Let’s start with the basics: carbs are not the bad guy. They are a vital part of a healthy diet and our bodies’ preferred source of energy, which makes them all the more important for active people and athletes.
As we learn more about the importance of ensuring we get the right balance of macronutrients — carbs, protein and fats — more of us are looking at ways to tweak our intake for optimum results in terms of workout performance and to maintain a healthy weight.
And this, the theory goes, is where carb cycling — the act of adjusting the amount of carbs in your diet around periods of heavy activity — comes in.
What is carb cycling?
Sports dietitian Renee McGregor puts it simply: "The [idea of] carb cycling is that you lower your carbs on low intensity days and raise them on higher intensity days." This can be modified over days, weeks and months, though that may require a fair bit of planning.
The aim is that you time your carb intake so that it provides maximum benefit when you need it most, limiting your carbs at other times. During low-carb periods, protein intake will usually remain similar to other periods, but healthy fat intake increases.
Renee McGregor is a leading sports dietitian, with over 20 years of experience working in clinical and performance nutrition. She has managed sport science teams leading into the 2016 Paralympics and is the founder of Team Renee McGregor, providing expert advice to athletes seeking support for a dysfunctional relationship with food and training.
Who is carb cycling for?
It has grown in popularity among endurance athletes (who will often carb-load before a big event) and bodybuilders, who, according to an article published the journal Sports, use carb-loading in the week before a competition to "enhance the appearance of leanness and vascularity."
Allied with this, a review in the European Journal of Sport Science suggests that reducing carbs and increasing fat intake could encourage the body to make use of fat as an energy supply, which could aid sports performance during periods of reduced carb availability.
It may also help the body to become more sensitive to insulin, which could aid carb utilisation when carbs are reintroduced or ramped up. However, more research is needed on the subject. As a discussion in the journal Nutrients put it, this kind of nutrient timing "is a nuanced topic."
And McGregor says: "You’re better off fuelling your training well and letting the training do the adaptation. When you train for endurance, even when you’re fueling well, you’re still improving your ability to burn fat and improving your ability to use more for fuel. That tends to have better outcomes than trying to decrease your carb intake."
In athletes and the very active, carb cycling would be carried out in line with a training schedule, so more carbs are taken in for high-intensity training or competition, and carbs are reduced for lighter days.
The idea is that you need fewer carbs during periods of lower-volume training and that if you do maintain your normal carb intake, you may see some weight gain because excess unused carbs are stored as fat.
Does carb cycling work?
As already noted, more studies are required. (What you may read on social media does not count as scientific research.) In its favour are the fact that it’s flexible and you don’t have to savagely cut your carb intake for long periods.
Because of this, it may also help those trying to lose weight, provided a calorie deficit is maintained. As a study in the Journal of Obesity and Metabolic Syndrome put it, “reducing daily calorie intake is the most important factor for weight loss."
But McGregor has concerns: "The problem I have with it is that it doesn’t take into account the fact that if you’re exercising every day your carb requirements are going to be quite high every day."
She also points to the lack of research on the topic. "There’s no real science behind this. There is science behind periodisation and science behind training low, which is where individuals in endurance will train in a carb-depleted or low state to try to improve their oxidation of fat to improve their endurance performance.
"However there are a lot of stipulations about how these sessions should be done. So although, yes, you can do certain sessions in a carb-depleted state, they need to be at a very low intensity, no longer than 60 minutes and generally no more than twice a week. And it’s very difficult to work out what that low intensity should be."
For those seeking weight loss through carb cycling, the planning and tracking of carb intake involved could be a turn-off. And bear in mind that high-carb days does not mean packing in the muffins.
Most of your calories should come from complex carbs rather than simple carbs. Complex carbs (such as fruit, vegetables, wholegrains and beans) take longer to digest and contain more fiber than simple carbs.
They’re more filling, so they’re a good option if you’re keeping an eye on your weight. Simple carbs (such as those found in cookies, soda and candy) are digested quickly and lead to a blood-glucose spike, so they are a short-lasting source of energy.
The amount of carbs needed for high-carb and low-carb days will be highly individual, depending on factors such as workout intensity, weight and age, so carb-cycling needs careful maintenance and you should consult a health professional before you embark on this or any other type of meal planning.
On high-carb days you might get 60% of your calories from complex carbs, while on low-carb days you might swap out some carb servings with healthy fats (such as those found in avocado, fatty fish, eggs and nuts). That said, McGregor has concerns that diets such as this raise the risk of disordered eating.
"There is a lot of misinformation on social media, in particular, with the idea of people only feeling they can eat carbs when they have done something and that’s really problematic from my point of view because we need carbs beyond exercise. We need carbs for our bones, our hormones and our brains, most important of all, so that’s where my concern comes in."
Should you try carb cycling?
As with any eating plan, you need to be careful you are getting the right amount of nutrients. Which is why it's vital that you talk through any dietary changes with a medical professional or nutritionist before you enact them.
And if you do try carb cycling, you will need to carefully track what you eat. It is not for everyone and while it may be beneficial for some health and fitness targets, hard evidence remains scant.
Overall, McGregor remains sceptical: "I don’t think its necessarily a way to improve athletic performance. I think there are much better ways to do it.
"Fueling your training well, knowing you have enough energy to work hard on the hardest sessions and still have enough energy to maintain your recovery sessions means your body is in a better position to adapt from that training and use the signalling at a cellular level to overall improve your performance."
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