If you’re confused about whether calorie counting is effective, you’re definitely not alone. Some insist that counting calories are useful because they believe losing weight boils down to the concept of calories in versus calories out.

Meanwhile, others believe that calorie counting is outdated, does not work, and often leaves people heavier than when they started. Both sides claim their ideas are backed by science, which only makes matters more confusing. This article takes a critical look at the evidence to determine whether counting calories works.

What is a Calorie?

A calorie is defined as the amount of heat energy needed to raise the temperature of 1 gram of water by 1°C. Calories are normally used to describe the amount of energy your body gets from what you eat and drink.

Calories can also be used to describe the amount of energy your body needs to perform physical tasks including breathing, thinking, and maintaining your heartbeat. The amount of energy that foods provide is normally recorded in thousands of calories, or kilocalories (kcal).

For instance, one carrot generally provides you with 25,000 calories or 25 kcal. On the other hand, running on the treadmill for 30 minutes generally requires you to use 300,000 calories or 300 kcal. However, because “kilocalories” is an awkward word to use, people often use the term “calories” instead.

Why it may seem like calories don‘t matter for weight loss

Biologically speaking, creating a calorie deficit is necessary for weight loss. Still, many people claim that when you’re trying to lose weight, what you eat is more important than how much you eat.

This claim is generally fueled by studies in which participants on low-carb diets appeared to lose more weight than those on high-carb diets, despite eating as many or even more total calories.

At first glance, these studies seem to suggest that a calorie deficit is not needed for weight loss. They are often used as proof that calorie counting is useless.

However, several other factors may influence the results of these studies. Plus, low-carb diets in addition to being difficult to sustain, the evidence does not support this.

People are bad at estimating what they eat

Many studies rely on self-reported data via participant food diaries rather than direct measurements to determine how many calories people eat or burn through physical activity.

Unfortunately, food and activity journals are not always completely accurate. In fact, studies report that participants significantly underestimate how much they eat and can underreport their calorie intake by as much as 2,000 calories per day.

Similarly, people tend to overestimate how much they move by up to 72%. This holds true even in cases where participants are paid to be accurate. According to one older study, even dietitians fall short when they’re asked to report their calorie intake accurately, although to a lesser extent than non-nutrition professionals

Low carb diets are higher in protein and fat

Low-carb diets are, by default, higher in protein and fat, which can make you feel fuller. This helps reduce hunger and appetite and may cause participants on low-carb diets to eat fewer total calories per day.

Protein also requires slightly more energy to digest than carbs and fat, which can contribute to the energy deficit needed for weight loss, at least to a certain extent. However, the slightly higher number of calories burned during protein digestion is unlikely to make a significant difference to your weight loss, according to some older studies.