Every time most of us think of calories, we think of fatty foods. In dietary food, calories are the amount of energy that food gives.
If we consistently consume more energy than we need, we will gain weight. In contrast, when do not take energy enough, we will lose weight, fat, and eventually muscle mass.

The definition of a calorie is the amount of energy needed to increase the temperature of 1 gram (g) of water through 1° Celsius.

The type and amount of food we eat will decide how many calories we take. For a lot of people on a weight-loss diet, the amount of calories in a food is a deciding factor in choosing if or not to eat it.
How and when we eat can also make a difference because the body uses energy differently during the day. Our body's energy will rely on how active we are, how efficiently our body utilizes energy and our age.
Through the 2015-2020 Dietary Guidelines for Americans, women are likely to need anywhere from 1,600 to 2,400 calories per day, and men between 2,000 and 3,000. Nevertheless, this relies on their age, size, height, lifestyle, overall health, and activity level.

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You should choose the right food:Counting calories is one good way of following a healthful diet. The 2015-2020 Dietary Guidelines for Americans suggest a calorie intake that ranges from 1,000 calories per day for a baby of 2 years to 3,200 for a male teenager aged 16 to 18 years.

As we grow older, our metabolic rates start to slow down as well.

This decreases their need for energy. From age 19 to 25 years, the suggested intake for women is 2,000 calories per day, yet after 51 years, this lows to 1,600.

Burning calories

For the human body to function, it needs energy: Approximately 20 percent of the energy we take in is provided for brain metabolism. Most of the rest is utilized in basal metabolism, the energy we need while in a resting state, for functions, for example, blood circulation, digestion, and breathing.

In cold conditions, we need more energy to keep constant body temperature, as our metabolism rises to produce more heat. In warm conditions, we will need less energy.

Smartwatch - sports watch - measures the pulse, steps, pace and quality of sleep. Also calculates calories burned.
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Also, we need mechanical energy for our skeletal muscles, to support posture and move around. Cells get energy by reacting oxygen with glucose to produce carbon dioxide, water, and energy will support cellular respiration through the metabolic process.

How efficiently energy from respiration converts into physical—or mechanical— power relies on the kind of food eaten, the kind of physical energy, and whether muscles are used aerobically or anaerobically.

It means that we need calories to provide bodily functions, such as breathing and thinking, to do activities, and to move around.