HELPING YOU MAKE SMART AND DISCERNING CHOICES
What is Hormone Syncing
In the last decade, there has been an increasing attention to the idea of women tracking their reproductive cycle and hormones for the purposes of aligning activity, nutrition, and exercise choices to improve our wellbeing and performance.
This awareness and resulting choices may be something you’ve always done, never considered or are thinking about signing-up to. Let’s see what’s useful to know.
Women's Reproductive Cycle
Most women’s reproductive cycle starts during puberty and continues rhythmically until perimenopause [1] before stopping at menopause. The menstrual cycle, the ovarian and the uterine cycle constitute the reproductive cycle and it often becomes a predictable part of life.
Once the reproductive cycle is established, many women become familiar with naturally tracking and adjusting certain aspects of their life in response to their menstrual cycle.
It's not the same for everyone
For some, the cycle can be absent or disrupted, often due to pregnancy and breastfeeding. Lifestyle and environmental factors can also disrupt reproductive hormones, as can stress and disorders, together with certain illnesses and structural anomalies.
There are also medications and contraceptives that can change or stop menstruation.[2]
Ancient practices
meet modern technology
Tracking the reproductive cycle, fertility and pregnancy duration is evident in ancient cultures, counting sticks in baskets, sewing strips of fabric onto garments and notching wood.
It’s been speculated that the earliest known mathematical artefact – the Lebombo Bone – from around 40,000 years ago, with 29 notched marks, might have been used to track a lunar cycle or menstrual cycle.
Technology and ‘wearables’
More recently, understanding the effects of reproductive hormones has allowed the tracking of cycles through temperature. Dutch gynaecologist Dr. Theodoor Hendrik van de Velde in the early 1900s, correlated changes in a woman’s basal temperature that occurs during the menstrual cycle with progesterone production.[3]
Today, science has been joined by technology and there are ‘wearables’ such as colour-coded beads together with smartphone apps that take measurements to track hormone cycles. There are urine tests that measure estrogen and luteinizing hormone (LH) for fertility.
The term that went viral…
‘cycle syncing’
Searches for cycle syncing started in 2021 and peaked at the turn of this year [4].
The viral search term ‘cycle syncing’ was successfully registered in the USA as a trademark in 2022, by FLO Living LLC.
FLO Living LLC was founded in 2012.
Company founder Alisa Vitta, released her book WomanCode in the spring of 2013, published by HarperOne becoming a bestseller in its genre. The app MyFLO followed, launched in 2017, an app that ‘provides daily insights, recipes, meal plans, workouts and productivity hacks customized to your unique cycle’ [5].
Multi-million app business
Similar name, but not affiliated with MyFLO, the app FLO is generally considered the market leader in period tracking apps, generating revenue through its premium subscription service.
According to Business of Apps - the leading B2B media and information platform - Flo made $275 million from its subscription service in 2025, with 77 million monthly active users that year and 300 million registered users since its launch in 2016. The number of downloads in 2025 make it one of the most installed health and fitness apps of the year [6].
And the apps keep coming
Launches of apps continue into 2026 with increased consideration to data privacy.
How to sync
Alisa Vitta’s Cycle Syncing method is described as a nutritional and lifestyle protocol aimed at managing hormonal imbalances such as PCOS, fibroids, and endometriosis.
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Menstrual Phase (Days 1–5): Low energy; focus on rest, gentle movement (yoga, walking), and nutrient-dense foods including eating iron-rich foods (leafy greens, beans).
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Follicular Phase (Days 6–13): Rising estrogen; high energy/optimism; good for starting new projects and higher-intensity exercise.
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Ovulation Phase (Days 14–16): Peak energy/confidence; good for social, high-stakes tasks.
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Luteal Phase (Days 17–28): Progesterone rises, then drops; energy dips; good for focused, detailed work and lower-intensity exercise.
Support and Criticism
Anecdotal support from women’s personal experience of aligning their reproductive cycle to lifestyle, exercise and nutrition is readily found on social media.
Whilst scientific evidence on effectiveness may be limited or inconclusive, it is promoted by some wellness coaches, nutritionists, and personal trainers. It has also been openly used by elite athletes.
There is on-going research into potential benefits, specifically around exercise and physical performance. Tracking your cycle and attention to your body may certainly have benefits, however strict, standardised - or barely customised - recommendations are unsupported.
Both the method and particularly the apps have received ample criticisim.
Following a 2019 New York Times article, vice.com stated of the creater of MyFLO ‘Vitti isn’t a doctor and doesn’t have a medical degree; the Institute for Integrative Nutrition, the “vocational school” where the New York Times asserts she studied, is not accredited by the U.S. Department of Education or any agency that assesses educational institutions, per an assessment by Credential Watch. Vitti has no other relevant credentials.’[7]
In 2021, FLO was found to be sharing sensitive data—including period dates and pregnancy status—with Facebook, Google, and other analytics providers without user consent, violating their own privacy policies. They have since implemented better protections, but as of 2026, lawsuits regarding privacy violations are still resulting in settlements, with a $56 million class-action settlement tentatively approved in the US regarding the sharing of personal information with third parties.[8]
Should I try it
There is anecdotal support for considering reproductive hormones in exercise, however in 2025 McMaster kinesiologists found ‘tailoring exercises to the menstrual cycle doesn't create a hormonal advantage or help build muscles or strength.’ [9]
No clear differences
A 2024 review and analysis of available data found ‘Energy intake may differ across the menstrual cycle, with some studies identifying greater energy intake in the luteal phase (LP) compared with the follicular phase (FP) and others finding no clear differences.’ [10]
A 2025 study concluded ‘Cycle syncing content on TikTok oversimplifies a complex literature involving tailoring diet and exercise to the menstrual cycle.’ [11].
A SIMPLE ALTERNATIVE?
It is possible to research and introduce changes aligned with your menstrual cycle and evaluate their impact without paying for nutrition advice, a personal trainer, or technology.
However, it could be that these options – or an alternative, perhaps a simple journal – create the focus and attention necessary to identify patterns any change and benefits that you can introduce aligned with your reproductive hormone cycle.
Hormone Syncing - Links to references and further reading:
[1] https://www.nhs.uk/conditions/periods/starting-periods/
[2] https://www.nhs.uk/symptoms/missed-or-late-periods/
[3] Van de Velde, T. H. (1930). Ideal marriage: Its physiology and technique (S. Browne, Trans.). Covici-Friede (Original work published 1928).
[5] https://floliving.com/pages/app
[6] https://www.businessofapps.com/data/flo-statistics/
[7] https://www.vice.com/en/article/cycle-syncing-period-pain-alisa-vitti-nutrition-exercise
[8] https://www.courthousenews.com/judge-gives-tentative-ok-to-56-million-menstrual-app-privacy-settlement/
[9] https://news.mcmaster.ca/researchers-debunk-common-beliefs-about-cycle-syncing-and-muscles/
[10] https://www.womenshealthmag.com/uk/fitness/a65896825/cycle-syncing-exercise/
Jessica A L Tucker, Seth F McCarthy, Derek P D Bornath, Jenna S Khoja, Tom J Hazell, The Effect of the Menstrual Cycle on Energy Intake: A Systematic Review and Meta-analysis, Nutrition Reviews, Volume 83, Issue 3, March 2025, Pages e866–e876, https://doi.org/10.1093/nutrit/nuae093
[11] Pfender E, Wanzer C, Mikkers L, Bleakley A. Sync or Swim: Navigating the Tides of Menstrual Cycle Messaging on TikTok. Perspect Sex Reprod Health. 2025 Jun;57(2):127-132. doi: 10.1111/psrh.70004. Epub 2025 Mar 17. PMID: 40091514; PMCID: PMC12204122.
https://www.bbc.co.uk/news/business-49426349
https://www.bbc.co.uk/sport/football/51559442
https://www.bbc.co.uk/sport/48243310
https://reproductive-health.ed.ac.uk/hope/hope-in-education/other-teaching-resources
This article is for informational purposes only.
For medical advice or a diagnosis, consult a qualified professional health care provider.