The Nutrition Calorie
Nutritionists measure the energy content of food in "calories" (sometimes capitalized and abbreviated as Cal or sometimes C, or abbreviated kcal as if small calories were being used), where each food calorie represents 4,186 joules. This is equivalent to 1000 of the calories used in chemistry, and thus the food Calorie would be called a kilocalorie if small calories were being used. However, in chemistry calories have been deprecated as a scientific unit of measure in favor of joules, and therefore in common modern usage the word "calorie" usually refers to a food calorie.
This situation provides two ways of talking about the amount of calories in food which look quite different but that express the exact same amount of energy. One may say that dietary fat has nine kilocalories (kcal) per gram, while proteins and carbohydrates have four kcal per gram, or, one may say that fat has nine Calories per gram while carbohydrates and proteins have four Calories per gram.
The amount of food energy in a particular food is measured by completely burning the food in a bomb calorimeter, a method known as direct calorimetry. Dieticians recommend counting calories to avoid obesity. The government of the United Kingdom recommends consumption of no more than 2000 Calories (2000 kcal) by women each day and 2500 Calories (2500 kcal) by men each day.
The Physics and chemistry calorie
In physics or chemistry, a calorie (abbreviated cal) is a unit of energy that equals the amount of heat necessary to raise the temperature of one gram of water by 1 degree Celsius, at a pressure of 1 atm. This amount of heat depends somewhat on the initial temperature of the water, which results in various different units sharing the name of "calorie" but having slightly different energy values:
* the 15 C calorie,
* the 4 C calorie,da
* the mean 0 C to 100 C calorie,
* the International Steam Table calorie,
* the thermochemical calorie,
The slight variations in these units can be seen if you convert them to joules. For example, one 15 C calorie is the amount of heat necessary to raise the temperature of 1 g of water from 14.5 C to 15.5 C. This is approximately equal to 4.1855 J or 3.968X10-3 Btu. The International Steam Table calorie is approximately equal to 4.1868 J and the thermochemical calorie 4.184 J.
Of these various units, what is most commonly meant by calorie in cntemporary English text is the 15 C calorie.
The nutritional Calorie represents 1000 of these 15 C calories. Since this could be a source of confusion and error, these units are now deprecated. The International System of Units (SI) unit for heat (and for all other forms of energy) is the joule (J), while the (obsolete) cgs (centimeter gram second system of units) system uses the erg (unit of energy and mechanical work in the centimeter-gram-second system) - From Wikipedia, the free encyclopedia.
Before start losing weight and counting calories you must first calculate the number of calories your body needs everyday, because this amount changes from person to person, depending on sex, age, weight, muscle content or height. Averages are situated around 2000 calories for women and 2500 for men. An easy, but not so accurate calculation is that for every 500 less than your normal amount of calories eaten every day you will lose up to one pound (453,6g) per week.
Counting calories must be included as part of your diet, because when you loss weight is best to know how many calories your food has, and so ensuring that the amount of calories burned each day is more than the amount stored. All nutritionists agree that a healthy low fat diet without counting calories could not exists, so take your time and solve that problem with various calorie calculators.
By knowing all the time the amount of calories consumed you can control how much you can eat and how it will affect your body. When dieting and counting the calories you can eat almost anything as long as you do not exceed the number of calories burned every day.
When you eat fewer calories, your body is forced to consume the fat stored to make up the deficit in your calorie count. Nutritionist's advice is that you must combine psychical exercises with healthy eating in order to create some calorie deficit.
沒有留言:
張貼留言