How Does Your Fat Intake Affect Your Fertility?

We know that both too much and too little fat can harm your fertility. And that omega-3 fat is great for fertility where as trans fat is harmful. But what about other fats? Does your omega-6, monounsaturated and saturated fat intake affect your fertility too?

How Does Your Omega-6 Fat Intake Affect Your Fertility?

When it comes to omega-6 fats and fertility, things get a bit more complicated. It’s generally agreed that most people consume a little much omega-6, particularly compared to omega-3. This is mostly in the form of oil from fried or packaged food. Omega-6 fats are known to be a bit inflammatory, which is generally something we want to limit. 

But some parts of conceiving actually require inflammation! 

For example, inflammation is thought to play a key role in implantation. It has been suggested that an increase in omega−6 at the time of implantation increases inflammation in the endometrium, making it more receptive and encouraging embryo implantation!  

This may explain why some studies show higher intakes of omega-6 are associated with increased pregnancy rates. 

For example, one study in IVF found women who became pregnant had higher levels of omega-6. Another compared the Mediterranean diet with a ‘health-conscious–low processed diet’, the main difference between the two being a higher omega-6 intake in the Mediterranean diet, which was found to increase pregnancy rates. Although these weren’t particularly high-quality studies they do support the idea that including extra omega-6 through whole food sources such as nuts, seeds and legumes around the time of implantation may be beneficial. (Ps. you could include your post-transfer fries in this category too if you want- they’re definitely inflammatory!!) 

However, when it comes to long term health, it’s still best to make sure you don’t consume excess omega-6 — particularly from oils and processed food.  A mouse study found that a diet high in omega-6 in the long term is associated with very poor reproductive success at advanced maternal age and in the short-term leads to very poor oocyte quality.

How Does Your Monounsaturated Fat Intake Affect Your Fertility?

Monounsaturated fats are generally considered to be a healthy source of fat in the diet. But how do they affect fertility specifically? Unfortunately, not much is known.

A large study in women with prior pregnancy loss found that higher blood levels of monounsaturated fat was associated with shorter time to pregnancy. However, other studies in both IVF and natural conception found no relation between monounsaturated fat and fertility. 

Interestingly, one mouse study showed high monounsaturated fat intake prior to conception lead to more females offspring. Whether or not the same goes for humans we don’t know!

We need more studies looking at monounsaturated fat and fertility. In the meantime, it’s a good idea to get plenty of your fat intake from food high in monounsaturated fat as they’re generally pretty healthy. 

It’s probably a good time to point out that most food has a variety of types of fat in it. For example avo, olive oil, eggs all have monounsaturated, saturated and omega-6 fats, in that order. If you’re eating whole plant foods, you’re likely to be having a good balance of at least a few different types of fat and that’s a good thing! 

How Does Your Saturated Fat Intake Affect Your Fertility?

Saturated fats are often referred to as “bad” or unhealthy fats. While I don’t love the terminology, it’s is true that excess saturated fat – particularly from red meat- has been shown to have some negative impacts on the body. But how does it affect fertility?

Like monounsaturated fat, there is less known about the effect of saturated fat on fertility than omega-3 and omega-6. Many studies (like this and this) found no direct association. One study looked at the levels of various fats in women’s follicular fluid, which is generally a reflection of a person’s intake. They found that higher levels of saturated fat and a higher ratio of saturated fat to polyunsaturated fat lead to lower numbers of mature eggs, even after factoring in the women’s age.

Animal studies have suggested that like with polyunsaturated fat, the specific types of saturated fatty acids may have different effects. This is an interesting idea but much more research is needed in this area. 

However thanks to the Nurses Health Study we do know that high levels of meat intake is associated with anovulatory infertility, so avoiding excess saturated fat, especially from fatty meat, seems like a good idea. 

I’ll talk more about dairy when we look at protein but I couldn’t talk about saturated fat without mentioning it! There is evidence that the saturated fat in dairy is not associated with the same cardiovascular damage as the saturated fat in meat is. 

In terms of fertility, the Nurses Health Study gave us some info on this too: full fat dairy intake was associated with less ovulatory infertility but low-fat dairy was associated with more. Another recent study in IVF found no difference between the two but an overall non-significant increase in live birth rates with dairy intake. But other studies haven’t found a relationship between dairy intake and fertility. 

So for now? No need to avoid dairy or increase your intake for the sake of fertility.

TLRD:

 In the last four posts, I’ve covered a lot of info about fat and fertility. Here’s a summary:

It’s important to include fat in your diet every day to support your cycles⁠
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Too much fat, particularly if it’s linked to unnecessary weight gain, can lead to insulin resistance and affect your gut health- both harmful for fertility⁠
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Marine omega-3s are the OG of the fats. They help keep your eggs young and embryos healthy, they support ovulation, fertilization, clinical pregnancy and live birth⁠
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Omega-6s are likely helpful in moderation, their inflammatory effect may actually help implantation! Go nuts for nuts in your TWW⁠
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Monounsaturated fats are a good source of fat in general, but probably won’t make too much of a difference to fertility directly⁠
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Saturated fats are fine in moderation, especially from dairy sources, but don’t go crazy on the fatty meat⁠
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Trans fats are truly the worst and you should avoid them at all costs!⁠