What Are Calories — and Should You Be Counting Them to Lose Weight?

Calories are found in virtually every food you eat and give you the energy to perform daily life functions from breathing to crushing a workout.
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Calorie, the ever-controversial word. Some people have stopped counting calories while others make the majority of their food choices based on them. Should we measure them, do they matter and what are they really?

What Is a Calorie?

Although the terms "calorie" and "kilocalorie" are used interchangeably, their meanings are not the same. The USDA defines a calorie as a measurement of the amount of energy it takes to raise the temperature of one kilogram of water by one degree Celsius. When you use the term calorie, you're really talking about a kilocalorie (kcal). The true calorie is really a small calorie, and it takes 1,000 of these to equal a kilocalorie. (So, if you ate 2,000 true calories per day, you would be eating virtually nothing!)



A kilocalorie is a measure of energy produced in the foods you eat. When you use the term calorie and are talking about food, you're technically referring to a kilocalorie. Truly understanding the definition of a calorie requires us to separate the science from its colloquial meaning. In simple terms: Calorie is the commonly used word — but kilocalorie would be the scientifically correct term. One kilocalorie is the same as one Calorie (note the uppercase C).

Read more:Recommended Caloric Intake for Weight Loss

So, for the sake of convenience, the term calorie is used instead of the more technically correct kilocalorie.

How Does Your Metabolism Burn Calories?

The primary reason we consume food is to provide energy that keeps us alive. When you eat and drink, your body converts the calories you consume into energy, according to the Mayo Clinic. Calories contained in the food you eat and beverages you drink combine with oxygen to release the energy your body needs to function.


This breakdown and conversion process, also known as your basal metabolic rate or your metabolism, continues 24 hours a day whether you're moving around or at rest. Physically active people, however, burn more calories than people who engage in little to no physical activity.

There are several variables that influence your metabolism over time:

  • Body composition:​ People with more lean muscle mass require more calories at rest. Muscle is more metabolically active at rest, meaning that it requires more energy to be maintained than fat does.
  • Age-related change:​ Once a person hits their 20th birthday, they burn about 150 fewer calories per decade, according to the American Council on Exercise (ACE). Unfortunately, as you lose muscle with age, your body holds onto more fat and there's an overall reduction of energy (calories) needed and used.
  • Chronic and acute illness:​ Unmanaged chronic illnesses can alter metabolism and accelerate reductions in energy expenditure.


So, How Many Calories Should I Eat a Day?

Daily energy needs vary by the individual. Your height, weight, age, activity level and muscle mass all play a role in determining how many calories your body requires at rest as well as for activities of daily living.

The 2015-2020 Dietary Guidelines for Americans provide a general recommendation for calorie requirements broken down by age, gender and activity level. Adult women can range between 1,600 and 2,400 calories per day with adult men ranging from 2,000 to 3,000 calories per day. The lower end of the range would be for sedentary adults while the higher end would be the goal for very active adults.


Both male and female adults ages 19 and up should get 20 to 35 percent of their total calories from fats (with no more than 10 percent of those calories coming from saturated fats and little no none coming from trans fats), 45 to 65 percent of their total calories from carbs and 10 to 35 percent of their total calories from proteins.


Calories are units of measurement, like an inch or a teaspoon, says the Cleveland Clinic. So, a calorie of protein contains the same amount of energy as a calorie of fat or a calorie of carbohydrates. The amount of energy contained in each "type" of calorie, whether it's from fat, protein or carbohydrates, is the same.

The density of fat, protein and carbohydrates, however, is different. A single gram of protein contains four calories while a single gram of carbohydrates also contains four calories. Fats are more dense with one gram of fat boasting nine calories.

Since fat is denser than protein and carbs, you may find that you're more easily satiated when you eat fat due to its greater energy density. Conversely, you may be able to eat a larger portion size of a food high in protein or carbohydrates for the same number of calories.

Read more:How Many Carbs, Fats and Proteins You Need on a 1,200-Calorie Diet


When making a choice about foods and their energy density, balance is key along with taking your individual health status into consideration. A person with a genetic predisposition for developing high cholesterol would benefit from being mindful of their saturated fat intake while a person with a family history of diabetes may want to pay special attention to the types and proportion of carbs they consume.

If you drink alcohol, it's worth noting that each gram of alcohol contains seven calories — not as much as fat but more than protein and carbohydrates.


The protective effects found in wine are only present when wine is consumed in moderation while excess intake has been linked with an increase in the risk of developing chronic illness. The current recommendations for adults who drink, according to the CDC, is to have no more than the equivalent of one drink per day for women and two drinks per day for men. And if you don't drink, then you really don't need to start!

Counting Calories to Lose Weight

Counting calories coupled with choosing healthy, nutrient-rich foods may help you lose weight.
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Counting calories doesn't always have a straightforward outcome. Although calorie counting can help people become more knowledgable about food choices and track their eating habits, calorie counting alone isn't sufficient for behavior change that faciliates sustainable weight loss, a 2016 study in the JMIR mHealth and uHealth journal found.


Similar to alterations in metabolism, there can be many reasons why a person gains weight. The systems involved are more complicated than calorie intake exceeding calorie output. The following reasons may contribute to weight gain:

  • Hormonal shifts:​ An imbalance or lack of sensitization of the hormones that signal hunger and satiety in the hypothalamus can result in weight gain.
  • Socioeconomic status:​ Having limited access to affordable healthy foods can result in weight gain.
  • Genetics:​ Genetics can influence how people gain and lose weight as well as how their bodies react to and metabolize macronutrients.
  • Energy balance:​ Taking in or consuming more energy than one expends can result in unintentional weight gain. Weight gain can also be the result of physical inactivity. The standard American diet supplies an overabundance of energy coming from refined grains, saturated fats and added sugars. Eating this way on a consistent basis can result in weight gain.
  • Stress:​ Stressors including poor sleep, extended workdays and working multiple jobs can call promote weight gain, according to a November 2017 study in the ​Scandinavian Journal of Work, Environment and Health​.

Intentional weight loss, done in a healthful and balanced way with sustainability in mind, requires both time and attention. Spurring weight loss should be an individualized approach that takes the whole person into consideration with long-term sustainability in mind. Quick fixes and crash diets should be avoided.

Creating a balanced eating plan with weight loss in mind will look different for each person. However, the base of a balanced diet should incorporate all macronutrients coming from whole and minimally processed foods while limiting added sugars, fats and salts. The quality of your food has a direct impact on how your body metabolizes and responds to what you have eaten!

Foods labeled "low-calorie" may not always be the right choice — as many of those packaged products have an abundance of additives and fillers that attempt to boost the foods' flavor to compensate for the reduction in calories. While you should be mindful of the amount of calories you consume in order to ensure you're achieving a deficit to spur weight loss, you should also take into account that the foods you eat should be healthy and nutrient-dense.

Choosing nutrient-dense foods coupled with cutting calories with the help of an interactive app like MyPlate can help you drop weight. For example, nuts are not a low-calorie food; however, people who included energy-dense almonds as part of their energy-restricted diets had better lipid profiles as well as smaller waist circumferences and decreased body fat, a December 2016 study in the ​Journal of Nutrition​ found.

Read more:How to Read a Nutrition Label — and Finally Get Your Macros Right


For some, adjusting the proportion of foods on the plate and using snacks to increase the overall nutrition for the day are great weight management tools. Ensuring that half to three-quarters of your plate at lunch and dinner contain non-starchy vegetables rounded out with a combination of lean proteins coming from plants or animals along with starchy vegetables, fruits, legumes, nuts, seeds and whole grains are great guidelines for balancing your nutrients.

Limiting ultra-processed foods such as baked goods, deli meats and candy bars is optimal for general health as well as reducing the risk of developing diet-related chronic illnesses.

While understanding the value of a calorie is important, a single calorie does not give you information on the nutrient profile of a food! Eating and moving with balance and sustainability in mind are sound ways to support your health goals.