The cycling internet will tell you how many carbs per hour to take on. It will give you a fuelling plan for your next century ride. It will debate gels versus real food until the end of time.
What it won't tell you is that the number changes depending on where you are in your cycle.
The reality about cycling nutrition advice is harder to ignore: almost all of it was built on research done on men. Young men, specifically. And for years, that was just accepted as fine. It isn't.
The Research Gap Nobody Talks About
Before 2010, fewer than six percent of sports science studies used female subjects. Six percent. The fuelling protocols you see plastered across every cycling forum, the 60-90 grams of carbs per hour that Professor Asker Jeukendrup's lab made famous, the recovery windows, the hydration targets — nearly all of it was developed using 18 to 25-year-old men as test subjects.
That doesn't mean the research is wrong. It means it is incomplete. Professor Louise Burke at the Australian Institute of Sport has been pushing for better representation in sports nutrition research for years, and the picture is improving. But the gap is still enormous, and the practical consequence is that women are following nutrition plans designed for bodies that don't work the same way theirs do.
Dr Stacy Sims put it best when she wrote that women are not small men. That single phrase has done more to shift the conversation around female sports nutrition than any single study. Her books ROAR and Next Level are the best starting points if you want to go deep on this, and I'll reference her research throughout this piece.
How Hormones Change The Fuelling Picture
Once you understand the basic hormonal picture, the practical advice makes complete sense.
The menstrual cycle has two main phases that matter for fuelling. The follicular phase runs from the start of your period to ovulation. The luteal phase runs from ovulation to your next period. Each one creates a different metabolic environment.
During the follicular phase, progesterone is low and oestrogen is rising. Your body stores glycogen well and uses it efficiently. You are more carbohydrate-tolerant. You can follow standard fuelling protocols — the 60 to 90 grams of carbs per hour for rides over 90 minutes that Jeukendrup's research established — and your body will respond roughly the way the textbooks say it should.
Here's where it gets really interesting. During the luteal phase, progesterone rises significantly. This changes several things at once. Your body shifts toward preferentially burning fat and becomes less efficient at accessing glycogen stores. Protein catabolism goes up, meaning your body breaks down more muscle protein. Your core temperature rises by roughly half a degree Celsius. Your blood volume drops because progesterone affects plasma volume through its interaction with aldosterone. You need more fluid and more sodium just to maintain the same level of hydration.
What this means in practical terms is that the fuelling strategy that worked perfectly last week might leave you feeling flat, underfuelled, and struggling this week. And it is not because you did anything wrong. It is because your hormonal environment changed.
Sims' recommendation for the luteal phase is specific and actionable: front-load 15 to 20 grams of protein before exercise, increase your sodium intake, and accept that your carbohydrate oxidation rates will be slightly lower. You are not losing fitness. Your body is just running on different fuel economics.
RED-S: The Risk Nobody Wants To Name
Let me be really clear about this, because it matters more than any carb-timing strategy.
Relative Energy Deficiency in Sport — RED-S — is not an eating disorder, though it can overlap with one. It describes a state where you are consistently taking in fewer calories than your body needs to support both your training load and your basic biological functions. And women cyclists are particularly vulnerable to it.
The reasons stack up. Endurance sport burns significant calories. Cycling culture has a long and damaging history of treating weight as the primary performance variable. Societal pressure on women around body image compounds the problem. And the symptoms are insidious because they develop gradually.
Dr Nicky Keay, an endocrinologist who has published extensively on RED-S, describes it as a spectrum rather than a binary state. You don't suddenly have RED-S one morning. You drift into it over weeks and months of marginally under-fuelling relative to what your body actually needs. The signs include missed periods — amenorrhea — which too many women and coaches still treat as normal for athletes rather than the red flag it actually is. Stress fractures. Hormonal disruption that affects everything from bone density to immune function. Declining performance that doesn't respond to more training, because more training is the problem, not the solution.
The estimated prevalence is staggering. Around 45 percent of female endurance athletes experience RED-S at some point. Nearly half. And the performance consequences go both ways — under-fuelling doesn't just hurt your health, it actively makes you slower.
The good news is that RED-S is fixable. It requires eating more relative to your training load, and it often requires working with a sports dietitian who understands endurance sport and female physiology. The first step is recognising it, which means tracking your cycle and treating any disruption to it as a signal that something needs to change, not something to power through.
The Iron Question
If you're a woman who rides and you've ever felt inexplicably flat on the bike — legs that won't fire, efforts that feel harder than they should, fatigue that doesn't lift with rest — iron might be the answer.
Iron is essential for haemoglobin production. Haemoglobin carries oxygen in your blood. Less iron means less oxygen delivery to your muscles. The maths is brutal and simple.
Menstruating women lose roughly one milligram of iron per day through menstruation. The recommended daily iron intake for women is 18mg compared to 8mg for men. That gap exists for a reason, and yet fuelling plans rarely account for it.
Dr Georgie Bruinvels at Orreco has done significant research on iron and the menstrual cycle in female athletes. Her work shows that iron deficiency is one of the most common and most fixable limiters of performance in women's endurance sport. The symptoms mimic overtraining: you feel tired, your numbers drop, and the temptation is to train harder or rest more when the actual problem is nutritional.
But here is the critical point: do not just start taking iron supplements because you read a blog post about it. Excess iron is toxic. You need to get your ferritin levels tested. Ferritin is the storage form of iron, and it is the number that matters for athletes. A ferritin level below 30 ng/mL is considered suboptimal for athletic performance even if the lab's reference range says you're technically normal. Many GPs use population reference ranges rather than athletic performance thresholds, which means you can get a "normal" result back while actually being functionally iron-depleted.
Get tested. Know your number. If it's low, work with a professional to bring it up. This is one of the highest-return interventions in women's cycling nutrition and it is uncomplicated once you have the data.
A Practical Fuelling Framework
I'm not going to pretend this is simple, because it isn't. Fuelling around a hormonal cycle that changes every two weeks requires more attention than following a static plan. But it doesn't have to be complicated.
During the follicular phase, you can fuel close to standard protocols. For rides over 90 minutes, aim for 60 to 90 grams of carbohydrate per hour. Your glycogen storage and utilisation are working well. Your body tolerates carbohydrate loads effectively. This is the phase where you'll feel most like the fuelling advice on the internet actually applies to you, because, for once, it does.
During the luteal phase, the adjustments matter. Add 15 to 20 grams of protein before your ride. This is Sims' recommendation and it is backed by the physiology: progesterone increases protein catabolism, so giving your body amino acids before exercise reduces the amount of muscle protein it breaks down for fuel. Increase your sodium intake in your drinks because progesterone's effect on aldosterone means you're retaining less sodium and losing more fluid. Accept that your carbohydrate oxidation rates will be slightly lower and don't chase the same intake numbers if your gut is telling you it's too much.
Post-ride nutrition is where women can get the most immediate benefit from being more deliberate. Protein within 30 minutes of finishing is even more important for women than for men. Sims has been vocal about this point. The elevated protein catabolism in the luteal phase means the recovery window is tighter and the cost of missing it is higher. A recovery drink or a meal with 20 to 30 grams of protein soon after finishing is the single most impactful change most women can make.
Hydration needs more attention than most riders give it. In the luteal phase, your blood volume drops and your core temperature rises. You are starting from a less hydrated baseline and losing fluid faster. Adding sodium to your bottles — not just relying on plain water — is important. This is not about electrolyte marketing. It is about the specific physiology of progesterone's effect on fluid balance.
Why Fasted Riding Doesn't Work The Same Way For Women
The fasted riding debate is one of the most persistent in cycling nutrition. And for women, Sims takes a strong position: don't do it. Especially not in the luteal phase.
The reasoning is direct. In the luteal phase, your body is already less able to access glycogen and is already breaking down more protein for fuel. Adding a fasted state on top of that hormonal environment means your body reaches further into protein catabolism to keep you moving. You are not teaching your body to burn fat more efficiently. You are teaching it to eat its own muscle.
Sims recommends that women eat protein before any morning session rather than riding completely fasted. Even a small amount — 15 to 20 grams of protein with some carbohydrate — is enough to shift the metabolic picture. It doesn't negate the aerobic training stimulus of an easy ride. It protects your muscle tissue while you get the work done.
This is one of those areas where advice that might work reasonably well for men actively harms women. The fat adaptation benefits that some male athletes pursue through fasted riding do not transfer directly to female physiology. The hormonal environment is different and the metabolic consequences are different.
If you take one thing from this section, make it this: eat before you ride. The cost of not eating is higher than you think.
Where To Go From Here
The single most important thing you can do is start paying attention to where you are in your cycle and how it affects your riding. Track it. Notice the patterns. Most women find that once they start looking, the connection between their cycle phase and how they feel on the bike is obvious in hindsight.
Get your iron tested. Know your ferritin number. If you've been feeling flat and can't explain it, this is the first box to tick.
Look at your overall energy intake relative to your training load. If your cycle has become irregular or you've lost your period, treat that as urgent. It is not a badge of commitment. It is your body telling you that something is wrong.
And stop following fuelling plans that were designed for someone else's physiology without adapting them to yours.
If you want to go deeper on any of this — or connect with other riders who are figuring this stuff out — the Roadman Cycling community on Skool is the place. We dig into this kind of evidence-based detail regularly, and the conversation is always better when more perspectives are in the room.
Your body is not broken. It is not less capable. It is different. And once you fuel for the body you actually have rather than the one the textbooks assumed you had, the performance follows.