What to Know About a Low-Carb Diet and Fertility

You’ve been doing all the things—tracking cycles, eating “clean,” cutting out caffeine—and yet, your positive test still hasn’t come.
It’s frustrating, disheartening, and you might be wondering if there’s something deeper going on beneath the surface.

One area that’s often overlooked in the fertility conversation is blood sugar—and specifically, how the foods we eat affect our hormonal balance. For some, especially those with signs of insulin resistance, PCOS, or irregular cycles, a high-carb or highly processed diet may quietly be making conception more difficult.

As a certified nutrition coach with a master’s degree in cell biology and a deep focus on gut health, fertility and pregnancy, I’ve seen how a strategic lower-carb approach can make a real difference for women who’ve been trying to conceive for over a year without success.

In this post, we’ll break down why a low-carb diet may help support fertility, what the science actually says, and how to make sustainable changes that nourish your body without feeling restricted.

Photo credit: Andrea Piacquadio

But if you’re thinking “great! I’ll just go keto”— not so fast…

Like everything in nutrition and fertility, there are many nuances you’ll want to consider when implementing a lower carb diet for fertility. We’ll dive into more of those details below, so keep reading on!

If you’d like to skip all the juicy details on all things carb, fat and protein for metabolism and fertility (which I really hope you don’t but understand you have tons of things to do and may not have time to nerd out like me) here are the key takeaways on how best to implement a low-carb diet for fertility based on all the research. 

Key takeaways from this article:

• A diet lower in carbohydrates compared to the standard western diet is safe when trying to conceive and can even be beneficial for fertility outcomes.

• This is especially true if you’ve been struggling with Polycystic Ovarian Syndrome (PCOS).

• Lower carb does not equal a very low-carb, ketogenic diet.

• Diet quality is just as—if not more—important than diet composition. Whole foods first.

• Aim for <40% of your caloric intake coming from carbs (Roughly <200g carbohydrates), at least 100g of protein with the rest coming from high-quality healthy fats.

• It’s important to ensure you’re getting enough calories if reducing your carb intake. 

• Carbohydrate source matters. Refined sugars and flours influence metabolism in a way that whole food carbohydrates do not.

But if you’re ready to arm yourself with the knowledge of how your body and metabolism functions and how it impacts your fertility, let’s get into it!

Keep reading to the bottom for more actionable tips and the link to your free 20-minute fertility audit below.

What exactly is a low-carb diet?

The term has been used for decades, but there is actually a lot of confusion around what actually constitutes a low-carb diet. 

For the purposes of this article I will clarify a very low-carb diet (or ketogenic diet) as <20-50g net carbs per day, low-carb as 50-120g/day, moderate-carb as 120-200g and higher-carb diet as >200g. 

Net carbs are the carbohydrates that you consume minus the grams of fiber you consume, since fiber does not affect blood sugar in the same way as other carbohydrates like simple starches and sugars.

Is a low-carb diet good for fertility?

You’ve probably heard success stories of people who “tried this diet and got pregnant” that seem to be completely conflicting. “I went vegan and got pregnant after years of trying!,” or “I went keto and got pregnant after years of infertility.” 

I believe these stories, but it doesn’t mean that one size fits all diets are the key to your fertility success. 

The person who got pregnant after going vegan may have had chronic undiscovered issues with milk protein immune response, and cutting it out was what made the difference, while the person who went keto may have been struggling for years with blood sugar regulation issues, or inadequate fat intake for optimal hormone production and that is what did it. 

With that being said, blood sugar issues are a main driver of fertility-related challenges with the current western diet based on refined flours and sugars, and studies have shown benefits and improved fertility outcomes when adopting a lower carb, whole foods diet.

The evidence indicates that a diet lower in carbohydrates compared to the standard western diet is safe when trying to conceive and can even be beneficial for fertility outcomes. 

A metaanalysis of seven fertility studies showed that diets with low to moderate carbohydrate intake improved fasting insulin and fertility outcomes compared to higher carbohydrate diets mainly for those who have PCOS and are overweight or obese. 

Another study showed that those who consumed the highest carbs and added sugar compared to those who consumed the lowest had a lower conception rate. Although, consuming at least 25g fiber, which is a carbohydrate, showed better conception rates. 

This means the type of carbohydrate matters as well as the amount. 

It’s important to note that most of these studies were done for 6 months or less, so the long term effects are less understood. There is research suggesting that while high fat or high protein/lower carb diets in the short term can have profound effects by improving blood glucose levels, weight, and other biomarkers, for sustained periods of time (>6 months) may have negative impacts on health. 

But I do pause here to remind everyone of the nuance in science and scientific studies.

You can’t take all study results at face-value

The difficulty with interpreting the research for how low-carb diets may affect fertility and hormones is the lack of general consensus over parameters. 

There is no definition of a “low-carb diet” that is universal in the literature. Also, diet quality is usually never addressed. 

One study I reviewed did address this, but lumped starchy vegetables like winter squash and sweet potatoes in with refined flours and sugars as “unhealthy carbohydrates” while lumping all animal protein in as “unhealthy proteins.” 

This lack of nuance makes it so difficult to find quality research for determining the optimal carbohydrate level for a whole-food, omnivorous diet.

The importance of a high-quality diet

Oftentimes, higher fat and protein diets can be correlated with increased risk of metabolic issues long-term because the quality of the diet is not being accounted for. 

For example, processed foods are typically very high in artificial trans fats and fats from highly refined industrial seed oils which have much higher omega-6 fatty acid content then we were designed to consume. Likewise, conventionally raised meat on grains have omega-6 fatty acid profiles that are up to 5x higher than grass-fed meat. 

This is important because omega-6’s are pro-inflammatory and used to elicit an inflammation response in our body, while omega-3s are anti-inflammatory. 

Both are essential to our health for sure, but we know that higher omega-6:omega-3 ratio than we’ve evolved to sustain leads to inflammation in the body. This may really be the driving factor for the increase in these metabolic issues over time. 

Ways you can reduce this effect are to eliminate industrial seed oils such as soybean, corn and sunflower oil as much as possible and to choose 100% grass-fed or pasture-raised for all land animal-based products. 

Remember, the sources of these oils are not bad for us. It’s just that making oils out of these products are A) unstable and produce free-radicals more quickly and B) allow for much higher levels in our diet than if we were to consume these fats in their whole food format.

Also, incorporating more omega-3 acids into your diet can counter balance the effects of too high omega-6. Fish is the best source because it includes beneficial DHA which is imperative for fertility and pregnancy, but plant-based omega-3’s like walnuts, flax and chia seeds are also beneficial.

Bottom line—it's important to watch how your body responds over time, but if you are focusing on a high quality, whole foods diet with sufficient (but not excessive) caloric intake, it is likely safe for longer periods of time. 

How many carbs should I eat when trying to conceive?

Research suggests that protein levels of 25-35% and a lower carbohydrate diet (<40% of caloric intake) with the balance made up of fat, can increase pregnancy outcomes more than four times compared to lower protein, higher carb diets.

This is corroborated by the metaanalysis cited earlier, showing <45% carbohydrates to be beneficial for fertility outcomes.

What’s interesting is that this dietary make-up closely resembles the best estimate of the ancestral human diet composition—AKA how we evolved to eat—which has been estimated as 35% of their dietary energy from fats, 35% from carbohydrates and 30% from protein.

It also may be beneficial to base how low-carb you are going based on your cycle. Eating higher amounts of complex carbohydrates like winter squash and sweet potatoes during your luteal phase can be beneficial for optimal progesterone production.

Photo credit: Nathan Dumlao

Is low-carb a good option for PCOS?

Because polycystic ovary syndrome (PCOS) has roots in insulin resistance, studies suggest lower carbohydrate diets do appear to be a particularly beneficial option for those diagnosed with this condition. 

Lowering your carbohydrate consumption while increasing proteins and fats can lead to better blood sugar regulation and weight loss, both of which are important for management of PCOS.

Studies have shown that short-term very low-carb ketogenic diet have been shown to improve reproductive hormone levels and fertility outcomes.

Considering supplementing with myo-inositol can also be very beneficial especially for those with PCOS, due to its effects for balancing blood sugar while still maintaining a moderate intake of carbohydrates.

Are low-carb diets bad for your hormones?

There is not a universal indication that low-carb diets with adequate caloric intake are bad for hormones, but some people do seem to respond better to higher carbohydrate levels. Usually it is the very low-carb diets that can lead to hormonal imbalances over time.

For some people’s systems, too limited of carbohydrates can cause stress in the body and tax the adrenal glands. But I believe the bigger risk to your hormones is insufficient dietary fat. 

Fats, specifically cholesterol, are necessary for making reproductive hormones, so ensuring adequate intake of healthy fat is key to reproductive and hormonal balance.

Saturated fats in particular have been unjustly maligned in the last half century, a stance which has been challenged by industry experts and is now being reviewed for the newest round of dietary guidelines. 

That doesn’t mean you need to be adding butter to your coffee, but just don’t take fat away. 

Buy whole-fat dairy products, use adequate oil when cooking, feel free to eat butter on your toast and eat fat-rich snacks like avocados, nuts, seeds and olives. 

Oh, and please I beg—don’t discard the yolks when eating eggs! That's where all the nutrient goodness comes from!

Photo credit: Jenna Hamra

The results are mixed for thyroid hormones. Studies have shown both decreased thyroid function associated with increased glycemic load and a low-carb diet. 

Some propose that a minimum level of 100g carbohydrates are needed for proper thyroid hormone conversion, while others suggest that a ketogenic, low-carb state makes us more thyroid-sensitive, leading to need for less conversion to take place. 

Definitely speak to your healthcare practitioner if deciding to implement a low-carb diet if you have a pre-existing thyroid disorder.  

Not eating enough calories can cause hormonal imbalance and fertility issues

One of your main priorities when it comes to eating for fertility is to ensure you are eating enough. 

I know it seems counterintuitive with all the diet culture talk out there, but especially if incorporating a diet like low-carb when you restrict or eliminate foods or entire food groups, eating enough can be one of the biggest issues causing cycle irregularities or fertility challenges. 

Carbohydrates do provide a good amount of calories for most people, so if you are limiting them be sure you are supplementing with other foods, especially healthy fats, as these have a very high caloric bang for your buck and are very satiating. 

Watch for changes in your menstrual cycle

Your menstrual cycle will be a big indicator of how things are going if you decide to implement a lower carb diet. If you have fully lost your cycle, also known as amenorrhea, this is a big signal that you need to increase your calories.

But even if you notice smaller changes in your cycle like your luteal phase shortening, or you notice decreases in your cervical mucus, definitely see how adding in more fat and/or complex carbohydrates affects the next cycle. These could be signs you are not providing enough fuel to support optimal fertility. 

Cortisol, insulin resistance and low-carb diets

Chronic cortisol increases the release of glucose stored in the body and actually decreases insulin sensitivity. This has been shown to lead to increased insulin resistance over time.

So a big question is “does a low-carb diet increase cortisol?”

Long-term calorie restriction increases cortisol, so it's possible that caloric restriction is the main driver in cortisol changes with implementing a low-carb diet.

However, in a study of different dietary compositions when calories were maintained, although the very low-carb diet (<50g carbs) showed the best biomarker improvements for insulin sensitivity, HDL, energy expenditure and triglycerides, it also showed the highest levels of cortisol. 

Because many of us already have chronic stress (ahem—fertility can be such a huge stressor in and of itself!) going very low-carb on top of that stress may tax your adrenals and cortisol levels too much. 

And remember that the quality of the diet, especially the omega-6:3 fatty acid ratio can contribute significantly to inflammation and cortisol levels. 

The studies showing cortisol increases with long-term low-carb diets may be due to increased fats and proteins of poorer quality. 

Many of today’s fat and protein sources are much higher in inflammatory omega-6 fatty acids than our body was designed to maintain—like 5x or more higher! These levels lead to chronic inflammation that can inevitably lead to higher cortisol levels. 

Cortisol works to combat inflammation in the body, so if there is more inflammation, there will be more cortisol released to help tame it. 

So what does this all mean?

It means balance, as with anything in life, is key. I don’t believe any extremes are necessary for reaching optimal fertility, and in fact, balancing carbs, fats and proteins seem to be the best approach. 

The basics for implementing a low-carb diet for fertility

If considering a lower-carb diet for fertility, I’d stick to the basics:

• Aiming for <40% carbohydrates (ideally, 100-180 g/day), 25-30% protein and the remainder of healthy fat. 

• Choose high quality whole foods instead of processed foods whenever possible. 

• Get enough calories, but not too many. Your body actually regulates this pretty well if you are eating a whole foods-based diet without processed foods that hijack your hunger cues.

• And maybe most importantly—always balance your blood sugar! I find it is most often not necessary to go very low-carb if you are mindful about how you are eating your carbohydrates. This can also allow for your body to produce a better carbohydrate tolerance over time as opposed to just restricting carb indefinitely. This means carbs with fat and protein always.

You can grab my 7-day meal plan for fertility (with downloadable PDF and grocery list!) here, which incorporates all of these principles.

Bringing it all together

A diet lower in carbohydrates than the standard Western approach can be not only safe when trying to conceive—but also incredibly supportive of fertility, especially for those navigating challenges like PCOS. 

That said, lower-carb doesn’t mean no-carb. There’s no need to go full keto unless advised by your provider. What matters most is focusing on whole, nutrient-dense foods and making sure you're still getting enough total energy to support hormone production and ovulation.

Aiming for under 40% of your calories from carbs (roughly <200g per day), at least 100g of protein, and filling the rest with healthy fats is a balanced, realistic place to start. And don’t forget: the source of your carbs matters. Whole-food carbs like fruit, root vegetables, whole grains and legumes support your metabolism and microbiome in a very different way than refined sugar and flours.

When done intentionally and with nutrient quality in mind, a lower-carb diet can be a powerful tool on your fertility journey—one that supports hormone balance without leaving you feeling deprived and your body stressed out.

If you're not sure where to start or how to make this work for your unique body, feel free to reach out—I’d love to help you build a nourishing plan that fits your goals. 

Book your free 20-minute fertility audit here to get the best next step for you to implement on your fertility journey, or if you are really ready to upgrade your fertility, save your spot in my Fertility Transformations 12-week program to totally transform your mind, body and spirit for optimal fertility!