Blood Glucose Data Analysis
hhmi BioInteractive
Activity Student Handout
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.
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.
arr
Lactase enzyme
+
&
HO
Lactose
H2O
Glucose
Galactose
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 diarrhea - all 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.
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Updated January 2020
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hhmi BioInteractive Blood Glucose Data Analysis
Activity Student Handout
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
0 minutes
15 minutes
30 minutes
45 minutes
60 minutes
Spencer Wells
117
128
146
160
152
Peter
97
111
135
154
143
Rachel
96
99
105
101
98
Katherine
95
97
99
101
102
Sarah
108
116
129
141
139
Michael
94
109
128
143
140
Arthur
97
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.
Blood Glucose Test Results
160
150-
140-
Spencer Wells
Blood Glucose (mg/dl)
130-
120-
110
100
90
80
0
10
20
30
40
50
60
Time (minutes)
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Updated January 2020
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hhmi BioInteractive Blood Glucose Data Analysis
Activity Student Handout
After graphing the data, answer the following questions.
2. For someone that is lactase persistent, explain why their blood glucose concentrations rise after drinking milk despite milk containing no glucose.
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 the data in the graph and table, 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. Explain why it is possible for lactose intolerant individuals to digest the proteins in milk even though they lack the lactase enzyme.
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Updated January 2020
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Activity
hhmi Biointeractive
Blood Glucose Data Analysis
Activity Student Handout
9. A milk allergy is the result of a reaction to one or more of the components of milk, such as the protein casein. Explain how an allergy to milk is different from lactose intolerance.
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.
With lactase
Lactase
Lactose
Glucose + Galactose
Small intestine
Without lactase
Gas (H2, CH2) +
Lactose
Lactose
Fermentation
Acids
Small intestine
Large intestine
Figure 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
5
6
9
8
5
Lisa
4
9
8
29
35
Dan
6
8
10
31
32
Cindy
4
7
6
9
6
Brian
Updated January 2020
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Enzymes & Reactions
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hhmi BioInteractive
Blood Glucose Data Analysis
Activity Student Handout
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.
Hydrogen Breath Levels (ppm)
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 non-persistent? 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.
Enzymes & Reactions www.BioInteractive.org
Updated January 2020
Page 5 of 5/nANSWER ALL THE QUESTIONS MENTIONED IN ASSIGNMENT FILE AND DO THE GRAPHS
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