Fuelling ‘on the run’ during a marathon race – by Colin Griffin

UPMC Sports Surgery Clinic
Race day nutrition is a topic of interest among many marathon runners. Questions such as ‘should I take a gel’ or ‘how many gels should I take during a marathon’ or ‘what type of gel is best’ are commonly asked.
There are a number of factors to consider when planning a race-day fuel strategy. These include:
·         Sources of energy
·         Amount of carbohydrate you need to (or can) consume
·         Your ability to digest products on the move
·         How often should you consume carbohydrate
·         Pre-race fuelling

Sources of energy

The sources of energy can have a small but significant impact on absorption and performance. Mixing sugar-based carbohydrate sources such as glucose, fructose, dextrose and starch-based sources such as maltodextrine and maize; can enhance carbohydrate absorption into the blood. It can be useful to look at the ingredients label on a particular gel or energy drink powder formula. You can analyse carbohydrate sources and also the sugar content under the nutritional value label. Most products have a one third sugar content of carbohydrate. For example a product containing 30g carbohydrates of which 10g is sugar-based.

Amount of carbohydrate

A carbohydrate intake of between 30-60g carbohydrate per hour is generally recommended for optimal gastric emptying and intestinal absorption. There appears to be an upper limit of 75g per hour, above which will have no additional benefits and may in fact inhibit absorption and cause stomach issues. Most gels contain 25-35g carbohydrates. Most self-prepared sports drinks with a 6% carbohydrate concentration will contain close to 30g carbohydrate per 500ml, which can be diluted accordingly. You can calculate this by looking at the label and knowing what 1 scoop or 100g contain.
Nutritional content of a typical sports drink
Nutrition UPMC Sports Surgery Clinic
Nutritional content of a typical gel product  

Your ability to digest carbohydrates on the move

The key objective is to keep blood glucose levels topped up during a race by consuming carbohydrate-based fuel. Whether that carbohydrate comes from a gel, solid food or drinks powder mix, is a matter of individual preference for the athlete. You will see from the above referenced labels, that a 500m energy drink mix with 30g carbohydrate content or one gel with close to 30g carbohydrate content; still provides the same amount of energy. It depends on how well the athlete can digest the product. Some athletes prefer to take a solid fuel such as a gel, a piece of energy bar or some jelly sweets; while others can only tolerate liquids. It is something that should be trialled and practiced on a few training runs well in advance of race day.

How often should you consume carbohydrate?

It is recommended that an athlete consume between 30-60g of carbohydrates per hour of activity if their event last longer than 1 hour. There are usually personal drink stations every 3 miles or so during a marathon race. A 2 hour 30 minute marathon runner, who consumes 250mls energy drink containing 10-20g CHO every 3 miles; should achieve sufficient fuelling throughout the race.  The athlete could substitute a gel for an energy drink every third or fourth 3 mile segment. For an athlete who may not be in a position to consume prepared drinks on the course and relying solely on water stations, could carry some gels with them and consume with water. It is best to begin fuel intake early on in the race, perhaps from the first drink station.

Pre-race fuelling

Many athletes ‘carbo-load’ in the days leading up to a race by increasing their carbohydrate intake. There is little evidence of any additional benefits of carbo-loading longer than 24 hours pre-race. When you taper your training but still consume the same amount of carbohydrates in meals and snacks, you will be increasing glycogen stores regardless. Some athletes don’t like the lethargic and often bloated feeling of being carbo-loaded.
The best advice is to maintain normal meal portions and carbohydrate intake the week of a race, with perhaps a little extra intake in the meal the evening before the race. Have a pre-race breakfast meal that has worked well in training and previous races. Carbohydrates consumed in the 60 minutes before the race should be liquid-based, but only in small amounts. One must also factor in race day anxiety and nerves, which can affect digestion and absorption. Sometimes ‘less is more’ in terms of food intake and perhaps allow for an increased pre-race digestion window than you would usually in training.


The most important fuel the athlete has available on race day is the glycogen stored in the muscles. Between 10-30% of carbohydrates consumed during a race is actually utilised. Most well trained athletes will have sufficient muscle glycogen stores to sustain a 2-hour effort. It is a good idea to include some occasional steady state runs in a low glycogen state to promote fat utilisation for energy. It is also good to complete other workouts in an adequately fuelled state to as to have that metabolic flexibility so that our bodies are trained for both fat utilisation and carbohydrate utilisation. Our bodies our smart at self-regulating! With a good aerobic engine and some fine-tuning, along with adequate fuelling; our bodies will find the most efficient way of fuelling performance early on and keeping energy reserves for the latter stages.
Click here for further information on Running Services offered at UPMC Sports Surgery Clinic, or to make an appointment call +353 1 5262030.

More News