Summary

In this lesson, students will learn about the chemistry of dietary fats in the food they eat. They will calculate the number of calories coming from fats, carbohydrates, and proteins based on a food label before completing a guided activity focused on investigating the chemical structures of different types of fats. Students will then engage in a literacy component where they will use an article about the biological role of various types of dietary fats and foods to answer a series of questions.

Grade Level

High School

NGSS Alignment

This lesson will help prepare your students to meet the following scientific and engineering practices:

• Scientific and Engineering Practices:

• Using Mathematics and Computational Thinking
• Analyzing and Interpreting Data
• Obtaining, Evaluating, and Communicating Information

Objectives

By the end of this lesson, students should be able to:

• Recall and apply the appropriate conversion factors to determine the amount of energy that is derived from given amounts of fats, carbohydrates, or protein.
• Distinguish between saturated and unsaturated fatty acids (including monounsaturated and polyunsaturated fatty acids) given a drawing of the structure.
• Identify foods that are high in unsaturated fats and foods that are high in saturated fats.

Chemistry Topics

This lesson supports students’ understanding of:

• Conversion factors
• Dimensional analysis
• Energy
• Structure of organic molecules
• Covalent bonding

Time

Teacher Preparation: 15 minutes
Lesson:

• Part 1, “Chemical Structure of Fatty Acids”: 45-60 minutes
• Part 2, “Food, Fats, and Health”: 30 minutes

Materials

• “Chemical Structure of Fatty Acids” handout (Part 1)
• Food labels from any food (ask students to bring labels, also have a teacher-provided selection)
• “Food, Fats, and Health” handout (Part 2)
• Access to Mayo Clinic article “Dietary fat: Know which to choose” (online or printed copies)

Safety

• No specific safety precautions need to be observed for this activity.

Teacher Notes

• This lesson consists of two parts:
  • Part 1, “Chemical Structure of Fatty Acids,” has students compare the energy content of fats to that of carbohydrates and proteins. Then, it introduces students to various conventions used when drawing organic molecules and has them compare chemical structures of saturated and unsaturated fatty acids.
  • Part 2, “Food, Fats, and Health,” has students answer questions based on a Mayo Clinic article, “Dietary fat: Know which to choose,” that describes how different kinds of fats affect your health and lists foods in which these nutrients can be found.
• The role of fats in human health and nutrition is very complex and new studies regularly add to our understanding of this topic. This classroom resource provides an overview of the general chemical structures of various types of fats, the role they play in the body, and the food sources that contain them, but it is not a substitute for professional medical advice. It is provided for general informational and educational purposes only. Please consult with the appropriate professionals before taking actions based on the information referenced in this resource.
• Anything pertaining to food is very relatable for high school students, which can make for great discussion, but keep in mind that discussion of fats could be a very difficult topic for students who may struggle with body image issues or eating disorders, or know people who do. Be sure that the material is presented in a scientific and non-judgmental way, and perhaps consider consulting with the school counselor prior to using this lesson.
• In this resource, students are looking at individual fatty acid molecules, rather than fats in the triglyceride form, to allow them to focus on the degree of saturation of one fatty acid at a time. The lesson could be extended to cover triglycerides in more detail if desired.
• Here are a few other resources with background information on diet, nutrition, fats, and health:
  • The Mediterranean Diet, from the Cleveland Clinic
  • Do Fats Make You Fat?, from the Cleveland Clinic
  • Dietary Guidelines for Americans, 2020-2025, USDA
    • MyPlate.gov is a resource that helps plan and track healthy meals

Part 1

• Students should work in small groups for Part 1, with the teacher circulating the room as they work. Students should check in with the teacher as indicated in the student handout – this may go fairly quickly if students are confident doing unit conversion calculations and/or have already been exposed to organic molecular structures before, or it may take longer with a bit more teacher guidance if these concepts are new to them.
  • Check-in points are indicated after questions 10 and 16, which you could do as a full class or by circulating among the small groups. If you wanted students to check in more frequently, you could add this instruction after questions 15 and 19 as well.
• Prior to using this lesson, students should be at least somewhat familiar with valence electrons, Lewis structures, covalent bonding, molecular shapes, and intermolecular forces to be able to understand the structural differences between saturated and unsaturated fats.
• This lesson uses the unit of “calorie” to represent the amount of energy in foods, since many students are more familiar with this unit in the context of food. If preferred, kJ could be used instead, as this unit is used more often in a thermochemistry context.
• The sample problem in the student worksheet (question 3) is designed to be completed as a whole class or in small groups, depending on how independent the students are with mathematical problem solving. That problem intentionally uses equal amounts (by mass) of fat, carbohydrate, and protein. When students calculate the calories associated with each nutrient, they should note that the calorie content is not evenly distributed, since 1 g fat has more than double the number of calories as 1 g protein or 1 g carbohydrate.
• If students are really struggling with the math, then you can use a pie chart visual to help explain proportional reasoning. If you round the “1 g fat = 9 cal” down to 8 cal to make the numbers work out more evenly, you have a very nicely divided pie chart into ½, ¼, and ¼ (see below). Since the 9 calories that come from fat is slightly larger than the 8 calories shown on the pie chart, the amount of energy (calories) coming from fat must be slightly greater than 50%.

• If you do not want to cut out food labels or have students bring in their own for question 5, you could create your own food labels for students to analyze using a free nutrition label generator.
• In question 11, a molecular structure is provided. (For your reference, it is capric acid, also known as decanoic acid.) You could remove it from the student document and have students copy it themselves from a reference image if you prefer.
• The zig-zag shape of the hydrocarbon chain in questions 11-15 could be easier for students to visualize if they could see a 3D molecular model – either a virtual model made with a free program such as MolView or a physical one made from a model kit.
• Be sure that students know that the drawings in questions 11-15 all represent the same molecule – all the hydrogens and carbons are still understood to be there even if they aren’t written explicitly. (You could introduce the term “implicit hydrogen.”) You might also remind them that when there is a double bond between two carbons, there are fewer hydrogens attached to those carbons. Depending on how familiar students are with interpreting skeletal structures of organic molecules, they may need more guidance from the teacher on these questions, as well as questions 16-18. If this is the case, consider using the AACT activity Naming Alkanes beforehand.
• Virtual or physical models could also be useful in helping students visualize the more bendy shapes of unsaturated fatty acids in questions 16-18.
  • Note that all the fatty acid molecules in question 18 have 18 carbon atoms, so students can compare them based on the shape of the molecule and number of double bonds. (The acids in 18a.–d., respectively, are oleic acid, α-linolenic acid, linoleic acid, and stearic acid.).
  • You could also ask students to compare melting points of monounsaturated fatty acids with different chain lengths or different double bond locations, saturated fatty acids with different chain lengths, etc. Students would likely have more trouble comparing molecules with multiple differences, such as a 16-carbon polyunsaturated fatty acid vs. a 10-carbon saturated fatty acid, but this could lead to great debate for more advanced students.

Part 2

• Part 2 could be completed as a homework assignment if class time is limited.
• There are a variety of ChemMatters articles that are related to these topics and could be used to supplement this lesson (see some examples listed below). The questions in Part 2 could be adapted to suit one (or more) of these articles if these would be more approachable for students than the suggested Mayo Clinic article.
  • Weighing in on Calories
  • The Big Reveal: What’s Behind Nutrition Labels?
  • Double, Double, Oil and Trouble
  • The Skinny on Fats
  • The Protein Myth: Getting the Right Balance

Extensions

• There are many adjacent topics that could be used to extend this lesson. Some related topics that students could investigate include:
  • Fatty acid nomenclature (delta vs. omega numbering, omega-3/omega-6 fatty acids, etc.)
  • The difference between “food” calories and “physical science” calories (1 food calorie = 1000 calories = 1 kilocalorie or kcal)
  • Recommended ratios of monounsaturated fat to polyunsaturated fat
  • Bond angles and hybridization (120° bond angles in sp² vs. ~109° bond angles in sp³) and how this affects the shape of unsaturated fatty acid molecules (relates to question 16 in Part 1)
  • Foods that are good sources of proteins and carbohydrates (since most of this activity focuses on fats) and the role of these nutrients
  • The biological role of micronutrients, such as vitamins and minerals; or subtypes of macronutrients such as fiber (a carbohydrate) or cholesterol (a fat)
  • Before our body breaks them down into individual fatty acids, most of the fats we eat are in the form of triglycerides, which are formed by a combination of three fatty acid molecules connected to a glycerol molecule backbone
  • The history of trans fats