Everything you need to know about alternating between high and low carb days, plus whether or not it's right for you.
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Sports nutrition concepts that were once reserved for elite athletes and bodybuilders are becoming totally mainstream: counting macros, eating for body recomposition, and refeeding days. While you might not want to use them all year round, they can definitely provide a helpful boost when you're trying to reach a specific fitness goal. The latest once-niche nutrition tactic to make it into the mainstream? Carb cycling. Here's everything you need to know about the practice, plus how to tell if it's right for you.
What Does Carb Cycling Mean?
"There's no formal definition for carb cycling, but the basic principle is that you alter your carb intake based on your varying needs throughout the week, month, or year," says Edwina Clark, a registered dietitian and head of nutrition and wellness at Yummly. The timing and amount of carbs consumed during each phase vary depending on the person, she adds.
"Carb cycling is often used among bodybuilders/physique competitors and high-performing athletes," notes Lauren Manganiello, a registered dietitian and certified personal trainer. But with the recent rise in popularity of the ketogenic diet, particularly for active people, the concept of carb cycling is becoming more common among everyday athletes.
Generally, carb cycling revolves around a person's training schedule. "On days when they are training more intensely, they would consume more carbohydrates, whereas low-carb days would occur on days when their training is less intense," Manganiello explains. "There are usually several high-carb, medium-carb, and low-carb days cycled throughout the week."
So why do it? "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 management, body fat losses, and boosting carb storage when carbs are reintroduced," Clark says. The idea is that by being strategic about when and how you eat carbs (your body's preferred fuel source for exercise), you can more efficiently power your workouts and achieve better results in terms of both performance and body composition.
Who Is It Right For?
There are two main groups of people that carb cycling can be helpful for, according to Clark: endurance athletes and active people on low-carb diets.
For those who focus on endurance sports like running, cycling, and swimming, "preliminary evidence suggests that varying carbohydrate throughout the year—specifically lowering carbs during high volume, pre-season training—may be helpful for increasing muscle glycogen stores and performance when carbs are reintroduced," Clark explains. Basically, lowering your carb intake before you go into your main training season (say, prepping for a marathon or triathlon), may help your body to better utilize carbs when you reintroduce them right before you need to hit your peak performance level.
For those more interested in weight control or fat loss, carb cycling can also make sense. "For some individuals, consuming a lower-carb diet can be helpful for weight maintenance and optimal health," Clark says. That's probably why keto is so popular at the moment. "That said, research indicates that carbohydrates are the predominant fuel for working muscles during high-intensity exercise, and consuming carbs before and after a tough sweat session is critical to get the most out of it." It's generally accepted that a low carb intake will reduce power output during high-intensity exercise, so carb cycling could help if you're eating a low-carb diet but want to complete a HIIT or weightlifting workout, for example. (BTW, here's more info on how to exercise while on the keto diet.)
And while carb cycling is popular with those who follow keto-like high-fat, low-carb diets, you don't have to be eating a high-fat diet to benefit from carb cycling. "You can absolutely cycle your carbs with any kind of diet," says Shoshana Pritzker, a sports nutritionist and registered dietitian.
In fact, it might be better not to carb cycle while on keto, especially if you're newer to the eating style. "Regular increases in carbs will take you out of ketosis, so if you decide to use carb cycling with a ketogenic diet, I would limit high-carb days to only once, maybe twice, per week," Pritzker says. After all, the point of keto is to get your body to use fat for fuel, so taking your body in and out of ketosis kind of defeats the purpose of the diet and might even make it hard to gauge whether the eating style is a good fit for you or not. (Related: Is The Keto Diet Bad for You?)
Does It Work?
Okay, so this all sounds great in theory, but what does science have to say about it? Uh, not much, actually. "Research on carb cycling for endurance performance is relatively new, and there's not a lot of data on the long-term effects of swinging between low and high carb intake," Clark says. The same goes for the potential fat-loss benefits—the evidence around carb cycling is mainly anecdotal.
The fact that the long-term effects of carb cycling are unknown is one of the reasons experts recommend trying it for short periods of time only. Plus, there's the fact that it takes a lot of planning, prepping, and tracking to do successfully. "It can be difficult to sustain long-term," Manganiello says. "Physique competitors and athletes usually only use it during their 'prep' phase for competitions, which is usually only a few weeks or months," she says.
And while it might give you more energy on training days, it can also be mentally draining. "As with any type of diet, you never want to become obsessed with counting, whether it's calories, macros, or something else, because it can promote a very unhealthy mindset and relationship with food," Manganiello notes. "Also, individuals tend to consume the same foods when carb cycling, therefore limiting variety within their diet."
How to Try It
If you think carb cycling might be right for you, here's how to get started. First, it goes without saying that you'll need to track your macros using an app or food journal. Next, you'll need to figure out how many grams of carbs to eat each day. This is highly individual, experts say. "There are several factors that go into figuring out how many grams of carbs to eat, such as body weight, age, sex, the intensity of your workouts, as well as listening to your body and hunger cues," Manganiello says.
But there are some general guidelines you can use to figure out a starting point. "On high-carbohydrate days, individuals often consume about 60 percent of their calories from complex carbs," Manganiello says. "On low-carbohydrate days, individuals will switch out some of their carbohydrates for healthy fats."
Another option is to use your low-carb days as a starting point to calculate your medium and high carb days. "If you consider that 50 grams of carbs per day is what is generally needed to reach ketosis, you could start there as your low-carb day," Pritzker says. "Work your way up from there and max out at 200 grams of carbs per day."
So your week might look like this:
Day 1: 50 grams carbs
Day 2: 100 grams carbs
Day 3: 150 grams carbs
Day 4: 200 grams carbs
Day 5: 125 grams carbs
Day 4 would be your most intense training day (heavy weightlifting, HIIT, or a long run), and day 1 would be your least intense (light cardio, mobility work, or a rest day). Then, you'd cycle back to day 1.
As for what to do with the rest of your calories, you have a couple of options. "You can keep your protein and fat intake the same and only change the amount of carbs you eat on a daily basis," Pritzker says. "Try to match high-carb days with tough workout days, that way you get the boost in energy you need for your workouts from the extra carbs." Another option? "Keep protein the same, but adjust fat when you adjust carbs. So if carbs go up, fat intake goes down to compensate for the shift in calories." This may be a better choice for those trying to lose weight or body fat.
Final Carb Cycling Tips
Fiber matters. Prioritizing high-fiber carbs on low carb days is a solid way to go. "With any lower-carb eating approach, getting adequate fiber is a concern, as whole-grain carbohydrates are a rich source of this important nutrient," Clark says. "Fiber supports satiety, cholesterol control, and your microbiome, among other things!" (P.S. Did you know that the microbiome of your gut is linked to the brain and mental illness?)
Quality matters. High-carb days shouldn't be filled with pizza and french fries. "Whole grains such as brown rice, quinoa, and whole-grain bread/pasta are healthier choices than more refined options such as sugar, cakes, cookies, and soft drinks," Clark says.
When in doubt, consult an expert. "The amount of carbohydrates required on high- vs. low-carb days varies greatly depending on calorie needs, the type and amount of activity you do, and your goal," Clark says. If you want personalized recommendations, check in with a registered dietitian. That way, you can ensure you're getting the fuel your body needs to achieve the best possible results.