One way to determine the total energy in calories of a food is to burn it in a device called a bomb calorimeter. The heat produced during combustion minus the heat added to begin the combustion is the total calories in the food. The typical human digestive tract does not absorb all of the calories in food; thus it is not 100% efficient. Furthermore, calories in undigestible organic compounds may

Question

not be absorbed at all, and thus can be considered to be zero calorie relative to human nutrition. Artificial sweeteners and fats are designed to produce desired sensation in the mouth without being absorbed. These are organic compounds that would release heat in a bomb calorimeter, thus they technically have calories. A. What does this suggest about the accuracy of the bomb calorimeter in determining available food calories for humans? What would be the results of bomb calorimetry of human feces? B. What is it about a particular food substance that may prevent absorption of its calories? C. What happens to the "zero-calorie" molecules as they pass through the digestive tract? What are the potential effects on defecation?

What will be an ideal response?

Answer 1

A. Bomb calorimetry is not 100% accurate, because it does not take into account that some calories are not absorbed. Human feces would be determined to contain some calories.
B. In order for nutrients in a food to be usable by the body, they must be chemically digested and absorbed. Digestive enzymes exhibit specificity, so they do not digest molecules that are different in structure from their substrate. If an artificial food additive is undigestible, this simply means that the body lacks the appropriate enzyme.
C. Gut bacteria may be able to digest and absorb these compounds. Extra organic solute present in the gut may cause retention of water and production of bacterial gas as the bacteria digest the substance in question. This can lead to distention, discomfort, and diarrhea.