FUELING
What, when and how to get going?
Training and competition require adequate hydration and nutrition, regardless of intensity or duration.
The needs of each individual vary daily, based on their level of activity.
A proper understanding of what to eat and drink in advance, during, and after exercise will positively impact our performance and well-being.
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Article links:
​Calorie restriction and energy deficit: the danger of LEA
Carbs: The magic macro for energy production
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Calorie restriction and energy deficit: the danger of LEA
Energy availability is defined as the energy that is left for the body to function, after the energetic cost of all physical activities (exercise energy expenditure) has been deducted from total dietary energy intake. Every day, we ingest food to provide energy (as in calories) to ourselves in order to perform all physiological functions, not just exercising. If we deprive our bodies of the necessary amount of daily calories, eventually that balance between energy in and energy out will become negative, and this is when we become at risk of LEA: Low Energy Availability. An EA threshold <30 kcal/kg FFM/day has been identified to be categorized as “low”, but this is assuming you know your body composition and your fat free-mass(FFM). There are also questionnaires available to screen if an athlete is at risk to LEA or under-fueling.
LEA has been widely studied in athletes, and endurance athletes are not immune to the phenomenon. Body image issues, lack of proper information about food, social media influence, peer pressure and misconception that “the thinner the faster”, will eventually result in poor performance and health deterioration - even onset early osteoporosis and hormone dysregulation. Although lower body weight is favorable in terms of performance for endurance athletes, it should not cross the line of undereating and disordered eating. Unlike the general and sedentary population, where calorie restriction might be beneficial to weight loss, athletes have higher energy requirements. Hence nutrition should be “periodized” around training days and load.
Before aiming for performance, we need to ensure we are healthy, with adequate calorie intake, in the form of a well-balanced diet, preferably from whole foods and sports foods when necessary (during training or racing). “Running on empty” on a regular basis while exercising not only will be a painful experience, but also will result in poor performance, increase the risk of injury, jeopardise the whole process of exercise adaptation, and ultimately have the potential to lead to serious health issues.
Research has identified that both male and female athletes (depending on their sport) can be prone to LEA and disordered eating. It is not just the case of the “female athlete triad” anymore. Even though most studies are observational and based on self-reported data from participants, some association has been established between LEA and self-reported illnesses, beyond hormonal dysregulation, bone health biomarkers and increased risk of injury.
Sports foods are a precious help when training or racing, as they are designed to facilitate quick energy production (providing simple carbs and electrolytes) for performance. So, fuel up before hitting the trails, the road, the tracks, or the body of water! And keep fueling your body throughout the exercise, especially if exceeding 90 minutes. Eat enough throughout the day to sustain bodily function as well as training adaptation, performance, and recovery.
Jagim, A.R., Fields, J., Magee, M, K., Kerksick, C.M. and Jones, M.T. 2022. Contributing Factors to Low Energy Availability in Female Athletes: A Narrative Review of Energy Availability, Training Demands, Nutrition Barriers, Body Image, and Disordered Eating. Nutrients. doi: 10.3390/nu14050986. PMID: 35267961; PMCID: PMC8912784.
Logue, D. M., Madigan, S. M., Melin, A., Delahunt, E., Heinen, M., Donnell, S.-J. M., and Corish, C. A. 2020. Low Energy Availability in Athletes 2020: An Updated Narrative Review of Prevalence, Risk, Within-Day Energy Balance, Knowledge, and Impact on Sports Performance. Nutrients. https://doi.org/10.3390/nu12030835
Sims, S. T., Kerksick, C. M., Smith-Ryan, A. E., Janse de Jonge, X. A. K., Hirsch, K. R., Arent, S. M., Hewlings, S.J., Kleinerg, S.M., Bustilloh, E., Tartari, J.L., Starratti, V.G., Kreiderj, R.B., Greenwaltk, C., Renteríak, L.I., Ormsbeek, M.J., Trisha A. VanDusseldorpl, T.A., Campbell, B.I., Kalmano, D.S. and Antonio, J. 2023. International society of sports nutrition position stand: nutritional concerns of the female athlete. Journal of the International Society of Sports Nutrition. https://doi.org/10.1080/15502783.2023.2204066
Wasserfurth, P., Palmowski, J., Hahn, A and Karsten, K. 2020. Reasons for and Consequences of Low Energy Availability in Female and Male Athletes: Social Environment, Adaptations, and Prevention. Sport Medicine. https://doi.org/10.1186/s40798-020-00275-6
Carbs: The magic macro for energy production
Carbohydrates (carbs for short) form a very broad family extensively studied, especially in the field of sports nutrition. They are present in many foods (from bread to green veggies), and they can vary from simple sugars to very complex forms (starch and glycogen).
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Why do endurance athletes love (and should love) carbs?
Carbs, and especially glucose, are, before anything else, the preferred source of fuel for our bodies to function. All carbs will be broken down to simple sugars (the main one being glucose), and glucose will be used to provide the energy our metabolism needs to perform all functions, in the form of the ATP molecule.
Glucose is critical to our brain as a fuel source. The brain needs glucose to function, and its average consumption is around 120 g/day (20-25% of all glucose ingested), which is not a small amount. And of course, our muscles will use glucose for contraction and movement. Our immune cells use glucose to perform many functions, protecting us from pathogens. Our digestive system will use energy (glucose) to process all our food!
How does it work? Carbs (broken down and converted to glucose) can produce energy in the form of ATP via both pathways: with oxygen (aerobic system: glycolysis and TCA cycle), or more rapidly without oxygen (anaerobic system: simple glycolysis and lactate conversion cycle). We use the anaerobic system when performing high-power and intensity effort, such as sprinting or jumping. When performing endurance exercise, we mainly use the aerobic system, which can produce a constant source of ATP, as long as there is enough fuel to be broken down, in the presence of oxygen.
Our bodies can store glucose for later energy use, in the form of glycogen (an extremely condensed form of glucose molecules packed together), in our muscles and liver.
How much can we store? Well, it depends on our muscle mass (the more muscle, the more storage capacity). Our liver storage is quite limited (around 100g) and will be used mainly to maintain important functions such as sending glucose to the brain, especially when fasting. Estimates from research place average glycogen muscle storage at around 400g, but it can be a bit higher in well-trained athletes. That is around 2000 kcal stores in total. Which will be completely depleted after 90-120 minutes of vigorous exercise, even at a moderate pace.
The higher the pace intensity and the longer the exercise, the higher the need for carbs (simple sugar) in order to keep going without “hitting the wall”!
However, more recently, the science of sports nutrition has developed a more personalised and detailed approach around training plans, called “periodized nutrition”, including some “low-carb” days. This is relevant in terms of training adaptation (basically putting more stress on your body so it becomes more resilient, or more able to use fat as a fuel source). But this should be highly personalised and preferably discussed with a qualified sports nutritionist or dietician.
Post-exercise, it is recommended to consume carbs (preferably high GI, a more simple source) to replenish the glycogen stores. Muscle cells have increased sensitivity to sugar after being exercised, so the glucose uptake will be quicker, under the action of insulin. Protein intake to repair damaged muscle fibres from exercise will be facilitated by insulin as well, in the presence of glucose.
Fats are an alternative source of fuel (more about this in a different post), but this is a slower system, consuming more oxygen to produce energy.
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Blaak, E.E., Riccardi, G. and Cho, L. 2021. Carbohydrates: Separating fact from fiction. Atherosclerosis. 10.1016/j.atherosclerosis.2021.03.025
Jeukendrup, A. Is sugar bad for athletes?. Mysportscience blog.
https://www.mysportscience.com/post/is-sugar-bad-for-athletes
Mergenthaler, P., Lindauer, U., Diene,l G.A. and Meisel, A. 2013. Sugar for the brain: the role of glucose in physiological and pathological brain function. Trends in Neuroscience. 10.1016/j.tins.2013.07.001
Moore, D.R., Sygo, J. and Morton, J.P. 2022. Fuelling the female athlete: Carbohydrate and protein recommendations. European Journal of Sport Science. https://doi.org/10.1080/17461391.2021.1922508
Thomas, D.T., Erdman, K.A. and Burke, L.M. 2016. Position of the Academy of Nutrition and Dietetics, Dieticians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. Journal of the Academy of Nutrition and Dietetics.10.1016/j.jand.2015.12.006.
How about hydration?
Water is often sidelined in our minds when thinking about nutrition, despite being a critical macronutrient essential to our survival. In the context of physical exercise, especially endurance in the outdoors, even more attention must be paid.
We know we are supposed to drink at least 8-12 cups of water daily, but how about when we venture out to exercise? Well, needs vary extensively depending on the individual, the duration and intensity of the activity, and also on the environmental conditions (seasons, geographical location, weather variations, terrain, etc).
But with the Hong Kong weather being warm (and very hot in Summer) and humid, fluid intake becomes the number 1 priority for all runners, especially those engaging in longer than 60-90 minute outings. The same goes for bikers and hikers.
Depending on individuals, it can mean several liters for 5-6 hours on the bike or the trails.
How much water do we need? There are a few rules and guidelines, even though it is highly personalized:
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Never start a training session or a race being dehydrated (make sure you drank enough the day before).
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Drink 5-10ml/kg/BW in the 2-4 hours or as soon as possible before your session. Example: for a 50 kg athlete, that would mean 250-500 ml. This is my daily routine before my early morning run: 500ml.
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Avoid losing more than 2% of your body weight during your session: if you have access to a scale, you can weigh yourself before and after, and this can help you to identify how much fluid you might need next time.
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Easy method: monitor the colour of your urine. The ideal colour is pale yellow (meaning you are in euhydration = proper hydration state). The darker the colour, the more dehydrated you are. If this is too pale, ease off on the drinking; you don’t want to lose too much electrolytes.
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Don’t overdrink: It is common to see people ingesting too much water, especially during marathon races. This can lead to a severe condition called hyponatremia, where the sodium in your blood becomes too diluted and your nervous system can’t function properly, your brain can swell, and you can go into a coma (water intoxication).
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Use electrolytes (sodium, calcium, magnesium and potassium): In hot and humid environments, such as Hong Kong, we lose a lot of minerals through our sweat, especially sodium. So, water itself after 2 hours won’t do the trick. Mix with some carbs (most commercial “sports drinks” and powders present the correct ratio of electrolytes and sugar/glucose).
What happens when we get dehydrated while exercising?
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Our blood thickens (because of the loss of water through sweating), which makes it more difficult for the heart to pump it to the muscles.
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HR will increase, and so will the sensation of muscle fatigue.
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It feels harder to perform, keep the pace.
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We might experience headaches.
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Our cognitive function might also get impaired, making us more prone to falls and injuries. The recovery will take longer.
Another factor: when our muscle cells produce energy (in the form of ATP), there will be some heat generated in the process. This natural heat production will increase body temperature (you can actually “feel” the warmth of your working muscles), which is why we start sweating, to cool down the body. When paired with extremely hot and humid conditions, this heat will be exacerbated. Potentially leading to heat illness (heat exhaustion, or even heat stroke).
Altitude will also impact our hydration needs: it is recommended to increase water consumption at >2000m altitude, due to a decrease in plasma volume. In a cold environment, when the feeling of thirst might be blunted, with less desire to drink and sometimes non-practical access to fluids, dehydration can happen and impact health and performance (>3% BW loss) as well.
Finally, even our swimming friends can become dehydrated: it is not because you exercise in the water that you don’t sweat. So, the same principles apply here.
Why add glucose to the hydration mix with electrolytes?
Studies have demonstrated that sugar and minerals will help rehydrate better than plain water. Hence, speeding up the recovery process. Milk and fruit juices, oral rehydration salts, and sports drinks are good options. Or your own homemade sweet and salty drink mix!
Burke & Deakin. 2015). Clinical Sports Nutrition. 5th Edition. Chapter 13. McGraw-Hill Publishing.
Jeukendrup, A. The role of sodium during exercise, Mysportscience blog. https://www.mysportscience.com/post/the-role-of-sodium-during-exercise
Shirreffs, S.M. The Importance of Good Hydration for Work and Exercise Performance. 2005. Nutrition Reviews. https://doi.org/10.1111/j.1753-4887.2005.tb00149.x
Thomas, D.T., Erdman, K.A. and Burke, L.M. 2016. Position of the Academy of Nutrition and Dietetics, Dieticians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. Journal of the Academy of Nutrition and Dietetics 10.1016/j.jand.2015.12.006.