How much energy does a snack food contain?
Food that we eat gives us energy to go through our day. It gives us energy by providing energy to the cells inside our body. Carbohydrates in food are used first. When they are all used up, the body then uses fats, and then proteins as energy sources. So carbohydrates, fats and proteins provide energy to our bodies through the foods that we eat.
The energy in the food that we it is measured in units of kilocalories or Calories. The Calorie (Cal, with an uppercase C) used to measure the nutrition in food is actually 1000 calories (cal) (with a lowercase c) or 1 kilocalorie (kcal). While the Calorie unit is used widely in the U.S., the kilojoule (kJ) is in widespread use internationally. The conversion factors for calories, kilocalories, joules, kilojoules, and Calories are as follows:
Energy Values used in Nutrition
1000cal = 1 kcal = 1 Cal
4184 J = 4.184 kJ = 1 Cal
Nutrition labels are currently a requirement on most packaged foods sold in the United States and internationally. The nutrition facts (as they are also called) usually include how many calories are in the food, how much carbohydrates, fat and proteins are present as well as the Calories per gram of each type of energy source. In order to determine the energy in the food, the food is burned in a calorimeter (described in more detail in the following section) in the laboratory to obtain the energy value in units of kJ/g or kcal/g, typically. A food sample is put into a steel container containing oxygen and in the surrounding chamber, a measured amount of water. The energy value is determined based on the mass of the food and water and the increase in temperature.
Use the information in this nutrition facts label to determine the amount of Calories (Cal = kcal) and kilojoules (kJ) from fat, carbohydrates and protein in the snack mix.
Step 1: List the known quantities and plan the problem .
KnownEnergy per gram
The amount of grams of each energy source (fat, carbohydrate, and protein) and the amount of energy per gram of each energy source is given on the label. Multiply the grams by the Energy per gram to obtain the Energy. Note: The Energy per gram is the conversion factor. It should be multiplied in such a way that the energy is on top and the grams are on bottom because you want your final answer to be energy in Cal or kcal or kJ.
Step 2: Solve .
Energy from Fat:11 g x 9 kcal/g = 99 kcal = 99 Cal
Energy from Carbohydrate:
12 g x 4 kcal/g = 48 kcal = 48 Cal
Convert to kJ
48 Cal x 4.184kJ/Cal = 200.832 kJ = 201 kJ
Energy from Protein:
5 g x 4 kcal/g = 20 kcal = 20 Cal
Convert to kJ
20 Cal x 4.184kJ/Cal = 83.68 kJ = 84 kJ
Step 3: Think about your result .For the snack food in this example, most of the energy is coming from fat first, then from carbohydrates and finally from protein when these three sources of energy are considered.
For more practice, find nutrition labels on the foods you consume at home or online and determine the amount of energy from fat, protein and carbohydrates in each.
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