What Is the CICO Diet and Can it Help You Lose Weight?

If you’ve ever been fed up by the latest diet fad, the minimalism of what's known as the CICO diet might seem pretty appealing. It stands for stands for “calories in, calories out” and in the past year, CICO has been all over the internet, especially on forums like Reddit. After failing at restrictive diets like Keto, one Redditor posted that she “had an epiphany that CICO isn’t actually a ‘diet’ to lose weight, but relearning to eat in the manner I would be if I was at my ideal size…I had to admit I had no idea how little my body needed.” Another Redditor canceled his weight-loss surgery after successfully shedding more than 200 pounds on CICO, while still another credited CICO with helping heal her knee injury.

Angela Lemond, a registered dietitian and spokesperson for the Academy of Nutrition and Dietetics (AND), thinks CICO has probably gotten a publicity boost as a counterbalance to the low-carb craze, since it proves you can lose weight without severely cutting back on carbs. “In the dieting industry, once one plan is really saturated, another comes out to refute it. It gives people another way to look at things,” she says.

Here's what you need to know before you commit to trying CICO.

A complete simplification of weight loss, CICO stands for “calories in, calories out”—and it’s a dieting concept that’s been around for decades, says Torey Armul, a registered dietitian and an AND spokesperson. Because losing weight ultimately comes down burning through more calories than you’re eating, “there is a lot of truth to it. It’s been gaining steam as a trendy diet,” she says. There’s no book or app or celebrity spokesperson: People just calculate their needs online, and then track how much they eat, drink, and work out in a given day.

Experts agree that the idea behind the CICO diet is, for the most part, true: Eating fewer calories than what your body needs to survive results in weight loss. If you’ve been defeated by restrictive diets in the past, the CICO mindset—which avoids the concept of “forbidden” foods—might help. “For someone who’s completely confused about conflicting nutrition messages, CICO can be a very simple, easy place to start,” Armul says.

Even just tracking calories for a few days can be very eye-opening. “People are often surprised by how many calories are in their food and how much is burned by exercise,” Armul says. “Knowledge is power. If you’re aware of what’s on a menu, that helps you to make better choices.”

While we could all benefit from making nutrition easier to understand, experts say CICO oversimplifies it. “We often think that the number on the scale dictates our health. But that’s absolutely not true,” Lemond says. If you follow CICO without paying any attention to where your calories are coming from, you can totally miss the mark on the nutrients, vitamins, and minerals you need to feel good and stay active, focused, and healthy, Armul says.

What’s more, the number of calories you actually need to lose or maintain weight varies a lot based on lots of factors, including your activity level and muscle mass. If you’re lean and active, you have what Lemond calls metabolic elasticity, which means your weight stays more stable with day-to-day caloric fluctuations than if you were a couch potato. Even your genetics may play a role in the balance of macronutrients you need to stay slim. “I have clients where we’ve just altered their macronutrients and it does affect their ability to lose weight on the same number of calories, although I haven’t seen it proven in large trials,” Lemond says. “I believe that suggests that, for each person, the balance may be just slightly different.”

Finally, not all foods are created equal: Some actually slightly increase your calorie burn. Known as thermogenic effect, fiber-rich foods like whole grains and veggies actually require calories for our bodies to break down. While we’re only talking tens of calories a day, in the long run that difference could play a nuanced role in the number of calories our bodies require to maintain a healthy weight, Armul and Lemond say.

The CICO diet doesn’t consider the quality of what you put in your mouth, as long as you don’t surpass your day’s total calorie count—and that’s not great for your overall health. Here are a few potential downsides and risks of eating an unbalanced CICO diet:

Counting calories involves lots of math and religious tracking, and that gets old fast. “At most you can ask people to do that for about a week, and then they get tired of it and just want to live their lives,” Armul says.

The high-convenience foods many of us fill up on are high in simple carbs, added sugars, and too much of the less-healthy kinds of fats, like saturated and trans fats. If you’re eating a highly-processed diet with lots of meat and/or simple carbs but no fruits and veggies, you’ll miss out on vitamins and minerals including potassium and magnesium, omega 3 fatty acids, calcium, vitamin D, and fiber, Armul and Lemond say. Since most of us already fall short on these nutrients, this kind of a diet boosts deficiencies, making you feel crappy in the short term.

Over time, a balanced diet is important for your immune system function and GI tract, Armul explains. A highly-processed diet that’s lacking in plant-based vitamins and minerals puts you at higher risk of high blood pressure and of high cholesterol, Lemond says, and it can increase the odds of being diagnosed with chronic conditions like heart disease and diabetes.

It depends on what you eat on CICO—but again, many of us tend to eat simple carbs like bagels, chips, and cookies. Those foods quickly spike and drop blood sugar, causing you to feel hungry and tired. “You’ll get an energy bump, but you’ll crash because it’s not staying in your stomach for long,” Lemond says.

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To stave off hunger and keep energy levels high, it’s better to combine high-fiber carbs (like oats, whole wheat, quinoa, brown rice, beans, lentils, chickpeas) with healthy fats (nuts, seeds) and protein (chicken, fish, lean meat, low-fat dairy). These foods take longer for your body to break down, Armul says, so they sit in your GI tract for longer, slowly releasing energy that your body uses over hours instead of minutes.

Eating fries and soda and skipping fruits and veggies isn’t doing your gut bacteria any favors. While research on the bacteria in our guts is still in its infancy, some studies suggest that a diet loaded with fruits and veggies is rich in fiber and probiotics that fuel the healthy bacteria in your gut. Those bacteria, in turn, have been linked to several functions throughout your body, including your mental health, ability to lose weight and maintain a healthy weight, and immune system function, Lemond explains, so it’s in your best interest to keep them happy.

Those chalky digestive powders contain a heavy dose of one nutrient that’s essential to keep you regular: fiber. If your CICO diet is low in whole grains, fruits, and veggies, you’re probably not getting enough fiber—which means there’s a good chance you’ll get stopped up and gassy, Armul says. “Too much sugar can also lead to gas and bloating, because they’re feeding the wrong kind of gut bacteria in your digestive tract,” she adds.

If you already tend to get headaches and migraines, they may get worse if you frequently spike your blood sugar with simple carbs. Magnesium deficiency has also been linked to headaches, and “it’s often the first thing to go when you’re not eating enough plant-based foods,” Lemond says.

When you go on a super low-calorie diet, your body thinks you’re starving, so it slows down your metabolism to save on energy, Lemond says—a change that may very well last for years.

What’s more, eating too few calories and not enough protein causes your body to burn muscle for energy. Because muscle requires more calories than body fat, you’ll need to eat fewer calories to maintain your new lower weight, Lemond says. Studies have shown that eating more protein while you diet minimizes muscle loss, but it doesn’t eliminate it, especially when your calories dip too low. “The more muscle you keep, the less fat you’ll gain back,” Lemond says.

Counting calories isn’t a good tactic for everyone. “I’ve found people who have more of an emotional relationship with food, [and] just tracking numbers doesn’t work very well. There’s so much more to food and eating than numbers, and CICO doesn’t tap into the social or emotional issues,” Armul says. “The fact that all the focus is on weight loss can be an unhealthy mindset.”

Nutritionists agree: CICO is not the ideal diet because it oversimplifies weight loss, isn’t sustainable, and it doesn’t consider the importance of nutrients or your overall health. When it comes to food, “we all need to talk more about health than pure weight loss,” Armul says.

It’s always a good idea to have a sense of how many calories your body needs to maintain a healthy, stable weight—but it’s also key to eat the right kinds of foods. “Ultimately, you want to find a diet that’s sustainable, flexible, and enjoyable,” Armul says.

The most data-proven diets for weight loss combine all three macronutrients—healthy carbs, healthy fat, and lean protein—on your plate every time you eat to maximize your energy and your metabolism, Lemond says. Most of your diet should consist of lots of fresh, whole fruits and veggies, whole grains, lean protein, and healthy fats (ideally from fish and plants).

Keep your weight-loss goals slow and steady to lose more fat and less muscle. That means not dipping too low with your calories—and every person’s minimum varies. “It depends on current body composition and other things such as genetic and hormonal factors,” Lemond says, so it's best to work with a nutritionist to determine the right calorie count for you. For a balanced diet, Armul suggests aiming for 50 to 60 percent of your calories from carbs, 15 to 30 percent from fat, and 20 to 35 percent from protein; to maintain muscle, Lemond suggests spacing out your protein to about 20 grams per meal.

To keep your metabolism up and your energy stable, try not to go more than four hours between meals, Lemond suggests—which means eating a hearty breakfast and lunch so all your calories don’t come right before you go to sleep, when you need them least. And avoid deciding what you’re having for lunch when you’re already hungry, because you’re more likely to pick calorie-dense foods that aren’t as good for you.

Also try to take a step back and think about why you’re eating. A lot of us eat because we’re in a social situation, we’re bored/sad/stressed, or just because it’s “time” to eat, without really being hungry. If you don’t get those factors in check, there’s a good chance you’ll surpass your calorie needs even if they’re your main focus, Lemond says.

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