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Manual do professor
Knowledge across English, Chemistry, Biology, and Physical Education

Let’s learn more about nutrition labels. Before you read the text below, think for a minute: Where do human beings get the energy they need to survive?



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Available at: . Accessed on: March 17, 2016



The Big Reveal: What’s Behind Nutrition Labels

By Michael Tinnesand

Nearly all of the foods we eat have a nutrition label that presents the essential values that foods contain. The label starts with a serving size and the number of calories per serving, followed by a list of key nutrients, including total fat, carbohydrates, and proteins. Other values may be included, such as the calories from fat, saturated fat, trans fat, dietary fiber, sugars, and various vitamins. But what do all these values mean, and how are they measured? How does this information help us to stay healthy?

Calories

Nearly all of us can be casual about the type and amount of food we consume. I recently stopped at a fast food restaurant and ordered a large caramel coffee frappé. I noticed a brochure near the counter and, as I finished my drink, I read that it contained 680 Calories!



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I happen to know that in order to burn 680 Calories at the gym, I would need to spend at least an hour on a stationary bicycle, spinning at high speed. Given that just three of these drinks would exceed my daily limit of total energy required (2,000 Calories), this forced me to pay close attention to the nutritional values of what I eat. But where to begin?

Let’s start with calories. Actually, the word “Calorie” (uppercase C) is what chemists call a “kilocalorie,” or 1,000 calories (lowercase c). To distinguish between the two, sometimes, the nutritional calorie is written as a Calorie—as in this article—as opposed to a calorie. More specifically, one Calorie (kilocalorie) is the amount of energy it takes to raise 1 kilogram of water 1°C at sea level.

The calorie content of food was determined in the late 1800s by Wilbur O. Atwater, an agricultural chemist. He built a device called a respiration calorimeter to make direct measurements of heat released by humans from the food they consumed. At 4 feet by 8 feet, Atwater’s calorimeter was big enough to allow a person to step into it. The device measured the amount of heat released by that person, along with the amount of oxygen consumed and carbon dioxide given off.



Using this device, Atwater was able to measure the precise amount of energy contained in thousands of food items. He found that carbohydrates and proteins were worth 4 Calories per gram and fats about 9 Calories per gram. This 4-9-4 system is how labels are determined today. In some cases, dietary fiber is subtracted from the total carbohydrate count because it is assumed that it provides no nutritional calories. Also, alcohol, if present, is accounted for as 7 Calories per gram.


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