I’m not going to tell you exactly what to eat...or not to eat for that matter. Even though I’m a nutritionist and people expect that from me, I don’t believe in giving people more “rules” around food. I may make suggestions based on certain goals. I may share the data as I understand it. I may share my working theories based on my research and clinical experience. However, I encourage you to take all of this in and come to your own conclusions about what’s right for you and your body.
Here we go.
One study of ~9,000 women found that female vegetarians and semi-vegetarians had more menstrual problems than their non-vegetarian counterparts. They experienced higher incidences of PMS, irregular periods, heavy periods and period pain. Vegetarians and semi-vegetarians also tended to have low iron levels and poor mental health (depression, anxiety, sleeplessness). This is despite the fact that they had higher levels of physical activity and were more likely to be in a healthy BMI range.
Several studies have corroborated the fact that vegetarians tend to have lower hormone levels than their meat-eating counterparts.
Another study showed that after two years on a low fat (<15% of total calories), high carbohydrate diet, women had estrogen levels that were 20% lower, progesterone levels that were 35% lower and FSH that was 7% higher. This might be helpful for women who are at high-risk for estrogen-sensitive cancers, but it’s no bueno for fertility.
Yet another study (though a small one) showed that 9 women each were placed on a vegetarian or non-vegetarian diet for 6 weeks. During this period, 7 of the 9 vegetarian women had anovulatory cycles; in contrast, 7 of the 9 non-vegetarian women maintained ovulation.
I hope you see that this isn’t just one study or one factor. Copious amounts of data confirm the fact that vegetarian women have more menstrual difficulties and irregularities than their non-vegetarian peers.
Why is this happening?
Several reasons, of course. [Let’s put aside the potential for disordered eating among vegetarians although that may be a factor.]
1. You need cholesterol and protein to make hormones.
One study actually found that the probability of menstrual irregularities was inversely related to protein and cholesterol content. In other words, the more protein and cholesterol you have in your diet, the less likely you will have menstrual problems. Sounds pretty counter to what we’ve been told for years, huh?
The reason for this is because sex hormones are made from cholesterol. Yes, you read that right. One of the raw materials necessary to make your sex hormones is cholesterol. And, plant sterols (the “cholesterol” equivalent from plants) just doesn’t do it for our bodies in the same way that cholesterol from animal products does. Also, your body does make its own cholesterol, but supplemental cholesterol from our diet may help us reach more optimal levels.
Second, protein from animal products tends to be more bioavailable than protein from plant products. Don’t get me wrong - there are plenty of sources of protein in a vegetarian diet (e.g., quinoa, rice and beans, lentils). However, it’s just not as quickly and easily digested and assimilated as animal protein.
2. Certain nutrients are only available in animal products, such as vitamin A (retinoids specifically), vitamin D (except maybe mushrooms!) and vitamin B12 (unless foods are fortified with these nutrients). Beyond this, the bioavailability of certain nutrients is better from animal sources than plant sources. For example, the conversion from ALA (from plant sources) to DHA is quite poor; it’s better to get DHA directly from oily fish. Also, heme iron (from animals) is more bioavailable than nonheme iron (from plants). This is likely why vegetarians tend to have lower iron levels than non-vegetarians. And finally, zinc levels are also is also lower on vegetarian diets. As you probably already know, vitamin A, vitamin D, vitamin B12, iron and zinc are all critical for the pre-conception and prenatal periods of development.
What does this all mean?
It means that if you are vegetarian and are currently having menstrual difficulties, you may want to consider strategically adding some meat back into your diet. In some cases, it can be really hard to restore a normal menstrual cycle without animal products.
If you’re happy with your cycles and your fertility, I’m happy too. If you’re not, maybe it’s time to consider another viewpoint of what’s healthy for you right now in the context of your fertility goals.