Can You Get Enough Protein from Vegetables?

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Vegetables contain protein, but is it possible to obtain enough protein from only vegetables?

Protein is found in every part of our body, including muscle, bone, skin, hair, organs, and enzymes. A vegetarian or vegan diet can meet the nutrient standards recommended by the 2015-2020 Dietary Guidelines by including a variety of plant foods that contain protein, including soy foods, grains, vegetables, nuts and seeds, and legumes. In fact, when calorie intake is adequate, vegetarian and vegan diets typically meet or exceed recommended protein levels. According to the Academy of Nutrition and Dietetics position paper on Vegetarian Diets, plant-based diets lead to reduced risk of heart disease, type 2 diabetes, hypertension, some types of cancer, and obesity.

What about Amino Acids?

Amino acids are the building blocks of protein, and for optimum health we need adequate amounts of 20 different amino acids. Our bodies make some amino acids, and we need to get the 9 other essential amino acids from our foods in order for our body to thrive. Animal proteins include all the essential amino acids. Most plant foods are low in one or two of the essential amino acids. If we don’t consistently consume all of the essential amino acids our body needs, our physical and mental health suffers. Consuming a variety of plant sources of protein, including soy, nuts and seeds, grains, legumes as well as vegetables ensures that if one food is low in a particular amino acid, another type of food will make up the deficit.

What are the Daily Protein Requirements?

The RDA for protein necessary for good health for the majority of adults is .8 grams of protein per kilogram of body weight, or .36 grams of protein per pound of body weight. Since plant proteins are digested a bit differently than animal proteins, vegetarians should consume .9 grams of protein per kilogram of body weight, or .41 grams per pound of body weight. A 150-pound adult needs 62 grams of plant protein per day.

Spinach is the only vegetable that contains all the essential amino acids. However, for our 150-pound person to meet her protein and amino acid requirements, she would need to consume 12 cups of cooked spinach every day. I doubt even Popeye would enjoy eating that amount every single day!

So here's our take on this question: While technically it’s possible to consume enough of the essential amino acids our body needs for good health by eating only vegetables, in reality it’s not always practical. The healthiest way to enjoy a plant-based diet is to enjoy a variety of foods from plants and not limit yourself to only vegetables.

By Lynn Grieger, RDN, CDE, CPT, CHWC

References:

• Dietary Guidelines 205-2020. Appendix 5. USDA Food Patterns: Healthy Vegetarian Eating Pattern. https://health.gov/dietaryguidelines/2015/guidelines/appendix-5/ Accessed 7-29-17.
• Vesanto Melina, Winston Craig, Susan Levin. Position of the Academy of Nutrition and Dietetics: Vegetarian Diets. J Acad Nutr Diet. 2016;116:1970-1980.
• Reed Mangels. Protein in the Vegan Diet. Vegetarian Resource Group. https://www.vrg.org/nutrition/protein.php, 2017.

PDF Handout: Vegetable Protein Handout