It’s early in the morning, and Lulu Hunt Peters, MD, sits at her desk, puzzling over the manuscript she’s writing about a miraculous weight-loss method she learned about back in her medical school days at the University of California. She spends hours thinking about the best, most entertaining way to explain the basics of a major nutritional discovery—the application of the concept of calories, a unit of energy, to food—made by a scientist named Wilbur Atwater, as well as her own research and the use of this new science in her life.
She knows it could help so many women like herself who struggle to lose weight and keep it off. The world has never seen anything like this before, she thinks.
Dr. Peters was always conscious, and self-conscious, of her weight, even as a child. But now, for the first time, she found something that seems to work—really work, to the tune of 70 pounds off the number on the scale. And she suspects there’s an eager population of women out there who will want her recipe for weight-loss success.
Flash forward a few months, and her book has sold 2 million copies. When Dr. Peters arrives home to Los Angeles from a trip overseas, she is informed that her book is now a national best seller. This is only the beginning. What Dr. Peters doesn’t know yet is that her book and new theory will change the very concept of food and diet in America.
This story sounds as if it could have taken place at any time over the past three decades. Except the year was not 2025 or 2008 or 1996. It was 1918. And Dr. Peters had simply discovered that by tracking what she ate and consuming only 1,200 calories per day, she could lose a significant amount of weight—a diet “method” we call “calorie counting,” which is so ubiquitous that restaurant-chain meals, and virtually every packaged grocery store product, now include calorie counts.
“Hereafter you are going to eat calories of food. Instead of saying one slice of bread, or a piece of pie, you will say 100 calories of bread, 350 calories of pie,” Dr. Peters presciently tells her readers. That, as we all know now, is exactly what happened.
Apps that track caloric intake have, collectively, hundreds of millions of users. And generations of women have spent decades of their lives twisting and contorting their eating habits to fit within the rigid guardrails of this scientific concept to achieve their health goals.
For over a century now, calorie counting’s popularity has ebbed and flowed, but the idea that it is the best and most effective way to lose weight seems to stand. After Dr. Peters published her book, girls as young as 11 and 14 wrote to her for calorie advice, cookbooks began to include calorie counts, and the trend firmly took hold at women’s colleges like Bryn Mawr. Notably, this was not related to weight loss but, rather, energy gain: It was an attempt to debunk the idea that educating women was “bad” because it resulted in “energy loss” that should otherwise be directed toward homemaking and children. Making sure a woman got enough calories to replenish her supposed mental energy expenditure was en vogue, says Nick Cullather, PhD, a historian and history professor at Indiana University.
Jump ahead a handful of decades to the ’70s and ’80s, when the Scarsdale, Atkins, and F-Plan diets—all of which were calorie-centric—started booming with the masses. In the ’90s, everything low-fat was the trend du moment, eclipsing other diet methods. “Heroin chic” became an actual term used to describe a popular model body type, suggesting that the low food drive experienced by people using heroin, and the resulting emaciated look, was somehow desirable.
In 2008, The New York Times ran the headline “Counting Calories Makes a Comeback” (not that it ever really went away!) as New York City enacted the first U.S. law requiring calorie labels on chain-restaurant menus, in an attempt to help consumers make more informed choices about their food—slapping noncomplying restaurants with up to $2,000 in fines. A year later, California became the first state to pass a calorie-count law. You also probably remember the 100-calorie snack packs of the early 2000s—eerily reminiscent of Dr. Peters’s own stern admonition to eat in 100-calorie increments—stashed in a kitchen cupboard to provide easy access for hungry moms. (There’s a reason Gen Z and young millennials coined the term “almond mom” in the 2020s on social media to describe the eating habits of their mothers—women who came of age during the low-cal, low-fat, low-sugar heyday.)
It’s easy to look back now and see the potential problems with this craze, and to understand how it turned into funny memes, but some experts don’t find it very entertaining: “I’ve been against it my entire career, and I’m not an extreme kind of person that takes strong stances. I’ve always known that calories are deeply misleading,” says David Wiss, PhD, RDN, founder of Nutrition in Recovery and the Wise Mind Nutrition app, who specializes in nutrition for addiction recovery and disordered eating. “It forces people to see a single data point at the expense of other critical data.” Wiss has never prescribed a calorie count to his clients.
Still, calories and calorie counting have irrevocably changed the way we think about food; no matter how hard we try, we just can’t seem to unsee the numbers attached to each banana or cookie or glass of wine. Yet our basic understanding of the calorie’s role in health and nutrition doesn’t paint a full picture; it should be only one piece of the proverbial pie, experts say.
Of course, Atwater’s and Dr. Peters’s original calorie teachings still hold some value. “Calorie counting creates awareness about portion sizes and food intake,” says Samantha Nazareth, MD, an NYC-based gastroenterologist and Women’s Health advisor. But, she says, “I see it as a positive, if it’s a first step to something [else].”
Welcome To Calorie Class
Think of a calorie, at its most basic, as a measure of energy in food. More technically, it’s the “amount of heat necessary to raise one pound of water 4 degrees Fahrenheit,” Dr. Peters explains in her book, Diet and Health with Key to the Calories. (The book’s title is a tongue-in-cheek allusion to another trendy-at-the-time book, Science and Health with Key to the Scriptures, a Christian Science manual by Mary Baker Eddy, published in 1875.)
Nowadays, when we hear the word calorie, our mind jumps to diets, Lean Cuisines, and food-tracking apps. But, notably, scientist Wilbur Atwater wasn’t interested in weight loss when he began his experiments to discover the calorie. He wanted to solve some key scientific and nutritional conundrums of his day—including just how much food a person needed to be a good worker, says Cullather.
Using a bomb calorimeter, Atwater was able to calculate each food item’s “calorie” or “energy” by burning the food and measuring the amount of heat generated, which he then equated to the amount of energy contained in that food item. But he didn’t stop at hypotheticals. Atwater took his research a step further, conducting experiments on volunteers from Wesleyan University’s student body—monitoring them as they ate and exercised in a sealed chamber—to determine how many calories humans burned each day and how many they needed to replenish that loss.
The experiments’ data could potentially help estimate calorie counts for large aggregates of people: How many calories of food did you need to feed a big factory full of people? Or a boat filled with soldiers? Keep in mind, the U.S. would soon be involved in the Spanish-American War, in 1898, and army nutrition was top of mind, per Cullather. Providing soldiers with safe, hearty meals was of utmost importance, especially following an embalmed-beef scandal (yes, you read that right) in which spoiled, toxic meat made soldiers sick and even proved fatal to some, due to dysentery and food poisoning.
Atwater’s findings seemed to provide an easy answer to some of these pressing national nutrition concerns. And they also suggested that humans put out the same amount of energy they take in, which, Cullather says, was “revolutionary” at the time.
Thanks to wide media attention on his student experiments, Atwater became an overnight celebrity scientist, says Cullather. And his caloric tables, or Atwater tables, became the accepted measure of calorie content in food. They are still used to this day; look on the side of any cereal box and you’ll see an Atwater calculation.
As these tables grew in popularity, people adopted them and applied them on an individual level, for their own caloric needs. And that’s where the problems start.
Atwater never intended his calculations to be used in this way—and physicians even warned against it, Cullather says. For one, the numbers were meant to be estimates for large populations of people, not individuals. For another, they were supposed to be used to fight hunger and malnutrition, not to help people drop pounds. Even Dr. Peters warned that calorie counts were variable, “depend[ing] upon age, weight, and physical activities.” But Americans were already hooked.
Power In Numbers
Personal daily calorie counts can (and should) vary significantly from person to person, as Dr. Peters originally tried to tell us, depending on sex, general body size, genetics, activity level, and age. For example, a 6′4″, 24-year-old construction worker is going to have very different caloric needs from a 5′1″, 65-year-old saleswoman. Yet the FDA still recommends people consume 2,000 calories per day, noting that this may vary based on sex, height, weight, and overall health. (The FDA number is what’s referenced on food packages.) Other guidelines, like those from Dietary Guidelines for Americans, recommend 1,600 to 2,400 calories per day for adult women and 2,200 to 3,000 for adult men.
If you’ve ever stumbled across a diet that tells you to target a meager 1,200 calories per day for weight loss? You can thank Dr. Peters for that one.
Calories are now so tied to the food we eat that, for some, it becomes an automatic mental association or calculation. Cupcake at a work event? Probably around 400 calories. Protein bar? 220 calories. Glass of red wine? 120 calories.
Experts agree that the calorie’s cultural power and resilience lie in its quantifiable status. “That’s the most important aspect of it…that it is a single number,” says Cullather.
Numbers mean data, and data can be observed, manipulated, and studied. “There’s no subjectivity, there’s no opinion, there’s no preference. It is a hard number,” says Karin Evans, PhD, RD, who specializes in eating disorders and women’s health. But the effect these numbers have on our brains is not so black-and-white.
Following cold, hard digits can help some people distract themselves from food anxiety and make them feel good about themselves, while also decreasing what Evans calls their “cognitive load.” If you’re a busy woman working a full-time job and juggling two kids and a partner, not having to think too hard about what you’re consuming—how much or how little—and instead just hitting a number can ease the mental burden and anxiety around mealtimes. It can even give you a little accomplishment boost because you “succeeded” by hitting an arbitrary “goal.”
But playing this numbers game comes with significant downsides, especially if it results in fighting against what your body needs, says sports dietetics specialist Kelly Jones, RD, owner of Kelly Jones Nutrition.
This entrenched morality tie-in is one that experts refer to over and over again. Losing weight or looking “lean” has taken on its own social status, especially in the age of Ozempic. We’ve co-opted this caloric-number system created to help ensure the masses got enough nutrients and turned it into both a punishment and a reward. If you manipulate your input, you’ll get a response from your body: “positive” physical change.
We see this in ads, on our apps (which “congratulate” us on hitting a goal or give us “points” based on the food we eat), and on TV. “The Biggest Loser [reality show] era set us up for this idea that it’s the person’s fault. [It shows people] ‘Look, I can fix it. All I have to do is make you eat 500 to 600 calories a day, and if you work out for 8 to 10 hours a day, you can be lean, too,’ ” says Fatima Cody Stanford, MD, MPH, an obesity medicine physician-scientist at Massachusetts General Hospital and Harvard Medical School. “It’s reinforcing this narrative that it’s up to the individual.”
There’s also concern from experts that calorie counting can quickly become psychologically problematic—especially for people who are prone to eating disorders, who have disordered eating habits, or who are struggling to lose weight. “It’s easy for it to become a little bit too obsessive and stressful, or it can end up turning into an all-or-nothing, where I’m going to calorie-count and log everything into an app a few days a week, and then other days I’m just not going to log anything at all, and I’m going to kind of go off the deep end,” says Jones.
Some of Jones’s clients come to her wanting a specific formula for reaching their health and fitness goals. And while calorie counting can fit the bill, it doesn’t always deliver.
Mythical Powers, Realistic Results
If Americans have lost the plot when it comes to calories’ general purpose (i.e., a way to measure the energy in our food supply and prevent widespread malnutrition/famine) and instead imbued them with mythical powers, we also seem to have forgotten why we are putting this food into our bodies in the first place.
You’ve probably heard this favorite phrase of dietitians and nutritionists: All calories are not created equal. While the “calories in, calories out” mantra encapsulates how many Americans think about their diet, Dr. Stanford says it’s “really not that simple.”
Two hundred calories from a vegetable will make your body—gut, hormones, metabolism, and energy levels—behave very differently than 200 calories from candy would, says Dr. Nazareth. That number offers only a small slice of the full nutritional picture. To her credit, Dr. Peters addresses this in her book, which is filled with breakdowns of what protein, carbs, fats, and “vitamines” are, how much you should be consuming, and examples of each. She did, in fact, want to make sure her readers were satisfied and nourished, even reminding them that “hunger, like cold feet, is hard to go to sleep on.”
As avant-garde as Dr. Peters’s complex nutritional formulas were for the time, her teachings seem to have gotten lost along the way. Instead, we got stuck with the plain old calorie. But it’s time for people to think about food as more than just calories and recognize the “actual profound signaling information” it holds for our bodies, says Wiss.
The recent wave of GLP-1 weight-loss drugs has put renewed attention on the importance of nutrient-dense foods and “good calories,” since the drugs slow gastric emptying and boost satiety, curbing people’s hunger and making them eat less. But doctors have warned of the dangers of not adjusting dietary habits while taking the drugs. A quick Google search will reveal a swath of surprising GLP-1 side effects related to poor nutrition: “Ozempic skin,” “Ozempic hair loss,” “Ozempic bone loss.”
Indeed, for people with a poor diet, whether they’re on a GLP-1 or not, eating less and not replenishing with nutrient- and protein-rich meals is a quick way to lose muscle, decrease bone density, and become malnourished. Even if you are getting enough calories, they have to be the right kind.
In other words, you should be focused more on the quality of food and variety of nutrients you’re eating, not just the quantity of calories. “If you’re not getting enough calories, you will lose weight faster, but you’ll also see your hair fall out, or your skin is gray and doesn’t look healthy. You can actually see it,” says Grace A. Derocha, RD, a spokesperson for the Academy of Nutrition and Dietetics. A nutrient-rich diet can help prevent all these things, including muscle loss, she adds.
Jones’s two biggies to focus on for weight loss (especially for those on a GLP-1): more lean protein and whole plant foods. “What you get there is a lot more satiety and a lot more high-quality nutrition,” she says.
Weight Loss, Unlocked
We now know that sustained weight loss and the mechanisms for weight loss in general are far more complex than Dr. Peters realized. For starters, while it’s true that extreme caloric-deficit diets (which Dr. Stanford calls “torture”) like the ones on The Biggest Loser can result in weight loss, it’s not sustainable, and your weight and eating habits swing back in the other direction once you stop painstakingly counting and restricting calories. “Lean does not equal healthy,” Dr. Stanford says. And counting calories does not always mean you’re making healthy, sustainable decisions, or nourishing your body properly.
“Why was there never a Biggest Loser reunion show?” Dr. Stanford asks. The answer? A National Institutes of Health study looking at 14 contestants six years after the show aired found that most had gained weight back, and in some cases weighed more than before. “Your brain is going to win every time,” she says. “It’s going to bring you back to that biological set point. It’s going to compensate.”
Another essential element in weight loss is the understanding that not everyone magically loses weight solely by working out more and eating fewer calories.
“If it was this simple, I wouldn’t have this job. I wouldn’t be talking to you right now,” Dr. Stanford often tells her frustrated patients.
Instead, what she tries to get them—and everyone else—to understand is that there are actually around 66 different biological, psychological, social, economic, maternal/developmental, and environmental factors that go into a person’s weight. Calorie input is just one small part of that puzzle. “Your genetics, your environment, your development, your behavior, all of these are intertwined to make us look a certain way,” she says.
This fact is emphasized by more recent findings from the National Academies of Sciences, Engineering, and Medicine: A 2023 study introduces a 5′4″, 139-pound, 22-year-old woman who doesn’t exercise much and has an estimated ideal caloric intake of 2,275 calories per day for weight maintenance (notably, not the FDA’s suggested 2,000). Yet even when the woman recorded eating an average of only 1,820 calories per day over two years, she still hadn’t lost any weight. If we’re going by the “calories in, calories out” rule, this deficit should result in weight loss. But it didn’t.
The study suggests that “a large number of factors” could be at play, keeping her weight steady. Of course, this is one person (and studies like this that rely on self-reporting can be flawed). There are many more examples in which calorie counting does result in weight loss. But the bigger takeaway is that weight loss is incredibly individual and requires a holistic, personalized approach.
Yet we still grab the 100-calorie low-fat cookie packs, the zero-calorie Diet Coke, and the Splenda packets without thinking about the chemicals that make them sugar-free. (While these sweeteners don’t cause cancer as previously thought, there is research linking long-term or daily use to higher risk of stroke, heart disease, and death, per the Mayo Clinic. The clinic also recommends consuming artificial sweeteners only “once in a while.”)
“It often feels like the goal of the calories is to eat less of them, right?” says Wiss. “So it kind of hinges on this assumption that a diet version [of a food or beverage] is better than the regular version, because it’s reduced calories. And I think that has been misleading for some people.”
Case in point: When Dr. Stanford shows her patients side-by-side photos of a 350-calorie slice of pepperoni pizza and a 700-calorie grain bowl, asking which one they’d choose, she gets a fascinating response: They hesitate. While they know a grain bowl is “healthier,” they’re stumped because they think they should be choosing the “lower-cal” pizza option. And this hesitation (between greasy pizza and a healthy grain bowl) is all the evidence you need to understand how strong a choke hold calorie counts have on us, and to see how we’ve let a single nutritional element become a god.
A Full-Scale Calorie Rebrand
We don’t necessarily need to do away with calorie counting altogether, but we do need to significantly reframe it so that you will think twice before reaching for your calorie-counting app to log the three and a half slices of apple you ate at 2 p.m.
Instead of obsessing over the numbers, focus on the basics: portion size; more vegetables, fruits, and whole grains; and an understanding of fats—read up on what foods have the “good” kind (i.e., unsaturated fats found in things like avocados and nuts) and the “bad” kind (i.e., saturated and trans fats found in things like fatty meat cuts and fried foods). “If we do take it back to those basics, that alone can help a lot of people,” says Jones.
With clients, she finds success in melding nutrition science (calories, macronutrients, vitamins) with intuition (Am I hungry? Am I full? Am I craving more protein?) and practicality (What does my day look like? What activities am I doing?). Once her clients learn more about macronutrients, they tend to have a better sense of the nutritional value of their food, beyond just calories.
Evans also emphasizes that it’s important to make sure you’re eating in a way that is enjoyable. (Spoiler: Scarfing down low-calorie branded foods while also monitoring everything you put into your mouth is not, shall we say, all that fun.) “As a culture, we look at food as inherently bad—that good food is bad for us,” she says. “We’ve somehow learned that in order to be healthy, we need to eat food that doesn’t taste good. And so I always tell people, if you’re eating something and it doesn’t taste good, then stop eating it.”
And if we’re truly trying to get back to the main message in Dr. Peters’s writings, we should spend a little less time obsessing over calories and a little more time genuinely learning about our food—what’s in it, the nutrients it carries, and how it makes us feel. At the end of the day, she was trying to democratize nutritional science, giving people the tools they needed to take control of their bodies and diets, or, as she wrote, “some lessons on foods and their values.” She’d likely remind us not to lose sight of her original teachings—and to stick to the science.
Recalibrating The Mindset
We can’t talk about weight management and calories without acknowledging the gravely serious health epidemic in America right now: New data suggests three in four adults are overweight or obese (or at least were overweight or obese in 2021, when the most recent results were reported). There are some positives that come from the calorie-counting process in this context, especially considering the substantial gaps in most Americans’ nutritional knowledge, experts say. Plus, only about one in two Americans (57 percent) spends time preparing beverages or cooking each day, per a U.S. Bureau of Labor Statistics 2022 report.
The less free time you have in your day, the less time you have to think about, much less cook, healthy meals. But humans need to eat—which means food “has to be fast and available,” says Dr. Nazareth. For those not prone to disordered eating, calorie counting can provide an approachable, easy way to take stock of what you’re putting into your body each day. It can also help you recognize eating patterns, says Dr. Nazareth. But calorie counting should still be a starting point, not the totality of someone’s dietary focus.
Currie Engel is the news & features editor at Women’s Health, where she works on zeitgeisty digital and print features for the magazine. She previously worked as as an award-winning local reporter specializing in health investigations and features, and as a freelance researcher at Time magazine. Currie was a spin instructor in college, but these days, with two marathons under her belt (New York and Paris), a sunny Saturday usually finds her running around the city. And a quick post-run stop for pastries at her favorite local bakery is a must!
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