Updated 23rd February 2023

Calorie counting and low-calorie diets for weight loss: An update

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Losing weight is tough. And keeping it off in the long run is even tougher. 

Millions of people try some kind of weight loss program every year. But most who are successful will regain the weight over the following years. 

In fact, people who go through cycles of weight loss and regain, a process sometimes called yo-yo dieting, are likely to weigh more than people who don’t have restrictive eating patterns. This is especially true for women.

In this article, we’ll focus on calorie counting.

Although it's one of the best-known approaches to weight loss, studies have shown that it’s an ineffective way to achieve and maintain a healthy weight in the long run.

A review and meta-analysis examining 80 weight loss clinical trials provides some evidence. The authors compared different methods of dieting, including low-calorie diets.

They found that a diet focused on drastically reducing caloric intake initially produces dramatic weight loss. But people's weight steadily rises back.

And at the 3-year mark, most people — around 80% — are rapidly approaching their starting weight. 

Prof. Tim Spector told us that “In real life, these figures are likely to be much worse without the backup of all the resources and psychological support of a clinical trial.”

Interestingly, the scientists also found that people who tried to lose weight using only exercise lost the least from any group. They also put the weight back on the quickest.

But today, we’re focusing on calorie counting and why it doesn’t work.

Calorie counting: The basics

On paper, calorie counting makes sense — if you take in fewer calories than you use up, you’ll lose weight. It’s a simple and alluring equation: Eat less, move more. Easy.

On the one hand, this arithmetic is right. If you can continuously take in fewer calories than you’re burning, it will work.

Over months and years, though, this plan falls apart because we are not simple machines.

Most people who try calorie counting and manage to reduce their calorie intakes will regain any weight they lost over the following years.

Here, we’ll explain the many flaws in counting calories, why it’s so difficult, and why it doesn’t work in the long run. 

We’ll also tell you what does work. And you’ll be delighted to learn that it doesn’t require a calculator. Spoiler alert: Food quality is key.

Part 1: Why calorie counting is impossible

This article has two main parts. In the first, we explain why accurately counting calories is impossible. In the second, we outline why calorie counting won't help you manage your weight.

What is a calorie?

One calorie is the amount of energy it takes to warm up 1 kilogram of water from 0°C to 1°C.

And different macronutrients have varying amounts of energy. Roughly speaking, it goes like this:

  • 1 gram of carbohydrate provides 4 calories

  • 1 g of protein provides 4 calories

  • 1 g of fat provides 9 calories

However, these are averages, and the real world is rarely average. So, when you see the calories listed on a food label, that’s really only an estimate — amounts can vary. 

Legally speaking, food manufacturers can be up to 20% out in their estimates, which could be significant. A "100-calorie" snack, for instance, might contain anything from 80–120 calories.

Plus, portion sizes are impossible to control accurately, and restaurant estimates of calories can vary by more than 50%.

Even professional dietitians struggle to measure their intakes with precision.

Then there’s the impact of cooking, and labels don't take this into account.

A raw stick of celery has 6 calories, but it has six times that (36 calories) when it's cooked. Across the board, the caloric content of food can be hugely affected by cooking.

So, that’s the first fly in the calorie counting ointment. 

An absorbing fact

As we’ve seen, you can never be 100% sure how many calories you’ve eaten.

But the issues don’t stop there. Even if you knew exactly how many calories were in your meal, you wouldn't know how many you’ve actually absorbed.

For instance, in one study, scientists determined how many calories participants had absorbed from almonds and compared these results to the standard method of calculating calories in food.

This method — called the Atwater general factor system — works out the calorie contents of foods by measuring their carbohydrate, fat, protein, and fiber contents.  

The researchers found that, on average, participants absorbed 32% less energy than the calories estimated by the Atwater method. 

And participants’ responses varied significantly: They absorbed between 56 and 168 calories from 1 ounce of almonds. 

So, given the same number of almonds, some people will absorb almost three times as much energy.

Structure matters 

Meanwhile, the structure of food affects how many calories you get from it.

Here’s an extreme example: Imagine you swallowed a metal ball filled with 500 calories of chocolate. 

The little ball won’t get broken down in your gut, so the chocolate inside won’t be broken down and digested. Both will exit in your poop, providing you with 0 calories.

In other words, not all the energy in food might be available. And what determines this availability is the food matrix. 

This is why there’s a difference between eating some corn on the cob and tortilla chips, even though they may have the same estimated number of calories.

What’s the food matrix?

The food matrix is the food's structure — how it’s held together — and the compounds it contains.

Thinking about the matrix helps explain why fruit juice is less healthy than whole fruit. When you break down the fruit’s structure, your body can digest it quickly and extract the energy more easily.

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A study from 1980 provides a good example. The researchers gave participants whole peanuts, peanut butter, or peanut oil. 

They found that when people ate whole peanuts, they excreted more fat than the other participants. This means they absorbed less of the fat — and its calories. 

Those who consumed the peanut oil pooped out the least fat, so they absorbed the most calories. 

A study published in 2007 generated similar results: Those who had the peanut oil absorbed more energy.

Why does this happen?

Much of the fat in nuts is trapped within cell walls that neither your gut bugs nor digestive enzymes can break down.

So, as with the chocolate-filled metal ball, if you can’t access the energy, it passes through you.

But if those cell walls are destroyed by processing, that energy becomes available.

The calorie counts for 100 g of whole peanuts and 100 g of pulverized peanuts would be the same on a food label. 

In reality, you would likely absorb much fewer calories from the whole nuts.

Part 2: Why calorie counting doesn't work

So, we've established that counting calories can never be accurate. Now, we'll explain why calorie counting — even if it was possible — wouldn't help you manage your weight.

Macronutrients make a difference

Research has shown that the type of nutrients in food makes a difference when it comes to weight loss.

For instance, a review on the topic explains: “High-protein and/or low-carbohydrate diets do yield greater weight losses after 3–6 months of treatment than do low-fat diets.”

The authors observe that even when people consume roughly the same number of calories, the amount of weight they lose depends on the macronutrient contents of their diets. Calories aren’t king.

High-calorie foods aren’t equal

Nuts, avocados, and olive oil are well-known for being high in calories. An avocado, for instance, has a similar calorie count to a burger.

But it’s not the number of calories that matters. Instead, the quality of the food is most important.

The number of calories in a food doesn’t tell you anything about the other nutrients present, how good it is for your gut microbiome, how quickly it gets absorbed, or how many additives and preservatives it contains. 

Food is so much more than the energy it provides.

It’s clear that 100 calories of avocado and 100 calories of soda don’t have very much in common. 

The soda will provide next to no nutritional benefits. The avocado, on the other hand, contains a range of vitamins and minerals, fiber to fuel your gut microbiome, antioxidants, and more. 

A look at ultra-processed foods

In many Western countries, ultra-processed foods make up a considerable chunk of our diets. In the United States and United Kingdom, they account for more than half of the population’s energy intake, and even more in children.

It’s increasingly clear that ultra-processed foods play an important part in weight gain.

You might have already guessed, but the high calorie contents of these foods aren’t the whole problem. The primary issue is their low quality. 

As in the avocado versus soda example above, when you eat ultra-processed foods, you’re not getting the nutrients your body needs or the fiber that your gut bacteria need to thrive.

Regardless of their calorie contents, these foods are designed to be hyper-palatable. This means you won’t want to stop eating them — they are scientifically designed to be delicious, not nutritious.

Because ultra-processed foods lack fiber and protein, they won’t keep you full for long.

So, you might find yourself hunting for snacks shortly after eating, as these foods often increase your appetite more than equivalent whole foods.

Missing out on nutrients

When counting calories, you tend to fixate on the calorie figures alone. This can mean choosing foods simply because their calorie counts are low. Sometimes, it might mean choosing ultra-processed “diet” snacks.

And because these products are nutrient-light, you may miss out on essential vitamins and minerals.

Similarly, if you’ve consumed a high number of calories early in the day — maybe a slice of cheesecake — you might severely restrict yourself in the afternoon to “catch up.” 

This might mean skipping a meal when you'd typically have vegetables or other nutrient-dense foods.

And as we’ve mentioned, some foods — like avocados and olive oil — are high in calories but also highly nutritious. Cutting out these foods to keep your calorie count in check is counterproductive.

It’s better to add these to your diet rather than skip them because of their calorie contents.

Disordered eating

By now, we’ve established that calorie counting is far from the best way to lose weight. 

There’s also growing evidence that for some people, it may increase the risk of disordered eating.

Disordered eating refers to behaviors that are part of eating disorders. Some examples include compulsive eating, binge eating, and chaotic eating patterns.

For instance, a study from 2017 recruited participants with existing eating disorders.

All the participants already used a particular app that counts calories and other health data. 

Around three-quarters of the participants reported that the calorie counting app contributed to their eating disorder. 

Similarly, another study from the same year identified links between calorie tracking apps and increases in disordered eating.

Although researchers are still investigating this relationship, evidence is mounting that calorie counting apps are bad news, especially for people susceptible to disordered eating. 

So, what should you do?

ZOE runs the largest nutrition study of its kind. We know that everyone is different, and people respond to foods differently. So, there’s no one-size-fits-all approach to weight loss.

The most important thing you can do to help reach your long-term health goals is to focus on food quality and ignore calories.

This means eating a diverse range of plants. Prof. Tim Spector suggests aiming for 30 different plants each week, based on his research. 

Rather than focusing on removing things from your diet, focus on adding vegetables, nuts, seeds, whole grains, legumes, and fermented foods.

But if you fancy a slice of cheesecake every once in a while, go for it. Food should be enjoyed, not counted.

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