

Less than 10% of people in the United States are vegetarian.2 And the remaining 90%? They get most of their protein intake from meat. But what I’m about to tell you might make you seriously consider Meatless Mondays!

Remember how I talked about the Nurses Health Study in the previous post? Researchers from the Harvard School of Public Health looked at meat consumption in relation to fertility.3 Just to refresh your memory, thousands of women were asked to answer a detailed questionnaire about their dietary habits every 2 years, over the course of 8 years. They were also asked if they’d been attempting to get pregnant and whether they’ve been at it for more than a year without success and whether they had issues with (a lack of) ovulation.

With this information in hand, researchers tried to figure out if dietary patterns were associated with fertility in any way.

The researchers found that women in the top 20% of total protein intake, that is, meat, fish, dairy, and beans had a much higher risk of ovulatory infertility.

Uh oh. That’s not good!

Each additional serving of meat per day (while holding the total number of calories the same) was associated with a 32% greater risk of ovulatory infertility. That means these women had a much-increased risk of not ovulating (and thereby, not being able to get pregnant).

Now the question on everybody’s mind is: which meats are the worst offenders. And the answer might be somewhat surprising!

Processed meats did not tip the scales of infertility much. Neither did fish consumption (okay maybe that one isn’t very surprising).

The big offenders were both red meats (beef, pork, lamb, venison) at a 42% increase in risk, and poultry (chicken, turkey) at a 53% higher risk of ovulatory infertility.

 

Looking a bit deeper: evidence from IVF

While these results are pretty damning, nothing in science is set in stone until it can be replicated many times over. Well, a recent study tested whether women undergoing IVF had lower antral follicle counts.4

If you’ve ever heard of the term “ovarian reserve” you’ve probably also come across the term “antral follicle count”. The antral follicle count are the number of egg-containing follicles early on in the menstrual cycle. If the antral follicle count is low, this could be an indication that your ovarian reserve is low (and you might enter menopause sooner).

Luckily, the researchers found no link between meat consumption and a lower antral follicle count.

So thus far, we’ve talked about 1 large epidemiological study suggesting that meats can be really bad for your ovulatory cycle, but also 1 smaller infertility study suggesting that meat consumption isn’t too bad, at least not when it comes to the number of eggs you have left. Unfortunately, there’s more to getting pregnant than just ovulating and having enough eggs.

One hypothesis is that the actual quality of the egg, and down the line, how well the embryo grows, is influenced by meat consumption

Researchers from Brazil tested whether meat consumption has an influence on the actual quality of embryos.5 In IVF, doctors tend to look for good quality embryos. The best embryos develop into something called a blastocyst after roughly 5 days of incubation. The not-so-good quality embryos never make it to day 5.

Guess what they found! The number of 5-day blastocyst embryos was:
– lowest
in women who eat a lot of red meat
– neutral for women who eat mostly chicken
– and highest in women who regularly consume fish!

So again, when it comes to animal protein, red meat is the boogeyman, and not just when it comes to ovulation, but also embryo quality!

 

Vegetable protein

lentils protein fertility

Let’s talk about protein sources that are not meat. Beans, lentils, cereal, cheese, pasta, soy, and tofu. There are many non-meat sources of protein, and there is some pretty convincing evidence that consumption of this kind of protein can actually help your fertility!

Unfortunately, one reason women may have trouble conceiving is because of Premature Ovarian Failure/Insufficiency (sometimes referred to as early menopause). And some studies have shown that higher vegetable protein intake is associated with a decreased risk of Premature Ovarian Failure.6

Just like before, researchers used data from the Nurses’ Health Study where the dietary habits of women were recorded for many years. They found that women who were in the top 20% of vegetable protein intake had a 16% lower risk of early menopause than women who consumed much less protein. Just increasing daily vegetable protein intake by 1% lowered the risk of early menopause by 6%!

And guess which specific sources of protein had the biggest impact on reducing the odds of early menopause…! Yeah, you’re probably not going to guess correctly…

It’s soy and tofu, and…. pasta, whole grain bread, and cereal! Yeah, like I said… you probably didn’t guess that one correctly 😉

In fact, an additional serving of daily pasta was associated with a 36% lower risk of early menopause!

Hold on, wait a minute!

Pasta isn’t usually seen as a high protein product (5-8 grams per 100-gram serving, depending on the type). But it’s still a bit odd seeing how pasta could win this shootout. My guess is that women who eat lots of pasta also tend to adhere to the Mediterranean Diet, which we know is associated with many positive health outcomes, including fertility.

 

Soy and tofu

tofu soy isoflavone fertility

Soy is a major source of protein for many across the world. And there’s a thing that makes soy, tofu and other derived products special.

Soy products contain something called isoflavones. And isoflavones have the ability to act or mimic the hormone estrogen, and because of that, it’s also called a phytoestrogen. These isoflavone phytoestrogens can bind to estrogen receptors, and are therefore called “estrogen binding disruptors”. And by binding to estrogen receptors, isoflavones are able to influence your reproductive system and by extension, also your fertility.

Now, exactly how this works and what influence isoflavones exert is still being investigated, but there are several studies that give us some clues. And it’s looking pretty good!

A 2019 study from the University of Sao Paulo in Brazil looked at female mice who were given soy isoflavones for 8-weeks. After that, the researchers looked at the mice’s ovaries.7 They found that the soy isoflavones had to ability to protect the eggs and could possibly even extend the ovarian lifespan!

And another study found that when female mice’s diet was enriched with soy, embryo quality improved substantially!8

So far so good, right?

Unfortunately, it’s not all sunshine… In one study thousands of women from the Adventist church were asked about their dietary habits. Why you might ask? Well, the church is known to encourage its members to lead healthy lifestyles and vegetarian diets.

Researchers found that in women over age 40, a very high soy isoflavone consumption of 50 milligrams per day was actually linked to a slightly lower chance of having children. But the difference was very minimal at only 4%.

To eat 50 milligrams of soy isoflavones you really need to put in an effort! The average isoflavone consumption in Western societies is less than 3mg.9 Tofu which is made of soy, for example, contains about 22mg of isoflavones per 100 grams,10 so to reach 40 or 50 milligrams every single day, you must really be a tofu-fanatic! And even then, the difference is only 4%.11

 

Soy isoflavones: so is it good or bad?

So far, we’ve seen some evidence that suggest that soy isoflavones are a good thing for egg quality and fertility in general, but also that at high doses it could even (slightly) harm fertility. What’s going on here?

Some recent studies tried to shed some light on this question. Do soy isoflavones actually help fertility or not? Well, the evidence suggests that there is one particular group that can expect a boost in fertility: couples having trouble conceiving!

Take this 2015 study from Harvard. Researchers looked at 315 women who were undergoing IVF treatment for infertility.12 They found that higher consumption of soy led to a higher chance of becoming pregnant and delivering a healthy baby.

And in yet another IVF study, high dose soy isoflavones lead to a much improved pregnancy rate of 30.3%, compared to 16.2% in women who only received a placebo pill.13

There are two ways isoflavones could be helpful with fertility: one is by improving the endometrial thickness, which is something researchers from Italy found in women undergoing intrauterine insemination (IUI).14

The other way soy isoflavones can be beneficial is by blocking the negative effects of Bisphenol A, also known as BPA. This substance found in many plastic products (think water bottles and food storage containers) and when it leaks into your food or drink, it is known to negatively influence fertility. BPA is man-made phytoestrogen, while soy isoflavones are natural phytoestrogens. Somehow, soy isoflavones seem to counteract or block BPA, thus in a way replacing the negative BPA with neutral or positive isoflavones.15

So are soy and tofu good for your fertility?

If you’re struggling to conceive, it could have a positive influence, especially if your exposure to BPA is high.

 

The bottom line

Protein is a really important building block of your body, and that also includes your eggs and eventually your baby too. Eating enough protein is very important.

Taking it all in, the most important message I can give you is that when it comes to fertility, animal protein is “worse” than vegetable protein, because…

  • Eating less meat can improve ovulation problems.
  • While eating meat is not associated with fewer eggs, egg and embryo quality can be improved by eating less meat (especially beef, pork, and venison).
  • Eating more vegetable protein, especially if that also means a reduction in meat consumption, is associated with better fertility and cycle regularity, especially if you’re a bit older.
  • Eating more vegetable protein could delay the onset of Menopause.
  • Eating more vegetable protein can help if you’re struggling with infertility.
  • Tofu and other soy products contain isoflavones which may help fertility.

So if you’re having trouble conceiving, simply cutting out meats from your dinner a few nights a week and replacing it with beans, lentils or tofu might not be such a bad idea!

 

References

1. Alexander MH, Lazan KS, & Rasmussen KM. (1988). Effect of chronic protein-energy malnutrition.
2. Reinhart RJ. (2018). Snapshot: Few Americans Vegetarian or Vegan. Gallup.
3. Chavarro JE, Rich-Edwards JW, Rosner BA, & Willett WC. (2008). American Journal of Obstetrics and Gynecology, 198(2), 210.e1–e7.
4. Souter I, Chiu YH, Batsis M, et al. (2017). BJOG: An International Journal of Obstetrics and Gynaecology, 124(10), 1547–1555.
5. Braga DPAF, Halpern G, Setti AS, et al. (2015). Reproductive Biomedicine Online, 31(1), 30–38.
6. Boutot ME, Purdue-Smithe A, Whitcomb BW, et al. (2018). American Journal of Epidemiology, 187(2), 270–277.
7. Teixeira CP, Florencio-Silva R, Sasso GRS, et al. (2019). Gynecological Endocrinology, 35(7), 586–590.
8. Oliva L, Santillán M, Ryan L, et al. (2013). Hormone and Metabolic Research, 46(2), 120–125.
9. Messina M. (2010). The Journal of Nutrition, 140(7), 1350S – 4S.
10. Bhwagwat S, Haytowitz DB, & Holden JM. (2008). USDA Database for the Isoflavone Content of Selected Foods. USDA.
11. Jefferson WN. (2010). The Journal of Nutrition, 140(12), 2322S – 2325S.
12. Vanega JC, Afeiche MC, Gaskins AJ, et al. (2015). Fertility and Sterility, 103(3), 749–755.e2.
13. Unfer V, Casini ML, Gerli S, et al. (2004). Fertility and Sterility, 82(6), 1509–1513.
14. Unfer V, Casini ML, Costabile L, et al. (2004). Journal of the Society for Gynecologic Investigation, 11(5), 323–328.
15. vom Saal FS, Welshons WV. (2016). Nature Reviews. Endocrinology, 12(5), 251–252.

 

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Hi, I’m Katelyn!

Mom, scientist, and fertility nerd extraordinaire.