Firstly, I’m not going to go into the ethical choices of vegetarianism/veganism. Everyone has their choice and if people choose a vegetarian/vegan diet then that is fine and it doesn’t mean it will hinder their goals. (performance, physique or health) And for what it’s worth, I’m definitely an omnivore (although some may say carnivore).
Adequate protein is a subjective matter as the amount will differ depending on a person’s activity level, exercise type and physique goals (cutting or bulking). The peer reviewed, published scientific studies agree that approximately 1.2g-2g/kg/day is an adequate amount. Many people tend to perform better, retain more muscle while cutting or are able to maximise muscle gains while bulking with higher intakes of around 2-3g/kg/day. Maintaining muscle mass (in a non hypocaloric state) can be achieved with the lower amount suggested by studies in most individuals. (1.2g/kg/day)
That covers total protein requirements but what about the “complete” and “incomplete” proteins. These terms indicate if a food contains all the essential amino acids (EAA) that form protein. These proteins cannot be produced by the body and can only be provided by inclusion in your diet. There are 9 essential amino acids and 13 non essential amino acids (NEAA). (1)
Omnivores will typically not have any issues getting all of the EAA in their diet as meat contains all of them. So without meat in the diet is it achievable for vegetarians to obtain all of the EAA? The answer is yes. Although proteins derived from plant foods (legumes, grains, and vegetables) tend to have less of one or more essential amino acids (2) a varied 0vo-lacto vegetarian diet would still include dairy and eggs. Cheese, eggs, yogurt, and milk and whey protein powders are complete proteins. Strict vegetarians who are cutting out dairy and vegans will not have this option. In this case, I would recommend eating a variety of whole food sources and possibly supplementing with a vegan friendly protein powder like pea, rice or soy proteins. Previously, food combining was considered the only way to get a balanced and complete diet for vegetarians, but modern research has found there is no need to worry about getting complete proteins at each meal. As long as the diet includes a variety of whole unprocessed foods then the EAA should be covered as they are not digested instantly. Our bodies pool the amino acids we need as we eat them, and we use them when needed. Some examples of vegetarian meals that have combined food types that contain all EAA are Mexican corn and beans, Japanese soybeans and rice, and Cajun red beans and rice, combine grains with legumes to provide a meal that is high in all essential amino acids. (3,4)
In summary, a vegetarian/vegan diet that comprises a majority of whole unprocessed foods will contain all of the EAA. If someone is falling short of total protein targets then supplementation with vegetarian/vegan friendly protein powders can be a good option.
A good summary of the various amino acids found in typical vegetarian/vegan foods can be found here. http://www.nomeatathlete.com/vegetarian-protein/
2. Young VR, Pellett PL (1994). “Plant proteins in relation to human protein and amino acid nutrition” (PDF). AMERICAN JOURNAL OF CLINICAL NUTRITION 59 (5 Suppl): 1203S–1212S.PMID 8172124
3. “The majority of plant proteins are incomplete because they lack at least one essential amino acid. As different plant sources are low in specific amino acids, you can combine complementary plant sources to create a nutritionally complete protein. For example, grains supply the essential amino acids missing in legumes, and legumes supply the essential amino acids missing in grains. Eating black beans on a corn tortilla, for instance, supplies your diet with all your essential amino acids.” Livestrong.com webpage entitled NUTRITIONAL SOURCES OF ESSENTIAL AMINO ACIDS
4. “Tillery points out that a number of popular ethnic foods involve such a combination, so that in a single dish, one might hope to get the ten essential amino acids. Mexican corn and beans, Japanese rice and soybeans, and Cajun red beans and rice are examples of such fortuitous combinations.”