Digestive Case Study 5*

Lactose Intolerance


Pei, a twenty-six year old Asian graduate student in computer science, had been experiencing occasional discomfort after meals. The discomfort reached a new peak last Thursday evening about an hour after eating a cheeseburger and a large chocolate milk shake. Pei spent much of that night in pain. She had abdominal cramps and diarrhea and also felt sick to her stomach. Pei went to the clinic and saw a doctor the next day.


The doctor asked Pei a number of questions and noted that Pei's discomfort seemed to be associated with dining out. Pei told the doctor that on most evenings she cooked for herself, usually preparing traditional Asian cuisine, and that she seldom experienced any discomfort after eating at home. Pei only experienced discomfort after dining out, especially, it seemed, after eating her favorite fast food meal, a double cheese burger and a chocolate shake. When asked if she used very much milk or cheese when preparing meals at home, Pei told the doctor that she almost never cooked with any dairy product.


The doctor suspected that Pei could be lactose intolerant and told Pei that she would like to have a test performed to verify her suspicion.  At the clinic lab, Pei was given a lactose rich fluid to drink and had her blood glucose level measured several times over the course of two hours. Later, her doctor informed Pei that her blood glucose level had not risen after drinking the lactose rich fluid and that that was evidence that she was lactose intolerant. The doctor told Pei about various products that contain lactase, the enzyme responsible for lactose digestion, and assured her that if she used one of those products, she could probably still have the occasional cheeseburger and chocolate milk shake.




1.  Decribe the mechanical and biochemical processes of digestion. Indicate where each takes place. 

2. In as complete a manner as possible, describe what type of molecule lactose is and list its subunits?

3. Describe what type of molecule lactase is and explain its function in the body. What component of enzyme structure is responsible for enzyme specificity?

4. What is lactose intolerance and how does a person get it? What groups commonly develop lactose intolerance?

5. How did the lactose intolerance test that Pei took provide evidence that she was lactose intolerant?

6. The hydrogen breath test is also commonly used to determine lactose intolerance. Where does the hydrogen come from? Explain.

How is lactose intolerance treated?


*adapted from McGraw Hill Online Learning Center, Essentials of Anatomy and Physiology,3rd ed.Seely/Stephens/Tate