Q: What is an “incomplete” protein?
A: When you hear that a food contains complete or incomplete proteins, this classification is referring to the kinds of amino acids in that food. Amino acids are the chemical compounds that make up proteins. Think of them like individual Christmas tree lights—when you string them all together you get protein.
There are two main classes of amino acids: essential and nonessential. It is essential that you get essential amino acids via your diet because your body cannot make them. Contrast this to nonessential amino acids, which your body can synthesize on an as-needed basis in addition to getting them via your diet.
When it comes to protein, all animal sources of protein will provide you with all the essential amino acids that your body needs. These are protein sources such as:
If you don't eat animal products, then you must get your protein from plant sources. The catch with plant protein sources is that they do not always contain all the essential amino acids in required proportions, making them incomplete proteins. Below are some plant protein sources that contain all the essential amino acids. [Tweet this list!] When looking at this list, it is important to consider the total amount of protein as well. While chia seeds do contain all the essential amino acids, one tablespoon of chia only contains three grams of protein.
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Finally here are common plant protein sources that are incomplete protein sources:
One of the first things nutrition students are taught with respect to people eating a plant-based diet is the importance of complimentary proteins. These are foods that alone are incomplete proteins, but when combined their amino acid composition is complimentary and you will get all your essential amino acids from a meal with that combination. The classic example of this is rice and beans. Rice is low in threonine, while beans are low in methionine and tryptophan. Combine them, and you get a delicious dish that has all your essential amino acids.
Complete Proteins, Incomplete Proteins, and Your Diet
Despite the fuss that is often made about complimentary proteins, it is important to recognize the context that is useful. In the American vegetarian diet, food choices are so varied and in such abundance that the lack of essential amino acids is rarely a problem. Especially when you also take into account the abundance of soy products consumed, preventing deficiencies in essential amino acids should not be a problem. And if you are a lacto-ovo-vegetarian, then you don't need to concern yourself with finding complimentary proteins for incomplete proteins, as the amino acid profiles for dairy protein and eggs are two of the best out there.
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In this case, as most, variety is key. Eating a variety of plant protein sources—not necessarily at one meal but throughout the day—is your best strategy. [Tweet this tip!] When you eat a meal or snack, take a couple seconds to identify the protein in your meal, and if you can't find any (complete or incomplete), then you have a problem.