// Eating on the run

by Sam Murphy

Eating a healthy, balanced diet is vital for a runner, who will regularly expend signifi cant amounts of energy. They also need more specifi c nutrients, vitamins and minerals to aid recovery and performance.

If you read running magazines or spend a lot of time with other runners, you’ll know that they are forever talking about carbs. Why are carbohydrates so important? Well, carbohydrate is your muscles’ favourite energy source, but since the body has only a limited storage
capacity, you need to take carbohydrate on board regularly in order to keep these stores topped up. Fail to do this by, say, adhering to one of the currently popular low-carb, high-protein diets, and you will soon feel fatigued and certainly not in the mood for a run. So how much
carbohydrate is enough? Of your daily calorie intake, 55 to 65 per cent should come from carbohydrate – some sports nutritionists suggest as high a level as 70 per cent, but it then becomes quite challenging to get sufficient amounts of the other nutrients, fat and protein. 60
per cent is a good figure to aim for. One way of determining how much carbohydrate you require is to base your needs on the amount of exercise you do. To use the following table, calculate your weight in kilograms:

So if, for example, you run for a total of three hours a week and weigh 60kg, you need approximately 240 to 300g of carbohydrate each day. 

But all carbohydrates are not created equal. There are two types – ‘complex’ starches and fibres and ‘simple’ sugars. The difference lies in
their chemical structure: starches and fibres are formed of lots of molecules joined together in chains while sugars are smaller molecules, consisting of just one or two linked units. Starches – pasta, rice, potatoes and bread – have always been hailed as the classic runner’s foods while simple sugars have had a bad press for giving a short, sharp burst of energy followed by a lull.

But it isn’t that simple. For a start, many foods contain a mixture of starches and simple sugars, and second, they may contain other
nutrients, such as fat or protein, or compounds (such as fibre), that determine how quickly or slowly energy can be released.

A better method of determining how quickly energy is released by a food is by knowing its glycaemic index (GI). This is a ‘ranking’ of food from 0 to 100, based on how quickly the food causes a rise in blood sugar levels compared to pure glucose. Foods which are lower than 50 are considered low-GI, moderate GI foods are 50 to 70 and high-GI foods are 70+. Surprisingly, you can’t predict what a food’s GI is simply by its appearance. For example, chocolate, while high in sugar and fat, has a low GI while white rice, a carb favourite, has a high GI.
Let’s take a brief look at GI ratings and exercise performance.


Protein is not so much stored as incorporated into the muscles and organs of your body. It is not one of the major fuel suppliers – your body
prefers to use carbohydrate and fat – but in some situations, such as when glycogen stores have been depleted, or when you aren’t Consuming enough carbohydrate, protein can be broken down to produce energy. For years, bodybuilders and other athletes lived on a diet of chicken breasts, steaks and tuna to ensure they had plenty of protein. The theory was that athletes break down their muscle tissue through exercise, so need more protein than the average person to aid with repair and recovery. But is it true? Well, for years the idea that active people need more has been disputed, but it seems we’ve now come full circle and many nutrition experts are, once again, advocating a higher protein intake for athletes. As a guideline, the average sedentary person is recommended to consume 0.75g of protein per kg of their bodyweight each day while regularly active people, such as runners, are recommended 1.2 to 1.4g per kg per day. (Those who regularly take part in strength training or strengthbased activities such as rock climbing should go for the higher figure).

Protein consumption should equate to approximately 15 per cent of your overall energy intake.


While ‘fat’ is a dirty word for many of us, it is an essential body fuel, and if you reduce your consumption too much you won’t benefit either your health or your running. The recent American College of Sports Medicine Position Stand on Nutrition and Athletic Performance stated that there were no health or performance benefits in consuming less than 15 per cent of your total energy intake in the form of fats. A more
realistic goal is 20 to 25 per cent.


Research in the early 1990s suggested that a low-GI pre-exercise meal or snack helped to sustain energy levels better than a high-GI snack. Subsequent studies have disputed this: recent Australian research has found no difference in exercise performance following a high- or low-GI pre-exercise meal. However, it is advisable to steer clear of fibre-rich foods (such as bran or wholegrains) that make you feel full and take longer to digest before a run, as these are most likely to cause stomach problems.


Almost all the evidence suggests that during exercise you need energy that is easily and quickly accessible, and that means high-GI. But that doesn’t mean you need to take a rucksack full of energy bars and sports drinks with you on every run. If you’re not running for more than an hour, there’s no need to consume anything other than liquid.

Anything less than 45 minutes and plain old water will do just fine.


After a long or hard run, your glycogen stores are likely to be low. Research shows that 75 minutes’ running at 80 per cent maximum heart rate (MHR) results in almost total glycogen depletion. Opportunely, the first two hours after your run is the time when your muscles are Most receptive to topping up (particularly the first half hour), so make sure you take some carbohydrate onboard before you zonk out on the sofa, or head off for work.

For optimal refuelling of glycogen, aim to consume 1g of carbohydrate per kg of your bodyweight in this two-hour window of opportunity. Some research has shown that consuming moderateor high-GI foods or drinks facilitates glycogen refuelling more successfully than low-GI items, but this is relevant only if you are training every day. In fact, many recreational exercisers make the mistake of overcompensating
for what they have burned through exercise by heeding advice meant for professional athletes that has made its way into running and fitness magazines. Unless you have completed a particularly long or hard session, or are running again the next day, you can allow your body to take care of its own glycogen refuelling.


So, if all body fuels can provide energy, let’s get on to that million dollar question. If we’ve got so much surplus body fat, why can’t we use
that instead of these more precious, less abundant nutrients, such as carbohydrate and protein?

The biggest determinant of what fuel you use during exercise is the duration and intensity of the exercise. At lower intensities, fat is the preferred fuel source, while at higher efforts, carbohydrate is the main provider. Of course, this is determined to an extent by how fi t you are, but the good news is that regular training can help teach the body to conserve glycogen and burn fat. One of the major eff ects of training is that it enables you to work at a higher percentage of your maximum capacity without producing excessive amounts of lactic acid. Research suggests that the presence of lactic acid blocks the action of adrenaline, the hormone that plays a role in stimulating the breakdown of fats. Therefore, raising your lactate threshold through regular running means that you spend more time working aerobically (below the lactate threshold) and can therefore utilise more fat as an energy source. 

Studies have shown that aerobically fit people not only release more fatty acids into the bloodstream for energy but that their muscles actually use more of what is released, too. In less fit people, the triglycerides are often released but are not wholly utilised, and
go back into storage. 

This article has been reprinted with permission from Fitpro (www.fitpro.com)


Sam Murphy

Sam has a first-class degree in sport and exercise science, is a qualified personal trainer with her own consultancy Personal Best, and is one of the UK’s leading fitness writers. Her books Weights for Weight-Loss and The Real Woman’s Personal Trainer, have been translated into nine languages and sold over 100,000 copies worldwide. Her latest book Run for Life is available at www.fitproshop.com