How to prepare for your first marathon: a beginner's guide
- Helen Morton
- 5 hours ago
- 8 min read
How to prepare for your first marathon, by nutritional therapist and runner Helen Morton. Practical advice on training, nutrition, hydration, fuelling and sleep.
In this article we will cover:
Signing up for your first marathon takes courage. What happens between that moment of excitement and the starting line is where a lot of first-time marathon runners either set themselves up for a great experience or an unnecessarily tough one.
The good news is that preparing well doesn’t require an expensive training plan or an elite athlete’s lifestyle. It simply requires consistency, a little forward thinking, and respecting what your body is about to be asked to do.
What do you need to know as a first-time marathon runner?
If you're brand new to marathon running, this article covers everything you need to know to support yourself as painlessly through the build-up process as possible. Equally, if you’ve run a marathon before and it didn’t quite go to plan, it’s worth reading on too, because the fundamentals covered here are the ones that most commonly get overlooked, regardless of experience level.
Marathons are exciting, and for many people, they can be a way to get fit and raise money for a charity they have an emotional connection to. Marathons also have very specific physiological demands. Being strong, fit, or active is a great starting point, but it doesn’t automatically translate to being prepared for sustained effort over 26.2 miles. The person who trains five days a week can be just as under-prepared as someone who trains twice a week if they haven’t thought about what their body will actually be asked to do on the day.
How do you train for your first marathon?
Let’s be honest: you can turn up to a marathon undertrained. A surprising number of people do it all the time. But it’s rarely an enjoyable experience on the day itself.
The body responds to what you ask of it, and a marathon distance is a very long way. The running training is what makes taking on the challenge of a marathon event enjoyable rather than just plain hard. There’s no shortcut that replaces simply doing the work, and by that I mean running the miles in the weeks and months beforehand.
Your long-run needs to gradually extend over months, not suddenly jump from a Parkrun to twenty miles over a few weeks. The more closely your training mirrors the demands of race day, the less your body will be surprised when it matters most.
You don’t need a complicated plan, rather you need consistency, enough time, and the honesty to ask yourself whether what you’re doing in training is genuinely preparing you for 26.2 miles.
What should you eat when training for a marathon?
There is no single “marathon runner’s diet” that works perfectly for everyone. What works brilliantly for one runner can leave another feeling sluggish, bloated, or under-fueled. This is one reason nutritional therapy exists: because food, and the way we respond to it, is personal, and getting it right for your body, training, and life makes a tremendous difference.
That said, there are some nutrition fundamentals that broadly apply. If you are preparing for your first marathon, you most likely don’t require a dietary overhaul, but a few additions and a little more attention will help.
A common marathon training mistake
One of the most common mistakes people make when marathon training is not eating enough. It sounds counterintuitive when many people sign up with half an eye on losing some weight, but under-fuelling during a training block leaves you fatigued, more prone to injury and slower to recover. Food is most definitely not something to restrict when you’re asking so much more of your body with all the miles that you are running.
In practical terms, a varied, balanced diet built around whole foods will serve most runners well.
Carbohydrates
Carbohydrate-rich foods like oats, potatoes, bread, pasta, vegetables, and fruits are your primary energy source and are not something to fear. Carbohydrate foods fuel your muscles and top up the glycogen stores you use during long runs and the race itself.
Protein
Protein, found in fish, poultry, eggs, beans and pulses, and meat, supports muscle repair and adaptation, and becomes particularly important on and around training days. Collagen is the body’s most abundant protein and a key component of connective tissues like tendons, ligaments, and cartilage, all of which work hard during marathon training. You can read more in our guide to what collagen is.
Healthy Fats
Healthy fats, like olive oil, avocado, nuts, and seeds, support sustained energy, joint health, and the absorption of key nutrients.
Meal timings
The timing of what you eat during marathon training matters:
Eat something substantial, like a bowl of porridge which contains complex carbohydrates, a few hours before a training run.
A meal that includes a portion of good quality protein eaten within an hour or two after running gives your body what it needs when it needs it most.
Track your progress
Your diet during marathon training does not need to be tracked obsessively; rather, it needs to be present and consistent. However, it's helpful to keep a food, training, sleep, and energy diary to get a feel for what’s working and what needs adjusting as the long runs get longer.
Where to find more in-depth nutritional guidance
If you have a chronic health condition, follow a restrictive diet, or simply want guidance tailored specifically to you and your training, it’s worth speaking to a qualified nutritional therapist. Generic advice can only go so far, and the right personalised support can make a significant difference to both your preparation and your experience on race day.
If you would like to learn more about the foundations of a wholefood diet, check out our self-guided online courses. Or, see our practitioner directory to find a nutritional therapist who can provide you with personalised support.
What are the top hydration tips for long runs?
We all know that staying hydrated matters, but hydration is something that new runners in particular often underestimate in practice. The most important thing to note is that by the time you feel thirsty, you’re already mildly dehydrated, and even mild dehydration has a measurable impact on performance, concentration, and how hard running feels.
During marathon training, your daily hydration baseline needs to go up. You will lose a lot of fluid through sweat and breathing, and if you’re not actively replacing it, your sleep, energy levels and recovery can be affected.
Electrolytes
Water is the basic foundation for staying hydrated, but fluid alone isn’t always enough. When you sweat, you lose electrolytes: primarily sodium, potassium, and magnesium. These minerals play a critical role in muscle function, nerve signalling and fluid balance. For shorter runs, electrolyte loss isn’t usually a concern, but for longer training runs, especially on warmer days, replacing electrolytes and fluid becomes increasingly important. This doesn’t need to mean expensive sports drinks; it can be as simple as eating a banana or using an electrolyte supplement. Here is our guide to the best electrolyte drinks and supplements for sports and health.
Individual requirements
When it comes to hydration during marathon training, individual needs vary considerably. How much you sweat, how salty that sweat is, your body size, and the conditions on race day all influence what adequate hydration looks like for you specifically. If you want to get this right, a conversation with a nutrition professional is a worthwhile investment.
Check your urine
A simple starting point: check your urine colour. Pale straw is the ideal colour. Dark yellow is a sign to drink more.
How do you practice fuelling during marathon training?
We are working on the final touches to this section, please check back in shortly.
How important is sleep when training for a marathon?
Getting sufficient sleep when training for a marathon is where recovery and repair happen. During sleep, your muscles repair, your energy stores replenish, and the hormones that support recovery, including growth hormone, do most of their work. Skimping on sleep during marathon training doesn’t just leave you feeling tired; it actively slows down the process of getting your body ready for the event.
Most adults need somewhere between seven and nine hours of sleep per night, and if you’re running consistently, you’ll likely find yourself needing more than usual. However, if you’re concerned that you don’t get enough hours of sleep on a regular basis, remember that the quality of sleep matters as much as the quantity.
Running, particularly intense sessions like intervals or a long run, raises your core body temperature and spikes adrenaline and cortisol. This is exactly what you want during a session, but it can leave you feeling that familiar “tired but wired” combination for a while afterwards. If late evening is the only realistic window you have to run, give yourself as much wind-down time as possible before bed. Things like a cool shower, some gentle stretches, dimming the lights, and cutting down on screen time can really help.
That said, we know that life is real. Not everyone can run at 7am, and a late evening run is always better than no training. If your sleep is taking a hit during heavy training weeks, it could be worth trying to fit in a short nap a few times a week. A nap of ten to twenty minutes in the early afternoon can help to restore alertness and support recovery without interfering with your night's sleep. Although a nap won’t replace the lost hours, it helps with rest and recovery. For more sleep support tips, see our guide on how to get a good night's sleep.
There are a few things consistently worth protecting in the weeks before race day: a reasonable wind-down routine, a cool and dark sleeping environment, and keeping your sleep and wake times fairly consistent, even on weekends. Your body responds well to rhythm, and the more consistent your sleep pattern, the better the quality tends to be.
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Key things to consider when preparing for your first marathon
Preparing well for your first marathon doesn’t mean turning your life upside down. Making small, consistent nutrition and lifestyle choices throughout your training block will add up to arriving at the start line feeling ready for an enjoyable race day.
The five pillars described above: training, nutrition, hydration, practice fueling, and sleep, work together rather than independently. Under-fuelling affects your energy and recovery. Dehydration makes every mile feel harder than it needs to. Poor sleep undermines your training adaptation and motivation. And training that doesn’t reflect the demands of race day leaves you under-prepared for what’s ahead. Get these fundamentals consistently right, and you’ll arrive at the starting line in a positive position.
Quick reference guide
Here’s a quick reference for the key points to carry with you throughout your training:
Train specifically: understand that 26.2 miles is a long way and you need to have put the running training in beforehand
Build gradually: progressive training over months creates the best experience. Rushing through training is more likely to lead to injury.
Eat enough: under-fuelling is one of the most common and most avoidable mistakes in marathon preparation
Prioritise whole foods: a varied, balanced diet built around real food will serve most runners well without the need for complicated plans
Time your nutrition: eat well before training runs and recover with good quality protein afterwards
Hydrate consistently: don’t wait until you’re thirsty; make hydration a daily habit, not a last-minute fix
Replace electrolytes on longer runs: water alone isn’t always enough
Practice your fuelling: experiment with gels, chews, and real food during your long runs so race day isn’t your first attempt
Protect your sleep: treat sleep and rest as part of your training
Get personal support if you need it: if you have specific health considerations or want tailored advice, a qualified nutritional therapist can help
In our next article, we’ll look at how to support yourself through race day itself, from the 24 to 48 hours beforehand right through to crossing the finish line of your first marathon.
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