Carbohydrates 101
When it comes to energy, carbohydrates rule supreme as king.
The simplest form of carbohydrates, glucose, is our bodies preferred energy source for normal bodily functions, cognitive processes and athletic performance. Although there is a strong case to be made for fats and lower intensity exercise but that will have to wait for another day.
Before we go any further, let’s touch on an extremely oversimplified outline of glucose metabolism.
Regardless of type, every carbohydrate we consume will be broken down to glucose, the simplest form of carbohydrate, by specific enzymes at various points as it passes through the digestive tract. For us to utilise glucose it needs to go through a few pathways. First up is glycolysis, which is not dependent on oxygen and occurs under both aerobic and anaerobic conditions. For aerobic exercise, the products of glycolysis then enter into the Kreb’s cycle before finishing their energy harnessing journey in the electron transport chain by undergoing oxidative phosphorylation. After going through all three pathways, one molecule of glucose will provide 38 molecules of the energy that powers everything, adenosine triphosphate (ATP). Anaerobic exercise is slightly different as it won’t be in the presence of oxygen so will produce lactate, a combination of pyruvate and two hydrogen ions, and will loop back around to the start of glycolysis. Due to this ‘looping’ it isn’t sustainable for very long. Explains why you can’t do an all-out sprint very far right?
When it comes to the general public, the RNI for carbohydrates is advised at 55-70% of total energy intake. I know what you’re thinking, ‘that’s vague’…
Caloric and macronutrient intake is highly individualistic and should be calculated on an individual basis. That being said, say you were eating the earmarked 2,500kcal/day, this would work out between 1375-1700kcal. Knowing that every gram of carbohydrate provides 4kcal of energy, you would be aiming for 344-425g per day. Carbohydrate intake for athletes can be refined even further.
The recommended carbohydrate intake varies by sport, intensity and duration. Athletes training at a moderate intensity for less than one hour should consume 5-7g of carbohydrates per kg of bodyweight a day (g/kg/day) to fuel their performance. For exercise lasting up to 3 hours at a moderate to high intensity 8-10g/kg/day will see you through and anything above 3 hours at a moderate to high intensity should be fuelled through 8-12g/kg/day (per recommendations from the American College of Sports Medicine).
Take an athlete weighing 70kg training moderately 45 minutes a day 3-5 days a week. They would be advised to aim for 7g per kg of bodyweight, working out as 490g/day. For reference, a serving of penne pasta (170g cooked) has around 60g of carbohydrates. If you’re aiming for 490g/day, even with a hefty bowl of Italian goodness, hitting your carbohydrate target can be a struggle.
When it comes to fuelling, type does matter.
On its own, glucose oxidation will peak at a carbohydrate ingestion rate of 1.0-1.1g/min. Meaning, if you take in 30g of carbohydrates in the form of glucose it won’t have to be broken down further but will be limited due to the one uptake site.
Had you ingested a combination of carbohydrates, such as glucose and fructose, the same 30g would have an oxidation peak of up to 1.8g/min. This is mainly due to the multiple uptake sites allowing for greater absorption. Single is good, mixed is better. Carbohydrates come in many shapes and sizes; glucose, fructose, galactose, maltose, maltodextrin etc. A key difference between all of them is the amount of sugar molecules they have which dictates how quickly they can be broken down and absorbed. You’ve likely heard the terms simple and complex carbohydrates, simple have one or two sugar molecules where as complex has many. The more sugar molecules the slower the absorption. If you’re within a few hours of line up to run a 200m sprint it wouldn’t make sense to consume complex carbohydrates whereas an easily digestible simple sugar would be ideal.
Pre-Loading or Carb Loading is typically implemented by most athletes and has been shown to increase performance by 2-3%. Again, there is a growing body of evidence in the case of fats for lower intensity exercise.
For exercise lasting less than 90 minutes, athletes should consume 6-12g/kg 24 hours before. For exercise lasting more than 90min, athletes should consume 10-12g/kg/day in the 36-48 hours before.
To top up glycogen stores, 1-4 hours before exercise consume a single carbohydrate dose of 1-4g.kg.
During exercise, if it’s less than 60min your muscle and liver glycogen stores will be enough. Personally, I wouldn’t say no to a gel.
For exercise lasting 60-150 minutes, aim for 30-60g/hour CHO at 6-8% consumed every 10-15mins
Lastly, for exercise more than 150 minutes aim for 60-90g/hour of mixed carbohydrate sources (glucose/fructose).
If you haven’t got the time before exercise, it’s during the exercise or if you’re prone to gastrointestinal issues mouth rinsing has been shown to elicit performance benefits through the carbohydrate receptors in our mouths.
Whatever the sport, whatever the distance, whatever the intensity, the right nutritional plan can make the difference between a bad day, a good day and an outstanding day at the office.
