Key concepts
Math
Biology
Food
Nutrition
Macronutrients

Introduction
Food advertisements and labels bombard us with enticing slogans and attractive images, luring us into consuming a certain food. But have you ever wondered how nutritious an advertised food is? Have you ever examined a nutrition facts label and wondered what the columns of words and numbers really meant? This activity will shed some light on the label. You will explore serving sizes and nutrients—and might find a discrepancy. Why would the sum of the nutrients not always add up to the total? Like a detective, you will gather the facts, brainstorm ideas and find evidence to support your proposed explanation. Can you crack the case?

Background
Food laws and regulations have been around for centuries. Their initial goal was to deter misbranding food, such as labeling and selling honey diluted with cheap corn syrup as pure honey. The mandatory U.S. nutrition facts label that we know today is a result of the 1990 Nutrition Labeling and Education Act. It informs consumers about what is in their food by listing serving size (the amount of food usually consumed at one time) and basic per-serving nutritional information including calorie (energy) content, essential vitamins and minerals, and recommended daily amounts of key nutrients. All of this information can be used to make informed decisions when deciding what to eat.

Foods mainly consist of fat, carbohydrates and protein. These are called macronutrients.

—Fats can enhance flavor and texture. Health experts advise you to avoid saturated and trans fats. That said, some fats, especially unsaturated fats, are an essential part of a healthy diet. As an example, they support healthy nerve and brain function.

—Carbohydrates are the sugars, starches and dietary fiber in our foods. Sugars and starches provide us with energy; fiber promotes healthy bowel function.

—Proteins are needed to build and repair the body. They are an essential part of a healthy diet, but consuming too much protein can damage the kidneys.

The other nutrients listed, such as vitamin A, iron, calcium, etcetera, are called micronutrients. Although they are present in much smaller amounts, they play an important role in a healthy diet. For easy reference, the labels show the percent daily value for most nutrients. This refers to the portion of the daily recommendations for this nutrient one serving provides.
 

Materials

  • Nutrition facts labels from a:

—dry food item, such as bread, crackers, etcetera

—a nut butter or dairy butter

—a moist food item, such as yogurt, canned fruit or vegetables, etcetera

—a water bottle

  • Additional nutrition facts labels (optional)
  • Calculator (optional)

Preparation

  • Gather all of your nutrition facts labels in one place. What do you think you might discover by comparing the foods you have selected?

Procedure

  • Read at the nutrition facts label of a dry food item such as bread or crackers. Can you find the mass of one serving of this food item? This will probably be measured in grams or ounces. (One ounce is about 28 grams.)
  • Skip the calorie information and go straight to the list of macronutrients: Total Fat, Total Carbohydrates and Protein. These are the nutrients that make up the bulk of our food.
  • Fats often enhance flavor and texture. Consuming them in limited amounts is essential for health. Can you find the mass (in grams) of fat one serving of this food contains?
  • Jump to the Total Carbohydrates. Carbohydrates are mainly found in plant-based foods like grains, fruits and vegetables. Our bodies break these down into sugar that provides us energy or into fiber that keeps our bowels healthy. Can you find the mass (in grams) of carbohydrates in one serving of this food?
  • Find the last macronutrient, Protein. Your body needs protein to grow and repair essential parts like muscles, bones and blood. Can you find the mass (in grams) of protein in one serving of this food?
  • Check if it all adds up. If you add the masses of fat, carbohydrates and protein in one serving, is this sum (almost) identical to the mass of one serving of this food? Why do you think this is the case?
  • Note: Other nutrients such as sodium (salt) might be listed as well. Their mass per serving is usually expressed in milligrams (mgs). There are 1,000 milligrams in a gram, so although these nutrients are important for a healthy diet, they do not add much mass to a serving of food.
  • Look for a nutrition facts label of nut or dairy butter. Can you find the mass of one serving of butter?
  • Next, look for the total masses of fat, carbohydrates and protein contained in a serving and add them up. Is the sum (almost) identical to the mass of one serving of this food?
  • Look for a label of yogurt or canned fruit or vegetables and repeat previous step. Are you surprised about the result?
  • Analyze a few more nutrition labels from different types of food. What do you notice? Does the sum of the masses of macronutrients (fats, carbohydrates and protein) in a serving match the total mass of a serving in some cases and not in others? Why would that be?
  • Group the foods where the sum is close. Do these food items have anything in common? Make a second group where the sum does not match. Do these food items have anything in common? Could there be something missing on the label that is absent in the first group but present in the second?
  • Get into a detective mode. Can you see a pattern? Can you come up with an explanation for what you noticed? Which cases support your explanation? Can you think of other food items that, when analyzed, could provide evidence for or against your explanation?
  • Look at the nutrition label of a water bottle. The serving size will probably be expressed in milliliters (mls) or ounces (ozs.). Can you analyze this label, knowing that one milliliter of water weighs one gram? How does the sum of the masses of macronutrients in a serving of water match up with the total mass of a serving of water? Does this support or refute your explanation?
  • Extra: Group foods that provide either lots of fats, carbohydrates or protein. Do some foods belong in two or even all three groups? Do some foods belong in none of them?
  • Extra: Rank your foods from smallest to largest serving sizes. Are you surprised about the variety in serving sizes?
  • Extra: Pick a food item you eat frequently and weigh out one serving as listed on the label. Is what you usually eat more, less or about the same as the serving size? Repeat for other food items. Do you observe a pattern in the mismatches in serving size and what you usually eat?
  • Extra: Nutrition facts labels list nutritional content per serving. Can you calculate nutritional content per 100 grams instead? For example, divide the amount of fats per serving (in grams) by the serving size (in grams). This will give you the amount of fats per gram of the food. Multiply this by 100 to get the amount per 100 grams of food. Now rank your foods from highest to lowest fats per 100 grams. How does this ranking compare with ranking by fats per serving? Which ranking would be more useful for consumers who are looking for food high (or low) in fats? Repeat for carbohydrates and protein.
     

Observations and results
Did you notice that for some food items, the sum of the masses of macronutrients (fats, carbohydrates and protein) in a serving is very close to the mass of one serving whereas for others it is not? This occurs because water has mass but contains no macronutrients.

Although consuming enough water is essential, it is not listed on the nutrition facts label. Thus, the water content of food influences its mass but not its nutritional content. Foods containing water will have servings that weigh more than the sum of the masses per serving of the three macronutrients. The mass discrepancies you observed informed you about the water content of the food items. The more water they contained, the bigger the discrepancy.

Listing nutritional content per serving allows consumers to compare different types of food at a glance and identify which provides more of a nutrient per serving. Pay attention to serving sizes though! You might find that you usually consume way more or way less than the listed serving size, making these comparisons a little trickier.

More to explore
How to Understand and Use the Nutrition Facts Label, from the U.S. Food and Drug Administration
Kids Corner, from Nutrition.gov
Burning Calories: How Much Energy Is Stored in Different Types of Food?, from Science Buddies
Get the Iron Out—of Your Breakfast Cereal, from Scientific American
Science Activities for All Ages!, from Science Buddies

This activity brought to you in partnership with Science Buddies

Science Buddies