Carb cycling for runners – all you need to know
If you’ve ever done a marathon, you’re probably familiar with the idea of ‘carb loading’ – that is, shovelling pasta or potatoes at a terrifying volume in the 24 hours prior to your race. Now, the dietary strategy known as carb cycling, also called carbohydrate periodisation by those who are fond of syllables, is being talked about as a potentially useful way to schedule carb intake across your training schedule more broadly.
‘Carb cycling is based on the theory that you tailor your carbohydrate intake to your volume and intensity of training daily,’ says sports dietitian Renee McGregor says. ‘While there are some benefits to this, the issue is that it doesn’t take into consideration the need for carbohydrate availability in the lead up to a run, particularly a longer endurance run or a higher intensity session such as tempo, hills or intervals.
‘The other thing it overlooks,’ she continues, ‘is that for those runners who are running most days – let’s say, four days-plus a week – you actually still need to consume a decent amount of carbohydrate in-between runs to allow for optimal recovery, adaptation and progression.’
How does carb cycling work for runners?
As McGregor notes above, carb cycling involves adjusting the amount you take on board each day depending on what level of training you’re doing. So days that demand more energy, where you might have a particularly intenseor longrun in the diary, should also be high-carb days, while on rest days or prior to low-intensity sessions, you would keep the carbs low, theoretically encouraging your body to burn more fat (this is known as fat oxidation).
What are the benefits of carb cycling for running performance?
Runners engaged in high-intensity efforts and endurance need to have enough glycogen stored up, so timing your high-carb days appropriately will help, as well as improving your recovery by providing enough glycogen to replenish. By factoring in low-carb days too, the idea is to make your ‘metabolic flexibility’ more effective, by encouraging your body to be better able to switch efficiently between using carbs or fat as its energy source.
What are the drawbacks and who should avoid carb cycling?
If a busy lifestyle means it’s already tricky to stick to a rigid training schedule in the months before a race, you may find it too difficult to be really strict around meal planning and timings in addition. It is important to get the balance between carb intake and exercise levels right, because going too far one way or the other can either lead to weight gain or weight loss. Restricting carbs can leave you with low energy levels and mood changes, while a glycogen deficit can also be a factor in developing the condition Relative Energy Deficiency in Sport, known as RED-S. Carb cycling may also be problematic for high-mileage runners who are running four or more times a week, as they require high amounts of carbs even on easier or rest days. Finally, carb cycling is not recommended to anyone who may struggle with disordered eating. It is ,of course, well worth consulting a doctor or sports nutritionist for expert advice first.
What is the latest scientific evidence around carb cycling?
A range of studies have come to differing conclusions around this subject, which suggest carb cycling, like all good potatoes, should be taken with a pinch of salt. This one, published in the journal Nutrients in January 2024, tested 17 very fit under-23 male cyclists over a period of five weeks, some doing carbohydrate periodisation and others simply consuming a high amount of carbs. The researchers concluded that there wasn’t any difference: ‘A Five-Week Periodized Carbohydrate Diet Does Not Improve Maximal Lactate Steady-State Exercise Capacity and Substrate Oxidation in Well-Trained Cyclists compared to a High-Carbohydrate Diet’ was the snappy headline news. Before that, a meta-analysis in the Journal of the International Society of Sports Nutrition in 2021 also found ‘no overall effect of CHO [carbohydrate] periodisation on endurance performance compared to control endurance training with normal (high) CHO availability.’
However, a studyin 2010, again on cyclists, found that ‘fat oxidation was increased after training with low muscle glycogen.’ Another, from 2014, suggested that ‘training low’, with reduced carb availability, can lead to, ‘in some instances, improved exercise capacity.’
So if you’re feeling pasta your prime, you might want to try carb cycling, but make sure to approach with caution or you could make a fusilli mistakes.
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