When it comes to a healthy diet, one of the most common terms we hear is calories. But do we really know what it means, and what the optimal calorie intake is if we want to eat in a figure-friendly way?
The word “calorie” comes from the French word chaleur (heat), and it is a unit of energy. One calorie of heat energy is required to raise the temperature of one gram of water by one degree Celsius. It’s a straightforward and logical unit of energy. The French scientist Nicolas Clément introduced it in 1824, and it was used worldwide as the official unit of energy until 1929, when it was replaced by the joule.
Today, most foods list their energy content in joules, but in nutrition science the calorie still persists. The conversion is 4.2. This means that a food containing 1000 calories equals 4200 joules, or 4.2 kilojoules.
What is the optimal energy intake?
People’s energy needs vary. They depend on body weight, lifestyle, and age. Older people, for example, require less energy since their bodies no longer undergo as many building processes, while children need significantly more energy relative to their body weight.
A petite, slim woman with a desk job might need around 1600 kcal per day, while a tall, 80 kg man with an active lifestyle may need twice that amount. On average, daily energy needs range between 2000 and 2500 kcal.
Our bodies obtain energy by burning (oxidizing) nutrients. After various transformations, this energy ultimately leaves the body as heat. The three main energy-providing nutrients are fats, carbohydrates, and proteins. Carbohydrates and fats are completely burned during use, while proteins are used not only as an energy source but also for building the body. Fats carry the most energy, while carbohydrates burn faster.
For adults, the optimal situation is to consume exactly as much energy as is expended daily. If this balance isn’t maintained, the body stores the excess, leading to weight gain. If overweight, one must consume less energy than is expended over a longer period.
Carefully measuring both calorie intake and energy expenditure can certainly help manage or prevent weight problems. However, calculations cannot replace healthy intuition and body awareness. In certain cases, though, accurate measurement of energy intake is vital — for example, for athletes or people with diabetes.
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