Hypothalamic Amenorrhea: Why under-eating might be sabotaging your hormones

"But I eat so clean, why would I need to eat more?"

I hear this often, and almost never from someone restricting on purpose. It usually comes from busy lives, young families, or a diagnosis like PCOS (now formally PMOS) that's made food feel confusing, sometimes even frightening.

If this sounds like you, here's the first thing to know: it's not your fault, and it's more common than you'd think.

What's actually happening in your body

It starts with something most women are never told. Making hormones is one of the most energy-expensive things your body does, and it will only do it when it's convinced there's enough fuel coming in to justify the cost.

Yes, every steroid hormone you produce, oestrogen, progesterone, testosterone, cortisol, is built from cholesterol. But your body makes most of its own cholesterol, so the raw material is rarely what runs short. The limiting factor is usually the signal, not the supply.

Here's how that signal works. Ovulation is driven by a carefully timed pulse of luteinising hormone (LH) released from your brain. That pulse is remarkably sensitive to energy availability. When your body senses it doesn't have enough coming in relative to what's going out, one of the first adaptive responses is to blunt that LH pulse. A flattened LH pulse is a well-documented reason progesterone production drops off, and progesterone is what stabilises your cycle, supports mood, and prepares your body for a potential pregnancy each month.

Put simply, your hypothalamus is constantly asking one question: is it safe to reproduce right now? When the answer is no, because there isn't enough fuel coming in, it quietly turns the signal down. Not because anything is broken, but because your body is doing exactly what it's designed to do under conditions it reads as scarcity.

This pattern has a clinical name: Hypothalamic amenorrhea. It's one of the more common causes of irregular or absent periods in otherwise healthy, active women, and it isn't about being underweight. Energy availability, the balance between what you eat and what you expend, is what drives it, not your BMI or how you look. A woman can be in a completely "normal" weight range and still be running a significant energy deficit, especially if she trains regularly, has a demanding job, or is simply not eating enough to match her output.

Why does this get missed so often?

Standard pathology testing checks whether your hormone levels sit within a broad population reference range, not whether they're optimal for your body, and not whether the pattern across several markers together points to chronic underfuelling. A single LH or FSH result can look unremarkable in isolation. It's only when you look at the relationship between markers, alongside ferritin, thyroid function, and the story your cycle has been telling for months, that the full picture becomes clear.

This is exactly where optimal ranges and functional testing add something standard labs often miss. It's not about running more tests for the sake of it. It's about knowing what to look for, and why.

Why "just eat clean" often doesn't move the needle

The advice women are usually given is to eat well, exercise, manage stress. All reasonable, none of it wrong. But if the actual issue is volume, not quality, tightening up what's already a clean diet can make things worse, not better.

This isn't about willpower or discipline. It's a physiological response your body is having to a genuine energy gap, whether or not that gap was intentional. And it isn't only about carbohydrate and fat. Iron status matters too. Ferritin, the protein that stores iron in your body, has a real relationship with energy and cycle regularity, and the level your body actually needs to feel well and cycle regularly sits meaningfully higher than the floor many labs use as their cutoff. A woman can be told her iron is "fine" while sitting well below where she'd feel her best.

A root cause approach

Rather than adding more restriction or more supplements, the starting point is almost always the opposite: making sure carbohydrate, protein and healthy fat are consistently present at every meal, alongside a genuine look at iron and thyroid status.

A simple way to check this without tracking or measuring: 

Half your plate vegetables, a quarter protein, a quarter carbohydrate, with a generous side of healthy fat. This isn't a diet. It's a floor, a way of making sure your body has what it needs to make and clear hormones properly, before we look at anything more targeted.

From there, functional testing can confirm whether hypothalamic amenorrhea, a nutrient pattern like low ferritin, or another driver entirely is what's actually happening, rather than guessing. Testing markers together, not in isolation, is what turns a "normal" result into a genuinely useful one.

If this sounds like you

Low or absent hormones are more dangerous than most of us have been led to believe. If your cycle has gone quiet, or you've been told your bloods are normal but something still feels off, that's exactly the kind of pattern I look for with clients.

If you want to understand what's actually driving your symptoms, exploring one of my services is your next step. Depending on the level of support you need, we can work together on a causal 1:1 basis, or in a high-touch supportive environment with coaching to get you through - Explore the services here