Question: Why is a combination of legumes and grains important to maintain a well-balanced diet for vegetarians?
About the article "Cereal", section "Nutritional facts".

Candidate passages:
Some grains are deficient in the essential amino acid lysine.
That is why many vegetarian cultures, in order to get a balanced diet, combine their diet of grains with legumes.
Many legumes, on the other hand, are deficient in the essential amino acid methionine, which grains contain.
Thus, a combination of legumes with grains forms a well-balanced diet for vegetarians.
Common examples of such combinations are dal (lentils) with rice by South Indians and Bengalis, dal with wheat in Pakistan and North India, and beans with corn tortillas, tofu with rice, and peanut butter with wheat bread (as sandwiches) in several other cultures, including Americans.
The amount of crude protein found in grain is measured as the grain crude protein concentration.
In several studies, vegans and other vegetarians were not found to suffer from iron-deficiency more than non-vegetarians.
However, while one study agreed that iron-deficiency anemia is not more common among vegetarians, they found "vegetarian children had ... reduced levels of haemoglobin and iron compared to omnivores" due "to the absence of animal iron sources with high utilizability".
Another study, in India, found that "strict vegetarian mothers as well as their newborns have a greater incidence and risk of anemia and iron deficiency.
"The recommended iron intake for vegetarians is 1.8 times that of nonvegetarians, because plants, dairy, and eggs contain only non-heme iron, and this is absorbed less efficiently than heme iron.
Although a lower "percentage" of non-heme iron is absorbed, greater "amounts" of non-heme iron are concentrated in many non-meat sources of iron (than the amount of iron per serving in meats), and therefore, cereals, eggs, nuts, seeds, and legumes (including soy foods, peas, beans, chickpeas, and lentils) are significant sources of iron, and a well-planned vegetarian diet should not lead to iron deficiency, but fruitarianism and raw foods diets should not be pursued for infants or children.
Meat, fish, and poultry (not dairy or eggs) are the only sources of heme iron; intake of heme iron may be associated with colon cancer.
Non-heme iron is more sensitive to both inhibitors and enhancers of iron absorption.
Vitamin C is an iron absorption enhancer.
The main inhibitors for most people are phytates (e.g.
legumes and grains), but other inhibitors include tannins (tea, wine), calcium and polyphenols.
Iron is an integral part of many proteins and enzymes which maintain good health.
In humans, iron is an essential component of proteins involved in red blood cells' oxygen transport.
Iron also helps regulate cell growth and differentiation. 
In 1971, as America was making its lunar landings, Frances Moore Lappé published Diet for a Small Planet which explained how essential amino acids might be obtained from complementary sources in vegetarian nutrition.
The book became a bestseller.
She wrote: Complementary protein combinations make for delicious recipes – they are combinations that formed the basis of the world’s traditional cuisines.
We use them naturally in our cooking without even being aware of it.
The three most common complementary protein combinations are: #Grains (rice, corn, wheat, barley, etc.)
+ legumes (peas, beans, lentils) #Grains and milk products #Seeds (Sesame or sunflower) +legumes For a time, The American National Research Council and the American Dietetic Association (ADA) cautioned vegetarians to be sure to combine their proteins.
In 1981, Lappé relaxed her position on protein combining in a revised edition of "Diet for a Small Planet", in which she wrote: "In 1971 I stressed protein complementarity because I assumed that the only way to get enough protein ... was to create a protein as usable by the body as animal protein.
In combating the myth that meat is the only way to get high-quality protein, I reinforced another myth.
I gave the impression that in order to get enough protein without meat, considerable care was needed in choosing foods.
Actually, it is much easier than I thought.
"With three important exceptions, there is little danger of protein deficiency in a plant food diet.
The exceptions are diets very heavily dependent on fruit or on [2 some tubers, such as sweet potatoes or cassava, or on junk food (refined flours, sugars, and fat).
Fortunately, relatively few people in the world try to survive on diets in which these foods are virtually the sole source of calories.
In all other diets, if people are getting enough calories, they are virtually certain of getting enough protein."
Pescetarianism is similar to many traditional diets emphasizing fish as well as fruits, vegetables and grains.
Many coastal populations tend to eat this way and these features characterize the traditional Mediterranean diet and the diets of many parts of Asia, Northern Europe, and the Caribbean.
These traditional diets tend to also include meat although it is peripheral.
In common with some vegetarians, pescetarians often eat eggs and/or dairy products, in addition to fruits, vegetables, nuts, and grains.
Pescetarians are sometimes described as vegetarian or pesco-vegetarian, but vegetarians commonly do not consider the pescetarian diet to be vegetarian.
For example, the Vegetarian Society, which initiated popular use of the term "vegetarian" as early as 1847, does not consider pescetarianism to be a vegetarian diet.
The definitions of "vegetarian" in mainstream dictionaries sometimes include fish in the diet. 
When protein is consumed, it is broken down into amino acids.
These amino acids are used to produce many things like neurotransmitters, enzymes, hormones, and chromosomes.
Proteins known as complete proteins contain all eight of the essential amino acids.
Meat, cheese, eggs, and yogurt are all examples of complete proteins.
Incomplete proteins contain only some of the eight essential amino acids and it is recommended that you consume a combination of these proteins.
Examples of incomplete proteins include nuts, seeds, legumes, and grains.
When animals are fed a diet deficient in essential amino acids, uncharged tRNAs accumulate in the anterior piriform cortex signaling diet rejection .
The body normally interconverts amino acids to maintain homeostasis, but muscle protein can be catabolilzed to release amino acids during conditions of amino acid deficiency.
Disruption of amino acid metabolism can affect brain development and neurophysiology to affect behavior.
For example fetal protein deficiency decreases the number of neurons in the CA1 region of the hippocampus.