Sat 28 Mar 2026
6 May 2026 • 13 minutes read
The under-fuelling epidemic is becoming increasingly common on social media and in clinic, with many runners, from recreational to elite, not eating enough to properly support their training. Knowing what to eat before, during and after a marathon can significantly improve performance, recovery and injury prevention.
The key principles are simple: prioritise carbohydrates for fuel, electrolytes and fluids for hydration, and protein for recovery. As an Accredited Practising Dietitian and marathon runner myself, this guide explains exactly how to fuel your long runs and race day.
It’s important to note, nutrition needs vary between individuals depending on gender, body size, training load and sweat rate. You can use this as a nutrition framework to guide you through your training block.
Grace’s Tip – “Don’t wait until race day to practise your fuelling strategy. Your long runs are the perfect opportunity to train your gut and find what works for you in preparation for race day.”
When training volume, particularly on long run days increases, and runners aren’t fueling enough, low energy availability can occur. This is where the body does not have enough fuel left over after training to support normal physiological function.
Over time, this can impair:
Your fuelling strategy should progressively build in conjunction with your training plan; consistency is key.
Carbohydrates are your primary performance fuel. They are stored as glycogen in your muscles and liver and are essential for energy use over long distances. Increasing your carbohydrate intake particularly in the hours before training and in the days leading up to heavy training loads, will ensure there is sufficient fuel available in these stores to meet training demands and support ongoing performance.
Carbohydrates from foods such as wholegrain breads, rice, cereal, potatoes, pasta, corn, fruit, and milk should form the basis of daily intake, with refined or lower-fibre options useful to incorporate around training when a quick energy burst is required. 1
For moderate to high marathon training loads:
Aim for 6 to 10g of carbohydrate per kilogram of body weight per day 2
You may need the higher end when:
If intake consistently falls below needs, glycogen stores remain chronically low, recovery slows and injury risk increases.
This is where many runners unknowingly under-fuel.
The night before is not about eating excessively. It is about eating adequately.
Your goal is to maximise glycogen stores while keeping digestion comfortable and your gut happy.
Reducing fibre and fat slightly helps minimise gastrointestinal discomfort and reduce unwanted trips to the bathroom during your longer runs.
The night before your long runs are the ‘rehearsal dinners’ for the night before the marathon. So keep it simple, familiar and try not to bring in anything new during your taper week.
After an overnight fast, liver glycogen is reduced. Starting long runs without topping this up increases perceived effort early on. Let’s start with a simple carbohydrate pre-run breakfast.
Small additions like this often make the first 5 kilometres feel significantly easier and set up a positive mindset for the long run.
For runs longer than 90 minutes, fuelling becomes a priority to maintain the same performance standard.
A practical starting target is:
Around 60g of carbohydrate per hour or approximately 30g every 30 minutes. 4
Some well-trained runners may tolerate up to 90-120g per hour using fructose and glucose carbohydrate blends. Again, your long runs during your training block are an excellent opportunity to find what works best for you.
Train your gut, just like you train your legs!
Each of these nutrition options contains a mix of glucose and fructose, which are absorbed through different pathways in the body and used for energy. Emerging research suggests that combining these two carbohydrates may help you absorb more than 60g per hour.
Under-fuelling long runs puts extra stress on the body and can lead to ongoing energy deficits, which increase the risk of bone stress injuries.
Hydration is often talked about in relation to performance, but it also affects overall stress on the body. Drinking enough fluids helps maintain blood volume, which supports oxygen delivery to your muscles while you run.
Many runners find it difficult to drink during a run, but long runs are a great opportunity to practise your hydration and nutrition strategy for race day. Doing this helps you plan and make the most of the drink and nutrition stations along the course.
Night before up to 2 hours before long runs, it is recommended to consume:
During long runs, a general guide is:
Warm and humid conditions can increase sweat losses, meaning needs may sit at the higher end. The more you sweat during your long runs, the more fluid you then need to replace after your runs to replenish what has been lost.
Chronic under-fuelling and dehydration increase physical stress, which can negatively affect recovery and bone health over time.
Recovery is where adaptation happens.
Aim to eat within the optimal recovery window of 30 to 60 minutes after finishing your run.
Include:
Examples:
Regularly skipping post-run nutrition increases the risk of low energy availability, especially during peak training phases.
Bone stress injuries are multifactorial. Training load, biomechanics, sleep, and recovery all play a role. However, inadequate fuelling is a significant and often overlooked contributor.
When the body does not have sufficient energy, it prioritises essential functions, and bone remodelling and repair can be compromised over time.
Eating enough protein and meeting your energy requirements is one of the best ways to protect your body. This is especially important for runners increasing mileage, female athletes experiencing hormonal changes around their menstrual cycle, and those returning from injury.
Even when your physical load is reduced due to injury, your energy intake should not drop, as your body still needs extra fuel to repair and recover.
Marathon training can be demanding on your body, your gut, and your mind. Some simple nutrition reminders to keep you on track include:
A well-fuelled runner is a smarter, stronger, and more resilient runner.
Fuelling for a marathon, as discussed, can be complex and overwhelming to navigate. Personalised guidance can make a significant difference.
At Grams of Health, our Accredited Practising Dietitians support runners both in-person and virtually through;
Run into your next marathon training block with confidence, CLICK HERE to book a consult and create your personalised nutrition plan. We want to support you to achieve your running goals and get to the finish line!
Should you eat before a morning marathon?
What you eat before a morning marathon provides you with the fuel to be able to run well and perform at your best. Depending on the time of the marathon, you should aim to eat a high carbohydrate, low fibre, low fat meal 60-90minutes prior. This could look like two pieces of toast with honey or jam. Then 15minutes before, have a fast acting carbohydrate source to top up your glycogen stores. This could look like a gel, glass orange juice, sports drink, or dates to name a few.
How often should you eat during a marathon?
Typically the recommendation is 30g of fast acting carbohydrates every 30minutes. This could be in the form of a gel, sports drink, blocks, dates, honey, and so on. The reason for this is to prevent energy crashes and promote a sustained energy release to keep performing over longer durations.
Is it possible to train your gut for race nutrition?
During your marathon training block, every weekly long run you do is an opportunity to train your gut and find out which nutrition sits best to then incorporate on race day.
Can dehydration affect running performance?
Fluid requirements vary between runners and are dependent on size, workload, sweat rate, environment and conditions the athlete is training in. If a runner is dehydrated, you will see a rapid decline in speed, endurance, and cognitive function. Prior to running, you should look to drink 10ml/kg BW on top of regular drinking habits 2 hours before. Drinking regularly throughout training is recommended to reduce the risk of dehydration by drinking up to 250ml every 15-30minutes.
Footnotes:
Get the latest races, coaching tips, and running club updates delivered straight to your inbox.
