As a general scientific term, a calorie is defined as the amount of heat required to increase the temperature of a unit of water from zero degrees Celsius to 1 degree. In nutrition, a calorie represents a unit of energy that comes from the foods you eat. Calories matter in your diet because they determine whether you gain weight, lose weight or maintain your weight. In addition, both the total number of calories you consume and the source of these calories can impact your health.
A food calorie – the energy your cells derive from the foods you take in – consists of 1,000 calories and is also known as a kilocalorie or kcal. Although this terminology might sound confusing, the important thing to understand is the calories listed on food labels are in units of food calories or kcals. You might also see a food calorie designated as a Calorie, with a capital “C.” In all cases, these numbers indicate the amount of energy, or fuel, your cells are able to extract from metabolizing the nutrients in the foods you eat.
The caloric balance of your diet is one factor in determining your overall health. You are in caloric balance when, over time, the number of calories you take in matches the number of calories you burn through metabolism and physical activity. In caloric excess, you consume more calories than you use and can lead to weight gain. In contrast, a caloric deficit means you are burning more calories than you consume, causing you to lose body mass. During times of growth, a caloric excess is necessary, but unintentionally eating more than you need leads to unwanted weight gain. Deliberately putting yourself in a caloric deficit can then help you shed unwanted pounds; however, losing weight when you don’t mean to can indicate a health issue that needs medical attention.
Keep in mind:
The proportion of calories you take in through the different macronutrients is as important as the absolute number of calories you consume. A healthy, well-balanced diet that supports all your body’s physiological processes offers 10 to 35 percent of calories from protein, 45 to 65 percent from carbohydrates and the remaining 20 to 35 percent from fats. Consuming only the number of calories you need to support your body’s functions also helps keep you healthy. Taking in more than you need can eventually lead to obesity, with an increased risk of cancer and metabolic disorders.