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What is the CICO diet and can it help you lose weight?

Trying to lose weight? A dietitian explains why it’s not all about cutting calories.
 When it comes to managing your weight, calories count — to some degree — but they don’t all count in the same way.
When it comes to managing your weight, calories count — to some degree — but they don’t all count in the same way.Photo Illustration/Getty Images

Some people think that losing weight is simple math. If you eat fewer calories than you burn then weight loss is inevitable, right? Well, that's the reasoning behind the CICO diet, but the truth behind weight loss is actually a lot more complex.

What is the CICO diet?

The CICO diet isn’t a book or an eating plan endorsed by a health expert or celebrity. It’s a more general approach that involves eating fewer calories than you burn. Basically, the CICO diet "plan" is not really a plan at all — it's more like a rough outline.

CICO stands for calories-in-calories-out. The logic behind CICO is simple. Since a pound is equivalent to eating about 3,500 calories, if you want to lose about a pound a week, you need to shave 500 calories from your daily routine — which equates to 3,500 calories in a week. In CICO, this calorie reduction is achieved either by eating less, exercising more or a combination of both.

This simple mathematical approach to losing weight sounds reasonable. But the truth is that people’s individual experiences vary considerably when it comes to weight loss, so it’s actually impossible to accurately predict how much weight you’ll lose based on this math.

How do you do the CICO diet?

The appeal of CICO is that there are basically no restrictions. As long as you stay within a calorie range that's in line with your body's needs, you can eat what you want and still lose weight — or maintain your current weight. To stay on track, people often use a calorie counter app when following a CICO diet. But managing weight with calorie restrictions isn't as simple as it sounds.

Not all calories "count" the same way

When it comes to managing your weight, calories count — to some degree — but they don’t all count in the same way. There are three kinds of macronutrients that our bodies use to function: Fats, proteins and carbohydrates. Each macronutrient breaks down into a different amount of calories per gram. Fats have 9 calories in a gram and proteins and carbohydrates each have 4 calories in a gram. So, not only does each macronutrient contain a different number of calories, the body breaks down each kind of calorie differently.

What is a calorie?

You can think of calories as the energy our bodies derive from food. Essentially, calories tell us how much energy it takes for our bodies to break nutrients down. Calories come from any food you eat — whether that’s an orange, orange juice or orange soda.

However, the way the food is processed by the body makes a difference in how the body uses the calories created by breaking down nutrients. Some kinds of nutrients make you feel full because they take longer to break down and therefore stay in your body longer and some are broken down quickly by the body and don't make you feel sated very long.

Some calories fill you up more that others

Certain foods are especially filling, which means that the calories from those foods give you a lot of bang for the buck — or a lot of fullness for the calories. The satiety index is a ranking that indicates how filling a food is based on equal calorie servings of numerous foods. The rankings show, for example, that calories from boiled potatoes are seven times more filling than the same number of calories from a croissant. Calorie-for-calorie, fish is more filling than beef or eggs. Oatmeal is more filling than bran cereal.

Rather than focusing solely on calories, it’s more effective to become aware of your calorie needs and to develop an understanding of how calories from various foods make you feel. If you manage your appetite with filling foods that are also in line with your body’s caloric needs will help you manage your weight and your hunger levels.

Calories from processed foods

Many Americans get a lot of our calories from heavily processed foods — like sodas and packaged snacks, such as potato chips. In fact, research shows that Americans eat about 60% of their calories from highly processed foods. While packaged foods are convenient, our reliance on these foods comes at the expense of other, more nutritious foods — like fruits and vegetables. Some studies also report that processed foods may be linked to unintentional weight gain and related problems, such as higher blood pressure, cholesterol levels and blood sugar levels.

In a study published in Cell Metabolism in 2019, researchers pitted a whole foods diet against a processed one. Twenty people went on both diets for two weeks, and while the meals varied dramatically, the calories, sugar, fat, fiber, carbs and protein were the same on both. Once meals were served, people were allowed to eat as much or as little as they wished.

Here’s what happened: On the processed food diet, participants ate many more calories (averaging an extra 500 calories per day) and they gained an average of two pounds. They ate faster, too, which may indicate they weren’t filling up sufficiently, or it may mean their brains didn’t have a chance to compute that they were full. There’s also the possibility that it’s especially easy to consume these foods quickly. Think about how fast you can eat a snack bar made with oats compared to a bowl of steel cut oatmeal.

Meanwhile when those same people went on to eat the whole foods diet, the opposite occurred; they lost two pounds. In other words, eating processed food really matters when it comes to gaining or losing weight. So, then, it's not just the quantity of calories that makes a difference to your body, but also the quality.

Calories from whole foods

One criticism of the CICO model is the fact that the method assumes that the number of calories that you absorb from every calorie is the same. That makes good hypothetical sense, but the truth is that our bodies don't actually work that way. Your body absorbs the calories consumed from eating whole foods differently, compared to processed ones.

For example, if you’re tracking your calories, there may be slight differences in the number of calories that you think you’re eating compared to the number you’re actually absorbing. This can work to your advantage if you’re eating mostly whole foods — and potentially to your disadvantage if you aren’t.

Studies that examine dietary patterns point to the fact that adults who consume the most servings of whole grains have lower body weights. One possible explanation is that calories from whole grains aren’t absorbed as efficiently as calories from refined grains.

In one study involving both men and postmenopausal women, participants were assigned to diets with varying amounts of fiber, whole grains and refined grains, but the diets supplied each person an amount of calories meant to keep weight steady. After six weeks, people who were eating whole grains experienced a lift in resting metabolic rate, which means they burned more calories when they were inactive. They also excreted extra calories in their stool. Together, this led to a daily deficit of 92 calories.

Studies involving almonds have similarly found that we don’t absorb as many calories from eating nuts as we would assume, which may be why they’re also linked with healthier body measurements. Expert-approved diets — like the Mediterranean diet — tend to include nuts.

Calories from liquids

Liquid calories are especially problematic because there’s clinical evidence that your body doesn’t register them in the same way it registers calories that you chew, so sodas and coffee drinks aren’t as likely to fill you up. That's because there are nerves in the stomach that help your body sense how full you are by how much your stomach stretches and it stretches less when you consume liquid. So, if you drink high calories beverages routinely, you may wind up in a calorie surplus because you still need to eat — and therefore, consume calories — to combat hunger.

What science says about the CICO diet

The authors of a study on the CICO diet published in 2021 called the method "tragically flawed." That's because researchers involved in the study found that when people eat high glycemic index foods — carbohydrates that cause a rapid jump in blood sugar — the body responds hormonally. The body starts to make more insulin — a hormone that directs sugar into the cells — and it makes more glucagon — a hormone used to release stored glucose. This hormonal reaction to eating foods with a high glycemic index effectively instructs our fat cells to store calories.

As you might imagine, consistently telling your body to store calories is not ideal for weight loss or regulation. So it really does matter what you eat — not just how many calories.

There are many factors involved in weight loss

Regulating your body weight is a dynamic process that involves not only the calories and quality of food you eat, but other factors as well.

Other factors that can affect your weight:

  • Your genetics, sex, age and overall health.
  • Appetite regulating hormones that tell you when you’re hungry and when you’ve had enough to eat.
  • Stress levels and sleep quality, which influence your food choices.
  • The confidence and mindset that you know how to navigate eating and exercising in various circumstances.
  • Access to affordable, nutritious food.
  • How often you intentionally exercise and whether you’re new to it or you’ve participated in it for a while.

Learn more about diets