Sports Nutrition for Female Endurance Athletes: Key Considerations
Most of the fuelling advice you will read was built on studies of men. For decades the default lab subject was a young, male, moderately trained cyclist, and the resulting numbers were then handed to everyone else. So if you are a woman training for a marathon, a sportive or a 70.3 and the standard advice has never quite clicked, that is not a personal failing. The guidance was never written with you in mind.
The good news is that the core principles still hold. Carbohydrate is still the fuel for hard work, the gut still needs training, and recovery still depends on eating enough. What changes are the details: how the menstrual cycle shifts fuel use, why under-fuelling is a bigger risk for women than for men, and which micronutrients need closer attention. This guide covers sports nutrition for female endurance athletes as it actually applies in training and racing.
Energy Availability: The Number That Matters Most
If you take one thing from this article, make it energy availability. This is the energy left over for your body to run itself after you subtract the cost of training from what you eat, expressed per kilogram of fat-free mass. Healthy function needs roughly 45 kcal per kg of fat-free mass per day. Drop below about 30 kcal/kg and you enter the territory of Relative Energy Deficiency in Sport (RED-S), where the body starts switching off things it considers optional: menstrual cycle, bone building, thyroid output, immune function and, eventually, training adaptation itself.
For a 60kg woman at 22% body fat, fat-free mass is about 47kg. That means a floor of roughly 1,400 kcal per day above the cost of training just to stay out of the danger zone, and closer to 2,100 kcal above training to be properly fuelled. A 90-minute steady run burns 700 to 900 kcal, so on that day total intake should land somewhere around 2,800 to 3,000 kcal.
The warning signs are worth knowing because they arrive slowly. Missed or irregular periods are the obvious one. Others include stress fractures, recurring colds, waking at 3am, a heart rate that will not come down between intervals, and the frustrating combination of training hard and getting slower. If two or more of those sound familiar, the answer is almost never more training. It is more food.
How the Menstrual Cycle Changes Fuelling
Hormones shift how the body uses fuel across the cycle, and while the individual effects are modest, they add up over a training block. In the follicular phase (roughly day 1 to ovulation, when oestrogen rises and progesterone stays low), the body handles carbohydrate well, glycogen storage is efficient and most women report feeling strongest.
In the luteal phase (ovulation to the next period), progesterone climbs and several things change. Resting metabolic rate rises by 100 to 300 kcal per day. Core temperature sits about 0.3 to 0.5°C higher, so heat feels worse and sweat rate increases. The body leans slightly more on fat and protein for fuel and is less efficient at storing muscle glycogen. Practically, this means three things for the second half of your cycle:
- Eat more carbohydrate, not less. Because glycogen storage is less efficient, you need to be more deliberate about pre-session and during-session carbs. Aiming for the upper end of your usual range, around 60g per hour on long sessions rather than 40 to 50g, helps offset the drop.
- Add protein. Progesterone increases protein breakdown. Target 1.8 to 2.0g per kg of bodyweight per day in the luteal phase, spread across four or five feeds of 25 to 30g.
- Drink earlier and add sodium. Higher core temperature and altered fluid regulation mean you are more prone to dehydration. Start long sessions well hydrated and lean towards 500 to 700mg of sodium per litre of fluid on hot days.
Carbohydrate Targets for Female Endurance Athletes
There is a persistent myth that women oxidise more fat and therefore need fewer carbs during exercise. It is true that at the same relative intensity women burn a slightly higher proportion of fat than men, but the difference is small (a few percentage points) and it does not change the fundamental point: above about 70% of max effort, carbohydrate is the dominant fuel regardless of sex. Sports nutrition for female endurance athletes should not be built around a lower carb ceiling.
The daily targets scale with training load. On easy days, 3 to 5g of carbohydrate per kg of bodyweight is enough. On moderate days with one to two hours of training, 5 to 7g/kg. On big days, long rides or back-to-back sessions, 7 to 10g/kg. For a 60kg athlete that is a range of 180g on a rest day up to 600g on a long-ride Saturday.
During exercise, the same evidence-based ranges apply. Sessions under 75 minutes need nothing beyond water. From 75 minutes to 2.5 hours, aim for 30 to 60g per hour. Beyond 2.5 hours, 60 to 90g per hour is the target, which requires a mix of glucose and fructose to get through the gut without trouble. A word of caution on the top end: women do tend to report gastrointestinal issues at higher intake rates more often than men, so build up to 90g per hour gradually across several weeks of long sessions rather than trying it for the first time on race day.
Iron, Calcium and Vitamin D
Three micronutrients need genuine attention. Iron is the big one. Between menstrual losses, foot-strike haemolysis from running and sweat losses, female endurance athletes lose considerably more iron than the general population, and studies put the rate of iron deficiency in this group at anywhere between 15% and 35%. The symptoms (fatigue, breathlessness on climbs, poor recovery) overlap almost perfectly with overtraining. Get a blood test at least once a year, ask specifically for ferritin rather than just haemoglobin, and aim for a ferritin above 30 ng/mL, with many sports doctors preferring 50. If you need to supplement, take it every other day rather than daily, which improves absorption, and avoid taking it with tea, coffee or calcium.
Calcium and vitamin D matter because bone is where energy deficiency does the most lasting damage. Aim for 1,000 to 1,300mg of calcium per day from food where possible (a large glass of milk or fortified plant milk is about 300mg; a pot of yoghurt roughly 200mg). Vitamin D is harder to get from food, and anyone training through a British winter is likely to be low between October and March. A daily 1,000 to 2,000 IU supplement over the winter months is a sensible default, and a blood test will tell you where you actually sit.
What We Use at FTP Endurance Fuel
The single most common problem we hear from women who buy from us is not that they cannot handle carbs, but that gels turned their stomach and they gave up on fuelling altogether. Pastilles solve a good chunk of that. Each of our pastilles delivers a measured dose of carbohydrate in a form you can eat one at a time, which makes it far easier to build up gradually from 40g per hour to 60g and beyond as your gut adapts.
The Mixed Fruit Energy Pastilles are the everyday training option: a glucose and fructose blend that most people find easy on the stomach at the higher hourly intakes. For the recovery side, the Tart Cherry Energy Pastilles pair the carbohydrate with Montmorency tart cherry, which is a natural source of anthocyanins linked to reduced muscle soreness and better sleep. Both come in 1kg bulk packs, which works out far cheaper per hour than single-serve sachets. If you are unsure which suits you, the taster pack is the low-risk way to find out on a long run rather than a race.
The short version: eat enough to cover your training with plenty to spare, adjust upwards rather than downwards in the second half of your cycle, hit the same per-hour carbohydrate targets as anyone else, and check your iron and vitamin D every year. If you want a fuel that makes the per-hour maths simple and sits well on a sensitive stomach, have a look at our bundles and start with a taster pack on your next long session.
