What Are Calories and How Many Do You Need?

Calories keep your body fueled and functioning properly, but what exactly is a calorie and how many do you actually need?

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Calories are undeniably mentioned everywhere you turn—from food labels to restaurant menus, recipe blogs, food tracking applications and even news headlines. All the talk about calories may have you wondering why they are so important. Better yet, what exactly are calories, and how do they work? Or maybe you have a general understanding of what a calorie is, but you are unsure of how many you should consume in a single day. Wherever you stand in your knowledge of calories, you'll learn more here. In this article, we break down what defines a calorie, factors to consider when determining your unique caloric intake, the link between calories and body weight, and the basics of calorie counting.

Understanding Calories

Every time you sit down to enjoy a meal, each food item and beverage contains energy locked away in chemical bonds. Once the food or drink is ingested, it is metabolized or broken down by your body to release the stored energy. Your cells then capture and use this unleashed energy to fuel normal bodily functions necessary for survival. To measure the energy extracted and used from food and drinks, we use a unit called a calorie. In other words, a calorie is simply a standard unit for measuring energy.

Here's a little scientific background you may be unaware of. The term "calorie" is technically defined as the amount of energy needed to raise the temperature of 1 gram of water by 1 degree Celsius, per the National Library of Medicine. However, the calories we use when we talk about the amount of energy in what we eat and drink are actually kilogram calories or kilocalories, a unit that equals 1,000 calories. The kcal is the most suitable unit of measurement for food and beverages because there is a large amount of energy stored in their molecules. After all, it is easier to say that one medium banana contains 105 kcal than 105,000 cal. But, in common, nonscientific usage, we use "calories" to mean "kilocalories." So, we say that banana has 105 calories.

Nearly everything we consume has a calorie count, and those calories come from three energy sources—carbohydrates, proteins and fats.

Macronutrient Calories per Gram:

  • Carbohydrates: 4 calories per gram
  • Fats: 9 calories per gram
  • Protein: 4 calories per gram


Of the three macronutrients that provide energy, carbohydrates often get a bad rap. However, when you eat carbohydrates, your digestive tract breaks them down into a sugar called glucose—the primary fuel source for your brain, red blood cells and nervous system. Depending on the number of sugar molecules they contain, carbohydrates can be classified as either simple or complex. Simple carbs found in table sugar and fruit juice can be easily broken down and utilized as energy, but they can also cause a rapid rise in blood sugar. Simple carbs are also present in whole fruits. But because whole fruit is packed with dietary fiber, the sugars are broken down more slowly. Complex carbs found in unrefined whole grains, legumes and vegetables are also broken down more slowly—providing longer-lasting energy. For every gram of carbohydrate consumed, 4 kcal of energy are produced.


Dietary fats play a pivotal role in protecting vital organs, insulating the body, producing hormones, and aiding in absorbing vitamins A, D, E and K, per a 2019 article in Advances in Nutrition. They can also be broken down and used as a source of energy. Although carbohydrates are the body's preferred energy source, fats are more tightly packed and store larger amounts of energy in less space. Therefore, fats are the body's main long-term energy storage molecules. In fact, when excess calories are consumed, they get stored in adipose (fat) tissue. One gram of dietary fat contains 9 kcal of energy—making fat the highest energy-yielding macronutrient. The higher amount of energy in fat comes in handy during prolonged low-to-moderate activities, such as taking a brisk walk or riding a bike. Foods rich in nutritious dietary fat include butter, eggs, fatty fish, avocado, oil, nuts and seeds.


Although energy can be obtained from protein, the body prefers to use this macronutrient to repair tissues, synthesize immune-protective antibodies, create enzymes, produce hormones, balance pH, and transport nutrients in and out of your cells. This means that protein is rarely used as an energy source. In order to reserve protein for its primary functions, carbohydrates and fats are used as fuel first. Therefore, consuming adequate amounts of carbohydrates and fats is crucial to spare protein from being converted into energy, per the UC Davis Library. However, if the body is not receiving a sufficient supply of calories from carbohydrates and fats, protein can be broken down to provide 4 kcal per gram consumed. Protein-rich foods include meat, eggs, dairy, legumes, nuts and seeds.

How Many Calories Do You Need?

According to the 2020-2025 Dietary Guidelines for Americans, the total number of calories an adult aged 19 to 59 requires daily ranges from 1,600 to 3,000 kcal. More specifically, adult females require about 1,600 to 2,400 kcal per day, while adult males need around 2,000 to 3,000 kcal per day. Of the total calories consumed, 45% to 65% should come from carbohydrates, 20% to 35% from fats and 10% to 35% from protein. To determine your individualized caloric needs, it is important to consider the following factors.

Basic Metabolic Functions

Your body requires a minimum number of calories to carry out the essential metabolic functions that sustain life. These basic functions include respiration, circulation, cell production, protein synthesis, nutrient processing and ion transport. The minimum number of calories needed to fuel these activities is referred to as your basal metabolic rate. BMR accounts for 60% to 75% of your body's total energy expenditure, per a 2019 article published in the Encyclopedia of Animal Cognition and Behavior. Multiple factors influence BMR, such as age, height, weight, body size, body composition, body temperature, climate, sex and hormone status. Therefore, caloric needs are unique for every individual.


Another important component of energy expenditure is exercise. Caloric needs vary depending on the type, duration, frequency and intensity of physical activity. For people who make exercise a regular part of their routine, energy requirements must be sufficient to fuel and maintain muscle mass. Individuals with higher amounts of muscle mass tend to burn calories more quickly. On the other hand, those who are physically inactive and have less muscle mass burn calories slower. Therefore, strength training exercises can help to increase the rate at which calories are burned.

Other Factors to Consider

The ever-changing stages of life also influence your caloric needs. During pregnancy, more energy is required to support the growth and development of an unborn baby. According to the American College of Obstetricians and Gynecologists, the second and third trimesters of pregnancy require an extra 340 to 450 daily calories. However, the opposite may be true as we age. During the latter years of life, caloric needs may decrease due to less physical activity and reduced muscle mass. Therefore, maintaining adequate muscle mass is important as you get older. Specific medical conditions can also increase or decrease caloric requirements. Your gut microbiome may also influence the number of calories you extract from food.

Working with your primary health care provider or a registered dietitian is the best way to identify your caloric needs in every life stage.

What Do Calories in Food Mean?

Certain foods may have the same number of calories, but not all sources of calories are created equal. When considering the number of calories in a particular food, it is also important to assess its total nutrient content.

Calorie-Dense vs. Nutrient-Dense

A food or beverage considered calorie-dense contains a high number of calories per serving; some of these foods also have few nutrients. According to the American Heart Association, these foods are often high in saturated fat, added sugars and sodium. Several examples of calorically dense, nutrient-poor foods include pastries, cakes, candy, sugary drinks, fried foods and highly processed meats.

Conversely, nutrient-dense foods contain high levels of nutrients, such as vitamins, minerals, fiber and phytochemicals, and sometimes with fewer calories. Nutrient-rich foods include fruits, vegetables, whole grains, legumes, nuts, seeds, dairy products, fish and unprocessed lean meat. These foods provide essential nutritional components for good health.

The key to creating a well-balanced diet is choosing nutrient-dense foods and limiting calorie-dense foods that are also low in nutrients, within your caloric needs.

What's the Link Between Calories and Body Weight?

Although there are several factors to consider for weight management, caloric intake plays a significant role. To maintain a stable body weight, the amount of calories you take in must be the same as those you expend through basic metabolic functions and exercise. However, if you wish to lose or gain weight, here is what you should keep in mind.

Weight Loss

To support weight loss, consuming fewer calories than you burn—referred to as a calorie deficit—is important. A calorie deficit can be achieved by either reducing your intake of calories or by burning more calories through physical activity—or a combination of the two. By eating fewer calories, your body taps into its fat reserves for energy. As a result, fat is the primary fuel source burned and weight loss occurs. However, losing weight is not always this simple. According to a 2018 article published in Obesity, when calories are restricted too much, your metabolism slows down, and hormones shift to preserve energy and prevent excess weight loss. Therefore, a calorie deficit is only one factor in weight management.

Weight Gain

When your caloric intake is consistently higher than the number of calories you burn, you enter into a calorie surplus and experience weight gain. If gaining weight is your goal, not only is it imperative to consume more calories, but you should also consider weight training to increase your body mass in muscle. To reach your daily caloric target, it may help to consume five to six meals spread out throughout the day. It is also crucial to prioritize high-calorie foods that are also high in nutrients to ensure your weight gain is healthful.

How to Count Calories

Keeping track of the calories you consume can help determine if you are meeting or exceeding your recommended caloric intake. The first step to counting calories is determining how many calories you need daily. You can estimate your caloric needs by using either the DRI calculator or the Mifflin St-Jeor or Harris-Benedict formulas. Once your daily caloric need is calculated, you can begin tracking the caloric content of each meal by taking note of the calories on the Nutrition Facts label or by looking up the calories of a specific food item using the USDA database. While many individuals turn to calorie-tracking apps to keep tabs on their energy intake, counting calories can also be done with a detailed food journal or with the help of a registered dietitian. Although calorie counting can be a useful strategy, it is important to note that it may not be helpful for those who are at risk for or have a history of disordered eating. Therefore, rather than solely focusing on tracking calories, it is more beneficial to focus on food quality and your overall eating pattern.

Frequently Asked Questions

1. What does calorie deficit mean?

A calorie deficit occurs when you consume fewer calories than you burn. It can be achieved by either reducing your intake of calories or by burning more calories through physical activity—or a combination of the two.

2. What does calorie surplus mean?

When your caloric intake is consistently higher than the number of calories you burn, you enter into a calorie surplus and experience weight gain.

3. How many calories should adults eat every day?

The Dietary Guidelines recommend that adults aged 19 to 59 consume 1,600 to 3,000 calories daily. More specifically, adult females require about 1,600 to 2,400 calories per day, while adult males need around 2,000 to 3,000 calories per day.

4. What are empty calories?

According to the AHA, foods containing empty calories have very few nutrients and a high number of calories.

5. How many calories should you eat per day to lose weight?

In order to lose weight, a calorie deficit is required. A general rule of thumb is to reduce your caloric intake by 500 calories daily. However, losing weight is not always this simple. When calories are restricted too much, your metabolism may slow down, as your body preserves energy and prevents excess weight loss. Therefore, a calorie deficit is only one of the things to consider when wanting to lose weight.

The Bottom Line

The energy released from the breakdown of food is measured using a unit commonly called a calorie. Calories play a critical role in fueling the many metabolic reactions in the body that keep you alive. Therefore, meeting daily caloric needs and consuming nutrient-dense foods is essential to ensure your body is fueled and functioning optimally. Your unique caloric needs depend largely on age, weight, body composition, physical activity level, sex, medical condition and hormone status. You may find it helpful to keep track of the energy you consume by counting calories. However, assessing food quality and overall dietary patterns is just as beneficial for managing dietary intake.

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