Calorie Counting 101: Does It Aid Weight Loss, How Safe Is It, and Which Way Is Best?

Calories weren’t always about food. The term started out as a measurement of energy in the 1800s, and it was several decades before it was used in conjunction with human nutrition, according to the Journal of Nutrition.

Today, however, most people think of calories as a way to keep track of how much they’re eating in a day, particularly if they’re concerned about weight loss, gain, or maintenance. There are lots of ways to do this, including a wide selection of apps and online tools. Research suggests calorie counting can be effective for weight loss, but there are also some downsides that give experts pause. Here’s what to know.

What Is a Calorie?

A calorie is a unit of energy equal to the amount of heat needed to raise the temperature of 1 gram (g) of water by 1 degree Celsius. One thousand of these units makes up what we know as 1 dietary calorie, which is sometimes denoted with a capital C and sometimes called a kilocalorie or kcal. In the United States, we simply use the term "calorie" without capitalization.

The French physicist Nicolas Clément introduced the concept of calories while giving lectures about heat engines in Paris in 1819. The first use of a kilocalorie or kcal in reference to human energy needs occurred in an 1894 medical physiology text, according to the aforementioned Journal of Nutrition article. Around the same time, the U.S. Department of Agriculture’s Farmers’ Bulletins, which were the earliest food databases, began using the term “calorie.”

By the 20th century, the concept of nutritional calories was well-established in American culture and nutritional policy, and began appearing on food labels in 1973, according to a National Academies publication on the history of nutrition labeling.

Calorie needs vary widely for each person, says Erin Holley, RD, who practices at the Ohio State University Wexner Medical Center. It depends on a variety of factors, including weight, height, age, gender, activity level, muscle mass, and life events (such as pregnancy, menstruation, disease state, and stress). “We can’t simply look at a person and know their calorie needs,” Holley says.

The current U.S. Department of Agriculture (USDA) Dietary Guidelines for Americans offers a range depending on sex, age, and activity level. For instance, moderately active men between ages 18 and 60 would need anywhere from 2,400 to 2,800 calories per day, and moderately active women in that age range would need between 1,800 and 2,000 calories per day. Men usually need more calories than women, and calorie needs decrease with age. The agency recommends using the DRI Calculator for Healthcare Professionals to estimate calorie needs based on age, sex, height, weight, activity level, and pregnancy or lactation status.

Still, even the most accurate calorie calculators won’t always be right, says Lisa Moskovitz, RD, the CEO of NY Nutrition Group. “It's impossible to know every single calorie your body needs every single day because we don't burn the same amount of calories every single day,” she points out. Instead, Moskovitz says, listen to your body to guide you toward when you need to eat (and take in more calories) and when you’re full.

Calorie density, or energy density, refers to the number of calories per weight or volume of food. Compare, for example, 100 g of romaine lettuce, which contains about 17 calories, with the same amount of unsalted butter, which contains 717 calories, according to the U.S. Department of Agriculture (USDA). The lettuce would have low calorie density, while the butter would have high calorie density.

Energy density depends on the macronutrients in a food (fat, with 9 calories per gram, is more dense than protein and carbohydrates, which both have 4 calories per gram) as well as the water content, research shows. As its water content increases, a food’s calorie density decreases.

Being strategic about calorie-dense foods can play a role in weight loss, Holley says. Consuming mostly foods with lower calorie density can lead to fewer calories consumed overall, which can result in weight loss.

It’s a popular school of thought that weight loss is simple math: calories in versus calories out. Indeed, some research does suggest that calorie counting is an effective way to lose weight. After examining a variety of weight loss strategies, researchers concluded that "reducing daily calorie intake is the most important factor for weight loss," in a study published in the Journal of Obesity & Metabolic Syndrome in March 2021.

This finding is consistent with article published in August 2017 in the Journal of Diabetes Research that found that dietary tracking was “an important component of successful weight loss.” Participants who tracked what they ate for at least five days each week lost significantly more weight, and kept it off over time, compared with those who tracked for fewer days or inconsistently. Consistent tracking was associated with an additional seven pounds of weight loss over 12 weeks.

Calorie counting came out favorably even compared with intermittent fasting, a popular weight loss method. After tracking 550 obese, overweight, and normal-weight adults for six months and analyzing the data, researchers concluded that timing of meals appeared not to matter and that “total overall caloric intake is the major driver of weight gain,” according to the study, which was published in January 2023 in the Journal of the American Heart Association.

Volumetrics, a diet based on calorie density, has repeatedly landed in the top 10 best diets in the annual ranking by U.S. News and World Report. Other diets that focus on tracking and cutting calories have been trendy as well, including the CICO diet, which stands for “calories in, calories out,” and the GOLO diet, which emphasizes staying within a certain caloric range.

“Calorie counting can be used as a tool to empower you to take control of your overall health,” says Kim Rose, RDN, CDCES, part of the professional team for the weight loss app Lose It! When done correctly, she says, tracking the calories can help you realize how much you’re consuming and where you could cut back, and encourage more mindful eating.

Research has repeatedly shown that people underestimate how many calories they consume, and that this may be more true for people with obesity. While a study published in March 2022 in the American Journal of Human Biology found no such discrepancy in self-reported caloric intake between obese and nonobese groups, the overall level of inaccuracy in self-reporting, the authors concluded, "raises questions as to the usefulness of written dietary records."

Still, reading labels or using tracking devices that help you understand how many calories you are actually eating will provide a better idea of what healthy portions of foods should actually look like, says Rose. It can also help you determine which foods are the most calorie dense and when you tend to consume them. For example, you might notice a sharp uptick in calories at 8:30 p.m., and realize that’s when you’re lounging on the couch, mindlessly snacking as you watch your favorite TV show. Being aware of those patterns can help you make healthy changes, she says.

Calorie counting can also be useful for people who are trying to gain weight, including athletes. The same study that compared calorie reporting among people with obesity and people of normal weight also identified active people as severe underestimators. “Especially if they’re trying to eat enough, having a general idea can help make sure they’re getting enough fuel for those who are trying to put on muscle,” says Moskovitz.

Apart from weight, counting calories may have other benefits. A lot of preliminary research in animals indicated that animals who consumed moderately fewer calories than they needed had greater longevity, so researchers conducted the first human trial. The results, which were published in February 2022 in the journal Science showed some promise of similar benefits, although further research is needed.

Not every expert agrees that weight loss is a simple math equation, however. In an  article published in Perspectives on Psychological Science, the authors wrote, “In the short term a reduction in energy intake is counteracted by mechanisms that reduce metabolic rate and increase calorie intake, ensuring the regaining of lost weight.” The article goes on to state that hormonal mechanisms that stimulate appetite are raised for even a year after dieting, and that “any successful approach to controlling weight needs to take a wider and longer-term approach than studying the intake of calories.”

Calorie counting was very popular about two decades ago, says Alexandra Sowa, MD, a dual-board-certified doctor of internal and obesity medicine and the founder of SoWell Health, but “it’s not really the healthiest, most sustainable way to lose weight.” Instead of focusing on the number of calories you’re consuming, and following a low-calorie diet, she says it’s more important to make sure you’re getting the right macronutrients. “If you consume a low-calorie diet without the right macronutrients — without enough protein, without enough fat to keep you full, and without enough carbohydrates – you’ll be ravenously hungry, and you’ll only be able to sustain a very low-calorie diet for a few days at a time,” she says.

Counting calories may also increase the risk of disordered eating. “For some individuals, calorie counting can become an addictive and dangerous activity, where they really don't allow themselves to eat, even if they're hungry,” Holley says. “They will not go above a certain number.” In one past study of 105 people diagnosed with an eating disorder, three quarters used an online tool to count calories, and 73 percent felt that doing so had contributed to their eating disorder. Counting calories was also linked to increased eating-disorder severity among college students, according to a study published in Eating and Weight Disorders in August 2018.

Even if you don’t develop an eating disorder, Holley notes that calorie counting puts “unnecessary focus on numbers instead of nutrients, taste, satisfaction,” and everything else that contributes to the eating experience. “I think it sucks the joy from eating,” she says. “I would prefer people follow intuitive eating signals, eating when they’re physically hungry and stopping when they feel full and satisfied.”

If you do decide to count calories for any reason, there are a number of options, and which you choose comes down to personal preference.

• Apps Smartphone apps are a great way to “get real-time feedback and accountability,” says Moskovitz. There are lots of options, such as MyFitnessPal, Lose It!, and FatSecret. Many are free. And a study that compared data from seven smartphone diet-tracking apps found only a 1.4 percent calorie discrepancy with the information supplied by the USDA, meaning that apps are fairly accurate at tracking calories, according to research published in JMIR Mhealth Uhealth in May 2019.
• Websites If you prefer not to download an app, you can visit websites like MyNetDiary to log your daily calories online.
• Pen and paper Buy a notebook that’s branded as a calorie counting journal, or use any old piece of paper. You’ll log every single thing you consume per day, checking its nutrition information in a book or online.
• Fitness trackers These devices are most helpful to monitor the number of calories you burn throughout the day. Options include the Apple Watch and Fitbit. These devices are not always accurate, however, and can be off by as much as 10 percent, according to one study published in the International Journal of Environmental Research and Public Health in August 2019.

Regardless of which option you choose for tracking your calories, there are some common obstacles. Sowa notes that it can be difficult to find the exact item you ate in some apps, and even if you do, it’s hard to know exactly how much you consumed. “People will get very quickly overwhelmed and disillusioned with tracking their calories because they’ll be like, ‘Well I don't know how many ounces this was, I don’t have a food scale here, I’ll just estimate,’” she says. That can lead to lots of inaccuracies with calorie counting.

The same can be true of other methods when it comes to whole foods or those where calorie counts or portion sizes may not be completely clear. “There’s always a small margin of error because sizes of food, especially fresh foods, vary,” says Holley.

Additionally, it can be tough to remember everything you ate, and awkward to pause before every meal, drink, and snack, especially when dining with others, to record calories.

To get started counting calories, first, decide what method you want to use. If you prefer to write down your calories, buy a notebook or journal and decide which reference website or book you’ll use to find out the nutrition content for what you’re eating. Then, meticulously record every single thing you eat and drink in a day, including your portion size and the amount of calories.

If you’d prefer to use your phone or tablet, try out a few apps before you decide which you like best. Signing up for one usually involves creating an account and inputting some personal descriptors, such as your weight and height, and you’ll be ready to go. “But remember that in order to get an accurate count, you really do need to log everything,” Sowa

Once you see how many calories you are taking in each day, you can adjust that amount according to your goals. If you find yourself obsessing, worrying, or constantly talking about calories, however, contact a registered dietitian who can you help you develop a healthy eating plan that doesn’t include counting calories, suggests Holley.