The Calorie Fallacy: Why Counting Calories Isn’t an Effective Weight-Loss Strategy

You can say one thing for Professor Mark Haub: He knows how to make a lesson stick.

Haub, who teaches nutrition at Kansas State University, wanted to prove to his students that weight loss is simply about calories. So, for 10 weeks, the professor proceeded to eat an 1,800-calorie diet consisting of a Twinkie every three hours. He also dined on Doritos, Little Debbies, sugary cereal and other junk food.

When he started, Haub tipped the scales at 201 pounds, which for his height was considered overweight. By the end of his snack-food spree, he had lost 27 pounds, putting him at a svelte 174. The story went viral, with the media dubbing Haub’s eating plan the Twinkie Diet.

Undoubtedly some who heard the news eagerly stocked up on the spongy yellow snacks. But Haub’s intention wasn’t to urge people to eat more Twinkies. The point, he said, was that he had consumed 800 fewer calories daily than the number needed to maintain his weight. In other words, the key to weight control is counting calories: If you take in fewer than you burn, you lose weight. It’s that simple.

Haub’s message has been standard advice for more than a century. According to many experts, it all boils down to straightforward math: Calories in minus calories out. Countless millions who struggle with their weight heed this message, dutifully tracking their calorie intake. But eventually many discover that all the counting is in vain.

One reason is that calorie counts aren’t always accurate.

In fact, the Food and Drug Administration (FDA) allows numbers on nutrition labels to be off by as much as 20 percent, and usually the error is an undercount. That means, for example, that ice cream claiming to have 180 calories per serving may actually have 215. Making matters worse is the widespread problem of unrealistic serving sizes. With ice cream, if you eat a cup (a normal amount) rather than 2/3 cup (the usual serving size), you could be getting as many as 325 calories instead of the 180 listed on the label.

Listed calories may also be wrong because of the way our bodies digest certain foods. Take almonds, for instance. Nutrition labels show them to have up to 170 calories per ounce. But this number doesn’t take into account the fact that almonds pass through the intestines partly undigested. As a result, the body doesn’t absorb all 170 calories. The actual count, according to research, is 129—a sizable difference.

Accurate or not, calorie counts aren’t available for everything we eat, so we sometimes have to rely on our own estimates. And according to research, these numbers are notoriously unreliable. For example, in a survey of 2,200 adults, consumers’ guesses about calories in popular restaurant foods ranging from pancakes to onion rings undershot the reality by an average of 165 calories.

Unconscious biases can further skew our calorie estimates. For instance, there’s the “health halo” bias, which makes us more likely to underestimate calories in foods that are marketed as healthful.

Online calculators, meanwhile, can tell you how many calories you expend each day, but it’s at best an approximation. Wearable devices are also an option, but research shows that their results are unreliable. Arriving at an accurate number is difficult because the calculation is complex, involving how much energy we need for basic functions like breathing and circulation at rest (known as basal metabolic rate, or BMR); how much we burn during everyday activities and exercise; and how much through digesting food (the thermic effect of food). A host of other factors, including age, gender, weight and body fat, play a role.

Given all the challenges of accurately calculating how many calories we need and how many we consume, it’s unreasonable to expect counting calories to be effective as a weight-loss strategy.

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The difficulty is reason enough to shun calorie counting. But there’s also an even bigger problem: Tallying calories fails to take into account other variables that can affect how much we weigh.

As we reduce calories and lose weight, biological changes kick in to preserve body fat and protect us from starvation. One such adaptation is a change in metabolism. The body of a lighter person has a lower BMR than that of a heavier person. As we shed pounds, we burn even fewer calories than expected for a person of our reduced size—a phenomenon that scientists call adaptive thermogenesis. In essence, our bodies become more fuel efficient, making it increasingly difficult to shed more pounds and to maintain weight loss with the same number of calories. Unfortunately, this evolutionary gift, designed to keep us alive in times of scarcity, isn’t something we can switch off or send back when we don’t need it.

Our genetic makeup also affects weight regulation. As evidence, look no further than those maddening people who seemingly can eat whatever they want and never gain an ounce. Conventional wisdom has it that such individuals are blessed with “good genes,” and research involving twins shows genes do affect how our bodies respond to calories.

In one study, for example, researchers observed 12 pairs of male identical twins for four months, supervising their every move. (Yes, the twins agreed to this!) The subjects were fed 1,000 calories a day more than their normal intake, and physical activity was limited. As you would expect, they gained weight. But the amount varied, ranging from about 10 to 30 pounds. What’s more, the difference in the amount of weight gained was much smaller between twins in a pair than among different twin pairs. In other words, twins in each pair experienced relatively similar increases in weight, suggesting that genetic factors influence how easily we put on pounds. Similar research suggests genetics affects how easily we lose weight as well.

Yet another possible contributor to weight is the mix of microbes in our gut. This community of bacteria, viruses and other microorganisms, known as the microbiota, helps break down food and extract energy from it. Studies show that the microbiota of obese people differs from that of lean individuals.

Though this research is still in its infancy, it suggests that two people can eat the same amount of the same food and experience different effects on their weight depending on the makeup of their microbiota. Those whose gut microbes harvest more energy from food may be more likely to pack on pounds because it’s the calories we absorb—as opposed to the ones we ingest—that matter when it comes to our weight.

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Counting calories can be effective for weight loss in the short term, and it may work long term for some. But for the vast majority of people, it eventually not only fails but also can do harm. For starters, it can detract from the pleasure of eating, turning meals into a tedious exercise of tallying and food weighing. This routine can be stressful and may contribute to an unhealthy relationship with food that makes it even harder to achieve and maintain a healthy weight.

What’s more, calorie obsession can lead to food choices and eating habits that undermine your health. Not all calories are the same—50 calories of broccoli doesn’t equal 50 calories of jelly beans—and a low-calorie diet is not necessarily a healthy one. Focusing only on calories can result in too little of things your body needs and too much of things it doesn’t need.

So what’s the alternative? While it’s good to keep a general eye on calories, don’t fixate on them. Instead, pay attention to the overall quality of your diet, emphasizing vegetables, fruits, whole grains, beans, nuts, seafood and lean meats, while minimizing highly processed foods such as chips, cookies, fried foods and sugary beverages.

To say our bodies’ weight-regulation mechanisms are complex is an understatement. After many decades of research, there’s still much that scientists don’t understand. So it defies logic that a simple food-scoring system conceived in the 19th century should be adequate for capturing this complexity. Yet calorie counting and calorie math continue to be mainstays of weight-loss efforts.

It is not surprising that our society’s preoccupation with this inadequate and error-prone metric has yielded such poor results. What is surprising is that we nevertheless continue to give it so much weight.

Adapted from Supersized Lies: How Myths About Weight Loss Are Keeping Us Fat – and the Truth About What Really Works by Robert J. Davis. Copyright © 2021 by Robert J. Davis. Reprinted by permission of Everwell Books.