While there isn’t one standard protocol, carb cycling typically involves alternating lower-carb days with higher-carb days. Typically fat intake increases on lower-crab days, and decreases on higher-carb days; while protein intake remains consistent.
Many advocates recommend this regimen: On days when you do strength training, consume a higher amount of carbs (say 200 grams), a low amount of fat, and a moderate amount of protein. On days when you do a cardio workout, eat a moderate amount of carbs (about 100 grams), protein, and fat. And on rest days, eat fewer carbs (30 grams), a high amount of fat, and a moderate amount of protein.
Another approach involves keeping both protein intake and fat intake fairly consistent, and modifying only your carbohydrates. With this method, lower-carb days are also lower-calorie days.
What are the benefits?
Proponents of carb cycling claim that the eating pattern helps increase muscle mass, decrease body fat, and improve fitness performance. But research on the diet is limited.
One 2013 study, published in the British Journal of Nutrition, looked at the effects of intermittent carb and calorie restriction in 115 overweight women aged 20 to 69, all of whom had a family history of breast cancer. The women were randomly assigned to one of three groups for three months. The first group consumed a calorie-restricted, low-carb diet two days per week. The women in the second group followed the same diet, but were allowed to eat unlimited amounts of protein and healthy fats (such as lean meat, olives, and nuts) on the low-carb days. The third group followed a standard, calorie-restricted Mediterranean diet seven days a week.
Researchers found that the women in both low-carb groups had better results: They lost roughly 9 pounds on average, compared to about 5 pounds in the Mediterranean group. Insulin resistance also decreased by 22% percent among the standard low-carb dieters; and 14% percent among those allowed extra protein and fat on low-carb days—compared to just 4% among the Mediterranean dieters. (The results were particularly significant for the study participants, as losing weight and lowering insulin resistance may help prevent breast cancer.)
While this study didn't involve the same carb cycling approach used by body builders and athletes, it does offer some insight into the potential benefits of limiting carbs part-time. But is doing so practical? Slashing carbs, even a few days a week, needs to be sustainable in order to generate lasting results.
The authors of that 2013 study also found that a higher percentage of women on the low-carb diets experienced constipation, headaches, bad breath, light-headedness, and food fixation. These unpleasant side effects parallel what I've seen with my clients who severely restrict their carb intake. In my experience, the side effects also the reason many low carb-dieters either give up, or wind up binging on forbidden foods.
Is there a more sustainable approach?
One of the main philosophies behind carb cycling is limiting carbs when the body doesn't need them as much. In a nutshell, carbs serve as fuel (like gasoline in your car) to help cells perform their jobs. Eating a large amount of carbs on days when you’re not very active doesn’t make much sense, because your body requires less fuel (much like how your car needs less gas for a ride across town compared to a road trip). Carbs that aren’t burned for fuel create a surplus—which can prevent weight loss, or lead to weight gain.
On the flip side, a carb limit of 30 grams is very low, even on less active days. That’s the amount of carbs in one cup of broccoli, one whole apple, and five baby carrots. For a better balance, I advise my clients to practice what I call “carb matching"—or aligning your carb intake with your energy needs, which may vary from day to day, or morning to afternoon.
In my experience with clients, carb matching helps with weight loss and improves fitness performance, while supporting all-day energy, and supplying a wide range of nutrients. It also makes sense. My pro athlete clients, who train or perform several hours a day, require more carbs than my CEO clients, who may fit in a morning workout, then sit in meetings the remainder of the day.
Carb matching also involves aligning your carb needs with your age, height, ideal weight, sex, and occupation. After all, a young, tall man with an active job and an ideal weight of 185 pounds is going to have a higher carb requirement than an older, petite woman with a sedentary job and an ideal weight of 135 pounds.
While carb cycling involves drastic shifts, carb matching is all about creating balance, and what I call the Goldilocks effect–not too little, and not too much. If you’ve tried carb cycling, and it either hasn’t worked for you, or doesn’t seem like a strategy you can stick with, try moderating your carb intake based on your activity level instead. And regardless of which approach you try, stick with these two important rules of thumb:
1) Always make quality a priority by choosing fresh, whole foods. (And remember not all carbs are created equal.)
2) Listen to your body! It’s cues are pretty good at guiding you toward a "just right" balance.
Cynthia Sass is Health’s contributing nutrition editor, a New York Times best-selling author, and consultant for the New York Yankees. See her full bio here.
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