Discuss with students the problems with rising obesity rates
in America. Draw from current events as appropriate to help illustrate the
point. Some suggested resources are listed under Related Resources, although
other, timelier, resources might be available for your classroom.
Discuss with students the causes for obesity. Keep in mind
(and point out to them) that there are many causes for obesity, some of which
may or may not be within a person's control, such as genetics and medical
conditions. Keep an eye out for comments from students that might imply obesity
is entirely an obese person's fault and address them if they come up. Have them
list causes that they can think of. Steer them towards considering rising
portion sizes as one cause. Explain that while there are many components of a
healthy diet, just like there are many causes for rising obesity levels, today
in class you will examine one: portion size. Remind students that this is an oversimplification
of a complex issue (refer to the list to imply just how complicated it is) but
it is one important element.
Increasing Portions, Expanding Waist Lines Article Activity Sheet
Increasing Portions, Expanding Waist Lines Activity Sheet
Increasing Portions, Expanding Waist Lines Answer Key
Have students read the Increasing
Portions, Expanding Waist Lines Article independently. Then, hold a brief class
discussion on what they read and learned.
Distribute the Increasing Portions, Expanding Waist Lines
Activity Sheet. Have students work through it, perhaps in pairs or groups of
three. If you don't want to stop and discuss the activity periodically with the
class, you should circulate and discuss different elements with groups, or
combine the two. You want to help push and refine student thinking, so even
students that have correct answers can be pushed to deepen their thinking.
In Question 4, there is intentionally a mismatch between
units. Students wrote their function in terms of weeks in Question 3 and they
have to answer Question 4 in terms of months and years. Help them work flexibly
through the many ways they can convert units to make it work.
In Question 5, caution students to use an appropriate viewing window when graphing the function.
Help them figure out what a reasonable viewing window would be for each
The calorie information in this activity was obtained from
the calorie calculator at MayoClinic.com. Adjust the information so that it is
slightly different for each group, or have students make their own hypothetical
person, if you prefer.
After groups have had a significant amount of time to work
(let them be at least halfway done) distribute overheads or poster paper for
them to record their work and share with the class, either via presentations or
a gallery walk. (During a gallery walk, groups walk around and observe each
other's work. This may be a good opportunity for students to assess each
As a closing activity, have students write or journal about
their own eating habits. Remind students that unhealthy weights can be too low
as well as too high. Give students a safe place to reflect on their
relationship with food. Be aware that you might have some students for whom
this can be a delicate issue. Keep an eye out for anyone who might be bothered
by this activity. If you are uncomfortable or feel you don't know your students
well enough to support them through a potentially sensitive journal exercise,
consider something more objective, like having students analyze the calories in
different school lunch choices or a restaurant menu and write about what
healthier choices are (or are not) available. Another alternative is to have students create a one day healthy menu for breakfast, lunch, and dinner that provides 2160 calories.
1. If obesity rates rise from 34% of the population to 42% of
the population (as implied in the LA Times article linked above), what percent
increase is that?
2. The LA Times article also claims a non-obese person has a 2%
chance of becoming obese each year, but that probability increases by .4% for
each obese person you know. If you have 5, 10, and 15 obese friends or family
members, what's your probability of becoming obese each year?
[4%, 6%, and 8%]
3. How many calories do you think a person eats in a year?
[Obviously answers may vary, someone on a 1500-to-2500
calorie/day diet would consume between 550,000 and 900,000 calories/year.]
4. Assume that the average person eats 2,000 calories per day for a year. Organic apples costs $2.47/lb and have 52 calories per 100
grams (there are about 450 grams in a pound). A McDouble costs $.99 and
has 390 calories. If the average person were to consume all of your calories a year in apples
vs. McDoubles, what would be the difference in cost?
[365×2000cal×(100gm/52cal)×(1lb/450gm)=3120 pounds of apples. 3120lbs×($2.49/1lb)=$7769.
365×2000cal×(1McD/390cal)=1872 McDoubles. 1872McD×($0.99/1McD)=$1854. The difference is $5915 more for apples.]
1. What should be the relationship between weight and calories
consumed? Should weight increase as you consume more calories or decrease? Does
your model reflect that?
[The more calories you eat the more you should weigh, the
relationship should be a direct variation.]
2. Does your model seem reasonable, or does it suggest you
would be gaining or losing way too much weight or far too quickly?
[If students wrote the correct model it should seem
reasonable (within limits). One thing to point out to students is that this
model projects linear growth forever. In reality, weight gain might level off
after awhile or even increase more and more quickly.]
3. How much weight is she gaining each week, according to the
[1.43 pounds and 2.59 pounds (the slopes).]
4. What are reasonable boundaries for this graph? How can you
[Encourage students to think about how far into the future
their model would work. This is a judgment call. Have them look for obviously
unreasonable predictions about weight and then "back up" to a number
they think is reasonable. This will differ some from group to group.]
5. Do you think the weight gain predicted in Question 4 is
[It's probably high. At some point she would probably go on
a diet before she hit 900 pounds. As she gains weight she will need more
calories to maintain her weight, too, so it's probably predicting too much
1. Why might people choose to eat food like McDoubles over food
[It's cheaper and it still fills you up (see opening
2. If you consumed your regular number of calories (whatever
you needed to maintain your current weight) but then started stopping after
school to get a McDouble for a snack every day, how much weight would you gain
in one 180 day school year?
[Assuming "one school year" is 180 days, 390
calories per McDouble, that's about 70,200 extra calories, so around 20 pounds.]
3. You decide to start eating healthier, so you get the 6 piece
chicken nuggets now instead of the McDouble, which have about 250 calories. How
much weight will you gain if you eat those everyday after school?
[250 × 180 is about 45,000 extra calories, so around 13
4. The following year you quit eating fast food altogether
and start taking your dog for a walk for 30 minutes a day every school day, which burns
about 100 extra calories. How long will it take you to lose the weight you
[About two years to burn off the 20 pounds from the
McDoubles (you need to burn off 70,000 extra calories at 100 calories/day), and
about 1 year and 3 months (1.25 years) to burn off the 13 pounds from the
- What strategies did you observe students using to come up with the various models? What were the common errors you observed? How did you help your students without "giving them the answer"?
- Were students able to adjust their models or did it seem
like they were starting from scratch with each one? If they were not able to adjust their models, how would you change your instruction to help students see the similarities of the situations?
- How well were students assessing the reasonableness of their answers?
- Describe the quality of the student's graphs? Did they
label/scale axes? Was an appropriate scale chosen?
- Student weight is a touchy subject for students. Describe how you met the needs of those students who may have been uncomfortable with this lesson due to their being overweight. Were you able to identify the parts of discussion where students were uncomfortable? What would you do differently in the future to make this lesson objective and factual to help students analyze the information?