On the species level, humans are amazingly resilient when it comes to fertility reproduction. As a group, we can keep the species going even under very harsh circumstances. Living in Siberia? No problem. Years of famine? Can do! Extreme stress? Sure. The Dutch Hunger Winter of 1945 was famous for the way that the famine changed gene expression in the babies of women who were pregnant at the time – but the really amazing thing is that anyone conceived and carried to term under those circumstances.
But individuals can struggle even though Homo sapiens as a whole is doing fine. If you’re personally having trouble conceiving, the survival of the species isn’t much consolation. So here’s a look at diet, lifestyle, and fertility, through the Paleo lens.
This is a topic where men and women have completely different experiences, so in case you don’t care about the opposite sex…
- Click here to go straight to women’s fertility issues.
- Click here to straight to men’s fertility issues.
Or keep reading to see both.
Diet can affect female fertility in several different ways, and a lot of them are related to the hormone insulin.
The Big Picture: Insulin
Insulin is an important hormone for fertility, but most people know it better as the hormone regulates blood sugar. It’s also directly responsive to diet.
If this is the first time you’re hearing about insulin and diet, go here to get the full story. It’s too complicated to summarize in just a few sentences!
Diet and lifestyle factors that can prevent insulin from doing its job include a diet high in refined carbs, a diet high in Omega-6 fats, accumulation of visceral fat, chronic inflammation, stress, and sleep deprivation. All of these problems can make your body less responsive to insulin signals, just like your ears get less sensitive to noise if you’re around loud noises all day. This is called insulin resistance. People with insulin resistance need to make more and more insulin just to overcome the insulin resistance and keep blood sugar stable.
High insulin levels are a major cause of female infertility. Chronically high insulin increases the production of androgens (male sex hormones), which impairs female fertility. Polycystic Ovary Syndrome (PCOS), a disease that causes insulin resistance among other problems, is the most common cause of female infertility.
Symptoms of abnormally high insulin levels include:
- Weight gain, especially fat gain around the stomach (apple shape)
- Constant hunger and sugar cravings
- (very rarely) extremely low blood sugar
Insulin resistance is often associated with high blood pressure, high triglyceride levels, and high cholesterol.
Eating for Fertility: Carbs
Women who want to conceive can improve their fertility with a diet that regulates insulin levels. But that doesn’t necessarily mean a low-carb diet!
Take a look at some studies done on low-carb diets and fertility.
- This study found that a low-fat, high-carb diet didn’t affect ovarian hormones at all.
- On the other hand, this one found that a high-carb, high-sugar diet was associated with lower fertility.
- This one found that a “fertility diet” pattern, including restrictions on refined carbs but not on total carbs, was associated with a lower risk of infertility.
All those conflicting results make sense, because insulin sensitivity is very individual. Just eating carbohydrates doesn’t cause insulin resistance all by itself, and restricting carbs isn’t always the answer.
In fact, for women without existing insulin problems, a low-carb diet isn’t necessary at all and might totally backfire. Carbohydrates are a physiological signal to your body that you’re getting enough to eat. If it thinks you’re not getting enough to eat, your body knows better than to have a baby.
The takeaway is not “eat a low-carb diet.” The takeaway is “eat a diet that supports healthy insulin function for you, whatever that diet happens to be.”
Diet and Hormones: Weight and Weight Fluctuations
Another way that diet and lifestyle can indirectly affect fertility is by affecting weight. This ties back to insulin in some ways, but it also has some effects independent of insulin.
This review goes over some of the weight-related hormone abnormalities that can affect fertility. Very low body weight, very high body weight, or significant changes in weight can all do it.
- Very low weight reduces fertility. You need a certain amount of fat tissue to send the hormonal signals to your hypothalamus that your body can support a healthy pregnancy. Without enough body fat, your body will simply shut down reproductive activity because it’s not safe.
- Very intense physical activity also impairs fertility, and it appears to work even if you’re eating enough to support it. (On the other hand, moderate exercise improves fertility)
- On the other hand, obesity is also associated with reduced fertility. Excess fat tissue can produce too much estrogen, and obesity typically comes with a higher level of insulin resistance. A review found that in overweight or obese women, losing weight by any means improved fertility. It might also have something to do with the diet that caused the obesity: this study found that a high-calorie cafeteria diet (basically the rat version of a human junk-food diet) reduced fertility in rats.
Diet and Fertility: Other Important Nutrients
The third way that diet can affect fertility is simply by providing enough important nutrients. Again, some of this has to do with insulin and some of it doesn’t.
The right fats are particularly important:
- Trans fats are associated with fertility problems, possibly because they increase insulin resistance and inflammation.
- The ratio of Omega-6 to Omega-3 PUFA may also be important, especially for women over 35 or so. If you don’t know what any of that means, go here. The ideal is a low total amount of PUFA, with a focus on Omega-3s (from fish and seafood) and a very minimal amount of Omega-6s (from industrial oils and soy).
- Saturated fat may be helpful. This study is fascinating: low-fat dairy foods might be dangerous to fertility while high-fat dairy foods may be helpful. The link was unrelated to lactose (the carbohydrate in milk), calcium, phosphorus, or Vitamin D. That’s following up on another study suggesting that saturated fat may be associated with healthy menstrual cycles.
What about micronutrients, like vitamins and minerals?
- Vitamin D is important for fertility, and may help reduce the risk of endometriosis. It’s worth paying attention to, because a lot of people actually are deficient in Vitamin D. You can get more from supplements or sunbathing.
- This review suggested that women undergoing infertility treatments might benefit from supplementing with folic acid, vitamins B6, C, D, and E; iodine, selenium, iron, and Omega-3 fats. That’s a really long list of different supplements!
- A Cochrane review found no convincing evidence that antioxidant supplements improved female fertility.
Pulling it All Together
Here’s a summary of advice based on all the studies above:
- If you have insulin problems, a low-carb diet may be helpful. Otherwise, it could easily backfire.
- Eat enough food. If you’re severely restricting calories, exercising intensely, or underweight, your fertility will probably be suboptimal. Eat more and spend some time lying around on the couch!
- If you’re overweight, weight loss may help.
- A Paleo approach to fat may be helpful. Focus on saturated and monounsaturated fat (animal foods, dairy, olive oil…) and Omega-3 fats (fish and seafood). Avoid excess Omega-6 fats and trans fats.
- When it comes to micronutrients, studies on supplements are confusing. A diet rich in all different fruits and vegetables is the best prenatal vitamin of all.
Since this is Paleo, it’s worth noting one final thing: celiac disease is associated with infertility. If you have celiac disease, looking into everything beyond gluten elimination may be helpful.
That was the ladies; now on to the gents!
For men, the hormonal issues typically aren’t as complicated, but men can still have diet-related problems with fertility. Mostly this shows up as problems with sperm quality and sperm motility. After ejaculation, sperm have to “swim” up through the cervix into the uterus, and then down the fallopian tubes until they reach the woman’s egg. Sperm with motility problems don’t stand a very good chance of fertilizing the egg even if there are plenty of them.
Weight, Testosterone, and Insulin
In men, diet can affect fertility by raising or lowering testosterone levels. This can happen indirectly through weight gain/loss or directly through fat consumption.
Like women, men are most fertile when they’re neither overweight nor underweight. For men, this is probably caused by testosterone levels rather than insulin. Men who are overweight or underweight typically have lower testosterone levels than men at a normal weight, which can reduce sperm count and fertility. But unlike female fertility, male fertility or sperm quality doesn’t seem to be directly affected by insulin resistance alone.
Weight loss isn’t the only way that diet can affect testosterone. An important dietary factor directly affecting testosterone levels is fat quality. Saturated fat (animal foods, coconut oil) and monounsaturated fat (animal foods, olive oil, avocados) are both important.
Diet and Fertility: Nutrients and Oxidative Stress
Men’s fertility is also affected by particular nutrients. The big picture here might be oxidative stress.
Oxidative stress is basically inflammatory damages to cells. For sperm cells, the real problem is oxidative stress damaging the DNA contained in the sperm, so the sperm can’t fertilize the egg. Oxidative stress is involved in the majority of cases of male infertility in one way or another. Because of the way sperm cells are built, they’re particularly vulnerable to oxidative stress.
Diet can affect oxidative stress in all kinds of ways:
- Omega-6 fats are very vulnerable to oxidative damage. Unsurprisingly, they’re associated with male infertility. This study found that men with infertility have a higher ratio of Omega-6 to Omega-3 fats in their blood and sperm, and fertile men have higher absolute levels of Omega-3s. Diet can directly affect the Omega-6 content of sperm cells, and this has a direct effect on sperm quality. This study found that dietary Omega-3 fats actually caused a measurable improvement in sperm quality.
- Sugar is another driver of oxidative stress, and it’s also associated with lower sperm quality.
- Antioxidants help fight oxidative stress. A review found that antioxidant supplements may be helpful, but a lot of the studies were of pretty low quality so take it with a grain of salt.
Fertility and Stress
Psychological stress is also important for male fertility, tying right back into the problem of inflammation and oxidative stress. Psychologically stressful situations (like exams, wars, work stress, or deaths in the family) can reduce sperm quality.
Summing it Up
Diet can affect fertility for men and for women, but it works a little bit differently depending on sex.
- For women, insulin resistance and metabolic health is a bigger deal. A lower-carb diet may be helpful for women with metabolic issues, but not necessarily for other women. For women who don’t have metabolic issues, restricting carbs might just be another stressor – and that’s actually bad for fertility.
- Both sexes are most fertile when they’re not overweight or underweight. Women in particular need a certain amount of body fat to conceive.
- Fat quality is important for both sexes: limit Omega-6 fats from industrial oils, and get enough Omega-3 fats from fish and seafood. Saturated and monounsaturated fats may help for healthy hormone production.
- Vitamins, minerals, and antioxidants are also important for both sexes, but studies on supplements are conflicting and underwhelming. It’s probably better to rely on a diet rich in nutrient-dense organ meats, fruits, and vegetables than a supplement.
And then there’s the role of stress. Stress is bad for fertility for both sexes, but struggling with fertility problems is one of the most stressful things around! It might help to schedule in concrete things you can do to reduce stress, like gentle exercise, taking walks in nature, or meditation.
If this looks a lot like out-of-the-box Paleo: well, yeah. That’s the idea! This is how we evolved to eat, and the whole point of evolution is successful reproduction. Sometimes evolution is a real pain in the neck (like the way we evolved to gain weight easily and hang onto it by every means possible) but in this case, it’s really on your team.