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What Is Calorie?
To survive we need to obtain energy from our food and this energy is measured in calories. In other words, a calorie is a unit of energy.
We generally speak of calories in relation to the energy in food but, in fact, any energy can be measured in calories. A calorie is scientifically defined as the amount of energy, or heat, needed to raise the temperature of 1 gram of water by 1 degree Celsius (1.8 degrees Fahrenheit). A kilocalorie is equal to 1,000 calories.
The scientifically defined calorie is a very small energy unit that is inconvenient to use because an average serving of any food typically provides thousands of these calories. For this reason, when speaking about food, we say 'calorie' when we mean 'kilocalorie'. For example, when you see '200 calories' on a food label, it actually means 200 kilocalories, or 200,000 calories using the strictly scientific definition. The same is true for physical activities: when a chart says that 30 minutes of vigorous walking burn 370 calories we mean that, in fact, 370 kilocalories (or 370,000 'scientific' calories) are burned. In this article and in the software we keep to the popular usage. When we say 'calorie' we always mean 'kilocalorie'.
Calorie vs. Kilojoule
The energy value of food can also be measured in kilojoules. 1 calorie equals 4.184 kilojoules (kJ). To convert kilojoules to calories, divide the number of kilojoules by 4.184. To convert calories to kilojoules, multiply the number of calories by 4.184.
Calories in our food come from proteins, fat, alcohol, carbohydrates and fiber.
The energy values of these substances are:
Knowing these values, you can calculate the number of calories in any food if you know how many grams of each nutrient it contains.
Remember that your body can use only a limited amount of calories at a time. Any excess calories that your body does not use for energy are stored as fat.
You may be wondering if the source of the calories is important. If we are only considering weight loss or gain, the answer is no, it is the total intake of calories that is important. However, if we are talking about nutrition and health, it definitely does matter where your food calories come from. Generally, carbohydrates and proteins are healthier sources of calories than fats or alcohol.
How Much Do I Need
The recommended daily calorie intake varies from person to person. It depends on your age, your height and weight, your body composition, your level of daily activity and your lifestyle.
To calculate the calories you need daily, you should take into account three main factors:
Your basal metabolic rate (BMR) is the amount of energy your body needs to function at rest (to keep your heart beating, your lungs breathing, to maintain your body temperature, etc). This comprises about 60 to 70% of your daily calorie requirement. Generally, men have a higher BMR than women.
The second factor, physical activity, includes all activities from making your bed to skiing. The number of calories you burn in any activity depends on your body weight, the type of activity and the duration of that activity.
The thermic effect of food is the amount of energy your digestive system needs to break that food down into basic substances, which can further be used by your body. To calculate the number of calories your body expends in this process, multiply the total number of calories you eat daily by 0.10 (10%).
Your daily calorie requirement is the sum of these three calculations – BMR, energy used in activity and thermic calories.
Some notes on calorie requirements:
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