By Alina Petre

If you are confused about whether calorie counting is effective or not, then you are definitely not alone.

Some insist that counting calories is useful because they believe losing weight boils down to the concept of calories in vs calories out.

Others believe that calorie counting is outdated, doesn't work and often leaves people heavier than when they started. Both sides claim their ideas are supported 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 one 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 provided by foods 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.

For the purposes of this article, the common term "calorie" will be used to describe kilocalories (kcal).

Bottom Line: Calories are used to describe the energy your body gets from foods or expends on various activities.

How Does Your Body Use Calories?

If you're wondering why calories matter, here's a quick overview of how your body uses them.

It begins with what you eat. Food is where your body gets the calories it needs to function.

During digestion, your body breaks down the foods you eat into smaller units.

These subunits can either be used to build your own tissues or to provide your body with the energy it needs to meet its immediate needs.

The amount of energy your body gets from the subunits depends on where they come from:

• Carbs: 4 calories per gram.

• Protein: 4 calories per gram.

• Fat: 9 calories per gram.

• Alcohol: 7 calories per gram.

Your body uses the calories produced from metabolizing these nutrients to power three main processes, which are listed below (1, 2).

1. Basic Metabolism

Your body will use most calories to perform basic functions, such as providing energy to your brain, kidneys, lungs, heart and nervous system.

The amount of energy required to support these functions is referred to as your basal metabolic rate (BMR). It makes up the largest proportion of your total daily energy requirements (1).

2. Digestion

Your body will use part of the calories you consume to help you digest and metabolize the foods you eat.

This is known as the thermic effect of food (TEF) and varies based on the foods you eat. For instance, protein requires slightly more energy to be digested, whereas fat requires the least (3).

About 10–15% of the calories you get from a meal will be used to support the TEF (3).

3. Physical Activity

The remainder of the calories you get from foods fuel your physical activity.

This includes both your everyday tasks and your workouts. Therefore, the total number of calories needed to cover this category can vary from day to day and person to person.

Bottom Line: Your body gets calories from the foods you eat and uses them to fuel basal metabolic rate, digestion and physical activity.

You Need a Calorie Deficit to Lose Weight

Once your body's immediate energy needs are met, any excess energy is stored for future use.

Some of it is stored as glycogen in your muscles, but most will be stored as fat.

Therefore, if you eat more calories than your body needs, you will gain weight, mostly from fat (4, 5, 6, 7, 8, 9).

On the other hand, if the calories you get from your diet are insufficient to cover your immediate needs, your body is forced to draw on its energy stores to compensate.

This is what causes you to lose weight, mostly from your body fat (10, 11, 12, 13).

This calorie balance concept has been proven time and time again and persists whether your calories come from carbs, fat or protein (10, 12, 14, 15, 16, 17, 18).

Bottom Line: In order to lose weight, you always need to burn more calories than you eat.

Not All Calories Are Created Equal

The seemingly simple question of whether calories from fat, protein and carbs are different is controversial, since it depends on how you look at it.

Just like inches and pounds, calories are a unit of measurement.

Therefore, purely in terms of weight loss, 100 calories will remain 100 calories regardless of whether they come from an apple or a donut.

However, in terms of health, all calories are not created equal.

It's important to make the distinction between quantity and quality. Even foods that have the same quantity of calories can be of different nutritional quality and can have very different effects on your health (19, 20, 21).

Different foods tend to affect your metabolism, hormone levels, hunger and appetite differently (22, 23, 24).

For example, eating 100 calories worth of donuts may not diminish your hunger as effectively as eating 100 calories from apples.

Therefore, a donut may make you more likely to overeat later in the day, preventing you from achieving the calorie deficit needed for weight loss.

Bottom Line: If you're just looking at whether you'll lose weight, a calorie is a calorie and you'll need to consume fewer calories than you burn. But in terms of health, not all calories are created equal.

Why It May Seem Like Calories Don't Matter for Weight Loss

Biologically speaking, a calorie deficit is always needed to lose weight. There's no way around it.

Yet, 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 (25, 26, 27, 28).

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, this is a poor interpretation of the evidence for the following three reasons.

1. People Are Bad at Estimating What They Eat

Many studies rely on participant food diaries rather than direct measurements to determine how many calories they eat or burn through physical activity.

Unfortunately, food and activity journals are notorious for being highly inaccurate.

In fact, studies report that participants generally underestimate how much they eat by up to 45% 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 51%. This holds true even in cases where participants are paid to be accurate (29, 30, 31, 32, 33).

Even dietitians fall short when they're asked to report their calorie intake accurately, although to a lesser extent than non-nutrition professionals (34).

2. 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 more full.

This helps reduce hunger and appetite and may cause participants on low-carb diets to eat fewer total calories per day (12, 35, 36, 37).

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 (3).

However, the slightly higher number of calories burned during protein digestion will not make a significant difference to your weight loss (14, 15, 38).

3. Studies Often Measure Weight Loss Rather Than Fat Loss

Many studies only report the total amount of weight lost, without specifying whether this weight came from loss of fat, muscle or water.

Low-carb diets are known to reduce the body's carb stores. Since carbs are normally stored together with water in your cells, lowering your body's carb stores inevitably leads to water weight loss (39).

This may make it appear as though low-carb diets help participants lose fat more quickly than they do.

Studies Controlling for These Three Factors Put the Myth to Rest

To truly settle the debate on whether calories matter for weight loss, look at evidence solely from studies that control for the above three factors.

Such studies consistently show that weight loss always results from people eating fewer calories than they expend. Whether this deficit comes from eating fewer carbs, protein or fat makes no difference (10, 12, 14, 15, 16, 17, 18).

Bottom Line: Certain factors help explain why calories can seem irrelevant to weight loss. However, studies controlling for these factors consistently show that a calorie deficit is needed.

Why Counting Calories Generally Works

Counting calories is a time-tested way to lose weight.

In fact, many studies show that recording your food intake and physical activity are very effective ways to lose weight (40, 41, 42, 43, 44, 45).

One recent review reports that weight loss programs incorporating calorie counting led participants to lose around 7 pounds (3.3 kg) more than those that didn't. It seems that the more consistently you do the recording, the better (46, 47, 48, 49).

For instance, one study reports that participants who monitored everything they ate for 12 weeks lost twice as much weight as those who monitored less frequently.

In comparison, those who didn't monitor at all actually gained weight (47).

There are three reasons why calorie counting works:

1. Tracking your calories can help you identify which eating patterns you need to modify to successfully lose weight (50).

2. Despite its lack of precision, tracking what you eat can give you an approximate baseline to work from and compare to when you're trying to reduce the total number of calories you eat per day.

3. Finally, keeping track of what you eat can help you monitor your behavior. This may help keep you accountable for the daily choices you make and motivate you to continue progressing towards your goals.

That said, it's important to note that calorie counting is not a requirement for weight loss (51, 52, 53).

What really matters is your ability to create and sustain the energy deficit needed to lose weight, even if you are not actively aware of how the deficit is achieved.

Calorie counting is simply a tool that some may find useful.

Bottom Line: Counting calories can help you lose weight by giving you an overview of what you eat each day. This can help you identify eating patterns to modify, keeping you on track to reach your goals.

The Best Ways to Keep Track of What You Eat

If you're interested in counting calories, there are several ways to go about it.

All involve recording what you eat, whether on paper, online or in a mobile app.

According to studies, the method you pick doesn't really matter, so it's most effective to pick the one you personally prefer (54, 55).

Here are five of the best online calorie-counting websites and apps.

You can somewhat counteract your natural tendency to inaccurately estimate how many calories you eat by using scales and measuring cups. These can help you measure food portions more accurately.

You might also want to try using the following visual guidelines to estimate your portion sizes. They're less accurate, but useful if you have limited access to a scale or measuring cups:

• 1 cup: A baseball, or your closed fist.

• 4 ounces (120 grams): A checkbook, or the size and thickness of your hand, including the fingers.

• 3 ounces (90 grams): A deck of cards, or the size and thickness of the palm of your hand, minus the fingers.

• 1.5 ounces (45 grams): A lipstick, or the size of your thumb.

• 1 teaspoon (5 ml): Your fingertip.

• 1 tablespoon (15 ml): Three fingertips.

Finally, it's worth mentioning that counting calories only allows you to evaluate your diet from a quantity perspective. It says very little about the quality of what you eat.

When it comes to health, 100 calories from apples will affect your health differently than 100 calories from donuts.

Therefore, avoid picking foods solely based on their calorie content. Instead, make sure you also consider their vitamin and mineral contents. You can do so by favoring whole, minimally processed foods.

Bottom Line: To count your calories most accurately, use a food journal combined with scales or measuring cups.

Take Home Message

The only way to lose weight is to eat fewer calories than you burn.

Some people are able to do this without actually counting calories. Others find that counting calories is an effective way to consciously create and maintain this deficit.

Those interested in giving calorie counting a try should keep in mind that not all calories are the same.

Therefore, make sure to build your menu around minimally processed, nutrient-rich foods and don't base your food choices on calories alone.

Reposted with permission from our media associate Authority Nutrition.