What Is CICO? Unpacking the "Calories in, Calories Out" Diet

If you’ve ever tried to lose weight or just become more mindful of your health, you may have come across the term CICO, which stands for “calories in, calories out.“

CICO is the idea that weight management comes down to balancing the amount of calories you consume with the calories your body uses for energy — basically, creating a calorie deficit.

A calorie deficit essentially means eating fewer calories than your body burns to drive weight loss. It sounds simple, but it’s not always straightforward. Many factors — like metabolism and hormones — can impact how your body processes calories and how you lose weight.

So, while CICO provides a helpful foundation, it’s just one piece of the puzzle when it comes to healthy, sustainable weight management.

We’ll explore how the CICO diet concept works in real life, and you can decide whether it’s the right approach for your needs and goals.

The CICO diet isn’t a specific, one-size-fits-all eating plan — it’s more of a principle or rule you can apply to any type of diet.

The main idea is that if you eat more calories than your body burns, it could lead to weight gain. Conversely, if you burn more calories than you consume, you may lose weight.

What Is Kcal vs. Calorie?

Calories (another term for kcals, which is short for kilocalories) are a unit of energy you get from food. Your body then uses that energy to fuel various functions.

You can follow a CICO approach no matter what eating plan you prefer, whether it’s keto, Mediterranean, paleo, or anything in between.

It might. CICO is based on the principle of creating a caloric deficit, which can drive weight loss.

A calorie deficit prompts your body to tap into stored energy reserves, primarily fat, to make up for the shortfall. This is what ultimately leads to weight loss. But everyone is different, so everyone’s calorie needs are different, too.

If you’re interested in learning what your calorie needs are to create a caloric deficit, you’ll need a few metrics:

• Basal metabolic rate (BMR). This is the number of calories your body burns at rest just to keep basic functions running (like breathing, digestion, and circulation).

• Activity level. You factor in your activity level, which will then help you figure out your total daily energy expenditure (TDEE) — how many calories you burn on an average day.

Once you have your TDEE, you can adjust your calorie intake to create a slight deficit (typically 250 to 500 calories per day) for weight loss without going too low and risking your energy or metabolism. You can use online calculators — including ours — to help you figure out all these metrics.

Check out the Hers TDEE Calculator.

That being said, the CICO diet may not always work since it’s pretty vague and doesn’t account for the whole picture.

Let’s dig into what the “calories in, calories out” mindset doesn’t account for.

So, let’s bust an important element of the calories-in-calories-out myth. Weight loss is often more complicated than just taking in fewer calories and burning more. This is because not all calories are equal, and everyone metabolizes them differently.

When you think about calories, it’s easy to focus on the number alone — but where those calories come from and how your body uses them is also critical.

Below, we’ll highlight three key factors that complicate calorie counting and provide some insight into how calories work.

1. Some Foods Only Provide Empty Calories

Some foods are high in calories but, but aren’t nutritious enough to fuel you throughout the day. These foods are known as empty calories.

Think of things like sugary snacks, processed carbs, and sodas. While they can contribute to your total calorie intake, they don’t provide much in the way of essential nutrients like vitamins and minerals your body needs to thrive.

Let’s look at an example of a study that compared two groups of people over two weeks. One group ate a diet of whole, nutritious foods, while the other group ate mostly processed foods.

The result? The processed-food group ended up eating about 500 more calories a day and gained two pounds, while the whole-foods group actually lost about two pounds.

Why the difference? Researchers think processed foods don’t provide the same level of satisfaction or fullness as whole, nutrient-dense foods. Eating them might lead to more cravings and ultimately increase your daily calorie intake.

Weight gain aside, highly processed foods can increase the risk of heart disease and other health conditions like type 2 diabetes.

2. Healthy Foods Can Fill You Up for Longer

Whole foods like fruits, veggies, lean proteins, and whole grains are nutrient-dense and high in fiber, which helps slow down digestion and leads to longer-lasting satiety (feeling full). This can reduce cravings that make you reach for unhealthy snacks and prevent overeating.

Processed foods, on the other hand, are often low in fiber and other essential nutrients that help you feel full. So you may feel hungry again soon after eating and then end up overeating — sometimes without even realizing it.

Fiber-rich whole foods can make portion control feel a lot more manageable without having to count every calorie. Plus, fiber has additional health benefits, like lowering cholesterol, which can reduce the risk of stroke and type 2 diabetes.

Healthy fats and complex carbs, like those from avocados, nuts, seeds, and olive oil, also contribute to this feeling of fullness and satisfaction. They take longer to digest and help regulate blood sugar levels — this is partly what keeps cravings in check.

Similarly, protein-rich foods, such as chicken, fish, beans, and eggs, are linked to weight loss. Protein helps curb hunger by promoting feelings of fullness and helping preserve muscle mass. This is especially important when you’re in a caloric deficit.

Long story short? It’s best to choose foods based on their nutritional value, not just how many calories they contain.

3. Not Everyone Metabolizes Calories the Same Way

Lots of things play a role in how someone burns or stores calories from food. This can include:

• Genetics. Some people are predisposed to use calories more efficiently and burn more calories at rest and during exercise than others. This influences how many calories they need to fuel them.

• Age. Metabolisms tend to slow down with age.

• Gender. Men and women may use calories differently. Though not always, men generally have higher metabolic rates.

• Body composition. This is the distribution of muscle, fat, and bone in your body. Having a higher percentage of muscle mass can help boost metabolism.

• Hormones. Certain conditions can impact how you process calories. For example, some people have hormonal imbalances that can interfere with their metabolism.

All this is to say, while CICO can be a good basic framework for weight loss, it’s not always that simple.

Another potential pitfall of the CICO diet is that it might lead to eating too few calories.

And while cutting back works for some, severely restricting calories also limits essential nutrients, which can actually be harmful to your physical and mental health.

Beyond nutritional deficiencies, this can elevate your risk for things like:

• Muscle loss. In severe or prolonged calorie deficits, your body can start breaking down muscle tissue for energy, leading to a loss of lean muscle mass and reduced strength.

• Decreased bone density. Inadequate caloric intake, along with low calcium and vitamin D intake, can increase the risk of bone fractures over time.

• Reduced metabolism. Ongoing calorie deficits can slow down energy burn. This can make losing weight or maintaining weight loss more challenging.

• Fatigue and weakness. When you’re not eating enough calories to sustain your energy, you’re more likely to feel tired. This can impact your mental performance and ability to be physically active.

• Hormonal imbalances. Calorie deficits can disrupt hormones, especially those involved in metabolism, appetite, and reproductive functions.

• Impaired immune function. Inadequate calorie intake can weaken immunity, making you more likely to get sick.

• Mental health effects. Ongoing calorie restriction could probably make anyone irritable. Not eating enough can lead to mood swings and increase stress.

• Disordered eating. Unsustainable calorie deficits could end up making someone overeat from hunger or cravings for restricted foods, potentially leading to long-term mental health issues.

The truth is that focusing too much on tracking calories can sometimes result in an unhealthy relationship with food.

If you do use the CICO method, focus not just on the number of calories you consume but also on the quality of those calories. The key is finding a sustainable approach that works for you — not one that feels restrictive or stressful.

Here’s how to work toward healthy weight loss:

• Focus on whole foods that fill you up for longer.

• Swap out things with added sugar, like simple or processed carbohydrates and sodas.

• Aim for 150 minutes of moderate-intensity aerobic physical activity a week (aka cardio exercise), plus a couple of strength training sessions.

• Make sure you get plenty of sleep and stay hydrated.

We should also note that weight loss is more difficult for some people, who may need more than healthy lifestyle habits to manage their body weight. Those with obesity or overweight could benefit from extra support from weight loss medications like GLP-1s (glucagon-like peptide-1 receptor agonists).

GLP-1 weight loss meds mimic the hormone GLP-1, which moderates appetite and blood sugar metabolism. They decrease appetite, slow digestion, and increase satiety, which can help with weight loss. Some examples of GLP-1s include Wegovy^® and Ozempic^®, which contain the active ingredient semaglutide.

You can take our free online assessment to find out if weight loss drugs might be a good fit for you. If so, you’ll get a customized treatment plan from a healthcare provider.

Do calorie deficits work? They can. The CICO diet (“calories in, calories out“ rule) has a simple foundation: Eat fewer calories than you burn, and you’ll likely lose weight.

It can be a helpful starting point for weight management. CICO isn’t inherently good or bad, but having a little more context can lead to a healthier, more effective plan.

Here’s what to remember about CICO:

• Not all calories are created equal. The quality of the food you eat, your body’s unique metabolism, and lifestyle factors like sleep and stress all play a role in how you manage your weight.

• While creating a calorie deficit can lead to weight loss, it’s crucial to prioritize whole, nutrient-rich foods that keep you full and satisfied rather than focusing solely on cutting calories. The goal is healthy, balanced living you can carry with you for the long haul.

• Finding an eating plan for sustainable weight management isn’t just about numbers or being “perfect.“ It’s about making mindful food choices and building healthy habits that support your body, energy, and overall health and long-term well-being.

When in doubt, consider reaching out to a registered dietician nutritionist. They can help you come up with an eating plan that works for your unique needs.

If you’re looking for more weight loss support or are considering weight loss medications, we can help you get started with our free weight loss quiz.