When you think about protein, you probably worry about getting enough to repair muscle tissue after a tough workout, to help your body build lean, strong muscles and lose weight while boosting your natural calorie burn. All that's true but protein also serves another critical function in the body: It helps power your immune system, stoking the cells that you need to fight off infection, both bacterial and viral, and keep your guard up against illness of all kinds.

Protein plays an important role in powering your body's T-cells, the agents that go out and attack opportunistic invaders that can get into your bloodstream and cause infection, and if you lack adequate protein intake, it can impair immune reaction, studies have found. A diet low in protein leaves you open to fatigue, weakness, and low immune response, all the more reason you need to get your essential amino acids from the food you eat (which is better than supplements). Meanwhile, your body is just as happy to get its full complement of protein from plants.

The protein you eat helps repair tissue and fight off viral or bacterial infection

Proteins make up the framework of your cells, including the cells of the immune system and just about every other. But you don't have to worry if you're eating mostly plant-based foods, since the source of protein is less important than getting a full array of essential amino acids, specifically the 9 ones your body can't make enough of on its own.

In rare cases of protein deficiency (very seldom in a healthy US population other than those patients being treated with chemo), your immune system can stall, but the more frequent scenario of eating too much protein can also dampen down your immune system by overtaxing your kidneys, which can't flush it fast enough. Americans, while obsessed with eating enough protein, are likely to eat too much, according to experts. On average we eat up to twice as much protein as they need, about 100 grams a day when 60 is closer to the average that most people should get. The latest studies show that the right amount of protein is critical for your immune system to be healthiest.

In hospitals where patients lack appetite and treatments can zap their immunity, especially when someone is on chemotherapy for cancer, they are often given arginine, an amino acid that contains the most nitrogen of any, and has been shown to help boost immunity and speed up healing, according to the latest research. Another amino acid, glutamine, travels in your blood cells to offer your intestinal cells curative effects, which can prevent microbial contamination from the food you eat. But for most of us, supplements are not the answer, a healthy diet with a variety of vegetables, grains, legumes, fruits, nuts, and seeds will do it.

How much protein is the right amount to support a healthy immune system

“The truth is that most Americans, including vegetarians and vegans, consume more than enough protein to help support basic physiological demands, and consuming more protein than you need won’t ‘boost’ your immune system," says Katie Mikus, Manager of Scientific Affairs for Glanbia, which makes a plant-based supplement called Gold Standard 100% Plant. "Most healthy adults should aim to get around 0.8 to 1.2 grams of protein per kilogram body weight per day –or roughly 55 to 80 grams of protein a day for a 150 lb adult."

For the right amount of protein for your size, activity level, age, and gender, check out this handy calculator.   "Those looking to build or maintain muscle mass may wish to consume as much as 2.2 grams of protein per kilogram body weight per day,” she adds.

What are the best sources of plant-based protein?

When it comes to protein quality, look for protein sources that are easily digested and contain all 9 essential amino acids. Essential amino acids are those that must be consumed through whole foods or supplements because the body cannot make sufficient quantities to meet demand.

The richest plant sources of proteins tend to be legumes like soybeans, chickpeas, and beans and whole grains like quinoa and amaranth as well as certain vegetables, nuts, seeds and fruit. For a complete list of the best sources of plant-based proteins, see the 20 top vegetables for protein, compiled by The Beet.

Incomplete proteins versus complete proteins, and how to get what your body needs

Many plant-based proteins are "incomplete," meaning they lack one or more of the 9 essential amino acids your body can't make on its own. "Complimentary incomplete plant proteins can be combined to create a complete protein. For example, grains tend to be low in lysine and high in methionine and cysteine, whereas legumes tend to be high in lysine and low in methionine and cysteine," Mikus explains. "So combining rice and beans will give you a complete protein, or peanut butter and whole wheat bread are examples of complementary proteins that make a complete protein when eaten together."

Complimentary plant proteins don’t necessarily have to be eaten together as long as you consume protein from a variety of plant sources throughout the day. For more on how to get your complete proteins, see The Beet's story on perfect plant-based proteins.

Complete proteins are found in these plant foods:

  • Miso (32 grams per cup)
  • Tempeh (31 grams per cup)
  • Tofu (with 10 grams a cup)
  • Edamame (17 grams per cup)
  • Amaranth (9 grams of protein per cup)
  • Quinoa (8 grams per cup)
  • Buckwheat (with 5.7 grams of protein per cup)
  • Ezekiel bread (4 grams of protein and 3 grams of fiber per slice)

But rather than worry about getting all 9 essential amino acids at one sitting, simply eat a varied plant-based diet throughout the day and your body can take care of the rest. One easy way is to combine rice and beans, but you can also just make sure to get a variety of plant-based foods and be sure to include legumes like chickpeas in your lunch salad. You don't have to eat all the building blocks at once, as nutritionists once thought since your body has the extraordinary ability to assemble them into the necessary proteins to operate at peak performance.

How can you create a perfect meal or day of eating for the best immunity?

Eating to support a healthy immune system is as simple as following the basic principles of healthy eating. Your best bet: Consume a variety of foods and try to fill half your plate with fruits and vegetables, and make at least half of the grains you eat whole grains.  Try to limit processed foods, excess sodium, added sugars, and saturated fats which drive up inflammation. In addition to proper nutrition and hydration, getting adequate sleep, minimizing and managing stress, and incorporating regular physical activity are all healthy lifestyle choices that help support a healthy immune system.

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