Are You Cutting Carbs at the Cost of Your Bones?
What a fascinating study on elite athletes can teach the rest of us about fuelling, restriction, and the food-culture myths we've all absorbed.
Low-carb. Keto. "Carbs are the enemy." If you've spent any time trying to get healthier, you've almost certainly been told, especially by the endless churn of social media, that cutting carbohydrates is the shortcut to getting lean, balancing your energy, or fixing your health.
I want to gently challenge that. Not with an opinion, but with a piece of research that genuinely made me stop and think, and that speaks to the heart of what functional nutrition is all about.
The study
In 2022, a team of sports scientists ran a beautifully designed experiment with 28 elite race-walkers. The clever part was how they separated two things that usually get mixed in studies: eating too little overall versus specifically cutting carbohydrates. For six days, everyone started on the same well-fuelled diet: high in carbohydrate, with plenty of total energy. Then they were split into three groups:
"The fuelled group" stayed on high-carb, high-energy — the control group.
"The low-carb group" dropped to under 50g of carbs a day (a ketogenic level), crucially in this group they kept their total calories high, topping up with fat.
"The under-eating group" ate too little overall, but kept a normal proportion of carbohydrate.
At the end, each athlete completed a 25km race-walk while researchers took blood samples to measure markers of bone turnover, the chemical signals of bone being built up (a marker called P1NP) and broken down (a marker called CTX).
What they found
This part is fascinating! The low-carb group (the ones who had plenty of calories), showed the biggest drop in bone-building of all. Their bone formation marker fell by around 26%. The under-eating group also saw a drop, but a smaller one of around 14%. And the well-fuelled control group? Their bone-building actually held steady, even nudging upward.
In other words, cutting carbs suppressed the body's bone-building signals nearly twice as much as under-eating did, despite the low-carb group not being short on calories at all. It wasn't about how much they ate. It was about the carbs. In addition, both the low-carb and the under-eating groups showed increased bone breakdown around exercise, while the fuelled group stayed in balance.
The researchers' conclusion: carbohydrate appears to specifically protect bone formation, while you need both adequate energy and adequate carbohydrate to keep bone breakdown in check.
Why carbohydrates matter more than diet culture admits
Here's the bigger idea, and it's the thread running through everything I teach. Your body doesn't just see food as calories. Food is information. Carbohydrate, in particular, does far more than "give you energy", it influences the hormonal and cellular signals that tell your body it's safe, fuelled, and able to invest in maintenance and repair. Bone is living tissue, constantly being remodelled, and it appears to respond to whether it's being properly fed.
When you severely restrict carbs, some of those "build and maintain" signals seem to quieten down. This is worth distinguishing from short-term fasting, which operates through different mechanisms and has its own body of research, what this study concentrated on was chronic or sustained carbohydrate restriction as a dietary strategy. For an athlete chasing performance that's one consideration but for rest of us thinking about long-term health, it's a reminder that sustained restriction is rarely the consequence-free act that the messages like to make you think.
An honest bit- what this study can and can't tell us
I care deeply about not overstating science. Research is searching for probabilities, patterns and correlations, signals in data that may not translate directly to every individual in the real world. This was a small study (eight to ten people per group), it ran for only six days, and every participant was an elite maleracewalker. It measured markers in the blood, not actual fractures or changes in bone density, and the authors are careful to say you can't extrapolate directly to long-term bone health, or to women, from this data alone.
So, this isn't proof that low-carb diets will break your bones. It is a well-controlled signal, consistent with other research, that carbohydrate plays a real and under-appreciated role in bone health and that "just cut carbs" is far too blunt an instrument.
Why this matters especially as we age
For women, bone health becomes a headline issue around menopause. As oestrogen declines, so does one of the body's natural protections for bone, and the risk of osteoporosis rises. This study didn't test menopausal women, but it does add to a compelling case that at that at the stage of life when we most need to support our bones, chronically under-fuelling or aggressively cutting carbohydrates may be working against us.
This connects to something I write about separately, the broader picture of what happens when active women don't eat enough to match their output. If that resonates, head to the blog on REDs here.
The functional nutrition takeaway
This is why I will never hand you a list of "banned" foods or tell you to fear an entire macronutrient. That approach treats symptoms and trends; functional nutrition asks what your body actually needs to thrive. The right carbohydrates in the right amounts for you aren't a guilty pleasure to be eliminated. They're fuel, and they're information your body uses to build, repair, and protect itself, right down to your skeleton.
If you'd like to explore what that looks like for you specifically, this is exactly the work I do at Empowering Nutrition.
Get in touch to start the conversation.
Reference:
Fensham NC, McKay AKA, Tee N, et al. Short-Term Carbohydrate Restriction Impairs Bone Formation at Rest and During Prolonged Exercise to a Greater Degree than Low Energy Availability. Journal of Bone and Mineral Research. 2022;37(10):1915–1925. doi:10.1002/jbmr.4658
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