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Gluten-free. Paleo. Intermittent fasting. Whole30. Keto. DASH. The list of trendy diets and their various rules and restrictions goes on and on. But the latest once-niche eating plan to edge into the mainstream is carb cycling. Here’s how the practice of carb cycling stacks up with other buzzy diets, and if (or how) it can improve your running performance.
What Is Carb Cycling?
There is no formal definition for carb cycling, but the gist of this eating plan is that you alter your carbohydrate intake throughout the week, month, or year. There can be high-carb, medium-carb, and low-carb days cycled during a period of time. Figuring out how many grams of carbs to eat each day is an individual choice, but as a general guideline, high-carbohydrate days entail getting about 60 percent of calories from carbs (or roughly 300 grams of carbs for a 2,000-calorie diet). Then on low-carbohydrate days, this can drop like an anvil to 5 to 10 percent of calories. Thus, a medium-carb day would be about 40 percent of calories from carbs, but some just stick to a low- and high-carb cycles to simplify things (there is only so much number-crunching people are willing to do).
For athletes, carb cycling generally revolves around a person’s training schedule. Your diet is tweaked based on day-to-day, week-to-week, and month-to-month ebbs and flows in training intensity and volume. On days when training is more intense, you consume more carbohydrates, whereas low-carb days occur when training is light. Some runners will taper down their carb intake during reduced-mileage periods like the off-season and then ramp up again when it’s time to pound out more miles.
Your body may not need as many carbohydrate calories during periods of lower volume training since you aren’t placing as much stress on it, but if you continue to load up on the same number of carbs as you do during periods of large training volumes, you may see your weight creep up. This could be due to two reasons: excess carbohydrates in the body that aren’t used for energy get stored as fat, but also, carbohydrates cling to water, so in some cases, this weight is simply water weight.
Also, many athletes consider themselves “weekend warriors,” meaning larger training loads take place on weekends with more downtime during the week. Periodizing your carbohydrate intake suggests you eat in a way to support these fluctuations. So you may not eat the same stack of pancakes on Tuesday morning as you do on Saturday morning when you’re getting ready to do (or just got back form) a long run instead of sitting at your desk all day.
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So why bother? The rationale behind carb cycling is that when your body receives limited carbs, it relies on fat as the primary fuel source, which can be helpful for weight control and fat loss and also helps your body be more sensitive to insulin to better utilize carbs when they are reintroduced. To that latter point, carb-cycling athletes believe that being strategic about how many carbohydrates are eaten at certain times can help you utilize carbohydrates (your body’s preferred fuel for higher-intensity exercise) more efficiently to power workouts and get closer to nailing a PR.
Many people find carb cycling’s flexible see-sawing between periods of different carbohydrate intake less onerous than sustaining longer periods of low-carb dieting like what is required on the Keto diet. It’s easier to march through a couple of low-carb days if you know that prerun bowl of pasta is on the horizon. Replenishing your body’s depleted glucose stores from carbohydrates (known as “refeeding”) can alleviate some of the loathed side-effects of low-carb eating such as brain fog and lethargy, making carb cycling a good middle ground.
But there are few downsides to carb cycling, too. The cycling period, as well as the amount and the type of carbohydrate is not defined, so you have to play around with this diet before figuring out what works best for your goals. The fact that it takes a lot of planning and tracking to do successfully means the diet can be mentally draining. And for some, obsessing about counting calories and macros can spiral into an unhealthy relationship with food.
Does Carb Cycling Actually Work?
Research on carb cycling for weight loss and endurance performance is pretty scant, and there’s not a lot of data on the long-term benefits or drawbacks of this dieting approach. In other words, what you hear on social media or in training circles is likely anecdotal.
With that said, there is one version of carb cycling that has some research muscle behind it—the “sleep low method.” This method entails performing a bout of high-intensity exercise to deplete your muscles’ carbohydrate (glycogen) stores and greatly limit carbohydrate intake afterward. Then, you perform a morning training session in a fasted state. Research suggests that training in this way with low-carb stores can amplify certain metabolic adaptations from endurance training and perhaps bolster overall performance. But before you jump to try this, know that this dieting method needs to be implemented very carefully. Being carb-depleted only works when training is performed at lower intensities, during which fat is the primary fuel source to power the engine.
At high intensities, muscles require carbohydrates to meet energy needs. So if you lace up for a spirited morning workout (anything above 75 percent max intensity) after eschewing carbs for several hours, you’ll likely hit the wall fast, which in turn diminishes overall calorie burn and training benefits. Instead, you want to periodize your carbohydrates to match your intended training efforts.
Some call this method “train low, compete high.” If planning an easy-does-it workout, you could experiment with performing it after following a low-carb diet, but if you want to crank it up, make sure to eat plenty of energizing carbs beforehand to keep your energy stores well-stocked. It’s important to note that this type of training diet should be undertaken under the supervision of a sports dietitian who can better help you pinpoint your carb needs based on your training schedule.
Bottom line: Carb-cycling isn’t as harsh of a commitment as other trending low-carb diets, but we simply need a lot more research to know if it’s beneficial for performance gains or weight loss. If you want to give carb-cycling a go, consider working with a trained professional and make sure the majority of your carbs are coming from wholesome sources such as whole grains, fruits and vegetables.
High-carb days shouldn’t be filled with muffins and candy. When you are trimming the calories you get from carbs, eat enough quality proteins and fats to help regulate hunger and ensure your body is getting the nutrition it needs. But remember that when carbs go high again, you’ll need to scale back your protein and fat intake to compensate for the shift in calories. And you should keep an especially close eye on your energy levels during your workouts. If they are consistently flagging, then messing around with your carb intake might not be best for you.