According to NUNM (2019), that is, the National University of Natural Medicine in Portland, seed cycling is when you rotate seeds into the diet based on the phase of the menstrual cycle you are in. Apparently this has shown to support hormonal health anecdotally. They report this to be beneficial because of the content of essential fatty acids in the chosen seeds, which aid hormone production. In addition to this, the fibrous content of the seeds aids phase III detoxification of hormones. In the follicular phase, one would consume seeds such as flax or pumpkin daily to support oestrogen regulation. In the luteal phase, this switches to sunflower or sesame seeds to support progesterone.
NUNM referenced the 1993 study by Phipps, et al. to support this article. Within the study the authors looked at flax seeds' (powdered) effect on the menstrual cycle. The lignans contained in flax seeds show weakly oestrogenic and antiestrogenic properties. The authors compared the second and third cycle of the women’s regular diet with the second and third cycles during flaxseed supplementation. None of the cycles during flaxseed supplementation were anovulatory, compared to 3 prior, and a slightly longer luteal phase. There were minimal hormonal changes; luteal phase progesterone/estradiol ratios were significantly higher, mid follicular testosterone concentrations were slightly higher during flax cycles (Phipps, Martini, Lampe, Slavin & Kurzer, 1993).
Perhaps this theory is more grounded in the nutritional content of each of the seeds. Dietary zinc may reduce or prevent premenstrual cramping, which doesn’t make sense when it was suggested to be consumed pre-ovulation (Eby, 2007). Or the addition of these seeds boosting magnesium (150mg in 28g of pumpkin seeds) or iron intake (by 1-2mg/d) suggesting some effect (Parazzini, Di Martino & Pellegrino, 2017). This seems unlikely, it is such a small amount, even everyday. Maybe they meant to suggest the omega-3 fatty acid content? As this has shown benefit in treating dysmenorrhea also (Rahbar, Asgharzadeh & Ghorbani, 2012). There are no published studies so any evidence towards this is based on theory or suggestion.
Healthline suggests flax seeds for their fibre, protein, magnesium, thiamine, manganese, and omega 3 content, but must be broken down or ground (Robertson, 2017; Osiecki, 2007). Chia seeds could easily be swapped here. Sesame seeds for their sesamin (lignand), however, contain a majority of the copper RDI. Pumpkin seeds for their phosphorus, magnesium and manganese, zinc and protein. And finally, sunflower seeds for their vitamin E, protein, magnesium and anti-inflammatory action (?) (Robertson, 2017; Osiecki, 2007).
I see the benefit of the added nutrition, but I do not seed the reason for cycling. Why not just make a mix of the four and use it daily?