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Iron-Rich Foods: How to Get the Most Out of Them

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Did you know that your body needs a certain amount of iron in order to stay healthy? Iron can be found in much of what you consume each day. Almond flour—frequently used in cookies—is just one example of an iron-rich food. However, only a small fraction of the iron in food gets absorbed by the body, partially because the body can only absorb dissolved iron. In this project, you will study whether the acidic environment in your stomach helps dissolve iron. You will use a color-based chemical test to measure how fast iron from food dissolves in solutions modeling an empty stomach and a full stomach.


Areas of Science
Time Required
Very Short (≤ 1 day)
Material Availability
This science project requires an iron test kit, available from our partner Home Science Tools.
Average ($40 - $80)
The chemicals in the test kit could cause irritation if not handled properly. Be sure to wear gloves, safety goggles, and work in a well-ventilated area. Adult supervision is recommended. The small amount of sulfites contained in the iron indicator tablets may cause an allergic reaction in people who have asthma.
Sabine De Brabandere, PhD, Science Buddies

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Use a color-based chemical test to measure how fast iron from almond meal dissolves in solutions of different acidity, modeling an empty and a full stomach.


Iron is essential to most forms of life, and a key part in maintaining good health. In humans, iron helps the body carry oxygen in the blood and plays a key role in brain and muscle function. A deficiency of iron—meaning too little iron—can prevent enough oxygen from reaching different parts of the body that need it. Iron deficiency can lead to anemia, a blood condition characterized by symptoms like fatigue, pale skin color, and decreased immunity.

The amount of iron in your body is mainly regulated by how much iron is absorbed by your intestines from food you eat or supplements (such as vitamins) you take. Some foods—like beef, spinach, and almonds—are naturally rich in iron. Most breakfast cereals have iron added to them to make sure you get enough iron in your diet. They are usually labeled "iron-fortified". Figure 1 shows how the nutritional labels and ingredients list on packaged foods let a person know whether or not that food has iron in it.

Pile of nutrition labels
Figure 1. The content description of packaged foods informs us if the food contains iron.

The recommended daily allowance (RDA) for iron depends on age and gender. According to the National Institutes of Health Office of Dietary Supplements, healthy people between the ages of 9 and 13 should have an intake of 8 milligrams (mg)/day, boys between the ages of 14 and 18 should have an intake of 11 mg/day, and girls of that age should have 15 mg/day.

Only a fraction—around 5%–18%—of the iron a person eats will be absorbed by the body. The bioavailability of iron in food refers to how easy it is for the body to absorb the iron. Several factors can reduce or increase the bioavailability. Iron found in meat, poultry, and fish is two to three times more absorbable than iron found in plant-based foods, like almonds or spinach and iron-fortified foods like breakfast cereal. The absorption is also affected by the other types of foods or supplements eaten at the same meal. Taking a closer look at what happens to the ingested iron might help you make educated guesses about what enhances or inhibits the absorption of iron by the body.

Iron can only be absorbed by the body if it is dissolved, or broken down, in a liquid (solid iron moves on into the waste stream of your body). Just like any other food, ingested iron passes through the stomach where it is broken down before it enters the intestines, which is where it can then be absorbed by the body, as illustrated in Figure 2.

Simple diagram of the human digestive system with the esophagus, stomach and small intestine labeled
Figure 2. When you eat a piece of food, it travels from your mouth, down through your esophagus, and to your stomach. As the food continues to be digested, it travels through the intestines. This diagram shows only part of the entire digestive system.

The fluids in the stomach are very acidic, with a pH of around 1–3. The pH scale measures how acidic or basic a liquid is. A neutral pH is 7; distilled water is an example of a liquid with this pH. An acidic pH is below 7, examples being lemon juice or vinegar. For a refresher on this information, see the Science Buddies Acids, Bases, & the pH Scale. Getting back to how iron is dissolved in the body, the acidity in the stomach helps break down food and dissolve iron. Since the presence of food decreases the acidity of the stomach—or in other words, increases the stomach's pH—would the presence of food in the stomach also decrease the rate at which iron dissolves? In this science project, you will model an empty and a full stomach and measure how fast iron dissolves in these environments. After the stomach, iron moves on to the intestines, a pH-neutral environment.

To study how fast iron dissolves, you need a chemical test to indicate the presence of iron in a liquid. For this chemistry science project, you will use a colorimetric test for iron. In this type of chemical test, you add a specific chemical to a clear liquid to create an indicator solution. This chemical produces a bright red color in the presence of iron. If the indicator solution stays clear, you can conclude that no iron is present. Any change in color to red indicates the presence of iron. The greater the amount of iron in the solution, the bolder the shade of red will be. Comparing the color of the indicator solution with a graded scale on a color chart—as shown in Figure 3—will allow you to read the amount of dissolved iron.

Pink solution in a test tube next to a color chart used to measure iron content
Figure 3. In your colorimetric test for iron, you will compare the color of a solution with a graded scale on a color chart to figure out the amount of dissolved iron in the solution.

Note that the color scale of this iron kit indicates concentrations in parts per million (ppm). A value of 1.0 ppm of iron in a liquid is identical to 1 milligram (mg) of the iron present in each liter (L) of liquid. To measure how fast iron dissolves in the indicator solution, you will measure the time it takes for the indicator solution to reach a specific intensity of red after an iron-rich food item is added. If the solution turns bright red in a very short time, you know the iron dissolves quickly. If it turns red over a long period, you know the iron dissolves slowly. You will use almond flour in this science project, as almonds are rich in iron and the grinding makes the iron easier to dissolve.

Getting curious about how fast iron dissolves in an empty stomach versus a full stomach? Let us get started!

The iron test kit tablets contain a small amount of sulfites, in addition to the indicator molecule bipyridal. Sulfites are added to dissolve specific forms of iron that otherwise would not dissolve in water. They will slightly enhance the solubility of iron found in food, regardless of the acidity of your solution.

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Experimental Procedure

Important Notes Before You Begin:

Be sure to read the Science Buddies Chemistry Safety Guide before you begin. Follow the safety rules, below, while doing the tests:

  • Wear disposable gloves and cover all skin to prevent irritation from vinegar, or the chemicals bipyridal and sulfites, which are in the iron indicator tablets.
  • Discard gloves and wash your hands after performing the tests.
  • Work in a well-ventilated area.
  • Wear safety goggles while working with chemicals to prevent liquids in the test tubes from splashing into your eyes.
  • Note that the iron indicator tablets contain a small amount of sulfites, which may cause allergic reaction in people who have asthma. Details about the iron indicator tablets can be found in the kit manual.

Preparing Your Test

In this science project, you will test how quickly iron in almond flour dissolves in solutions of different pH levels to model how the iron dissolves in a control environment, a full stomach and an empty stomach.

  • A first solution will have a neutral pH (pH = 7). It is used as a control solution, to show the baseline for this science test. It will show how quickly iron dissolves if no acids are present. It is interesting to note that this is also an environment similar to the intestines. Distilled water from an unopened bottle has a pH of 7. When left exposed to air, distilled water will turn slightly acidic.
  • A second solution will have a medium acidity (pH around 4). This models the conditions found in a full stomach. You will dilute vinegar with distilled water to obtain this solution.
  • A third solution will be very acidic (pH around 2.4). This models the conditions found in an empty stomach. Pure vinegar will be used for this.
  1. Copy the following table into your lab notebook. You will use it to record your measurements.
 Amount of Iron
Dissolved in the Solution
Trial 1
Trial 2
Trial 3
(pH around 7)
.5 ppm     
1 ppm     
5 ppm     
Full Stomach
(pH around 4)
.5 ppm     
1 ppm     
5 ppm     
Empty Stomach
(pH around 2.4)
.5 ppm     
1 ppm     
5 ppm     
Table 1. Table in which to record the amount of time —expressed in minutes (min) —that it takes a certain amount of iron (expressed in ppm) to dissolve.
  1. Set up your work space:
    1. Choose a table or work space that will not be damaged by any accidental spills of water or vinegar.
    2. With the permanent marker, write "C" for "control" on your first test tube, "F" for "full stomach" on your second test tube, and "E" for "empty stomach" on the third test tube. Note that the kit contains one more test tube, which can be used in case one breaks.
    3. Set out three clean, empty drinking glasses, identifying each with a sticky note (≈ means "approximately"): one should read "pH ≈ 7 - Control", another should read "pH ≈ 4 - Full stomach," and the third should read "pH ≈ 2.4 - Empty stomach." These glasses will be used for your tests. You will need one more glass later to create a dilution of vinegar (see step 3, below).
    4. Put the corresponding test tube in each glass (tube C in glass "pH ≈ 7 - Control", etc.), and add a skewer to the drinking glass, as shown in Figure 4.
Three side-by-side champagne glasses, two glasses are filled with a test tube and wooden skewer
Figure 4. Drinking glasses hold the test tubes that will contain solutions modeling an empty stomach, a full stomach, and a control solution. The skewers will be used to mix the solutions. Note that the test tube for the control is not present in this figure.
  1. Dilute vinegar with water to create a liquid with a pH that is approximately 4.

    To make your work during the testing easier, you will create a liquid that contains 1 mL of pure vinegar mixed with 39 mL of distilled water. Scientists call this a 1 to 40 (typically written 1:40) dilution of pure vinegar.

    1. Use your graduated cylinder to measure 9 mL of distilled water. Transfer this water into the fourth, unlabeled drinking glass.
    2. Use your graduated cylinder to measure 10 mL of distilled water. Add this to the glass.
    3. Repeat step b. two more times so the glass contains 39 mL of distilled water.
    4. Use the pipette (medicine dropper) to add 1 mL of pure vinegar to the glass. This solution has a dilution of 1:40.
    5. Swirl the solution in the glass to mix this solution well.
    6. Put a sticky note on this glass reading "1:40 dilution of vinegar - pH ≈ 4."
  2. Optional: Measure the pH of your solutions.

    As the pH values we have quoted can differ slightly from the actual values in the liquids you use, it is best if you can measure the pH of your samples using pH strips, and quote your measured values on your science fair report. Details on how to measure the pH can be found in the Science Buddies resource Acids, Bases, & the pH Scale.

    1. Measure the acidity (expressed as pH) of the distilled water.
    2. Measure the acidity (expressed as pH) of the 1:40 dilution of vinegar created in step 3, above.
    3. Measure the acidity (expressed as pH) of pure vinegar.
    4. Write your measurements down in your lab notebook. Note: Your measured values may slightly differ from the quoted values in this description.

Testing How Fast the Iron Dissolves

You will need to perform three trials to gather enough data to make reliable conclusions. Before you start a trial, be sure you can make observations during the next 2.5 hours.

  1. Create the control (pH ≈ 7) indicator solution.
    1. Use the 10 mL graduated cylinder to measure 10 mL of distilled water.
    2. Transfer the water to the test tube marked with a "C."
    3. Add one iron indicator tablet to the test tube.
  2. Create the indicator solution modeling the environment of a full stomach.
    1. Use the 10 mL graduated cylinder to measure 10 mL of the 1:40 vinegar dilution created in the Preparing Your Test section .
    2. Transfer the vinegar dilution to the test tube marked "F."
    3. Add one iron indicator tablet to this test tube.
  3. Create the indicator solution modeling the environment of an empty stomach.
    1. Use the 10 mL graduated cylinder to measure 10 mL of vinegar.
    2. Transfer the vinegar to the test tube marked with an "E."
    3. Add one iron indicator tablet to the test tube.
  4. You just created three indicator solutions of different acidity levels. Wait 5 minutes to let the tablet dissolve completely in each tube. Use the skewer placed in the same glass to stir each solution a couple of times.
  5. Rinse your graduated cylinder several times with distilled water and let it dry.
  6. Important: You will need to add the almond flour (an iron-rich food) to each test tube (as described in steps 7–10, below) as quickly as possible, once the 5 minutes are over, and start timing so that the almond flour is in each test tube for the same amount of time, so remember to work fast for the next three steps.
  7. Scoop out 1/2 tsp. of almond flour, level it with a clean skewer—as shown in Figure 5—and use your clean funnel to transfer the almond flour to the test tube marked with a "C." Transfer any residual almond flour sticking to your measuring spoon or funnel to the test tube.
The side of a wooden skewer is used to level powder held in a measuring spoon
Figure 5. Leveling the content of a measuring spoon with the flat side of a skewer or knife allows accurate measurements.
  1. Repeat step 7, now adding almond flour to the tube marked with a "F."
  2. Repeat step 7, now adding almond flour to the tube marked with an "E."
  3. Immediately start your stopwatch.
  4. After a little less than 30 seconds (sec), compare each test tube with the color scale:
    1. Stir all three solutions. Always use the skewer that is sitting in the same glass as the test tube.
    2. Let the almond flour settle a little.
    3. Perform the following for each solution, one at a time:
      1. Compare the color of the solution to the color chart by holding the test tube in a well-lit space in front of a white background, as shown in Figure 6.
      2. Determine if the color in the test tube is identical to the color calibrated as .5, 1, or 5 ppm. If so, record the time in your table like Table 1. If not, it might need some more time and you can go on to the next step.
      3. Put the test tube back in its corresponding glass.
Pink solution in a test tube next to a color chart used to measure iron and copper content
Figure 6. The concentration of iron in the solution is determined by comparing the color in the test tube to a calibrated color scale.
  1. For the next 5 min, repeat step 11 every 30 sec. Remember to stir all three solutions and to let the almond flour settle a little before you compare with the color scale. Record the time in your data table if the color in the test tube is identical to the color calibrated as .5, 1, or 5 ppm.
  2. For the next 5 min after that, repeat step 11 every 1 min, again recording the time in your data table if needed.
  3. After about 10 min, you can increase the time between comparisons to 5 min for four comparisons and then to 10 min for the remaining time. Continue checking on the test tubes for a total of 2 hours after you added iron to the test tubes. (It might take 2 hours or more for a full stomach to empty.) Do not forget to stir before comparing colors and to record the time in your data table if the color in the test tube is identical to the color calibrated as .5, 1, or 5 ppm. Note:
    1. Your solutions might never reach the 5 ppm level, which is fine. If you prefer to change the test in order to increase the range of your measurements, consult the Frequently Asked Questions for advise.
    2. You might see one solution change color quickly while the others take a long time. These are interesting observations. Note them down in your lab notebook and move on with the test. While you are analyzing your data, think about what these measurements might mean for the bio-availability of the iron in the food. Hints can be found in the Frequently Asked Questions.
  4. Optional: At any time, you can take a picture of all the test tubes. Remember to show the labels on the test tubes and/or glasses in the picture. You should also consider adding a time indicator. You can then use these pictures to illustrate your science fair display board.
  5. Once you are done with the observations for this trial; empty your test tubes in the sink.
  6. Rinse all test tubes well with distilled water. Check the test tubes well for any residual almond flour sticking to the glass and clean it out.
  7. Use paper towels and a skewer to dry your test tubes.
  8. Discard the wooden skewers, as they might have absorbed part of your solution.
  9. This completes one trial.
  10. Repeat steps 1–20 for a second trial, and then one more time for a third trial.

Analyzing Your Results

  1. Calculate the average time it takes to reach a specific concentration of dissolved iron for each solution you tested.
    1. Start with the measurements for the control (pH ≈ 7) and concentration .5 ppm. To calculate the average, first add up the measurements for each trial and then divide the result by 3, as you performed three trials. Note the results down in your table like Table 1.
    2. Continue with the measurements for 1 ppm and, if available, for 5 ppm.
    3. Repeat steps a.–b. for the measurements for the solution modeling a full stomach (pH ≈ 4), and the solution modeling an empty stomach (pH ≈ 2.4).
  2. Make a line graph of the average time it takes to reach a concentration of .5 ppm for the different environments (i.e. the control, a full stomach, and an empty stomach). Put the environment on the x-axis (the horizontal axis going across) and put the average time (in minutes) on the y-axis (the vertical axis going up and down).
    1. You can make a graph by hand or make a graph using a computer program.
    2. Remember to add a title and label each axis.
  3. Repeat step 2 of this section for a concentration of 1 ppm and, if available, for 5 ppm.
  4. Look at your data table and graphs, and try to draw conclusions from your results.
    1. Do your measurements support the statement that iron dissolves faster in an acidic environment with respect to a neutral environment (the control)?
    2. Do your measurements show a different rate for different levels of acidity, like the very acidic environment of an empty stomach with respect to the medium acidity environment of a full stomach?
  5. Looking back at the Introduction, your research, and your data, try to answer the following questions:
    1. Do you think the iron in almond flour eaten after a big meal (such as in a full stomach) would dissolve as easily as when it is eaten on an empty stomach?
    2. Knowing iron can only be absorbed by the body in dissolved form, would having the almond flour after a big meal or on an empty stomach make it more or less easy for the body to absorb the iron?


For troubleshooting tips, please read our FAQ: Iron-Rich Foods: How to Get the Most Out of Them.

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  • In this science project, you used almond flour as the iron-rich food. Try using wheat germ, ground beans, or an iron-rich vegetable.
  • Iron is part of what makes vegetables, like spinach, green. If the iron dissolves in the cooking water or solution, the vegetable turns from bright green into a more yellow-green color. Test this by putting a cut-up vegetable (like baby spinach) into the indicator solution and measure how the color of the vegetable changes for different levels of concentration of iron in the solution. You can rate the color of your vegetable by comparing it to the color intensity in a color wheel used by artists, as shown in Figure 7.
Two plastic cups containing green paste sit above a color wheel
Figure 7. Comparing the color of a green vegetable with the color indications of a color wheel can help quantify color test results.
  • Several breakfast cereals are fortified with iron. Does iron in all breakfast cereal dissolve at the same rate? To compare, make sure you start with the same amount of iron in the test food. As an example, test a sugary flake cereal and use similar sizes of flakes for each test tube.
  • In this science project, you used vinegar to mimic the environment of a stomach, while the stomach contains a different type of acid, called hydrochloric acid. Would the type of acid play a role? Before you use hydrochloric acid, be sure to read the safety warnings on the bottle. More on how to model an artificial stomach can be found in the science project Calcium Carbonate to the Rescue! How Antacids Relieve Heartburn.

Frequently Asked Questions (FAQ)

If you are having trouble with this project, please read the FAQ below. You may find the answer to your question.
Q: How can I change my test so I use the full range of possible concentration measurements (up to 10 ppm)?
A: If the maximum concentration you measured is 1 ppm or 5 ppm, but you would like to make better use of the full range of your indicator solution, you might try the following:
  • Increase the amount of food used in the test (for example, from 1/2 tsp. to 1 tsp.), while keeping all other measurements the same.
  • Let the solutions sit for a longer time and measure the obtained concentrations after several hours. Do all of them level off at the same concentration?
Q: My food has a lot of iron. Why don’t any of my test solutions reach the 1 ppm, 5 ppm or 10 ppm concentration?
A: The indicator solution only measures dissolved iron, so the question becomes: why is more of the iron in my test food not dissolving? Below are some potential reasons.
  • Did you use a fine grind? Finer grinds allow the iron in the food to dissolve more easily.
  • Even if the label on the food you are testing shows it to be rich in iron, the type of iron in the food might not dissolve well in your solutions. The iron in the food might not be bio-available.

First, note your observation down in your data table, and ponder what it might mean for the bio-availability of the iron in the food you are testing. Then, consider the following options:

  • If you are using a coarse grind, consider grinding the food further, to a fine powder;
  • Try increasing the amount of food used in the test (for instance, from 1/2 tsp. to 1 tsp., while keeping all other measurements the same), which will increase the concentration levels so you can make clear measurements;
  • Opt to test a different food item or brand and see if the bio-availability is higher; or
  • Leave this as the outcome of your science project (after you have confirmed this result with several trials).
Q: Why do some of my test solutions never reach the 1 ppm, 5 ppm or 10 ppm concentration, while others get there quickly?
A: Some reactions of iron with the indicator solutions are slow. If you have a reaction that is having trouble getting to 1 or 5 ppm, while others are getting there easily, you may need to let it sit a while. If you are seeing a specific final level (1 ppm, 5 ppm, or 10 ppm) with some pHs, but not with others, then do not worry; just note that in your data table. This is an interesting observation worth noting.

Always think about what your measurements might mean for the bio-availability of the iron in the food.


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De Brabandere, Sabine. "Iron-Rich Foods: How to Get the Most Out of Them." Science Buddies, 20 Nov. 2020, https://www.sciencebuddies.org/science-fair-projects/project-ideas/HumBio_p043/human-biology-health/iron-rich-foods. Accessed 4 Mar. 2024.

APA Style

De Brabandere, S. (2020, November 20). Iron-Rich Foods: How to Get the Most Out of Them. Retrieved from https://www.sciencebuddies.org/science-fair-projects/project-ideas/HumBio_p043/human-biology-health/iron-rich-foods

Last edit date: 2020-11-20
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