What Creatine Actually Does In Your Body (Before You Even Think About Buying It)

My sister texted me last week. Four words: "Which creatine should I get?"

I started typing back the kind of detailed answer I'd give a client, then stopped and laughed at myself a little. Because this is now one of the most common questions I get asked — clients, friends, and apparently my own sister, who I didn't realise was paying quite this much attention to her wellness corners of the internet.

Creatine has gone from a niche gym supplement to something almost everyone seems to be talking about. And when something becomes this popular this fast, the shelves — and the algorithm — fill up with options of wildly different quality, fast.

So before I tell you which product to buy (that's Part 2), I want to walk you through what creatine actually does in your body. Because "which one should I take" only really makes sense once you understand why you'd bother taking it at all — and why I'd never recommend a product without knowing it's actually pure. You're trying to improve your health. The last thing you need is a supplement that hasn't been shown to be exactly what it claims.

Where does the creatine in your body actually come from?

Most people assume creatine is something you only get from a tub of powder. It isn't. Your body makes its own, every day, in a two-step process — the kidneys convert the amino acids glycine and arginine into a compound called guanidinoacetate, and the liver finishes the job, turning that into creatine.

The rest comes from food, mainly red meat and fish. Creatine isn't found in vegetables, fruit or grains, which is why vegetarians and vegans tend to run lower on it than people who eat animal protein regularly.

Roughly half of what your body needs each day comes from this internal production line. The other half is meant to come from your plate.

Why is creatine considered "conditionally essential"?

This is a term I use a lot in clinic, and it confuses people, so let me explain it plainly.

Creatine isn't classified as an essential nutrient — your body can make it, so technically you don't "need" to eat it or supplement it the way you need, say, vitamin C. But "conditionally essential" means that under certain circumstances, your own production plus your diet may not be enough to keep your stores topped up.

That includes lower dietary intake (plant-based or low-protein eating), ageing, higher physical or cognitive demand, and — relevant to basically every woman reading this — being female. Women generally synthesise less creatine than men and tend to eat less of it too. More on why that matters for midlife specifically, below.

It's not that your body is broken. It's that the maths doesn't always add up in your favour.

Creatine isn't just a muscle thing

This is the bit that genuinely surprises most people. Around 95% of your body's creatine does sit in skeletal muscle — that's the part everyone associates with the gym. But the remaining 5% is distributed through tissue you'd never think to connect it to: your brain, eyes, nervous system, heart, kidneys, skin, gut lining, and reproductive tissue.

That last 5% matters more than the number suggests. Your brain alone uses around a fifth of your entire body's energy, despite being a small fraction of your body weight. Creatine plays a role wherever cells have a high or fluctuating demand for energy — which is a lot of places.

So what is it actually doing once it's in your cells?

This is the part I find genuinely elegant. Inside your cells, creatine pairs up with a phosphate molecule to form phosphocreatine — think of it as a stored, ready-to-use energy reserve sitting right next to where the energy is needed.

When a cell suddenly needs a burst of energy (a muscle contracting hard, a neuron firing rapidly), it can't always wait for the slower process of normal metabolism to catch up. Phosphocreatine steps in and instantly hands over a phosphate group to regenerate ATP — your cells' actual energy currency — keeping things running without a lag.

It's a buffering system, in the truest sense. Not the energy source itself, but the reserve tank that smooths out the gaps between energy demand and energy supply, in muscle, in brain tissue, and beyond.

Why this matters specifically for women in midlife

Here's where it gets personal, and where I think most of the marketing aimed at women misses the point entirely.

Research suggests women synthesise around 20% less creatine than men, and on average eat 30–40% less of it through diet. That gap doesn't close on its own — if anything, hormonal shifts across the menstrual cycle, pregnancy, postpartum and the menopausal transition appear to influence how creatine is used and replenished in the body.

For postmenopausal women specifically, research combining creatine with resistance training has shown support for muscular strength, lean mass and functional performance.

Longer studies have also looked at bone — with some findings around preservation of bone mineral density and improvements in bone strength markers over 12 months to 2 years, again alongside resistance training.

None of this is a promise of an outcome, and creatine isn't a substitute for resistance training, good nutrition or proper medical care. But understanding that your body may genuinely have lower reserves than a man's of the same age — and that those reserves matter for muscle, bone and brain energy in a decade where you're actively trying to protect all three — changes how I think about this nutrient for my midlife clients.

Why I won't recommend a product before talking about purity

Creatine monohydrate is made synthetically.

That's not a red flag in itself — it's simply how it's produced. But it does mean the manufacturing process can leave behind by-products if it isn't tightly controlled: things like excess creatinine, or residues from the synthesis process itself.

Pharmacopoeial-grade material — the kind manufactured to recognised standards like USP — is tested against strict limits for exactly these by-products, using validated lab methods. Commodity-grade creatine often isn't tested at all, or the testing simply isn't disclosed.

This is the part that actually matters to me as a practitioner. You're taking a supplement to support your health. The product itself should be able to prove it's clean before it ever reaches your cells.

What's next

In Part 2, I'm getting practical: how much creatine you actually need, whether loading is necessary, what micronisation means and why it might matter for your gut, how capsules, powder and gummies stack up cost and ingredient-wise, and the specific products I stock in the Foxy Shop and why.

Read Part 2: How to Choose a Quality Creatine Supplement →

Frequently Asked Questions

Where does the creatine in your body come from?

Your body makes roughly half of what it needs from the amino acids glycine and arginine, processed through the kidneys and liver. The other half comes from dietary sources, mainly red meat and fish. Creatine isn't found in plant foods, which is why vegetarians and vegans tend to have lower baseline levels.

Is creatine only relevant for muscle and exercise?

No. While around 95% of the body's creatine is stored in skeletal muscle, the remaining 5% is found in tissues including the brain, eyes, heart, kidneys, skin and reproductive tissue — anywhere cells have high or variable energy demands.

What does "conditionally essential" mean?

It means your body can usually make enough creatine on its own, but under certain circumstances — lower dietary intake, ageing, higher physical or cognitive demand, or being female — your own production and diet combined may not fully meet your needs.

Why might women in midlife need to think about creatine differently than men?

Research suggests women synthesise less creatine than men and consume less through diet, and that hormonal shifts across the menstrual cycle, pregnancy and the menopausal transition may influence creatine use in the body. This is an area of active, ongoing research.

Why does creatine purity matter before choosing a product?

Creatine monohydrate is manufactured synthetically, and the process can leave behind by-products if not tightly controlled. Pharmacopoeial-grade creatine is tested against defined limits for these by-products; commodity-grade material often isn't tested at all, or doesn't disclose it.

Want personalised guidance on whether creatine is right for you?

If you'd rather talk this through than guess, my Quick Script Consult is a focused 30-minute appointment built exactly for questions like this — what you're taking, what you're trying to achieve, and whether it's actually the right fit.

Book a Quick Script Consult →

Or browse practitioner-grade options already vetted for quality in the Foxy Shop →

And if you’re wondering whether any of this changes depending on your life stage — your twenties versus your fifties — that’s exactly what Part 3 covers.

Read Part 3: My Sister Asked If Her Daughter Could Take Creatine Too →

Cherice Baker is a Registered Natural Medical Practitioner (NHPNZ) with over 25 years of clinical experience in nutritional medicine, herbal prescribing and functional health. She practises from Rolleston, Canterbury, and consults with clients across New Zealand online.