Protein is a crucial nutrient that benefits your body — from the strength of your muscles to the health of your skin, hair and nails. Protein also contributes to the repair of tissue and helps with neurotransmitter functioning. All foods contain some protein.
If you're on a vegetarian diet, you don't need to worry about being unable to get your protein from animal sources. Eating a variety of vegetables, grains, legumes, nuts and seeds will supply all the amino acids you need to fulfill the protein requirements for good health.
A diverse selection of plant foods eaten throughout the day will supply your body with all the essential amino acids it needs to make sufficient protein — no special food combinations required.
What Are Amino Acids?
The food you eat is made up of an array of nitrogen-containing organic compounds called amino acids. Amino acids are often described as the building blocks of life because they bond together to create long chains called proteins. Amino acids make up 75 percent of your dry body weight. All of your hormones, neurotransmitters and signaling molecules that influence the activity of your brain and body are made from amino acids.
Although there are more than 50 naturally occurring amino acids, the protein in your body is derived from 20 of them in specific combinations. These form the functional and structural components of your cells. Eleven amino acids can be made by your body and are known as nonessential amino acids. The remaining nine are known as essential amino acids because your body has to get them from your diet.
The Essential Amino Acids
Of the nonessential amino acids produced by your body, several are classified as conditionally essential. These can become essential when your body is under stress, such as with an illness. For example, arginine is considered nonessential, but when fighting certain diseases, such as cancer, your body may be unable to meet the demands. So in this situation, arginine needs to be supplemented from your diet and becomes essential.
Each essential amino acid has a different function in your body, so each has different deficiency symptoms. Many foods contain one or more of each type of amino acid.
Leucine: Leucine is the amino acid needed for the maintenance of muscle strength and growth. It helps stimulate the release of insulin and regulates your blood sugar. It also acts on neurotransmitters in the brain and might aid in the prevention and treatment of depression.
Isoleucine: Isoleucine is an isolated form of leucine. It's heavily concentrated in muscle tissue to help with muscle metabolism. Isoleucine is also important for hemoglobin production, your immune system and energy regulation. Isoleucine deficiency is marked by muscle tremors.
Lysine: Lysine is an amino acid that converts fatty acids into fuel and helps your body absorb calcium for bone health and collagen production. A deficiency in lysine can result in symptoms of nausea, depression, fatigue, muscle atrophy and osteoporosis.
Methionine is the only amino acid that contains sulfur, which it uses to form cartilage. It is also needed for muscle growth and the absorption of zinc and selenium. A deficiency of methionine may contribute to developing arthritis, tissue damage and poor healing.
This amino acid is not only found naturally in plants, it's also chemically produced to enrich foods. Phenylalanine works with tyrosine to make proteins that assist the brain and thyroid. A deficiency can cause depression and other cognitive disorders.
Threonine helps your heart, nervous system, liver and immune system. It also produces other essential amino acids that are required for proteins such as elastin and collagen, which contributes to healthy skin, hair, nails and bone. Threonine in the liver assists fatty acid digestion.
Histidine is needed to produce histamine, vital to the immune system as a neurotransmitter. It also aids in digestion, sexual function and your sleep cycles. A deficiency of histidine can cause hearing loss.
Tryptophan: You probably associate this amino acid with the last turkey dinner you ate. Tryptophan in turkey is responsible for that relaxed and sleepy feeling you may have encountered after a big Thanksgiving dinner. Tryptophan converts to serotonin in the brain, which contributes to lower levels of stress and depression. It is vital for a healthy nervous system, brain health and overall function of neurotransmitter function.
Valine: Valine is particularly involved in stress, energy and muscle metabolism. It helps maintain your muscles and is vital for growth, repair and regeneration of tissue to ensure endurance. Valine deficiency can cause neurological defects in the brain.
How Much Do You Need?
Although protein is a necessary nutrient for all your bodily functions, you don't need large quantities of it. The Vegetarian Resource Group says that, after accounting for plant proteins being digested differently from animal proteins and considering the combination of amino acids in some plant proteins, vegans need 0.9 gram of protein per kilogram of body weight, or 0.41 gram per pound. That would put the recommended intake for vegans and vegetarians close to 10 percent of calories coming from protein.
This amount is in accordance with Dietary Guidelines for Americans, which advises that 10 to 35 percent of your calories should come from protein. USDA suggests 46 grams daily for women and 56 grams for men per day.
The key to making sure you get enough high-quality plant protein each day is to eat a variety of foods, including fruits, vegetables, seaweed, leafy greens, nuts, seeds, whole grains and legumes. Every food has at least one or more important amino acid. Generally, legumes are low in the amino acid methionine, while most other plant foods — grains in particular — are low in lysine.
Complete-Protein Plant Foods
Although animal-based protein generally contains all the essential amino acids, many plant foods do too. The right plant-based foods can be a better source of protein because they usually contain more nutrients, often with fewer calories than animal products, and less fat and no cholesterol. In the Permanente Journal report "Plant-Based Diets: A Physician's Guide," vegetarian diets are considered a healthier source of protein, because they're filled with fiber, potassium, iron, magnesium, folate, and vitamins A and C.
A number of foods or food combinations are considered complete proteins and contain all nine of the essential amino acids in varying amounts. Including these in your vegetarian diet helps ensure your protein needs are met.
- Soybeans, tofu, tempeh and edamame
- Chia seeds
- Beans with rice
- Hummus and pita
- Pumpkin seeds
- Sprouted brown rice
- Spirulina and grains or nuts
- Sprouted-grain bread
- Peanut butter and bread
Other plants considered to be good proteins that vegetarians still need to combine with other foods for a complete amino acid profile include lentils, chickpeas, almonds, grains and legumes. Don't worry about combining foods at each meal to get all the amino acids. Your body is perfectly capable of recycling and mixing the absorbed amino acids in your body to make the protein it requires. Just make sure you eat a variety of plant-based foods throughout the day. You don't need to eat essential and nonessential amino acids at every meal, but getting a balance of them over the whole day is important.
- UC Davis Integrative Medicine: The Essentials–Part One
- PETA: 11 Complete Protein Sources That Every Vegan Should Know About
- Medical News Today: Top 15 Sources of Plant-Based Protein
- New World Encyclopedia: Amino Acid
- World Journal of Biological Chemistry: Targeting Amino Acid Metabolism in Cancer Growth and Anti-Tumor Immune Response
- PubChem: Phenylalanine
- PubChem: Valine
- PubChem: Threonine
- PubChem: Tryptophan
- PubChem: Methionine
- PubChem: Leucine
- PubChem: Isoleucine
- PubChem: Lysine
- PubChem: Histidine
- Scientific Reports: Essential Amino Acids: Master Regulators of Nutrition and Environmental Footprint?
- Dietary Guidelines 2015-2020: Nutritional Goals for Age-Sex Groups Based on Dietary Reference Intakes and Dietary Guidelines Recommendations
- The Vegetarian Resource Group: Protein in the Vegan Diet
- Vegan Health: Protein Part 1—Basics: Plant Protein and Amino Acids
- The Permanente Journal: Plant-Based Diets: A Physician’s Guide
- T. Colin Campbell Center for Nutrition Studies: Where Do You Get Your Protein?