The CICO diet: How it does and doesn't work for weight loss

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
By Samantha Cassetty, RD

Have you ever heard that losing weight is simply a matter of eating fewer calories than you’re burning? This is what’s referred to as the calories-in-calories-out method, or CICO. The idea is that a pound is equivalent to eating about 3,500 calories, so if you want to lose about a pound a week, you’d need to shave 500 calories from your daily routine, either by eating less, exercising more or a combo of both.

It may sound reasonable, but people’s individual experiences vary considerably so it’s impossible to accurately predict how much weight you’ll lose based on this math. When it comes to managing your weight, calories count — to some degree — but they don’t all count in the same way.

The CICO diet isn’t a book or an eating plan endorsed by a health expert or celebrity. It’s an approach that involves eating fewer calories than you burn. The idea is that 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.

Here’s what we know about calories and how they pertain to weight loss.

What is a calorie?

You can think of calories as the energy derived from food. Calories come from any food you eat, whether that’s an orange, orange juice or orange soda. However, the way the food is processed makes a difference. In this example, the orange is much more filling than the orange juice or soda.

Calories that fill you up

Certain foods are especially filling, which means that the calories from those foods give you a lot of bang for the buck. 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 better to be aware of your calorie needs and to develop an understanding of how calories from various foods make you feel. Managing your appetite with filling foods that are also in line with your body’s calorie needs is a good way to manage your weight and your hunger levels.

Calories from processed foods

Over time, we’ve been eating much more of our calories from heavily processed foods, like sodas and packaged snacks, such as potato chips. In fact, Americans eat about 60% of their calories from highly processed foods. While convenient, we rely on these foods 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, the quality of those calories mattered when it came to gaining or losing weight.

Calories from whole foods

One factor that gets ignored in a CICO model is the fact that there is some variability in the number of calories that you actually absorb from whole foods compared to processed ones. So 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 nuts have similarly found that we don’t absorb as many calories from these foods, which may be why — as part of a Mediterranean Diet — they’re also linked with healthier body measurements.

Calories from liquids

Liquid calories are especially problematic because there’s good evidence that your body doesn’t compute them in the same way it computes calories you chew, so sodas and coffee drinks aren’t as likely to fill you up. If you drink these routinely, you may wind up in a calorie surplus because you still need to eat (and therefore, consume calories) to combat hunger.

Other factors involved in weight regulation

It's important to remember that 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.

Some of the other factors that can affect your weight include:

  • 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 exercise across 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