Friday, October 31, 2008

What Is A Calorie?

Calories are actually a measure of energy; scientifically, the amount of energy it takes to raise one gram of water by one degree Celsius. The term we use as Calories are really kcals or 1000 Calories. We use kcal because if we didn’t, a Three Musketeers Bar would have 285,000 calories and no one would ever eat one!

Calories are measured by an apparatus that burns the edible portion of a food and measures the energy that is released. Calories people burn are measured by monitoring the amount of oxygen taken in and carbon dioxide released during certain activities.

In grade school we learn that oxygen is what we breathe in, and carbon dioxide (CO2) is what we breathe out. Where does the carbon come from? The Carbon (C) that we breathe out comes from the energy yielding nutrients: Carbohydrates, proteins, and fats. The other nutrients—vitamins, minerals, and water—neither contain carbon, nor provide Calories.

People burn most of their calories by their continuous body functions (heart beating, breathing, regenerating new cells, etc). This is called your Basal Energy Expenditure and accounts for about 2/3 of the daily calories burned by most people. When you add to this your movements and exercises during the day (even the process of digestion), you find your total calories expended.

How do we calculate the number of calories in a food? There are a few basics to begin with: Carbohydrates provide 4 calories per gram. Protein provides 4 calories per gram. Fat provides 9 calories per gram. The only other substances that provide calories are drinking alcohol, and sugar alcohols (such as sorbitol, found in sugar-free gums and candies).

You can calculate the calories in a food by reading the label that shows grams of carbohydrates, grams of protein, and grams of fat. The gram weight of a food will be more than the total of the carbohydrates, protein, and fat, because of water weight. Water can compose of up to 90% of some foods (fruits in particular) but is present in very small amounts in high fat foods, such as butter.

For example, a teaspoon of sugar weighs approximately 5 grams. Only about 4 grams are carbohydrate (the rest a little bit of water). If you multiply 4 grams x 4 calories/gram, you find 16 calories in a teaspoon of sugar! Let’s try to calculate butter: a teaspoon of butter weighs about 5 grams. There are 9 calories in a gram of butter (fat). Take 9 calories/gram times 5 grams and find that there are 45 calories in a teaspoon of butter. Hmmm, butter sure has more calories than sugar!

Try doing the math on food labels you find around your house: On a label of bread you might find 12 grams of carbohydrate (x 4 is 48 calories) and 3 grams of protein (x 4 is 12 calories) and the total calories in a slice will be near 60 calories. The slice of bread weighs 30 grams, but the rest of the weight is from the water content.
I hope you enjoyed this little nutrition class :)

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