Your Hormones & Metabolism Are Joined At The Hip

Yesterday I glibly texted “F*** me I could smash a Big Daddy right now” to a confused recipient, without my ravenous brain considering anything other than the (incredible) M&S Big Daddy chocolate bar could be being implied.

Like many women, I’ll have days when I wake up insatiably hungry. My appetite is a bottomless pit, and I want to inhale chocolate to a degree that feels feral - and as of yesterday, a little embarrassing. Yes, we all know the stereotype: hormonal = chocolate and we typically brush this off as part of the female experience and leave it there.

Away from chocolate and in our daily lives, most women have been handed our hormones and our metabolism as two completely separate subjects – one lives with the gynaecologist, the other with whoever does your blood tests, and never the twain shall meet – when inside your actual body they’re actually just one system, running each other, all day, every day.

Big Daddy!

What if we could see what was happening inside our bodies?

This is exactly the question we’ve been working closely on: trying to understand the relationship between women’s hormonal and metabolic health and digging into what becomes visible when you look at hormone levels, glucose and women’s lived experiences as one system.

Today we know that the two hormones defining you cycles also have a direct impact on how your body handles food. Insulin is the hormone that moves sugar out of your blood and into your brain and muscles after eating, and oestrogen – which runs the first half of your cycle – helps it do that job. Progesterone, taking over after ovulation, does the opposite: it makes your cells a little less responsive to insulin so the sugar from a normal meal stays in your blood at a higher level for longer than it would do normal and eventually, your body, (getting less out of what you’ve eaten) asks for some more, please! The result is a metabolism that visibly shifts gear twice a month – which means a whole genre of guidance has spent decades advising women about lunch whilst blind to the hormonal context in which they’re eating it.

For most of history, research in this domain meant a sporadic blood sample – sometimes even just one measurement per phase of the cycle, which, as a method for understanding a system that changes by the day, is roughly equivalent to understanding a friend’s month from one text and a photo of her lunch. That, unsurprisingly, leaves quite a lot unseen between the measurements! It wasn’t until a study tracked women’s glucose continuously, day and night, alongside daily hormone levels across their whole cycles and symptoms that the picture sharpened. Across these women, a rhythm emerged in their daily blood sugar: lowest in the days before ovulation, highest in the luteal phase after it. The shift wasn’t crazy, but it persisted even after the researchers accounted for how much the women were walking and what they reported craving – and in fact the cravings themselves trended alongside the higher glucose. Many women will not be at all surprised to find that their cycle is relevant to their metabolic picture - because we historically hadn’t measured it, it has typically been explained away as a lack of willpower or just disregarded… Instead, it’s a big, exciting signal!

After ovulation, progesterone takes over for roughly two weeks to prepare your body for a pregnancy that, most months, doesn’t happen. As a result, your core temperature rises by a few tenths of a degree and stays up, your resting heart rate creeps higher, your sleep gets lighter, and your cells become a little less responsive to insulin, so a normal meal pushes your blood sugar a bit higher than usual and then keeps it there longer. As your body is dealing with fuel less efficiently, it starts to ask for more of it, which is where the appetite comes from; one study measuring hormones daily alongside what women reported eating found that higher oestrogen went with eating less and higher progesterone with eating more, and a 2024 meta-analysis of 15 datasets covering 330 women found intake higher in the luteal phase by around 168 calories a day on average. As someone who definitely experiences appetite changes, I’d certainly welcome a better understanding of it before thinking I should show more determination in the face of lunch!

So you may ask, why only now? Well, mostly because the measurements weren’t possible; to see how hormones and glucose interact you need both, daily, in the same woman, across whole cycles, and until roughly the last decade neither existed outside a research ward because it’s unsurprisingly challenging to gather. But! That has changed! Today, we can collect reams of continuous data from own bodies and from the comfort of our own homes, and excitingly the research is catching up as a result, (finally!).

However, for female physiology, sadly what hasn’t caught up has been the interpretation and reading of it. Most of what interprets this data still treats hormonal variations and cycle as noises to be smoothed out – which seems a strange thing to discard, given these are two of the most important patterns your body produces... The models that reads these signals all together and learns what your normal looks like rather than what a textbook says it should be, is what we’re so stoked to be building.

We think it’s better to know than be in the dark when it comes to your health, if you want to be first to see, the sign-up list is at nurihealth.ai. Come join!