Calorie
A calorie is a unit of measurement used to quantify energy, essential in various fields, notably nutrition. There are two main types: small calories (the energy needed to raise the temperature of one gram of water by one degree Celsius) and large calories, or kilocalories (kcal), which are typically used in food measurement. One large calorie represents the energy required to increase one kilogram of water by one degree Celsius, equating to one thousand small calories. In nutrition, calories help assess energy intake from macronutrients—proteins and carbohydrates each provide 4 kcal per gram, while fats provide 9 kcal per gram.
Daily caloric needs vary based on factors like age, sex, weight, and activity level, with general guidelines suggesting an intake of about 2,000 kcal for adults to maintain weight. Weight management relies on the balance between caloric intake and energy expenditure: consuming more calories than expended leads to weight gain, while consuming fewer results in weight loss. Foods are categorized as high-calorie or low-calorie, influencing dietary choices; high-calorie foods can be nutritious, while low-calorie foods, like fruits and vegetables, are often recommended for weight loss. Understanding calories is fundamental for making informed dietary decisions and managing health.
Calorie
A calorie is a unit of measurement used to quantify energy. While its most familiar application is in the field of nutrition, calories can also measure heat energy in sources such as coal and natural gas, or the energy expenditure generated by specific physical activities. From a scientific standpoint, there are two different types of calories, informally known as small calories and large calories. A small calorie represents the amount of energy needed to raise the temperature of one gram of water by one degree Celsius. It is sometimes called the fifteen-degree calorie, as its most precise application increases the temperature of one gram of water across the fifteen-degree threshold, from 14.5 to 15.5 degrees Celsius.
A large calorie, on the other hand, is the type of calorie used in nutrition and is defined as the amount of energy required to generate a one-degree increase in one kilogram of water. Thus, one large calorie is equal to one thousand small calories, which is why food packaging labels sometimes use the term kilocalories (kcal).
Role in Weight Gain and Weight Loss
Nutritionists divide all sources of food energy into three categories known as macronutrients. The three macronutrients are proteins, carbohydrates, and fats, and each has its own standard calorie value: proteins and carbohydrates each provide 4 kcal of food energy per gram, while fats provide 9 kcal of food energy per gram.
General nutritional guidelines typically recommend that adults consume approximately 2,000 kcal per day to maintain their body weight. However, actual daily calorie requirements for weight maintenance depend on a range of factors, including age, sex, weight, and activity level. The basis for calculating actual calorie requirements is a formula that determines what is known as an individual's resting energy expenditure, or REE. This is the amount of energy a person needs to meet all basic bodily functions without performing any movements or physical activities whatsoever.
The REE formula for a male is 10 x (weight in kilograms) + 6.25 x (height in centimeters) + 5 x (age in years) + 5. For females, REE is calculated using the formula 10 x (weight in kilograms) + 6.25 x (height in centimeters) + 5 x (age in years) – 161.
These basic formulas can then be adjusted to account for the individual's average level of activity to determine how many kilocalories the person should consume per day to maintain his or her current weight. This adjusted total represents a person's total daily energy expenditure, or TDEE. Conventional models define four different levels of activity: sedentary, light activity, moderate activity, and intense activity. These levels can alternately be identified as not active, somewhat active, moderately active, and very active.
For the purposes of calculating TDEE, sedentary is defined as normal daily activity with little to no intense energy expenditure. A sedentary person's TDEE is calculated by multiplying his or her REE by a factor of 1.2. Light activity is deemed to be any physical activity or combination of activities that burn an additional 200 to 400 kcal of energy in a female or 250 to 500 kcal of energy in a male, generating an REE to TDEE calculation factor of 1.375. Moderate activity burns between 400 and 650 kcal of additional energy in a female or 500 to 800 additional kcal in a male, generating a TDEE of 1.55 times the person's REE. Intense activity burns more than 650 kcal in a female and more than 800 kcal in a male; a person at this activity level has a TDEE of 1.725 times greater than his or her REE.
Take, for example, a thirty-one-year-old moderately active female who weighs 55 kilograms and stands 160 centimeters tall. For this subject to maintain her current body weight, she would have to multiply her REE by a factor of 1.55 to determine her TDEE. Her REE would thus be 10 x (55 kilograms) + 6.25 x (160 centimeters) + 5 x (31 years of age) – 161. This leads to an REE of 550 + 1000 + 155 – 161 = 1544. Her TDEE would be 1544 x 1.55 = 2393.
Therefore, this subject would have to consume approximately 2,400 kcal per day in food energy to maintain her current weight of 55 kilograms.
Weight is gained or lost by consuming more or fewer calories than are required, based on the person's level of total daily energy expenditure. A person will gain one kilogram if he or she consumes 7,700 more kilocalories than he or she expends; conversely, a person will lose one kilogram if he or she expends 7,700 more kilocalories than he or she consumes. Adjusting for the imperial system of measurement used in the United States, a person will gain one pound for every 3,500 kcal of excess food intake, or lose one pound for every 3,500 kcal of excess energy expenditure.
High-Calorie vs. Low-Calorie Foods
Nutritionists tend to divide foods into two main categories: high-calorie and low-calorie. High-calorie foods are those that contain a large amount of calories relative to their weight. Many such foods are high in fat, since fat contains 2.25 times more energy than proteins or carbohydrates. Many high-calorie foods also have very dense concentrations of sugar. While high-calorie foods are widely perceived to be unhealthy, some actually provide a great deal of nutritional value; for example, nuts and fatty types of fish are high-calorie foods, but both are also considered highly nutritious.
Low-calorie foods are those that contain relatively few calories for their weight, typically due to high water content. Fruits and vegetables are common examples of low-calorie foods and are strongly recommended to people who want to lose weight or follow a calorie-reduced diet.
Some nutritionists also refer to the concept of empty calories. Empty calories are generated by foods that offer little to no nutritional value from vitamins, minerals, or other beneficial substances. Many processed foods, snack foods, and sugary beverages fall into this category, and as such, most experts recommend that people keep consumption of these foods to a minimum.
Bibliography
Bolton, Dan. "Flexible Dieting: How to Calculate Your Macros." Healthy Eater. Healthy Eater. Web. 8 Feb. 2016. https://healthyeater.com/how-to-calculate-your-macros
Szalay, Jessie. "What Are Calories?" LiveScience. Purch. 13 Nov. 2015. Web. 8 Feb. 2016. http://www.livescience.com/52802-what-is-a-calorie.html
"Understanding Calories." NHS Choices. Department of Health, Gov.UK. Web. 8 Feb. 2016. http://www.nhs.uk/Livewell/loseweight/Pages/understanding-calories.aspx