Carbohydrates, everybody’s favourite macronutrient by far and the pound for pound champion of enhancing sports performance. This article is not another cookie cutter article piece looking at why pasta is important before a race, oh no, we are going to get into some of the science around carbohydrates as it pertains to performance.
First things first, it might be useful to look at how much carbohydrate you might need depending on what you are doing. A general rule of thumb would be to increase your hourly intake rates the longer you are on your feet or on the saddle, a rule of thumb I work on with my clients would be to hit between 30-45g/hr carbs for sessions under 90mins, aiming for intakes of 60-75g/hr for sessions between 90-150mins and aiming for 90g or more per hour for sessions in excess of this. The research base has shown very clearly that the absolutely clear fact is that the higher your carbohydrate intake during exercise, the better your performance, there is a linear relationship between 0-70g/hr in terms of improving finish times. Some research has recently shown that intakes as high as 120g/hr has increasing benefits on performance for a multitude of reasons.
Carb intakes during exercise prevent muscle glycogen breakdown, which is the bodies carbohydrate store, and in a sense, you can think of it like the funds you have to pay for your performance, as your funds run out, performance becomes increasingly difficult, when you run out, that’s you done – this is commonly called bonking. Glycogen and blood sugar stability are not the only factors in terms of why you would want a higher carb intake, research has shown that carb feeding will force blood flow to your gut wall, supporting continued function of your gut, minimising risk of GI issues. Moreover, higher carb intakes have been shown to increasingly reduce levels of muscle damage, with the highest carb intakes showing the smallest amounts of muscle damage, which is a majorly useful tool for ultra-endurance athletes and those who need rapid recovery (for example if training the day after a long brick session). Lower carbohydrate intakes are associated with poorer cognitive function, poorer heat tolerance and an increased rate of perceived exertion.
Now that we know how much, we need to know how much of what – there are limits (which are being challenged in research at present) that have been shown in terms of how much we can absorb in our intestinal tract, and the way to conceptualize this would be to think of it as specific entrances for specific molecules – namely we are looking at two doorways here, which would be the GLUT5 transporters (which absorb fructose and other pentose sugars) and the SGLT1 transporter (which absorbs glucose and other hexose sugars). The research has shown that we can absorb about 60-70g/hr of hexose sugars, and that we can absorb an additional 30g of pentose sugars per hour, though the recent findings of beneficial effects of 120g/hr versus 90g/hr, have posed the idea that we may not have the full picture. You will hopefully have noticed that this may be where the coveted dual carb source in their 2:1 ratios has emerged from.
In terms of ratios of carbohydrates and the effect on performance, it is beneficial to include dual carb sources, even at lower carb intakes, as the presence of fructose in a drink will spark off liver metabolism, which can help to further stabilize blood sugar. Dual carb sources versus single carb sources will be more beneficial for performance if dosing is matched. If we get slightly more granular, we know that a ratio of 1:0.8 for hexose:pentose carbs is superior for promoting fuel usage compared to 1:0.5, 1:1 or 2:1. We can look further still at osmolarity, which refers basically to how hard on the gut a specific type of carb will be based on how much water it may drag into your gut or slow down gastric emptying. The lowest osmolarity carb source is branched chain cyclic dextrin (BCCD), followed by dextrin, follow by maltodextrin – you will notice that these are the hexose sugars in sports products, and the lower the osmolarity, the higher the price.
So what can we do with this info, see below:
1) Aim for the highest carb intake you can tolerate
3) Opt for BCCD or dextrin if you have a sensitive gut
4) Practice using carbs in training to allow your gut to adapt
Happy trails, Evan Lynch – The Aid Station dietitian & performance nutritionist