By now, you’ve likely heard about the ketogenic diet, the weight loss plan that calls for dramatically reducing how many carbs you eat, moderating your protein, and upping your fat intake. After you follow the ketogenic diet, or keto for short, for a few days, your body will enter ketosis, a state that a study in the May 2021 issue of Nutrients linked to weight loss, better glucose control, and improved cholesterol.
Not all health experts recommend the diet, though, as it can lead to kidney trouble, increased intake of “bad” fats, nutrient deficiencies, and an obsession with food, according to Northwestern Medicine. Another big downside of keto is that it's difficult to keep the body in ketosis. While you're on the keto diet, you’ll typically consume a maximum of 20 to 50 grams (g) of carbohydrates per day, as the Harvard T.H. Chan School of Public Health advises. To put that into perspective, the U.S. Department of Agriculture notes that one medium-size pear has 27 g of carbs.
Suddenly getting so few carbs can be a shock to the body. “One of the challenges that many people encounter when they try the keto diet for the first time is the drastic lack of energy they experience in the first few days. This is the time when the body is learning to use fat for energy rather than readily available carbs,” says Susan Kieffer, the department chair of the school of nursing at Purdue University Global in Helena, Montana. “You can feel very tired during this time and even a little fuzzy in your thinking.”
This experience is so common that it’s been dubbed the “keto flu.” Another reason the diet is tough to stick to? Carb cravings.
Enter keto cycling. Keto cycling involves following the keto diet for a certain amount of time and then taking a day (or more) off. “It’s also called carb cycling,” says Molly Devine, RD, the founder of MDS Nutrition in Durham, North Carolina. “That’s another term for it, because there are higher-carb days and lower-carb days.”
The idea is to make the keto diet easier to follow. Knowing there’s a day in the near future when you’ll be allowed to eat carbs again might help you stick to the diet for longer.
Keto cycling doesn't have a strict definition. Some people choose to have five or six days on keto followed by a day or two off. Others will do keto for 10 to 12 days followed by three to four days off.
Devine typically doesn’t recommend taking more than two days off keto. “Several higher carb days in a row almost always lead to ‘falling off the wagon’ and the return of intense carb and sugar cravings for most people,” she says. She says to start with just one day so you can see how your body responds and how quickly you return to ketosis afterward.
“If you have too many carbohydrates, you’re going to build up your glycogen stores, and it’s going to be very hard for you to get back into ketosis,” she says. She says to think about your glycogen stores, which are your body’s supply of stored carbohydrates, as a gas tank. “As long as we don’t let that tank dip over, we can deplete it pretty quickly again and get back into ketosis,” she says. “But as soon as we go beyond that three or four days [off keto], our tanks flood and you start to store some of that glucose as fat, and it becomes very difficult to deplete that tank again and get back into ketosis.”
On those higher-carb days, Devine recommends sticking to whole foods with low amounts of sugar rather than going on a full-blown carb binge. Foods like fruit, sweet potatoes, and whole grains — all considered complex carbs — rather than white bread and sweets will make it easier for the body to re-adapt to ketosis. Consider what time of day you’re eating these carbs, too. It’s best to eat carbs (again, opt for those complex choices) in the daytime when you're most active (if that's true for you) as opposed nighttime, Devine says.
Devine says not to jump right into keto cycling. “I would definitely not try keto cycling until you’re about two to three months into your keto diet,” she says. “That's because you need to make sure your body is fat adapted so that it can get back into ketosis easily.” In her practice, Devine has noticed that if the body is used to being in ketosis, it’ll snap back more quickly after eating a carb-heavy meal than if a person is new to keto, though there’s not enough research to confirm that this is always the case. She doesn’t encourage keto cycling unless the individual has been following a clean keto diet, which calls for sourcing the healthiest version of keto-approved foods, such as grass-fed meat and whole foods, for at least three months and has a regular and rigorous exercise plan. This should allow them to eat higher carbs without seeing weight gain or intense cravings.
Devine says to follow up a high-carb day with vigorous exercise the next morning. The idea is to force the body to burn the glycogen you took in so it can get back to working on fat burn.
Because keto cycling is so new, no studies have examined the benefits and risks yet. Kieffer says cycling in and out of ketosis — eating carbs then not eating carbs — might be dangerous. “If you eat a high-fat diet one day (like what is recommended in the keto diet) and then go back to eating carbs the next, I think a person could be in danger of storing much of that consumed fat, which can result in high triglycerides and cholesterol,” she says. She explains the body may not have time to convert fat to energy, so it may stick with using the carbs for energy and storing the fat.
There isn't much research on keto cycling, though one small study was published in September 2020 in Nutrients. The researchers found that keto cycling resulted in an amount of weight loss in young, healthy men similar to that engendered by a nutritious diet that cut 500 calories per day. The weight loss for the keto cyclers, however, was from a combination of decreased body fat, water, and lean body mass, whereas the other dieters primarily lost body fat.
Some anecdotal evidence suggests that people are more likely to stick with keto if they incorporate cycling. You could also end up losing more weight if you stick with the diet for a longer period than you otherwise would have.
Some people believe elite athletes benefit from keto cycling because their bodies use extra carbohydrates as energy to power through difficult workouts and races. “For an avid athlete, timing carbohydrate intake based on intensity and type of activity can have performance benefits,” Devine says.
After all, research has shown that the strict keto diet impairs exercise performance. One study found keto hurts athletic performance more than a high-carbohydrate diet or one that includes periods of high carbs and low carbs (which is similar to keto cycling).
It seems the body uses high-quality carbs as exercise fuel. “Running on glucose (carbs) during intense strength training workouts can be beneficial,” Devine says. Another study, published in Nutrition Today in January 2018, found that carbohydrates are the only macronutrient that can be broken down quickly enough for the body to use during high-intensity exercise.
Be careful about starting keto cycling or keto in general if you’re pregnant or nursing. Kieffer recommends that these women consult their primary care provider first. People with type 2 diabetes should also consult their doctor, and those with type 1 diabetes or kidney problems should avoid the diet, as should anyone with conditions related to their pancreas, liver, thyroid, or gallbladder, according to University of Chicago Medicine.
If you’ve cleared the approach with your healthcare team and weight loss is your ultimate goal, know that keto cycling won’t be nearly as effective as traditional keto, Devine points out. “It can halt your weight loss by taking those days off because during that time you’re not going to be burning any fat and you could be putting more on,” she says. “I have seen ‘cheat days’ turn into cheat months and just backfire for the client completely. It creates a very ‘yo-yo’ approach to weight loss which can be very discouraging.” Kieffer adds that the results of keto cycling are never as dramatic as when the body is kept in a constant state of ketosis.
On the other hand, if you take the approach of following the keto diet most days but cycling helps you stay on course, cycling could help you stick to the keto diet longer.
What it boils down to is this: You need to know yourself and your self-control. “If you’re able to have a higher-carb day that includes healthy carbs and be able to get back on track the next day, then it might work for you,” Devine says. “But if you’re somebody who kind of loses control when you get around sweet foods, and one doughnut means the entire case of doughnuts, you’re going to have trouble with it.”