(L.J. Davids/For the Washington Post)

L ow-carb diets continue to be popular for weight loss, with the keto diet being the latest craze. But these diets can result in low energy levels and headaches, and research has generated conflicting results on their long-term safety. One recent study of almost 25,000 U.S. residents found a ­32 percent higher risk of premature death among participants who ate a low-carb diet. The negative side effects and growing concerns about the safety of low-carb eating have left some dieters searching for a more middle-of-the-road approach to consuming carbohydrates. Enter carb cycling.

Carb cycling is a nutrition strategy in which you alter the amount of carbohydrates you eat on a daily, weekly or monthly basis to maximize sports performance and to build muscle and lose fat and weight. This approach has been practiced for years by bodybuilders and elite athletes in sports where body weight has an impact. It’s only lately that, because of our societal obsession with carbs, the approach has spread to the general public, showing up in mainstream health and fitness publications and as a hashtag in more than 350,000 Instagram posts. Compared with low-carb dieting, the theory goes, carb cycling could put your body under less stress, allow you to enjoy more flexibility in your diet and enable you to take advantage of the physiological perks that come from carbohydrate-rich foods, such as the benefits of fiber.

What's the idea behind carb cycling?

Carb cycling’s benefits are still theoretical because it’s mostly based on research on the effects of either low-carb diets or periods of high-carb consumption (“carb loading”) on athletes — not on alternating between the two. But here are some of the reasons athletes believe adding some higher-carb days to a low-carb diet could be beneficial.

On any diet, restricting calories causes your metabolic rate to slow down and affects hormones that cause hunger, making weight regain more likely. Research shows that carb loading can temporarily raise metabolism and increase levels of leptin, a hormone that blunts hunger, which, together, could help promote weight loss. Research has also shown that carbohydrate-rich foods boost athletic performance and recovery, and that carbohydrates burned for energy spare protein, which then can be used for muscle growth rather than for fuel. Thus, the thinking goes, higher-carb days once in a while can help even non-athletes prevent a metabolic slowdown, enhance the effectiveness of their workouts, trim fat and build muscle. And lower-carb days the rest of the time can encourage the body to burn fat for fuel.

(As a side note, although there is some evidence that low-carb diets promote weight loss in the short term, a Harvard study of 811 overweight adults found that whether participants were assigned a lower-, medium- or higher-carb diet, there was no significant difference in weight loss after two years. So, although low-carb diets seem to help some people lose weight, ­higher-carb diets can work just as well when calories are reduced.)

But, as noted above, we don’t have research studies on carb cycling to tell us whether these diets are effective, much less safe over the long term. Another drawback is that they aren’t that easy to implement: Carb cycling takes plenty of math, meal prepping and weighing, and even more patience and experimentation. There isn’t a proven formula.

How does carb cycling work?

(L.J. Davids/For the Washington Post)

Anyone who wants to try carb cycling should talk to their doctor first, and meet with a registered dietitian to ensure they are meeting their energy and nutrient needs — and to help with the mind-boggling calculations that need to be done first. But here are some general guidelines.

First, calculate your energy needs to know how many calories to aim for each day. You can get a rough estimate by multiplying your weight in pounds by 10 for weight loss, by 12 to maintain your weight and by 15 to gain weight. On higher-carb days, you would try to get about half of your calories from carbohydrates, and on lower-carb days, you would try to get about 25 percent of your calories from carbs. You would aim to consume one gram of protein per pound of body weight, and make up the rest of your calorie budget from fat. (Each gram of fat is nine calories and each gram of protein or carbohydrates is four calories.) Your protein amounts will be pretty consistent day-to-day; it’s your carbs that you’re altering up and down. Then adjust your fat amounts to get the calories you need. Your low-carb days will be higher in fat and your higher-carb days will be lower in fat to meet your energy needs.

Start with four high-carb and three low-carb days per week. It’s usually best to have higher-carb days on the days you’re exercising, so that you can benefit from the boost in energy, performance and recovery. But your exercise routine, body type and health conditions all affect how often you need carb-rich foods and how much of them. You’ll probably need to adjust your carb-cycling plan until you find something that works.

Wondering what a couple of days of carb cycling might look like? On a lower-carb day, you could start with a breakfast of scrambled eggs with cheddar cheese, mushrooms and asparagus. Lunch could be a salad topped with salmon and oil and vinegar dressing, snacks might be celery with natural peanut butter or cottage cheese, and dinner could be cauliflower rice with a grilled chicken breast and sautéed snow peas.

On a higher-carb day, you might add a slice of whole-grain toast at breakfast, a scoop of quinoa at lunch and some brown rice to your dinner while reducing the amount of oil you add to your salad and during ­cooking.

Keep in mind that you still need to hit specific calorie goals to lose weight or build muscle, and you should be focusing on healthy, high-quality whole foods. The types of carbs in your diet affect your health. For example, added sugars, such as soda and candy, and starches, such as white rice and white bread, aren’t the most nutritious choices. Choose mostly nutrient-dense carbohydrates that are low on the glycemic index such as sweet potatoes, oats, quinoa and beans.

Another word of caution: Be careful not to overdo it on the higher-carb days. The difference between your lower-carb and higher-carb days could be narrower than you expect. Higher-carb days aren’t a “cheat day,” so don’t think this diet is your license to go to an all-you-can-eat pasta bar.

The bottom line

Carb cycling may be easier to stick to over the long term than a low-carb diet. It also may help people move beyond weight loss or training plateaus. Further, modest reductions in carbohydrate-rich foods, especially those high in refined carbohydrates, may help promote fat loss for some people.

At this point, we don’t know enough about carb-cycling diets for me to recommend them. What we do know is that consistency is key when it comes to getting results, and choosing the right types of carbs in moderate amounts as part of a healthy eating pattern is linked to a lower risk of some types of cancer, heart disease and stroke. Rather than focusing on the grams or percentages of carbs, protein and fats, you could home in on a variety of whole foods, such as vegetables, beans, fish, poultry, fruit, whole grains, nuts and seeds. The best diet is one that’s sustainable and doesn’t require endless calculations.

Christy Brissette is a registered dietitian, nutrition writer, TV contributor and president of 80TwentyNutrition.com . Follow her on Twitter @80twentyrule.