Pass the Peas (Just Add Some Corn): Protein Quality 101 for Vegetarians

I am a failed vegetarian. 

I gave it a good 10 months, but my effort was doomed from the start. I was still exclusively breastfeeding my oldest daughter, getting no sleep, and did very little research before embarking on my meatless lifestyle (this was before dietetics school, obviously). 

Note to nursing moms: Never read Michael Pollan’s Omnivore’s Dilemma when you are sleep-deprived and emotional unless you are ready to go veg. You may never want to eat an animal again. 

I have total respect for vegetarians and may give it another try at some point. I think a well-planned vegetarian diet is one of the healthiest and most environmentally sustainable ways to eat. 

Lately, I’ve had many questions related to quality protein sources for vegetarians. Because of the circles I run in, most of these inquiries have come from either athletes or concerned parents, which is interesting because these are two populations that often need more protein than the standard recommendation for healthy adults. 

I do Crossfit, which often includes heavy weightlifting, 4 times per week. Protein is key in muscle building, recovery, and adaptation to exercise. Protein needs for athletes vary depending on the frequency and intensity of their workouts; however, many athletes need 1.2 grams or more of protein per kilogram of body weight per day (compared to 0.8 grams per kilogram of body weight per day for most adults).

Children often need a bit more protein than adults to support growth. Protein needs among healthy children are highest in infancy and decrease per kilogram of body weight gradually as the child ages. 

So here is the protein pickle vegetarians (and especially vegans) may encounter: The highest quality proteins are found in animal products, including meat, fish, dairy, and eggs. Quality proteins are those that include all nine essential amino acids—which are the building blocks of protein—in adequate amounts. 

The good news for vegetarians is that you can pair plant-based protein sources in specific ways to ensure that you are not missing out on essential amino acids. Proteins that are combined to create a quality protein source are called complementary proteins.

For example, white rice is too low in the essential amino acid lysine to be considered a quality protein. If you eat it with either corn or Cremini mushrooms, however, that combination of foods would yield a quality protein and better meet your body’s needs. 

So how do you know if a food is a quality protein? Magic? Telephone psychic? 

The internet, silly! I am a big fan of Self Magazine’s NutritionData website, which gives very detailed analysis of protein quality. Here’s how to see how your favorite plant proteins stack up: 

  1. Navigate to NutritionData
  2. Type in the food you want to look up in the search field located at the top right of the screen. Be as specific as possible. In this example, I will use frozen green peas. 
  3. Click on the option from the list that is closest to the one you are planning to eat.
  4. Scroll down to the box that says “Protein Quality.” The nine spokes represent each of the nine essential amino acids. If one of the spokes is not completely filled, then that amino acid is deficient in that food. A food that has an overall score of 100 or more is considered a complete or quality protein.

Our frozen peas have a score of 84, which indicates that they are not a complete protein. The limiting amino acid is methionine + cystine. If you are not familiar with the abbreviations on the graph, you will learn what they mean in step five (so read on!). 

5. This is where the site is really nifty. Rather than making you guess as to which foods might complement the food item in question, NutritionData makes it easy for you. If your food’s score is less than 100, just click on the link that says “Find foods with complementary profile.” At the top of the list, NutritionData provides the full name of the limiting amino acid. 

You can filter the results at the top to include only vegetable-based items, or to include dairy or egg products if you are a lacto-ovo vegetarian. If you create an account, you choose to show only items that meet your dietary preferences. 

hoosing a food from the complementary protein profile can help fill the gaps in your diet and ensure that your body has the tools necessary for growth, muscle development, muscle retention, etc. Just to finish out our example, one of the veggie options that NutritionData lists for peas is corn, meaning that if you mix your peas and corn, you will have a higher quality protein. 

retty cool, huh? 

Vegetarian readers, what are your favorite sources of protein? Did you learn anything about them by plugging them into NutritionData? Do you use another method to determine protein quality?