Results of a first-of-its-kind research study on cycle syncing were released by FLO Living in spring of 2026. As early as 30 days into the study, a majority of participants reported fewer and less severe PMS symptoms, especially regarding mood, energy, and blood sugar control. These benefits increased by 60 days and remained consistent at 90 days.
Due to significant limitations, the study probably won’t convince cycle syncing skeptics, but it will likely shore up support amongst the live-in-harmony-with-your-hormones faithful. It may even encourage the rest in the middle to give it a shot.
What is cycle syncing?
FLO Living founder and author of Dans le Flo et Code femme Alisa Vitti developed the Cycle Syncing® Method, which promises to help women “sync your nutrition and fitness with your cycle to optimize your weight, energy, mood, and productivity.” According to FLO Living, the company Vitti founded, “This method is designed to reduce symptom burden and severity across the menstrual cycle by optimizing insulin and cortisol balance, thereby enhancing progesterone production and promoting effective estrogen metabolism through a flexible lifestyle approach.” We know that over the course of the cycle, œstrogène shifts do in fact affect blood sugar levels and progestérone can impact mood, as just one example. But, to date, we lacked evidence on whether specific interventions could lead to symptom improvement (let alone identifiable hormone level changes).
Since the method’s introduction via Dans le Flo in 2020, cycle syncing as a broader concept has rapidly gained popularity in wellness circles, with many spinoff applications launched in the last few years. Vitti herself has been profiled by mainstream outlets like Le New York Times.
Results from the first-ever cycle syncing research study
In 2025, FLO Living announced that it had received institutional review board approval for a three-month trial to test whether the Cycle Syncing® Method reduced PMS symptoms.
Results from that trial were released in a spring 2026 white paper par FLO Living, which reported that 92% of participants experienced significant improvement in PMS symptoms after just 60 days of use [1]. According to a Communiqué de presse, 81% of participants reported fewer PMS symptoms, 94% felt their blood sugar was steadier, and 89% perceived mood improvements. What’s more, these benefits continued at 90 days.
Perhaps most reassuringly, according to the white paper, these results were achievable without perfect compliance to the MyFLO app personalized daily exercise and nutrition recommendations. In reality, users achieved approximately 72% adherence to the five daily activities (breakfast, lunch, and dinner recommendations, along with suggested exercise and focus activity).
Limites de l'étude
If it all sounds too good to be true, it might be. As always, the devil is in the details, and the FLO living study results are markedly less impressive under scrutiny.
Many participants dropped out
First of all, there were just 60 participants (aged 22-42) to begin with, but more than one-third had dropped out by the end of the three-month-long trial, with no explanation as to why this might have been the case.
No control group for comparison
Additionally, there was no control group. Ideally, the study would have compared PMS symptoms in women who practiced cycle syncing to PMS symptoms in women who did not, to explore whether PMS symptoms may ebb and flow naturally over time.
No mention of objective health data from urinary hormone monitor
Additionally, while study participants utilized continuous glucose monitors from Hello Inside, and urinary hormone monitors from Mira, along with the MyFLO app cycle syncing recommendations for cycle phase-specific eating and exercise, the white paper made no mention of what data were tracked with Mira, nor what the results were.
Continuous glucose monitor data didn’t show improvements after cycle syncing
Furthermore, while participants reported “feeling” that their blood sugar levels were more stable, Hello Inside scores of blood sugar control remained essentially unchanged from baseline to the end of the study.
Overreliance on user perception
In fact, the study’s emphasis on user perception is arguably its biggest limitation. Questions were written to ascertain “feelings” about health more so than to obtain objective measures of health. For instance, participants were asked after 30, 60, and 90 days, “Did you feel like your blood sugar was more stable this way (syncing meals with cycle phase)?” “Do you feel like you have more consistent energy?” “Are you happy with how your body looks/feels after this month?” “How satisfied are you with your overall hormonal health now?”
Certainly, when it comes to PMS in particular, perception of symptoms is very important. But when subjective and objective data don’t agree, as in the example above of participants “feeling” that their blood sugar control was better even though it was pas objectively better, the efficacy and value of cycle syncing are called into question.
When subjective and objective data don’t agree, as in the example above of participants “feeling” that their blood sugar control was better even though it was pas objectively better, the efficacy and value of cycle syncing are called into question.
4 criticisms of cycle syncing
Amidst its growing popularity, cycle syncing has not been without its detractors. Critics point out that the minimal research cited by cycle syncing apps to support the idea that athletic performance et injury risk vary by cycle phase, is:
- Very new, less than five years old
- Often based on elite female athletes rather than average women
- Survey-based assessments of user perceptions, rather than an objective measurement of data
Critics also cite, as one example, a petite étude 2025 finding that healthy young women’s muscle protein production didn’t differ meaningfully between the follicular and luteal phases (of note: this study did accurately identify participants’ cycle phases with urine and blood tests, whereas previous research often used calendar estimates to predict cycle phases) [2].
Le bilan
Women who struggle with PMS have nothing to lose by trying out cycle syncing, but results from the first-ever research trial of the Cycle Syncing® Method are unclear on how much they can reasonably expect to gain. More research is needed to assess how hormonal levels, as one example of an objective biomarker, do or do not improve in response to cycle phase-specific nutrition and exercise adjustments. We commend FLO Living and fellow femtech companies Mira and Hello Inside’s efforts to honor and support women’s natural hormonal rhythms, and look forward to future, more rigorously conducted research.
