Amino acids are well known as the building blocks of protein—substances necessary for most biological processes in the body. It’s for this reason that proteins, and the amino acids that form them, are considered crucial to our survival. Some amino acids can be produced by the human body and are therefore called nonessential amino acids, but the remaining essential amino acids must be obtained through diet. While animal protein has generally been considered the easiest (and best) way to get all the essential amino acids, if you’re vegetarian or vegan, it’s helpful to know that you can still get everything you need from plant sources—the trick lies in simply eating the right types of plant foods. So come with us as we break down the essential amino acids in vegetables and uncover what you need to know to make sure you’re getting the amino acids your body craves.
Protein Sources: Animal vs. Plant
When we think of dietary protein, most of us probably think of meat, fish, and dairy products. Our minds don’t naturally land on hemp seeds, kale, or whole grains. But while animal sources do contain higher levels of quality protein than plant sources, people who rely on animal-based sources of protein are also at greater risk of developing many of the diseases most commonly associated with the traditional Western diet, including:
- High blood pressure
- Heart disease
Moreover, a recent study indicates that the majority of Americans may actually be eating too much protein—and they’re getting the bulk of it from red and processed meats, both of which are associated with a higher risk of cardiovascular disease, cancer, and premature death.
What’s more, plant sources of protein, in addition to decreasing the risk of excessive protein consumption and chronic diseases, also offer additional health benefits that animal sources do not. Some of these benefits include:
- Improved gut health
- Immune system support
- Increased longevity
Complete vs. Incomplete Proteins
Animal-based proteins are considered complete proteins because they contain relatively high levels of all nine essential amino acids:
Yet many plant proteins are considered incomplete, as they lack or have low levels of one or more of these amino acids. Moreover, it used to be believed that to make incomplete proteins complete, they had to be consumed together to compensate for each other’s lack of amino acids. Many of us probably even remember our parents instructing us in these complementary proteins, such as beans and rice.
But according to the Academy of Nutrition and Dietetics, this entire thought process is actually flawed, as it’s been shown that an optimal amino acid profile is perfectly obtainable by eating a variety of protein sources over the course of a day.
Essential Amino Acids in Vegetables
If we take a look at some of the best sources of plant-based protein, nine of the top contenders are:
- Chia seeds
- Hemp seeds
Although every plant on this list isn’t universally considered a vegetable, deciding whether something is a fruit, vegetable, or something entirely different isn’t always straightforward. So, with this in mind, we’re going to omit the true nuts and seeds from our discussion and keep the legumes—but don’t forget the importance of all these sources when it comes to your actual diet!
The starchy vegetables, which include potatoes, taro root, and corn, may not contain complete proteins, but they do deliver more protein than you might think. For example, a large baked russet potato with the skin on contains 7.9 grams of protein, while a cup of cooked taro root has 5.7 grams and a cup of corn dishes up 5.4 grams.
The starchy vegetables also furnish all nine essential amino acids, but many contain lower levels of lysine and the sulfur-containing amino acid methionine.
As the term “sulfur-containing” suggests, the amino acid methionine helps increase the uptake of sulfur, but it also aids in the absorption and bioavailability of selenium and zinc and the removal of heavy metals.
Lysine is the second most abundant essential amino acid in muscle protein and is a necessary component of immune, bone, and cardiovascular health. Lysine is also a precursor of the amino acid carnitine, which is responsible for delivering fatty acids to the mitochondria—the so-called powerhouses of the cell—for use as energy.
The protein-rich legumes, whose members include beans, peas, and lentils, help pick up where the starchy vegetables leave off. For instance, several varieties of beans, including kidney beans, black beans, and garbanzo beans, can conceivably furnish a full day’s supply of lysine. However, like the starchy vegetables, the legumes also tend to contain lower levels of methionine.
Green Leafy Vegetables
While the leafy greens also contain relatively high levels of protein, they tend to contain higher levels of the amino acids leucine, phenylalanine, threonine, and tryptophan.
Phenylalanine is a precursor of tyrosine, which is itself a precursor of neurotransmitters and thyroid hormones. Leucine is important in muscle building, while threonine is essential for nervous system health and tryptophan is needed for the production of niacin, melatonin, and serotonin.
The cruciferous vegetables, such as cauliflower and broccoli, also have high levels of protein and tend to contain higher quantities of isoleucine and valine, which are important for hemoglobin synthesis and regulation of blood sugar and energy levels (isoleucine) and muscle growth and tissue repair (valine).
The marrow vegetables include pumpkin and zucchini and are rich in leucine, isoleucine, phenylalanine, threonine, and tryptophan.
The stem vegetables include celery and asparagus and are relatively high in tryptophan.
The allium vegetables include onions, garlic, and leeks. Because this group of vegetables is high in sulfur, it actually contains relatively high levels of methionine, in addition to tryptophan.
Plant-Based Complete Proteins
Among plant-based protein food sources, both quinoa and soy contain high levels of all nine essential amino acids—hence, their designation as complete proteins. But as we’ve discussed, the term “complete” is now considered misleading, so while including quinoa and soy in your diet is certainly not a bad idea, it’s still possible to achieve a complete amino acid profile through other sources.
As you can see, Americans who choose to eat a plant-based diet don’t need to fear that they’ll end up deficient in protein and amino acids as long as they are including a diverse array of high-protein plant sources in their diets. Even so, several factors can affect the nutritional profile of any food, including soil quality and the method of storage and food preparation.
Which is why, in addition to eating a healthy diet and aiming for both variety and adequate calories, you may want to consider supplementing with essential amino acids to make sure you are obtaining all the different amino acids your body needs.
Essential amino acid supplements enhance your muscle strength and mass and provide benefits that even the highest quality dietary proteins cannot. But single therapy supplementation, such as with lysine, won't meet your protein needs. All amino acids need to be present in their optimal amount for supplements to be truly beneficial.