Marathon runners: how to execute carb-loading

Libby Limon BSc NT mBANT / Apr 19, 2016

​ If you are planning on doing a marathon or endurance event this summer, no doubt you have heard of carb loading. Many an amateur distance runner has spent the night before the big event chowing down on bowls of pasta, however to get effective results it is not as simple as that. Carb loading is often misunderstood and poorly executed, in many cases not helping with performance and even potentially counter productive.


With the London Marathon just a week or so away, we speak to VITL’s Head of Nutrition, Libby Limon, to get the low down on how to incorporate carb-loading effectively to your tapering training.

The idea behind carb-loading is to saturate the muscle with stored sugars known as glycogen. These can then be released by the body to fuel you when needed on race day.

The Original Carb Loading Technique

The original technique was devised in the 1970s and was used by many endurance cyclists, cross-country skiers, and runners prior to their long-distance races. It began a week before your event when, after an exhaustive workout, carbohydrate intake would be kept at a minimum for 3 days to deplete glycogen stores. This stimulates production of the  glycogen synthase enzyme. Then, in the 3 days prior to the event, as tapering continues with light workouts, high levels of carbohydrate heavy foods such as bread, pasta, potatoes and even biscuits would be consumed to super-saturate the muscles with glycogen.

In the 1980s the theory behind carb loading was developed further and it was discovered that there were only certain conditions under which muscles would actually absorb glycogen. . During sleep or before a meal, muscle fibres pull less glucose from the blood to be stored. Consequently, eating a carbohydrate heavy meal before bed is less likely to get results. Muscle fibres have the highest propensity to increase the level of glycogen and stockpile it within the 2 hours after strenuous physical activity, hence the birth of the “2 hour post workout window”.

Modern Nutritional Science Optimises the Technique

More recently, the Ohio State University developed the “2 hour window” theory further and found that by consuming 30g of carbohydrate food every 15mins during the 2 hour window, glycogen saturation increased by 20%, which was a 90% improvement on the original method.  Although this  means consuming a lot of carbs in a relatively short space of time an extra 20-90% stored energy available to your muscles on race day cannot be underestimated in terms of potential performance. For more serious runners this can be increased to a 4 hour carb-loading in practice.

This is a pretty intense strategy and, whilst the performance benefits are proven by studies, in practice a lot of endurance athletes struggled with the protocol. Many athletes find the carb depletion phase difficult and experience side effects including lethargy, cravings, irritability, lack of concentration, and increased susceptibility to illness.

Carb Loading Made Easy

In 2002 by scientists at the University of Western Australia, developed a carb loading strategy that was easy, practical as well as effective. It condenses the depletion and loading phases into a one-day time frame. The key is the type of exercise which triggers glycogen depletion and therefore resultant bodies replenishing of glycogen stores.  In this strategy, a single, short workout is performed 24hrs before the event at extremely high intensity, working on both slow-twitch and fast-twitch muscle fibers.

A Practical Plan

Perform a short-duration, high-intensity workout consisting of two and a half minutes at 130% of your VO2max (about one-mile race pace) followed by a 30-second sprint. Then in the next 24 hours consume 10g of carbohydrate per 1 kg of body mass. So if you weigh 75Kg then you would need to consume 750g of carbs which, over 6 meals, is 125g of carbs per meal.  Whilst this is a lot of carbs, you should also include some protein and healthy fats too.  Antioxidants are also key to protect cells and therefore protect against injury or illness, and micronutrients such as B Vitamins and Coq10 support energy production and hydration to maximize performance,which is why adding the VITL Greens blend of maca, green tea, spirulina and supergreens can be an incredibly beneficial addition to your pre-marathon nutrition plan .

Overall, you calorie intake should be no different to normal.

A typical meal plan aiming to get a healthy 100 - 125g of carbs per meal could look like this:

Post Work-Out

2 natural sports gels with a smoothie made from 1 banana, 150g yoghurt and 100g frozen dark sweet cherries and a sachet of VITL Greens


300ml Beet and Carrot juice

Salad of 180g pre-cooked quinoa, 2 cups of roasted butternut squash, 50g spinach, olive oil and lemon dressing


6 medjool dates and 1tbsp peanut butter

250ml Apple juice


2 baked sweet potatoes with 120g fillet of salmon, 1 cup of roasted mediterranean veg

1 cup of mango and 1 cup of pineapple

Pre-Bed Snack

Warmed 300ml brown rice milk with 2 slices of sourdough toast with raspberry jam

Pre – Race Breakfast

50g soaked gluten-free oats soaked in 300ml brown rice milk and a sachet of VITL greens with 2 sliced bananas


Most studies of glycogen storage have been conducted on male athletes.  However, some studies suggest that females may be less responsive to carbohydrate loading, especially during the follicular phase of the menstrual cy