I'm a Renowned Female Health Expert—and I Want You To Know The Truth About Marathon Training and Your Cycle

As a marathon runner, female health expert and registered nutritionist, I'm hugely passionate about educating women on their menstrual cycle, as well as how their period can impact their day-to-day lives. A former NHS doctor, I set up The Food Medic back in 2012, and have written two books - The Female Factor in 2022 and Not Just a Period in 2025.

But today, I want to get into training around your cycle. The biggest myth about periods and performance? That you can’t perform at your best during your period. You absolutely can. Women compete, set personal bests, and win gold medals while on their period.

That’s not to say it doesn’t make things harder for some. Symptoms and practical concerns - like managing period products, changing tampons mid-race, or worrying about leaks - can take up a lot of mental space.

While there’s definitely more awareness and conversation than ever before, I think some brands and influencers are overstating or oversimplifying the evidence, particularly around things like cycle syncing. We need to be careful not to replace one extreme with another, and the goal should be evidence-based, flexible guidance that helps women understand their bodies without creating more rules on what they can and cannot do.

With the London Marathon just gone, what better time to deep dive into how best to approach marathon training and your menstrual cycle? Interest in running is at an all-time high, with the highest number of runners ever completing the iconic course on Sunday, setting a new Guinness World Record (59,830 runners). Not just that, but the largest number of female finishers crossed that finish line over the weekend - a total of 26,071 women, up 4.6% from 2025.

Without further ado: keep scrolling for my science-backed take.

How does the menstrual cycle actually affect endurance performance across a marathon training block?

Across a full training block, the menstrual cycle is unlikely to have a consistent or predictable impact on endurance performance, but there may be a small dip in the perimenstrual window (just before and during your period).

In a study of 195 Australian athletes preparing for the Tokyo Olympics and Paralympics, many reported that they felt they performed worse during their period, so perception plays a big role.

I would say, though, the effects are small and variable, so training, fuelling and recovery remain far more important than cycle timing alone.

There’s some evidence that the late follicular phase (after your period) may feel better for higher-intensity work, as oestrogen is higher and progesterone is low, which may support recovery and reduce perceived effort. The early to mid-luteal phase may also be well-suited to endurance work, as higher oestrogen can promote greater fat utilisation and help spare glycogen, potentially supporting longer efforts.

However, rising progesterone may offset some of these benefits, particularly by increasing body temperature and making exercise feel more demanding, especially in the heat.

In short, if you're a runner considering adapting your training plan across the four phases of your cycle, you don't need to.

Is it realistic—or even necessary—for amateur runners to sync marathon training with their cycle?

No. While there may be small changes in performance and recovery across different phases of the menstrual cycle, the impact is small for many and can vary between women. So it’s not evidence-based or necessary to follow a cycle-synced running programme, and it may hold you back from making progress if you’re only “allowed” to do high intensity or long runs on 1-2 weeks of the month.

What is helpful, though, is being cycle-aware and understanding your own needs and being guided by your symptoms. For example, if you wake up with tender breasts, fatigue, bloating and so on in your premenstrual week and you have the option to move your longer/harder run to later in the week, then why not?

Often women don’t realise their cycle is a vital sign and tells us so much about their overall health - so if your period suddenly goes missing or your cycle length is progressively getting longer during a training block, that’s a red flag! This often occurs when the body doesn’t have enough energy to support both exercise and essential functions such as hormone production, bone health, and recovery – a state called Low Energy Availability (LEA). When this happens, the body switches off signals from the brain to the ovaries, stopping ovulation and periods until more energy becomes available. Most women think that losing their period isn’t a big deal (maybe convenient?), but it can have important consequences for both health and performance. Studies have shown low energy availability is associated with reduced bone density, a higher risk of stress fractures and injury, impaired recovery, low mood, disrupted sleep and reduced performance in exercise and sport.

While this has traditionally been documented in elite athletes, it’s increasingly being seen in everyday active women, too. In one study of nearly 2,000 female recreational runners, 53% were identified as being at risk of low energy availability and around 62% reported menstrual disturbances.

How should nutrition shift across the menstrual cycle when training for a marathon?

In the luteal phase, there may be a small increase in metabolic rate, so you might feel hungrier. Rather than resisting that, it’s important to lean into it by increasing overall intake, particularly carbohydrates, to support training and recovery.

A regular menstrual cycle can be a useful sign that you’re fuelling adequately, although this feedback isn’t the same if you’re using hormonal contraception.

Rather than drastically changing nutrients by phase, the priority is getting the basics right. One key nutrient for female runners is iron. Iron deficiency is relatively common in runners, particularly women, due to factors like menstrual blood loss, higher training demands, and foot-strike haemolysis. Low iron can impact oxygen transport, leading to fatigue, reduced endurance, and poorer performance. So try to include iron-rich foods regularly (especially around menstruation) and consider checking levels if you’re experiencing persistent fatigue.

Should I change my recovery strategies throughout my cycle?

Ideally we want to be consistent across the cycle but you might find markers of recovery (like HR, HRV and readiness score/recovery score if you use something like a WHOOP) decline in the luteal phase and sleep disturbance is more common here also so I would priortise sleep hygiene more so in this phase, respect rest days, integrate stress management and try not consume alcohol (which will worsen recovery further).

Final note for marathon runners keen to take their cycle into account?

If you’re not on hormonal contraception, use your cycle as monthly report card to check in on how you’re balancing training and nutrition – and don’t ignore any cycle changes like irregular or missing periods.

Managing your period can be tricky if you’re doing a long run so choose routes with bathrooms you can access, use period products that you trust and are comfortable with, limit your caffeine and fibre intake before runs (because period poops are a thing, and running can impact that more!). If you choose to take painkillers, Ibuprofen is best avoided before or during long runs as it can put extra strain on your stomach and kidneys, especially if you’re dehydrated. If you’re really uncomfortable with cramps/heavy flow, perhaps move your longer/harder runs to day 4 or 5 of your cycle when your symptoms should be easing.

At this point, you don’t need to worry about matching up your training to your cycle, but if you consistently have 1 week of the month where your symptoms are bothersome or you notice a significant dip in performance, you could strategically place a deload week here with shorter, easier runs – but for most women, this isn’t necessary. Let your cycle and symptoms guide you but you don’t need a rigid cycle syncing plan.

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