We often hear about calories and calorie burning. But what exactly are calories and how do they play a pivotal role in our daily lives? In a nutshell, a calorie is a unit of energy. It refers to energy consumption of food and drinks and also energy usage through physical activity. Comparably, a mid-sized apple has about 80 calories while you burn about 100 calories in a 1.5km walk.

There are two basic indicators for calories. One is referred to as small calories (cal). In reality, 1cal is the measurement given to the amount of energy required to raise one gram of water by one degree Celsius. The other is large calorie (Cal or kcal). 1Cal or kcal is the amount of energy required to raise one kilogram of water by one degree Celsius. Hence, 1,000 small calories equal 1 large calorie (1kcal).

With food, 1 gram of carbohydrates contains 4 calories, protein contains 4 calories but fat contains 9 calories per gram. In regions such as the European Union, energy data on food labels is expressed in joules (kilojoules). 4.18 joules make a calorie. An average adult should consume about 1,800 calories a day. There are also empty calories. These are calories we consume that have very little nutritional value. They are also known as discretionary calories and prime examples are solid fats and added sugars. These are common ingredients used in the processed foods industry. They make food and beverages taste better but have almost no nutritional value. The table below is from Harvard Medical School.