Good and Bad Lipids (page 2)

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Author: Michael Calhoun

Research Questions

  • What is a lipid?
  • What is the difference between a saturated and an unsaturated fat?
  • Why is tincture of iodine a good indicator to use to test for the presence of unsaturated fats?
  • Which of the tested lipids has the least number of double bonds?
  • Which oil has the most number of double bonds (required the most number of iodine drops)?
  • Based on the degree of saturation which lipid is a better choice to spread on food, butter or margarine?
  • Which oil do you think is the healthiest?
  • What was the control for this investigation and why was it chosen? 

Terms, Concepts and Questions to Start Background Research

Lipids, fats, oils, glycerol, fatty acids, triglyceride, saturated fatty acid, unsaturated fatty acid, and Tincture of iodine

Experimental Procedure

  • Put on gloves! Get the following supplies, test tubes, graduate cylinder, Tincture of iodine in a dropper bottle, vegetable oil, distilled water, butter, margarine, fish oil, olive oil, corn oil, and sunflower oil.
  • Allow the solid fats to melt into liquids. The butter and margarine will melt just by placing them in the warmth of the radiant heat produced by sunlight.
  • Place about 10 ml of each test oil and fat into separate test tubes. Prepare a control by pouring 10 ml of distilled water into a test tube. 
  • To each tube slowly and carefully add Tincture of iodine drop by drop, shaking the tube after each addition.

  • If the iodine changes from brown to clear the lipid is unsaturated. If the iodine does not change colors the lipid is saturated. Record the results in a table similar to the one shown.
Test Sample Name
             Saturated or Unsaturated

Olive oil


Fish oil


Corn oil


Sunflower oil

Vegetable oil  
  • For the lipids that are unsaturated, the degree of un-saturation can be determined by placing 10 ml the unsaturated lipids into clean tests tubes.
  • To each tube slowly and carefully add the Tincture of iodine drop by drop, shaking the tube after each addition.
  • The iodine should be added just until the point when it changes from a brown color to clear. Record the number of drops needed to bring about full de-colorization.
  • The number of drops required to turn the iodine clear indicates that all the double bonds in the oil and/or fat have reacted with the iodine.
  • For a more scientifically accurate investigation the entire processed should be repeated twice more. Record the results in a table similar to the one shown below.
    Unsaturated Lipid

                                  Iodine Number

Sample Name

 Trial 1
 Trial 2
 Trial 3
        Average of Trials

(Olive oil, example)

  • The degree of lipid saturation for the samples tested can be displayed in graphical form. Using the data in the table plot a bar graph of the average iodine discoloration numbers along the to the Y-axis verses the names of the various unsaturated lipids along the X-axis.


Title: Complete Fats and Oils Book, Author: Lewis Harrison, Publisher: Avery Press, ISBN-10: 0895297051 and ISBN-13: 978-0895297051

This book explains the differences between “good” and “'bad” fats, describes their connections to diseases and cholesterol levels. Also covered are details on buying foods, cooking with oils, and using fats and oils properly. 

Title: Fat Chance: Surviving the Cholesterol Controversy and Beyond, Author:  Dennis Willmont, Publisher: Willmountain Press, ISBN-10: 0974125733 and ISBN-13: 978-0974125732  

This book explains and demystifies fats and oils and the different terms used for them. Fats and oils are then discussed in relation to relevant disease categories including liver, heart, and circulatory disease.

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