Enzymes & Reactions
Updated January 2020
www.BioInteractive.org
Page 1 of 5
Activity
Student Handout
Blood Glucose Data Analysis
INTRODUCTION
Although we can easily digest milk as babies, most of us lose this ability as adults. This is because we usually stop
producing lactase, an enzyme that breaks down the main sugar in milk. However, about one-third of people
worldwide still produce lactase as adults. In this activity, you will learn about a test for whether someone is likely
to produce lactase. This test is based on the amount of a sugar called glucose in a person’s blood.
MATERIALS
ruler
colored pencils
BACKGROUND
Milk is packed with proteins, fats, and carbohydrates that support the growth, development, and survival of
baby mammals. The main carbohydrate in milk is a sugar called lactose. To digest milk, lactose must be cleaved,
or broken down, by lactase, an enzyme produced in the small intestine. Lactase cleaves lactose into two smaller
sugars, glucose and galactose, which are easily absorbed through the walls of the small intestine. Once these
sugars are absorbed into the bloodstream, they can be delivered to the cells of the body and used for energy.
Figure 1. A diagram showing how the lactase enzyme cleaves the sugar lactose.
As baby mammals grow up and stop drinking their mother’s milk, their bodies usually stop producing the lactase
enzyme (presumably because it is no longer needed). Individuals that do not produce lactase as adults are called
lactase nonpersistent. Most mammals are lactase nonpersistent and do not drink milk as adults. Humans are
unusual in that some adults continue to drink milk from other mammals, such as cows.
When an individual who is lactase nonpersistent drinks milk, they cannot easily break down the lactose in the
milk. The lactose passes from their small intestine to their large intestine, where it is fermented by bacteria.
Fermentation produces various gases in the large intestine, which can cause abdominal pain, bloating,
flatulence, and diarrheaall symptoms of lactose intolerance, the inability to digest lactose. Most adults are
lactase nonpersistent and thus typically lactose intolerant (although some may not know it because their
symptoms are mild). However, about 35% of the global human population continues to produce lactase into
adulthood. These individuals are called lactase persistent and are typically lactose tolerant, meaning that they
can digest lactose easily and drink milk without problems.
Activity
Student Handout
Blood Glucose Data Analysis
Enzymes & Reactions
Updated January 2020
www.BioInteractive.org
Page 2 of 5
PROCEDURE
There are several ways to test whether someone is lactase persistent or nonpersistent. One method, the blood
glucose test, is shown in the short film Got Lactase? The Co-evolution of Genes and Culture. Table 1 shows the
blood glucose levels of the film’s narrator, Spencer Wells, and six other individuals over time. The glucose levels
were measured using glucose strips and a glucose reader similar to the one in the film. After baseline levels (i.e.,
the ones at “0 minutes”) were measured, each person drank a liter of milk. Their blood glucose levels were
measured again at 15, 30, 45, and 60 minutes after drinking the milk.
Table 1. Blood glucose test results for seven adults tested in Sarah Tishkoff’s laboratory.
Blood Glucose (mg/dL)
Individual
15 minutes
30 minutes
45 minutes
60 minutes
Spencer Wells
128
146
160
152
Peter
111
135
154
143
Rachel
99
105
101
98
Katherine
97
99
101
102
Sarah
116
129
141
139
Michael
109
128
143
140
Arthur
96
94
83
88
1. Plot the data in Table 1 on the graph below, which already includes the results for Spencer Wells. Add more
entries to the legend as needed.
80
90
100
110
120
130
140
150
160
0 10 20 30 40 50 60
Blood Glucose (mg/dL)
Time (minutes)
Blood Glucose Test Results
Spencer Wells
Activity
Student Handout
Blood Glucose Data Analysis
Enzymes & Reactions
Updated January 2020
www.BioInteractive.org
Page 3 of 5
After graphing the data, answer the following questions.
2. Why might someone’s blood glucose levels after drinking milk indicate their lactase activity?
3. Divide the individuals in Table 1 into two groups (A and B) based on their blood glucose test results. Write
the names of the individuals in each group, including Spencer Wells, below.
Group A:
Group B:
4. Explain your rationale for dividing the individuals into these two groups. Use data from your graph to
support your answer.
5. Based on these data, do you think the individuals in Group A are lactase persistent or nonpersistent?
Describe the evidence that supports your answer.
6. Based on these data, do you think the individuals in Group B are lactase persistent or nonpersistent?
Describe the evidence that supports your answer.
7. If the blood glucose test was performed on people from the Maasai population in Kenya, would their results
be more like those of the individuals in Group A or Group B? Explain your prediction. (Hint: As discussed in
the film Got Lactase? The Co-evolution of Genes and Culture, the Maasai traditionally raise cows for food.)
8. A person taking a blood glucose test is usually told to fast (i.e., to not eat or drink anything but water) before
the test. Why do you think that might be necessary?
Activity
Student Handout
Blood Glucose Data Analysis
Enzymes & Reactions
Updated January 2020
www.BioInteractive.org
Page 4 of 5
EXTENSION: The Hydrogen Breath Test
Another common way to test whether a person is lactase persistent or nonpersistent is the hydrogen breath
test. This test uses the amount of hydrogen in a person’s breath to check for lactose fermentation. As described
in the “Background” section, undigested lactose is fermented by bacteria in the large intestine. Fermentation
produces several gases, including hydrogen, that can exit the body through the anus. These gases can also be
absorbed into the blood, circulated to the lungs, and eliminated through the breath.
Fig
ure 2. A diagram comparing what happens to lactose in the intestines of individuals with and without the lactase
enzyme.
Table 2 shows the levels of hydrogen in the breath of four adults tested for lactase persistence. As in Table 1, the
measurements at “0 minutes” represent baseline levels before drinking milk. The other measurements were
taken at various times after drinking milk.
Table 2. Hydrogen test results for four adults.
Hydrogen Breath Levels (ppm)
Individual
0 minutes
30 minutes
60 minutes
90 minutes
120 minutes
Lisa
5
6
9
8
5
Dan
4
9
8
29
35
Cindy
6
8
10
31
32
Brian
4
7
6
9
6
Activity
Student Handout
Blood Glucose Data Analysis
Enzymes & Reactions
Updated January 2020
www.BioInteractive.org
Page 5 of 5
1. Create your own graph of the data in Table 2. Your graph should include a title, labels for the x- and y-axes,
and a legend.
After graphing the data, answer the following questions.
2. Which individuals in Table 2 are likely to be lactase persistent? Use data from your graph to support your
answer.
3. Which individuals in Table 2 are likely to be lactase nonpersistent? Use data from your graph to support
your answer.
4. Think of another type of test to determine whether a person is lactase persistent or nonpersistent. Describe
your idea in one or two sentences.