A vegan, or "strict vegetarian," may want to pay closer attention to the types of protein sources because plant based foods are incomplete proteins. That doesn't mean they don't contain enough protein, it means they don't contain all the essential amino acids. Combining different protein sources ensures an ample supply of all them.
A Little Amino Acid Chemistry
Let's talk about amino acids for a minute. Amino acids are the building blocks of protein. Your body needs them to make the protein structures that build and maintain the tissues in your body.
There are many different amino acids; they all have similar structures, but are differentiated by their side chains. All proteins, no matter what food they come from, are made up of amino acids. But the number and order of the amino acids that make up a cow's rump or a navy bean are different from the ones that make up your body parts.
When you eat round steak or baked beans (or anything that contains any protein at all, even a tiny amount), your digestive system breaks it down into amino acids that are absorbed into your blood stream. From there, the amino acids are used to build the proteins that make up your muscles, organs and lots of other tissues.
Back to Essential Amino Acids
Not all amino acids are essential. Your body can make many amino acids from the leftover bits of old amino acids and a few other raw materials found in the body, but there are some amino acids that the human body can't manufacture. These amino acids are called the essential amino acids because you have to consume them.
These are the essential amino acids:
Animal proteins all contain every single one of these essential amino acids, so they're called complete proteins. If you're an ovo-lacto vegetarian (you eat eggs or dairy products) you can get complete proteins when you eat the eggs or dairy products.
Plant proteins are a little different. Each plant that you eat has a different amino acid profile. For example, grains and cereals are extremely low in lysine. So low that they can't even be considered a source of lysine. If you only eat grains and cereals, you won't get enough lysine, and that's bad.
However, legumes such as peanuts, peas, dry beans and lentils contain a lot of lysine -- all the lysine you really need. On the flip side, legumes aren't good sources of tryptophan, methionine and cystine, but those amino acids are found in grains and cereals. As long as you eat some grains and some legumes, you'll get some of each essential amino acid.
Grains and legumes are called complementary proteins because when you combine them, you get all of the essential amino acids. Nuts and seeds are also complementary to legumes because they contain tryptophan, methionine and cystine.
You don't need to eat complementary proteins together at every meal. As long as you get a variety of proteins throughout the day, you'll get ample amounts of each amino acid. But, just in case you're interested, here are some ways to combine your complementary proteins.
Grains and legumes:
- Black beans and rice
- Pasta and peas
- Whole wheat bread and peanut butter
- Bean soup and crackers
Nuts and seeds plus legumes:
- Roasted nuts, seeds and peanuts
- Hummus (chickpeas and tahini)
- Lentils and almonds
Soy is the one plant protein that contains all the essential amino acids. It's also a good source of healthy fats and phytochemicals (plant chemicals that may be good for you). It's usually served as tempeh or tofu, and soy milk is a popular replacement for milk.More on Vegetarian and Vegan Proteins
- How to Get Protein on a Vegetarian Diet
- Is Nut Butter or Peanut Butter Better for You?
- Getting Enough Nutrients on a Vegan or Vegetarian Diet
- Seven Quick Tips for Vegetarian Health
- Simple Tofu and Vegetable Stir-Fry with Ginger
- Sun-dried Tomato and Walnut Penne Pasta
- Szechuan Style Chinese Noodles