Seed cycling has been touted as helping to regulate menstrual cycles. One is supposed to take a combination of flax and pumpkin seeds (1-2 tablespoons each) during the first half of the cycle (from when your period starts until you ovulate, the “follicular phase”) and then sesame and sunflower seeds during the second half (after ovulation until your period starts again, the “luteal phase”). And if you have no period, you’re told to follow the cycle of the moon, taking the flax/pumpkin seeds from full moon to new moon, and the sesame/sunflower combo from new moon to full moon.
quick summary of evidence-based recommendations:
I find no support in the medical literature for the idea of switching seeds based on cycle phase, in fact, every study uses one (or two) seeds consistently for weeks to months at a time before benefits are seen. The highest quality evidence suggests flax seed for increasing luteal phase length, and sesame seeds for women with PCOS (increases sex homone binding globulin, which is typically low in women with PCOS). I recommend using these seeds consistently, not switching back and forth. If you do not currently have menstrual cycles, the strongest evidence suggests benefits of daily flax seed consumption.
Info on seed cycling
In some places discussions of seed cycling seems reasonable – like this article at Natural Health Perspectives, or this one at Herbal Academy where they discuss the lignans from the seed hulls as helping to modulate hormones (these are phytoestrogens that can affect your hormone levels) and fatty acids in the seed body that provide omega fatty acids that provide the building blocks for making the hormones estradiol and progesterone. And then there seems to be a protocol making the rounds where the explanation is that during the follicular phase that you use flax and pumpkin seeds “to block excess estrogen” and then sesame and sunflower seeds during the second half of the cycle “to help block excess estrogen”. Um, what? that makes no sense. There are times in your cycle when you need and want estrogen! (like when the follicle is growing during the follicular phase).
In line with my ongoing series examining supplement use and recovery of missing periods (hypothalamic amenorrhea), I wanted to examine the scientific underpinnings of this idea. Is there any real basis to switching seeds during the middle of the cycle (especially when the explanation of how the seeds are affecting hormones seems to be the same in both phases…)?
what is the evidence for seed cycling?
If you look in the medical literature (pubmed or google scholar searches), there are no published studies comparing seed cycling with any kind of control, or looking at alterations in hormone levels when using the variation of seeds. So the only evidence we have is inference from other studies, and anecdotes.
There is some evidence for the individual seeds. I covered flax seed in a recent post, In summary, flax seed has been shown in clinical studies to be associated with more ovulatory cycles, longer luteal phase, lower stress hormones and perception of stress. I do think that having 10g (ground) flax seed per day is a worthwhile addition to your daily fare, based not only on the cycle related benefits I just listed, but also overall health benefits.
So now let’s look at the other seeds. In seed cycling, flax seed is supposed to be paired with pumpkin seed.
I only found one study examining effects of pumpkin seed consumption in human females. This was a case-control study looking at breast cancer risk in postmenopausal women, and one finding was an association between higher intake of sunflower and pumpkin seeds with reduced estrogen-receptor positive breast cancer risk. This suggests that the seeds may possibly reduce estradiol and thus cause a slightly decreased risk of estrogen-receptor positive breast cancer (12% decrease). However, the association is not strong at all – I will spare you the details here, but include my thoughts in a note at the end of the post if you’re interested.
Other than that, all I could find is some information regarding pumpkin seeds and extracts thereof and benign prostatic hyperplasia in men (and a disease model in rats), as well as some information from studies of tumor cells. None of this convinces me in the least that there is value to taking pumpkin seeds, from the perspective of the female menstrual cycle.
Two experiments in rats (1, 2) found non-significant decreases in prostate size with a diet containing pumpkin seed extract. In both cases, a decrease in hyperplasia is seen, along with an increase in the testosterone/estradiol ratio in the test groups, based on non-significant increases in testosterone and decreases in estradiol in both cases. However, the control groups with no hyperplasia show totally opposite results with regard to estradiol – in the first study, the rats on the pumpkin seed diet have a 15% higher estradiol level, in the second, they have a 25% lower estradiol level. In the test groups, the differences are 3% and 0.6% respectively. I’m not convinced there is any effect at all.
One experiment in cancer cell lines showed a dose-response increase in estradiol production upon application of pumpkin seed extract, along with a decrease in estrogen receptor alpha and progesterone receptor in one of three cell lines. The second experiment showed the inhibition of growth of prostate cells as well as other cancer cell lines by pumpkin extract was not due to activation of the progesterone receptor, estrogen receptor, or androgen receptor. Nothing particularly indicative of an effect that would play a big part in regulating a menstrual cycle.
All in all, I find the evidence for pumpkin seeds having a beneficial effect on female menstrual cycles rather lacking, and I don’t particularly recommend pumpkin seeds for the purpose of regaining cycles or regulating them. However, pumpkin seeds do contain a number of valuable nutrients, so it’s certainly not going to hurt to eat them… but it’s good to do so with a clear understanding of what they can and cannot do.
Might as well discuss sunflower seeds next, given we already covered the study regarding sunflower/pumpkin seeds and breast cancer risk. In seed cycling, sunflower seeds are supposed to be taken during the “second half” of one’s cycle – either after ovulation, or after the new moon if you are not cycling.
The study discussed above is again the only one examining effects in human females, and possibly showed a small effect of lowering estrogen (in conjunction with pumpkin seeds – different from the seed cycling protocol), although the individual lignans did not show any effect. Six out of the other seven studies were performed in cows, the seventh was in hens.
The cow studies showed the following:
- Flax and sunflower seeds (given to separate groups of cows) had no effect on pregnancy rates
- No effect of sunflower seed on fertility or time to ovulation after cows gave birth
- Flax seed fed to cows for 28 days prior to ovulation increased the size of ovulatory follicles ~2mm over those fed with sunflower seeds, with no effect on follicle number, corpus luteum size, or progesterone production. Similar pregnancy rate, but lower rate of miscarriage in cows fed with flax.
- Cows fed sunflower seeds versus control diet had higher progesterone levels after 19 days of sunflower consumption, but not after 7 days. Higher pregnancy rate.
- Lower LH release in response to GnRH in postpartum cows after consuming sunflower seeds.
- Estradiol levels in cows fed flax seed or sunflower seed were not different from control fed cows (although the trend was higher levels in the sunflower seed group and lower in flax), plasma progesterone levels were ~20% higher in the flax and sunflower seed groups from days 2-11 after ovulation, very marginally higher in the sunflower group vs flax from days 2-4, and follicular progesterone levels were actually lower in the flax and sunflower seed groups.
- In the hens, a sunflower seed-based diet instead of a soybean-based diet led to increased estradiol and progesterone, by about 10% after two weeks of consumption, and continuing through eight additional weeks.
There is nothing in these studies that particularly supports use of sunflower seeds over flax – maybe there is a small effect on hormones, but it’s hard to be certain. There may be an effect on progesterone levels but that was not seen in every study so the evidence is weak. Also, it’s worth pointing out that every single study kept the animals on the same seed type through the entire length of the study, and aside from post-ovulatory progesterone in study 6, effects were not seen (e.g., in study 4 and 7) until 14+ days of consumption. Once again, however, sunflower seeds are a great source of a number of different vitamins and minerals, so there’s no reason not to eat them – just no evidence they will particularly help with menstrual cycle regulation or restoration.
Alright, last but not least – sesame seeds. These are also supposed to be taken during the second half of the menstrual cycle, post ovulation.
There is a crossover study that was conducted in menopausal women that looked at some sex hormones after ingestion of sesame seed powder that gives useful information to guide our assessment. There were two arms to this study; in the first, women consumed 50g sesame powder daily for five weeks, went through a three-week washout period, then consumed an equal amount of rice flour each day for an additional five weeks. The second arm reversed the two interventions. This is great because each women serves as her own control, although unfortunately data were not presented in that manner. The findings suggested that sesame seed powder could potentially have beneficial effects for reducing heart disease risk due to decrease in total cholesterol, LDL-C and an increase in gamma-tocopherol (not seen with flax seed, so a benefit in that regard – but also no changes in cardiovascular risk markers seen in a separate study). On the sex hormone front, sesame seeds reduced DHEAS and SHBG (sex hormone binding globulin) suggesting possible positive effects in a women suffering from PCOS, where SHBG is often low and plays a part in elevated free levels of androgens. In HA, however, SHBG is typically already quite high. The study found no change in estradiol levels.
Aaaaaand… that’s all she wrote. No other relevant studies of sesame seeds. Once again, sesame seeds are high in a number of nutrients with great health benefits, just nothing particularly associated with menstrual cycle regulation.
The other reason that is sometimes given for changing seeds at different times of the month is that the varied nutrients will theoretically support the follicular and luteal phases differently. I’m not really sure what to think of this. There is evidence in the medical literature for differential use and mobilization of nutrients during the different phases of the cycle, but I’m not sure this translates into needing MORE of a particular nutrient during a given phase. For example, this study found calcium levels in the blood were higher in the follicular phase than during menstruation in 50 normally cycling women, and magnesium was highest during the luteal phase. This one similarly found increased magnesium during the luteal phase, along with a decrease in zinc, in five women across three menstrual cycles. But does that mean supplementation is required? I’m not sure that necessarily follows. Even if it does, the zinc content of the seed-cycling recommendations is fairly similar across both phases. The Mg2+ level is ~30% higher in the seeds recommended for the follicular phase… but supplementation helping to reduce PMS symptoms, shows effects when used through the luteal phase. (And it’s worth pointing out that the amounts of magnesium used to reduce PMS symptoms are much higher than what one gets from these seeds – the values reported in the tables below are per 100g seeds, which is around 12-14 Tbsp, with 1-2 Tbsp recommended per day for seed cycling). It is worth noting the high calcium levels in sesame seeds which might be a good source of dietary calcium for bone health, but that’s independent of menstrual cycle effects.
The selenium content of sesame and sunflower seeds is supposed to “assist the liver in detoxification to clear hormones” however, I have to call bullshit on that. I have not been able to substantiate that with *any* medical literature. It is true that there are a number of enzymes that use selenium, but they have nothing to do with “clearing hormones” – rather, they act as antioxidants (I honestly don’t even know what “clearing hormones” is supposed to mean.) Here is a very thorough review of the literature on selenium, note that the section on female reproduction (2.3.2) is quite small. There was a cool study that found glutathione peroxidase, a selenium containing antioxidant enzyme, in growing follicles, with more Gxp in larger, healthier follicles. And other studies suggesting the importance of selenium in maintaining progesterone levels (note this is in cows during pregnancy). Given that the recommended amount of selenium for supplementation is 100 micrograms, the ~7 micrograms that one would get from 1Tbsp per day each of sunflower and sesame seeds is not going to make a material difference. In addition, once again, in studies examining effects of selenium, the supplements are taken for weeks at a time, so no evidence for two weeks on and two weeks off. Selenium does seem to be beneficial; based on some of this evidence I might suggest supplementation with sodium selenium (and of course feel free to eat sunflower and sesame seeds; just know that the levels of selenium are probably not high enough to make much difference.)
Once again, I do not find support for switching seeds during the menstrual cycle, or in order to recover missing periods.
There is no solid reason for switching between seed types either during a menstrual cycle or switching at the phases of the moon if you’re not cycling naturally. Is it going to hurt anything? probably not. And it may be the case that it’s helpful to get the different nutrients that are in each of the seed types. However, the evidence that is quoted for effect of these seeds on reproductive hormones, or as providing minerals necessary during different phases of the cycle is not in the least convincing, and therefore, I do not see the need to bother with switching seeds around for someone trying to restore missing periods, or for general menstrual cycle regulation.
I know that there is plenty of anecdotal evidence for the benefit of seed cycling; I am lead, based on all this information, to wonder if similar results would be achieved with use of a single seed type or mix of seeds on a consistent basis, rather than switching back and forth. Given the promotion of the seed cycling protocol across the internet, I think it’s unlikely that anyone has tried this, so it is impossible to say if there truly is benefit in the changes in seeds versus consistent use of one seed type.
The highest value information I found suggests flax seed is beneficial for increasing luteal phase length, and sesame seeds are beneficial for women with PCOS. In both these instances, the evidence points to using the seeds daily rather than switching between types, as was done in the clinical studies that show these effects. So if you have PCOS and would like to try increasing SHBG, you could consider consuming ground sesame seed each day and see what happens. If you have a short luteal phase after HA recovery, consider flax seed.
If you are still working to regain cycles, consuming flax seed daily (the study showing hormonal effects used 10g/day) is a reasonable step to take given the overall health benefits, potential cycle benefits, and lack of demonstrated harm.
Note about sunflower/pumpkin in breast cancer study
Note: Regarding the association between breast cancer risk and consumption of sunflower/pumpkin seeds: I’m not convinced this is a real effect for a few reasons. First, the association is not seen in the crude odds ratio, only after adjustment for confounding factors, and the statistical significance is weak (0.04 for unadjusted and 0.02 for adjusted) and not corrected for multiple testing. Some things I looked at: the median intake in both groups (breast cancer cases and age-matched women not suffering from breast cancer, a.k.a. controls) was identical at 2.05g/day. The 25% and 75% intakes were also the same, 0.41g/day and 4.45g/day. The percent of women ingesting sesame/pumpkin seeds was 55.9% versus 57.5% in women with and without breast cancer, with a p-value of 0.5 (i.e. not at all significant). Digging deeper, among cases consuming S/P seeds, 49.2% were consuming a “low” amount versus 50.8% consuming a “high” amount (below and above the median value), compared to 47.6% and 53.7% respectively among controls, p-value of 0.04. This difference in percentages consuming low vs. high amounts in the two groups is what the reduction in risk is based on. The other caveats of the study (using food frequency questionnaires to determine intake amounts, the association only seen when the questionnaires were given withing six months of breast cancer diagnosis, no association seen when consumption of the lignans contained in the seeds was estimated and tested ), lead me to be uncertain of the validity of this finding.