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Dietary fats and BMI

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  • SL Core /
  • Molecular biology: Activities for Learning/
  • Dietary fats and BMI

Dietary problems and BMI

In November 2013, the U.S. Food and Drug Administration (FDA) required the U.S. food industry to completely phase out artificial trans-fats. Why did they do this? This lesson looks at how we modify molecules like fatty acids in the production of food. What is the evidence that trans fats are dangerous in the diet and how can we evaluate the quality of these studies?

Linked to the problem of dietary fats, how do we measure the build up of fats in the human body. Students will use two methods to calculate their own BMI and then evaluate the two methods scientifically.

Lesson Description

Guiding Questions

What foods contain saturated and unsaturated fat?

What is the difference between Cis and Trans fat?

What makes a reliable scientific study about food or health?

Activity 1 - Trans fat - and you thought lard was bad!

Watch the first 20 minutes of this video lecture and keep brief notes of the main points relevant to this topic on the worksheet below.

Use this Trans fat - student evaluation sheet. to make notes while watching the lecture. Click the eye icon to display it.

Activity 2 - Want to find out more about cis-fatty acid and trans-fatty acid?

Both of these fats are unsaturated. Unsaturated fats are more fluid and less likely to stick in our arteries, so why the worry?

Read more from these faty acid weblinks. Use the evaluation form to decide how reliable each source you read is.

Cis-fatty acids

Trans-fatty acids
Health Effect Generally good for health unless consumed in unreasonably high quantities.

Detrimental — lowers good cholesterol and increases the level of bad cholesterol in the body. Increases risk of heart disease.
Occurs naturally Yes While some natural trans fats occur in meat and dairy products, the majority of trans fats come from processed foods (i.e., hydrogenated oils).
Arrangement of atoms The chains of carbon atoms have hydrogen atoms on the same side of the double bond, resulting in a bend. Hydrogen atoms are on the opposite side of the double bonds of the carbon chain, making the fat molecule straight.
Melting Point Usually low. Some cis fats are liquid at room temperature. Usually high. Trans fats, like saturated fats, are solid at room temperature.

Activity 3 - Evaluating a practical research method.

Calculate you BMI using the Wolfram Alpha BMI calculator below, then use the nomogram below to work out your BMI. .
(pop ups will need to be enabled in your browser)

*

This nomogram can be used to calculate BMI - join your height to your weight with a line and read the resulting BMI

Question

  1. Scroll down the results page of the Wolfram calculator (which pops up) to see what your BMI value means.
    Describe the conclusion you can make from your BMI?
  2. Compare your BMI to the BMI values of other people.
  3. Which of the methods of calculating BMI values is the most precise?  Try to explain why.

    The peer review process for scientific publications includes an evaluation of the methods used in the study. Many factors are considered including:

    • The quantity of data in the data set
    • The length of the study
    • The way the data are selected - do they cover an appropriate range of ages genders etc.

    It also includes an evaluation of:

    • The technique used to measure the data.

Teachers notes

This activity is a nice way to bring the theoretical biochemistry back to real examples from everyday life.

The lesson could begin with a discussion of the student's favourite snacks and these could be compared to food products containing trans fats. Fast food restaurant chip and fried meats are a rich source of trans fat.

In these resources there are no strong examples of evidence that trans fats are not harmful. There is some suggestion that the effects of saturated fats on women is very different from it's effect on men in the Wall street journal article.

Activity 1: It is only necessary to watch 20 minutes of the lecture, but the end of the lecture and the disscussion are really quite relevant and interesting. Students could complete the video at home, or the BMI calculating activity could be left out to allow time for students to watch the whole video.

Activity 2 Want to find out more? could be used to consolidate the evaluation of scientific claims, or it could be used as a homework task.

Activity 3 The nomogram could be printed or used on a whiteboard with a metre ruler.

Discussion of the results of the BMI value calculated could involve more than just mention of the problems of trans fats and obesity, it is equally possible to use BMI walues to identify people who are under weight.