Carb loading in 2021

As an endurance athlete you’ve probably dabbled in the dark arts of carbohydrate loading at one point or another. How did it go for you? Throw a comment below – we’d love to hear about it.

We say dark arts, but that is just a reference to ideas like super compensation that have pretty much been consigned to the sports nutrition bin.

A more moderate form of carb loading is definitely bathing in the light of performance-driven scientific consensus. In 2021 the hot knife of science says there is almost always a place for carb loading before events, definitely within them.

Sensibly upping carb consumption the day or two before an event will deliver the primary carb loading benefit: topping up muscle glycogen stores. All endurance athletes will benefit from the energy-giving goodness of periodical high-carb intakes – a baseline about 80 years of research backs.

“The general consensus still recommends eating carbs in the days before a race, but not necessarily weighing or measuring a certain amount or eating more calories overall, it’s more just making sure that carbs as a proportion of your general food intake is high,” says Andy Dixon, editor of Runner’s World magazine in the UK.

But hyper-loading carbs? Or depleting carb intakes in the days before an event then moving into a mega load – sometimes known as super compensation? Not so much.

The science just doesn’t support it. Either the boosted carb levels are processed more quickly by the body thus negating their presence in the first place; or these excessive low-then-high carb intakes unsettle the body’s energy processing systems. The result is the same: not performing enhancing.

There is also the extra water weight that comes with shovelling in the carbs – every carbohydrate gram the body stores as glycogen is accompanied by about three grams of water.

Add in the fact many carbs are consumed via fluids and gels and it’s easy to comprehend the frequent gastro issues that can arrive before or on race day, especially in running events where the gut-sloshing effect can be disastrous.

Definitely not performance enhancing.

Fuelling for the work required

So moderate carb loading then – still quite a leap from the assortment of low-carb variants that dominated in endurance circles in recent years, says Nick Morgan, former Ironman and founder of UK-based sports nutrition consultancy, Nutrition Integrated.

“From a carbohydrate point of view, the paradigm has completely shifted,” he notes. “Carbs are fundamental to endurance performance. I think practically that has been shown: typically 5g to 7g per kilogram of bodyweight and an athlete won’t go into the event carb depleted.”

It’s in-event feeding that is harder to get right for many endurance athletes. “A lot of amateurs struggle with initial sensitization and they get excited and go at a higher pace than planned which accelerates the whole carbohydrate mismanagement and then they end up in a pickle,” Morgan says.

There is always some variance due to minor physiological shifts and environmental factors but the athlete that can refine, define and stabilize their carb throughput is already a step up from the shockingly large numbers of athletes who fail to do this – at all levels.

“Doing that in-event feeding well is much more likely to define the success of the day than a few grams per kg bodyweight in advance,” Morgan says.

And just because an athlete might go in for a bit of moderate carb loading doesn’t mean periodic carb restriction in training to boost fat adaptation is off the menu. Especially in longer events like ultra-marathons, ultra-bike races and Ironmans, some level of fat oxidizing adaptation is pretty important for endurance athletes.

Morgan: “There are still proponents of high-fat but it is about fuelling for the work required, which basically means in preparation for a 200km bike race you might do some efforts in low-carb states to improve fat adaptation and various adaptive cellular mechanisms, but then you would still do your high-intensity training and the race itself with high carbohydrates.”

At wearable glucose tracking firm Supersapiens, director of applied science and content David Lipman, and scientific affairs VP Federico Fontana, agree low-carb training efforts can boost “cell signalling, gene expression and training-induced increases in oxidative enzyme activity/protein content” but warned exercise performance did not always improve.

“Particularly for athletes doing a high volume of training, exercising in the overnight-fasted state could more likely lead to a negative energy balance, which can be associated with hormonal and immune dysfunction,” Fontana and Lipman said, while still supporting “a potential role of both”.

The Supersapiens duo highlight a specific role for glycogen in muscle function toward the end of hard efforts.

“It is now recognised that glycogen availability can directly modulate contractile function of the muscle,” they say. “This is likely to be important during situations where higher power output and sprint finishes are required in the late stages of a race.”

Raising carb processing rates

Training the gut for in-event feeding, as we detailed here, can be some of the most important training of all. While admittedly at the extreme end of the spectrum, research is showing carb oxidisation rates in some individuals can be pushed much higher than the 60-90g/hour typically considered the upper limit, even in elite athletes, and which throws light on potential to challenge the 30-60g/hr thresholds for other mortals.

Rates have scaled as high as 120+g/hr in gut-trained trail and mountain runners and cyclists. Some researchers suggest certain bodily energy transporters with names like SGLT-1, GLUT5 and GLUT2 could be responsible for these elevated levels under the right conditions in certain individuals.

33-year-old Irish cyclist Ronan McLaughlin worked with Supersapiens to develop a nutrition plan that reportedly had him processing a whopping 145g of carbs per hour during his 6-hour+ Everesting world record effort in March this year.

“This pursuit was probably aided by the intermittent nature of the attempt – repetitions up the hill were taking 5-5.5 minutes – which allowed a nice spacing of fuelling, with a downhill to both lower his heart rate and take in fuel,”  Lipman and Fortana told us.

High-end stuff, but the kind of efforts and research that inevitably provokes incremental shifts in what concepts like carb loading can mean for athletes at all levels.