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With input from Ling Ping Sing & Fabian Lim
A proper nutrition plan is essential to maximize your training adaptations and competition performance. With an increase in training volume, the body’s nutrient requirements also increase. There are several pertinent nutritional considerations that relate to running performance:
- Depletion of muscle glycogen stores and consequent low blood sugar (hypoglycaemia), will cause central nervous system fatigue and deprive exercising muscle of fuel especially during a distance race
- Dehydration
- Gastrointestinal discomfort. During endurance races, the digestive system has to compete with the working muscles for blood, and with priority going to the muscles, the digestive tract often does not function optimally, making it difficult to ingest and absorb the food and fluids we take
- Mineral deficiency e.g. iron or calcium
- Electrolyte imbalance e.g. sodium
Macro- and Micronutrients
In order to use nutrition as a tool to improve your performance, you must first understand your body’s nutritional needs during exercise. Let us look at the requirements in terms of macronutrients (carbohydrates, proteins, fat), micronutrients (vitamins, minerals, antioxidants), and fluids.
Carbohydrates
 Carbohydrates comprise glucose and glycogen. Glycogen is made up of many molecules of glucose, and serves as a storage depot for glucose. Our bodies can use carbohydrate, fat, and protein, in that order of preference, as fuel sources — hence, these macronutrients are also called energy substrates. At rest, we tend to use fat as the main energy source. Fat is mobilized slowly, but this slow rate is fine as the body consumes calories slowly while at rest. Take my body’s energy substrate utilization for example (I weigh 64 kg) — when I am resting, an analysis of my respiratory gases (i.e. oxygen and carbon dioxide) shows that I have a resting metabolic rate of 1,427 kilocalories (kcal)/day (i.e. my body expends 1,427 kcal per day if I sleep all day), and that 56 per cent of this energy comes from burning fat and 44 per cent from carbohydrates (see figure 6.2).
When we start exercising, our muscles burn calories at a faster rate. Because there is a limit to how fast body fat can be released, the body becomes more dependent on carbohydrate as a fuel substrate, especially at exercise intensities exceeding 70 per cent of VO2 max. The figure below (figure 6.1) demonstrates the increasing use of glucose by the muscles as the intensity and duration of exercise increases. When I run at 14 km/h during a marathon, respiratory gas analysis shows that I expend 1,155 kcal per hour, with 68 per cent of my energy needs supplied by carbohydrates and 32 per cent by fat.
Figure 6.1. Carbohydrate utilization at various exercise intensities and duration.
Carbohydrates can be mobilized quickly to meet the muscles’ needs, but unfortunately, its stores are limited. A 70-kg individual running at 10 km/h will require slightly more than 3,000 kcal of energy to complete a marathon. However, the average person has 600 g of carbohydrate stores in the muscle and liver (see figure 6.3), providing only 2,400 kcal of energy (1 g of carbohydrates produces 4 kcal of energy). Another estimate places the glycogen stores at 1,800 kcal and 1,550 kcal for well-trained male (averaging 68 kg) and female (averaging 54 kg) endurance runners. From these estimates, we can see that the carbohydrate store is insufficient for the whole marathon.
Figure 6.3. Carbohydrate and Fat Stores
When our carbohydrate stores are depleted at around the 30 km mark or 3 hrs 20 mins into the race, we ‘hit the wall.’ To overcome this, marathon runners will need to:
- Boost their carbohydrate stores through regular training and pre-race carbohydtrate
loading
- Replenish carbohydrates during the race, and
- Train the body to be better at mobilizing the fat stores during the run, thereby sparing
the carbohydrates such that they last longer
Regular training and increasing your mileage helps to enhance the carbohydrate stores by about 10 per cent. The increase is especially marked in untrained runners, since they are starting from a low baseline. But to tolerate the high training mileages, we need to have enough carbohydrates during training. Your daily carbohydrate requirement is based on your training load e.g. intensity, duration, and frequency:
It is important to have sufficient carbohydrate before, during and after training to maximize the performance. We will discuss how to replenish your carbohydrate stores during a race, later in this chapter. After racing and training, replenishing your carbohydrate stores quickly, by ingesting carbohydrates within 30 minutes after training, enhances recovery and reduces fatigue.
Protein
During training, microtrauma occurs in our musculoskeletal system, but as part of the adaptation process, we repair the microtrauma at the same time. If our training stimulus is optimal, the rate of repair ‘overshoots’ the rate of microtrauma, and we get stronger, fitter, and even more resilient to injuries. But if the rate of repair lags behind, then we suffer overuse injuries. Protein intake is critical in ensuring adequate repair and recovery, as much of our muscles, tendons, and bones are made up of proteins.
Protein is also a minor fuel source for the muscles. If our carbohydrate intake is adequate, then we spare the protein and can better channel it towards repair and recovery. Hence, those who are on extreme diets tend to lose lean body mass, and this is certainly counterproductive to peak performance.
The recommended daily allowance for the general population is 0.8 g of protein per kilogramme body weight. For the endurance athlete, the research consensus is to increase the protein intake to 1.2 g to 1.6 g of protein per kilogramme of body weight. With a healthy, balanced diet you should be able to meet the increased protein requirement without the need for protein supplements. Bodybuilders, on the other hand, have a higher requirement of 1.8 g of protein per kilogramme body weight, and protein supplements are usually required to achieve such levels.
Some studies have found that the combination of carbohydrate and protein intake after exercise enhances the protein uptake compared to ingesting protein alone. Therefore, a balance diet is recommended.
The dangers of an excessively high protein intake include:
- Not getting enough carbohydrate to meet energy needs. This may cause the body to use protein as an energy source, resulting in muscle wasting
- Urinary frequency places an undue load on the kidneys and also risks dehydration
- May increase urinary calcium loss
- Increased fat consumption, because most high protein foods tend to be high in fat as well
Fat
At rest, our body relies mostly on fat as an energy source. As exercise intensity increases, the carbohydrates contribute an increasingly higher proportion of the energy relative to fat. While the proportion of fat utilisation diminishes, the absolute amount of fat oxidation actually increases with increasing exercise intensity, due to the higher overall energy expenditure. Well-trained endurance athletes are better at mobilizing fat than untrained individuals, and hence they are able to tap on a larger total pool of energy reserves and exercise for longer durations.
Although fat is a significant energy source, endurance runners do not have to make a conscious effort to accumulate fat stores. The reasons are, firstly, that there is a substantial amount fat in our diet. Someone who does not pay special attention to his/her diet may have about 40 per cent of their calories coming from fat. If you consciously avoid excessive fat intake, your fat intake may be reduced to the recommended under-30 per cent. If you can reduce this to 20 per cent, you would have done exceptionally well. The second reason is that our pre-existing fat stores are sufficient for our training and competition needs, even if we are quite lean. Take for example a lean, 65 kg endurance runner with 15 per cent body fat. He would have 9.8 kg of body fat, and since each kilogramme of body fat can deliver 7,700 kcal, he would have a fat store that is worth over 75,000 kcal! He only needs about 3,000 kcal to run a marathon (if all the energy for running the marathon were to come from fat, and this is clearly not the case), or about 3,000 kcal per day to sustain his bodily functions and training needs.
Fat is stored not only under the skin (subcutaneous fat) where it is visible, but it is also stored around your internal organs (intraabdominal or visceral fat) and within your muscle cells (intramuscular fat). Intraabdominal fat is strongly associated with chronic diseases like diabetes and hypertension, and exercise is an effective way to remove excessive intrabdominal fat. Both subcutaneous and intraabdominal fat represent ‘dead weight’ that the runner has to carry around while running, slowing him down. Intramuscular fat, on the other hand, is more useful to the runner, as it can be mobilized faster and help supplement carbohydrates as an energy source during exercise.
Micronutrients: Vitamins, Minerals and Anti-oxidants
Micronutrients are required by the body in small amounts for optimal function. Iron, for example, is a micronutrient that is required for the production of haemoglobin and oxidative enzymes, and is thus important for endurance athletes. Adequate intake of vitamin and minerals is important for optimal health and maintain performance.
Dietary surveys show that most runners are able to meet their daily vitamin and mineral requirements without supplementation. With a balanced, wholesome diet encompassing the recommended two servings of fruits and vegetables daily, it is unlikely that you will suffer any nutritional deficiencies. But if you want to play it even safer, you can supplement your diet with a multivitamin daily.
Do bear in mind that the body requires nutrients in an optimal range — too little and you suffer nutritional deficiencies; too much and you suffer toxicities and place an extra load on your body to try to remove the excess. Excessive vitamin A, for example, is toxic. By taking lots of vitamins and minerals, all you are doing is producing expensive urine. You benefit from supplementation only if you are lacking in certain vitamins or minerals.
There is no evidence that increasing training loads will increase the requirement for antioxidants. Therefore, it is not necessary to supplement your diet with anti-oxidants if you are eating a wide variety of food.
Fluids
Water is important for sustaining a high cardiac output and for preventing the body from overheating during exercise. While running, we lose water through our expired air, skin (perspiration), and our kidneys. If fluid intake is not able to match fluid loss, we become increasingly dehydrated. Our body will attempt to conserve water by producing less urine, but we will continue to sweat, as the body needs to prevent itself from overheating. With greater degrees of dehydration, our cardiac output starts to drop, our performance deteriorates, and we eventually stop sweating and begin to overheat.
The simplest way to assess the degree of dehydration is to track changes in bodyweight. Each kilogramme of weight loss during exercise is equivalent to 1 L of fluid deficit. Runners can tolerate up to 2 per cent of dehydration (i.e. 1.2 kg of water losses for a 60 kg runner) without much consequences. When fluid losses exceed 2 per cent of bodyweight, performance can be impaired by up to 20 per cent. Hence, it pays to be well hydrated before, during and after running. Depending on the degree of dehydration, you may need four to 24 hours to completely replace your fluid losses.
While dehydration compromises performance and puts you at risk of heat injuries, overhydration is dangerous and can be fatal. Excessive fluid intake dilutes the blood, thereby reducing the plasma concentration of sodium and resulting in hyponatremia. Hyponatraemia causes the brain to swell, resulting in coma and eventually death. Slower runners are more prone to dilutional hyponatraemia as the slow pace allows the runner to drink amply.
To avoid under- or over-hydrating, our fluid replacement needs to match our fluid losses. You can calculate your total fluid losses by following the steps below:
- Weigh yourself before and after at least one hour of exercise under conditions similar
to competition or a hard training session
- Weigh barefooted, with minimal clothing. For the post-exercise weighing, be sure to
towel dry and weigh as soon as is practical after exercise (e.g. less than 10 min)
- Total fluid loss (in litres) = bodyweight before exercise (in kg) – bodyweight after
exercise + fluid consumed during the exercise (in litres)
For example, if you weigh 60 kg before running and 59 kg after running for an hour, and you drank 0.5 L of water during the run, then your total fluid loss is 1.5 L per hour. Your degree of dehydration would be (60-59) x 100 / 60 = 1.7 per cent
To limit dehydration during a distance race, follow these tips:
- It is a good habit to drink regularly throughout the day
- Two to four hours before the race, drink 400 – 700 ml of fluid
- Drink 150 – 250 ml of fluid at regular intervals to match your fluid loss. Alternatively, work out how much you need to drink at each water station in order to match your fluid loss. You will notice that it is quite difficult to match your intake to your fluid loss during a marathon — if unable to do so, then do the best you can and ensure that at the end of the race, you are not more than 2 per cent dehydrated. It takes some practice to be able to tolerate drinking the intended amount of fluid at each drink station.
- After the race, weigh yourself to determine how dehydrated you are, and replace 150 per cent of your fluid deficit over two to sixhours, e.g. for 1 kg of fluid lost, replace with 1.5 L of fluid
- Do not depend on your thirst — if you drink just enough to satisfy your thirst, you are replacing only approximately 2/3 of your fluid losses
- Check your urine colour — it should be almost colourless two hours after the run.
During exercise, blood is shunted away from the gut to the exercising muscles. The gut is even more deprived of blood when we are dehydrated, and this disturbs intestinal motility and impairs gastric emptying rate. A high gastric emptying rate ensures that ingested fluid passes through the stomach quickly and into the small intestines where absorption can occur. Otherwise, the fluid sits in your stomach, sloshing around and causing abdominal discomfort. As dehydration slows down gastric emptying and fluid absorption, it is best to hydrate well before we become dehydrated.
What is the best fluid to drink during and after running? Generally, for low intensity of less than 90 minutes, plain water will suffice. However, with higher intensities and durations exceeding 90 minutes, sports drinks are generally recommended.
Sport drinks contains 5 – 8 per cent of sugars and some electrolytes (e.g. sodium and potassium in specific concentrations). The sugars help provide some energy (not very much), while the electrolytes help replace that lost through our sweat. The sugars and salts in the right concentrations optimise gastric emptying rate. Chilling the sports drink further enhances gastric emptying.
But which brand of sports drink should we use? If you look at the nutritional labelling of the sports drink, you will notice that the sugar and salt concentrations are all very similar. The major difference between brands is the flavouring. Hence, the brand you use is not particularly critical. By choosing a brand that is most palatable to you, you will be encouraged to drink more and minimize the risk of dehydration. Before a major race, do find out which brand of sports drink will be provided at the drink stations, and use that brand during practice to get yourself accustomed to it.
Soft drinks, fruit juices, and cordials are not the best replacement fluids as the high sugar concentration delays gastric emptying. Some energy drinks are not good replacement fluids during exercise due to their high osmolarity, or concentration, (as much as five times greater than sport drinks). Avoid alcohol for 24 hours after exercise — alcohol acts as a diuretic and interferes with rehydration and other recovery processes. |
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