Fuelling a Marathon. Carb Loading and Race Day Nutrition

There are two big fuelling traps that runners fall in to before they run a marathon.


  1. They go into the race under fuelled
  2. They eat loads the night before


Carb-loading has evolved over the years. In the 1970-80s there was the process of doing a really hard run the week before your marathon, then having little or no carbs for 2-3 days before eating a very carb-heavy diet for 3 days leading into the race.  This was in the belief that if you emptied the muscles of carbs, when you then introduce them again your muscles will hold on to them.  However, some runners would get really run down with 2-3 days without carbs, some fell ill and with the more recent sports science studies showing little benefit, the carb-depletion phase is very rarely used nowadays.


The practice of carb-loading though, is very much still alive and recognised as essential to good endurance performance.  This is because unless you are going to run your marathon at a very easy effort your body will be burning mostly carbohydrates.


According to research from the Mayo Clinic, runners working at a moderate intensity will use up their normal stores of glycogen (energy stored in muscles) after about 90 minutes. Unless you are planning to beat the world record by half an hour, you will need to top up your energy levels in order to continue running without issue.


To help to increase this 90-minute period you should try to increase the amount of glycogen stored in your muscles you should be increasing your carbohydrate intake in the three days before your marathon. This is not increasing calories but increasing the percentage of carbohydrates you consume – the Mayo Clinic suggests that about 70% of your calories should come from carbohydrates in those final three days.


As you’ll be tapering and running less (see blog for how to taper) the increase in carbohydrates will be naturally increasing your glycogen stores.


How should we be getting the carbs?

A three-day carb-fest sounds great, but in reality, it is hard to be able to eat enough carbohydrates for the needs of a marathon and you risk feeling heavy and bloated on race day unless you carb-load wisely. Choosing low-fat options may help, as fat delays stomach emptying and promotes fullness, something you don’t really want just before race day.


Those who are prone to gastrointestinal distress should choose low-fibre carbohydrate sources. Too much fibre may result in diarrhoea or cramping on race day. White bread, white rice, pasta, sports bars and sports drinks are better compared to the brown, more fibrous options.


Another way to increase your intake of energy is to consume carb-rich drinks. Not only will this increase your carbohydrate intake, but it will also help to fully hydrate you prior to race day. You can include fruit juices or sports drinks as your carb-rich drinks.


How much carbohydrates is enough?

Most information relating to carb-loading suggests consuming between 7-10g of carbohydrates per 1kg of bodyweight. Personally, I always aim to go for the 10g per 1kg as then if you fall short (it is tougher than you think) you will still be way above the 7g per 1kg minimum amount.


I start to increase my carbohydrate intake from breakfast on Thursday (when running a Sunday marathon). The key to carb-loading is preparation. You need to look at the amount of carbohydrates in a portion size of foods you are likely to eat. Then choose the foods with the highest amount of carbohydrates as that means eating less food overall.


I will have written a list of what I need to eat in advance and have bought everything. This way I can break up the foods and drinks into manageable amounts, plus it is thought that most people can only absorb 90-100g of carbs per hour. I continue this through Friday and then on Saturday I eat 90-100g of carbs from waking until about 3pm when I have a normal sized carb-rich evening meal together with sports drinks.


As I mentioned earlier, most people think a massive carb-rich meal on the Saturday night is the most important thing to do. However, depending on the speed of your digestive system, if eaten later in the evening, the meal may still be sitting heavy in your stomach as you start the marathon. This increases the risk of having stomach issues during the race. By finishing the carb-loading process by mid-Saturday afternoon, your stomach should be emptied the following morning.


This is my carb-loading menu to give you an idea of what I consume in the days before a race of half marathon distance and above.  If you do not eat any of the foods on the menu then please look for foods you do eat that have similar carbohydrate values (you should be able to open this photo in a new tab or save it to view it in more detail).



For those of you who like to weigh yourselves before races, you may notice an increase in weight of 2-4lbs. However, this should be fluids and not body fat because each gram of carbohydrate stores about four grams of fluid. Once you get running you shouldn’t notice this and it is a good thing as, you’ll start more hydrated and need less fluids during the marathon. Don’t worry about the number on the scales.


Marathon Day

Your race day breakfast should have been practiced as part of your long runs. You should aim for 1-4g of carbohydrates per 1kg of bodyweight, about two to four hours before you run. This will help to promote steady blood sugar levels early in the marathon. I tend to have my breakfast about three hours before the start and then sip on a sports drink while heading to the start, finishing about 30 minutes before running.


During the Marathon

If you think of your glycogen stores as your fuel tank, you want to stop that fuel running out during the marathon, known as “hitting the wall”. A lot of new marathon runners will have heard horror stories of people who can’t run a step further and end up painfully shuffling to the finish while others run effortlessly by. All that has happened is that those hitting the wall have failed to prepare properly or have failed to follow a sensible race day plan.


Proper carb-loading will have helped to fill your fuel tank and what you consume during the race will stop that fuel from running out.


As with breakfast, this should have been practiced during your long training runs.  The Academy of Nutrition and Dietetics recommends 30 to 60g of carbohydrate per hour for events lasting 1 to 2.5 hours, and up to 90g of carb per hour for events 2.5 hours or longer.


As most people reading this will be aiming for a finish time over 2.5 hours we should be aiming for as close to 90g of carbohydrates per hour as possible. If you haven’t practiced with 90g of carbohydrates per hour, don’t expect your stomach to be happy with this on race day. Stick to roughly what you’ve practiced with and you know your stomach can tolerate.  For any future events, practice consuming more carbs each week on your longer runs so that your stomach will tolerate more in your next marathon (there’ll always be another…..).


Start to consume carbohydrates after the first 30 minutes of the race and then keep taking them at regular intervals, taking in as much as you know your stomach can tolerate.


I always stick to sports nutrition products when running a marathon. These have been designed to be consumed while running and work as quickly as possible. Carb-gels usually have around 20-25g of carbs per gel and so 2-3 of these per hour will keep the energy levels of most of the quicker runners topped up. Gels are easy to consume and many now can be taken without water. These are better for those working at a harder effort when it may be difficult to chew whilst running.


For those who are running for over 4 hours, or those running at an easier effort or taking walk breaks, energy bars or real food can be used as well as or instead of gels. Taste fatigue (when you get fed up with the same thing or flavour) can occur for those who are running for longer and a variety of carb sources may help. You don’t want to get fed up with what you have with you and then stop consuming carbs as this will eventually end up with you hitting the wall.


Just remember that you want to be consuming carb-rich products if not using sports nutrition. Some people use jelly sweets as an alternative, just make sure you have enough and know how many to consume and when.


Finally, always carry a little extra. There is always the possibility of dropping something as you run.


It is useful keeping a food diary around your long runs and races. You can log what food and drinks you consume, how many carbs in each product and how you felt and performed in each race. You can then replicate this for future races (there’ll always be more).


A big caveat to all this information is that those with diabetes or other specific health conditions should always speak to their doctor or consultant before adjusting their carbohydrate intake. Plus, those with any specific allergies or intolerances to certain types of carbohydrates may need to do further research to minimise possible illnesses or stomach distress.


Finally, if you’ve completed every run on your plan, eaten all your carbohydrates, drank all your fluids and consume your carbs regularly during the race, you can still hit the wall. This is because the final piece of the jigsaw is pacing. Aim to run at an even pace based upon your realistic and practiced target time. If you go out too fast you will be burning your energy too quickly (think about your fuel tank when you speed in your car). Once you get into energy deficit you cannot consume enough carbs to pull it back without slowing right down or stopping. Even starting 10-20 seconds a mile too quickly can cause an encounter with the wall.


I give the runners I coach, when they are going for a specific finishing time, a 10 second per mile window based on their target and training times. If they keep each mile within this pace window and fuel as discussed above, there should not be any energy deficit and they should be able to finish strong and evenly paced. If in the last few miles they feel good, they still have the energy to push on and finish faster.


To summarise:

  • Consume 7-10g of carbs per 1kg of bodyweight from Thursday to Saturday afternoon (for a Sunday marathon)
  • Eat a normal sized carb-rich evening meal the day before race day
  • Have a practiced race day breakfast of 1-4g of carbs per 1kg of bodyweight
  • Don’t start too fast
  • Aim to consume between 50-90g of carbs per hour during the race


If you follow all of this, I have no doubt that you can have the best race day experience possible. Marathons are hard work, but let’s not make it any harder than it needs to be and let’s make sure we don’t encounter the fabled wall.


I hope that you can take something away from this blog. I would love to hear your thoughts and I’ve set up a very supportive Facebook Community where like-minded people can share their experiences of life and exercising. Please feel free to join and invite others you know who may be interested.


Want to know more about running or personal training?

Do you want a personalised training plan?

Contact me today to ask any questions or to book your FREE consultation

Call me on 07815 044521 or email me at martinhulbertpt@gmail.com

Martin Hulbert

Personal Trainer & Running Coach Leicestershire

MH Health and Fitness Online Community



Tapering for your marathon

Tapering For Your Marathon

Over the last few months your training should have been gradually getting harder, you should have been running more and more miles, both your midweek and long runs.  As you have now completed, or about to complete your longest week and your longest run of your training, you may well be thinking about the taper.


What Is Tapering?

A taper is a reduction in training intensity before a major race or event to give the body time to recover and adapt to reach a peak in performance.  Simply put, you are going to reduce mileage for the last couple of weeks before your marathon so that you don’t have tired muscles when you start your race.


As your training builds, your fitness will increase with your increase in mileage. However, as your training builds you will also notice your fatigue (tiredness) levels increase. As you can see from the example graph below, I coach people to have cutback weeks every 3-4 weeks. This is to lessen the ongoing fatigue that runners feel during training. It also helps your body adapt and recovery, lessening injury, keeping motivation to train, and helping you to push harder and further in the next few weeks. For those who use training plans without cutback weeks, the line of fatigue (black on the graph) will just increase and increase until you are just knackered and lose the motivation and energy to train, or suffer an overtraining injury.  By cutting back every now and then you lessen the fatigue and can push harder next week.



  • Fitness builds as mileage builds, but so does fatigue
  • Cutback weeks reduce fatigue
  • Peaking (Taper) phase reduces fitness a little but fatigue by a lot, meaning you feel fresh on race day


And this is where the taper really comes in. I like to call it a peaking phase as that sounds more positive to most runners, especially those going for a certain time or personal best.  You are reducing your mileage over the course of usually the final 3 weeks. The taper period will vary from 2-3 weeks depending on the mileage you’ve been doing, how hard the weeks between 10-14 have been (if you have had a week out for any reason a 2-week taper will be better) and how your body reacts to higher mileage. For the purpose of this blog I’ll use a 3-week taper.


Week 13 will be your highest mileage week. You will be doing your longest or hardest long run at the end of your hardest block of training. You should feel tired and ready for lower mileage.  That is a good sign because it means that you have loaded your body with fatigue which means you will create fitness adaptations with less mileage.


If you are having a 3-week taper you will start to lose a little fitness before race day. However, it is not really noticeable (only really from physiological testing) and you will actually feel fitter on race day due to the reduction of fatigue. As you can see in the graph your fatigue levels drop dramatically in the final two weeks. The bigger the gap between fitness and fatigue the better you will feel.


How to Taper

Week 14 should contain roughly 65% of the mileage of week 13. As an example, if you ran 50 miles in week 13 you want to run roughly 33 miles in week 14.  I would usually say the long run in week 14 should be between 14 miles for less experienced runners to 16 miles for people on higher mileage.  Include some miles at your race pace to get used to it during a longer run. Practice your pre-race breakfast and the fuel you will consume during your marathon.


Week 15 should see your mileage total being roughly half of your longest week (13). This means that there is not a big reduction from week 14 and it mainly comes from the longer run, which will vary from 8-10 miles for less experienced runners to 10-12 miles for those coming from higher mileage. Include some miles at your race pace to get used to it. Practice your pre-race breakfast and the fuel you will consume during your marathon.


Week 16 (race week) is where the most noticeable change comes in. You want to be at roughly 25% of the mileage from week 13 (this doesn’t include race day miles), so from 50 miles a week you will be running around 12 miles only.  A typical race week for people I coach will be along the lines of:

Monday – Rest

Tuesday – 5 miles (1m steady, 3m at race pace, 1m very easy)

Wednesday – Rest

Thursday – 4 miles (1m steady, 2m at race pace, 1m very easy)

Friday – Rest

Saturday – 3 miles (1m steady, 1m at race pace, 1m very easy). Run in race kit

Sunday – 26.2 miles at race pace!


You will notice that you are still running regularly in this final week. Doing nothing just gets your legs conditioned to doing nothing. You want to still be running in that final week, but from previously running far longer than these distances, plus the rest days in between, your legs should start to feel more rested and more bouncy as the week goes on.


The second thing to note is that there is still a certain amount of intensity in your runs. There are known neuromuscular connections that are built by practicing race pace. In the final two weeks before your race, you should include some amount of race pace miles in each run. This means that on race day you are used to how this pace feels and more importantly, it feels normal.  People in the past have complained about either doing nothing in the final week, or running very easily and then on race day their race pace feels really hard. That is just a lack of practice.


Tapering after compromised training

I’m writing this in September 2020, 4 weeks before the Virtual London Marathon. This year has been very disjointed with the spring cancellation of marathons.  Some people expected the autumn rescheduled events to be cancelled, some have lost motivation with the uncertainty surrounding the lack of definite events, some have been homeschooling, been injured, ill or just couldn’t be bothered. For those, depending on how your recent weekly mileage has been you may want to consider the following.


If you have not trained much in the last few months and still need to build mileage for fitness or confidence reasons, you can have a 2-week taper.  If so, look above at the week 15 information but reduce mileage by 50% of your week 14.  Then continue week 16 as described above.  The is known as an aggressive taper and something similar will also be used by some more experienced runners who find a 3-week taper doesn’t work for them.


It is important that your longest run is no closer to race day than 14 days. You may struggle to reduce your fatigue levels enough if your long run is 7-10 days prior to race day. You also do not get any physiological benefits in the last 10-14 days, you just risk starting with tired legs.


Race Week

Make sure that you use the extra time in the last week to prepare your race kit, get your race day plans finalised (if you haven’t already) and prepare your carb-loading (another blog to follow on that).


Think of your taper as the icing on your cake.  The taper won’t work without the training base and the training base can be compromised without a well thought out and executed taper.  Do it right and everything will be in place for you to hit your targets on race day.


Stay positive, be confident and trust in your training.


I hope that you can take something away from this blog. I would love to hear your thoughts and I’ve set up a very supportive Facebook Community where like-minded people can share their experiences of life and exercising. Please feel free to join and invite others you know who may be interested.


Want to know more about running, personal training?

Do you want a personalised training plan?

Contact me today to ask any questions or to book your FREE consultation

Call me on 07815 044521 or email me at martinhulbertpt@gmail.com

Martin Hulbert

Personal Trainer & Running Coach Leicestershire

MH Health and Fitness Online Community