Proteins are large molecules formed by the union of several amino acids (name used to denote a certain type of smaller molecules).1 They play an essential role in our body as they are involved in all the biological processes that occur in our body.
The main reason for this to happen is due to proteins, which are the main structural elements of cells and they act as biochemical catalysts and important regulators of gene expression. Therefore, any alteration in protein and amino acid nutrition affects all the biochemistry and physiology of the human organism.
When we consume proteins, our body separates the amino acids from them and after putting them together to form the proteins used by our organism. By this reason, food proteins are essential for growth and enzyme formation, digestive juices, plasma proteins, hemoglobin, vitamins, hormones and various secretory body fluids. They are also involved in carrying various nutrients such as fats, vitamins and minerals, and help to maintain the normal osmotic relationship between body fluids.
A diet without animal products can provide us perfectly with the proteins we need to live healthily. Good sources of proteins are legumes (chickpeas, black beans, red beans, lentils…), cereals (rice, wheat, corn…), nuts (walnuts, almonds, hazelnuts…), seeds and food known as “pseudo cereal” (name given to some grains of broad leaf plants such as quinoa, amaranth or buckwheat, which have a similar use to cereals). Of course, products derived from these foods like vegetable burgers and vegetable sausages, bread and pasta, tofu, seitan, vegetable yogurts, soya drink, etc. are also good sources of protein.
We are going to look all this in more detail.
Proteins accomplish many functions. Some of them are as follows.
They act as support filaments, cables or layers to give strength or protection to biological structures. Examples of these proteins are the following:
Certain proteins fix or transport specific molecules or ions from one organ to another. Proteins also act as transport gases such as oxygen and carbon dioxide in the blood, and function as shock absorbers, helping to maintain the reaction of diverse means such as plasma.
A number of proteins give to cells the ability to contract, change their shape or move.
There are proteins used to perform a catalytic activity, in other words, they are involved in chemical reactions that occur in the molecules of our cells.
The antibodies in our body are defensive proteins that oppose infections, wounds or foreign agents.
Proteins with this function regulate physiological or cellular activity.
These are required as nutrients for growth and proper nutrition.
It is recommended to consume daily between 0,9 and 1 gram of protein per kilo of body weight. That is, a person who weighs 50 kg has to consume between 45 and 50 g of protein per day.
This doesn’t mean that we have to eat 50 g of protein rich food per day (such as chickpeas). This really means that the total amount of protein contained in all the food that we have ingested throughout the day should be 45 to 50 g. This ratio is based on the ideal weight that someone should have: when someone has a lower or greater weight, the calculation of the amount of protein that a person should eat needs to be done based, not on the actual weight, but on the ideal weight of that person.
Protein deficit can cause problems in the body, especially in children, where their lack can cause problems of development and growth. On the other hand, a serious excess of protein may be associated with kidney stones, kidney problems,2 or a loss of body calcium. This is important because in many places most people consume much more proteins than actually needed, so their concern should not be if they are eating enough proteins but whether they are eating too much of them.
It is also important to keep in mind that the recommended amounts vary in the case of pregnant women, children, infants, elderly and people with specific nutritional requirements.
Currently, the most widespread view is that there are 9 essential amino acids, which we must provide to our body through nutrition. These essential amino acids are: valine, leucine, isoleucine, threonine, lysine, methionine, phenylalanine, histidine and tryptophan.3
In order to form the necessary proteins in our body we need to consume all of these amino acids. If we consume all but one of them, and instead, we consume large amounts of the others, we will have a problem. We will lack an essential element which enables us to build our proteins.
Fortunately, this is not a problem, because we can consume all the essential amino acids with a vegan diet. The foods mentioned above (legumes, grains, seeds, nuts and pseudo cereals) contain these essential amino acids.
It is true that some of them are found in a lower proportion than is recommended. They are called “limiting amino acids” because they limit the amount of protein that can be built. Even though there are enough other amino acids to form proteins, by not having sufficient limiting amino acids, the total amount of resulting proteins is lower. But this is not a problem, not only because our protein intake is usually sufficient even happening this, but also because we usually do not eat just one single food, but several throughout the day. And limiting amino acids are not the same for all plants, as they just coincide for certain groups (cereals, legumes, nuts, etc.). And, since it is normal that our diet is not limited just to one type of food, because it use to include foods from different groups, the amino acids for all of them end up being combined together, and they offset each other in terms of these limitations. That is, if one food is not abundant in a certain amino acid, another food will have it in a higher proportion. In this way, the formation of protein will be more effective.
The “limiting” essential amino acids to highlight are lysine in cereals and methionine in legumes. Grains contain practically all the essential amino acids in the recommended ratio, but the amino acid lysine is presented in a lower proportion. We can eat a greater amount of this food or another similar one throughout the day so, that the amounts of that limiting amino acid increase to achieve the necessary quantities, or if not, we can eat other foods rich in lysine.
By contrast, legumes generally contain sufficient lysine but lesser amounts of methionine, something that also happens in the case of many animal products. Despite this, there are exceptions, since chickpeas and some products derived from soya contain enough amount of methionine. This implies that they are excellent sources of protein. Cereals and pseudo cereals are especially rich in methionine, as well as sesame seeds, sunflower and pumpkin seeds, Brazil nuts and pistachios.
For all this, it is good to eat a variety of foods to consume all the essential amino acids. In the past, it was believed that, to achieve this, it was necessary to combine different foods into the same meal. Nowadays, it has been shown this is not true and there is a consensus that it can be done in different meals. That is, if you eat cereals at midday and legumes for dinner, your body will combine the amino acids that you will get first from the cereals with those that you will get later from the legumes. This will happen even though you ingest them in different meals.
It has to be into account that it is not necessary to do this daily. There is no need to have a significant intake of protein every day, unless we are in a specific case (athletes, growing adolescents, pregnant women…). However, it is important to consume protein in a regular way. But, as we have seen, this is easy with a varied vegan diet.
With 3 or 4 servings of protein food with proteins per day we will ensure an adequate profile of essential amino acids. A couple of examples of the required daily consumption of these 3 or 4 rations would be:
Finally, to get an idea of the amount of proteins contained in different foods, we can consider the following examples:
The amino acid lysine is especially important in the vegan diet. Chickpeas, red beans and lentils are excellent sources of lysine, both in a cooked or sprouted state. Quinoa, amaranth and also pumpkin seeds are good sources of this amino acid. An adequate diet must contain around three servings each day of foods rich in lysine, as well as a combination of foods that contain lysine in much smaller amounts.4
Soya has a very high lysine content and a protein profile similar to that of animal protein. Soya products, such as tofu, tempeh and drinks and burgers are recommended as good sources of vegetable protein. On the other hand, even though these foods are excellent sources of proteins, it is not necessary to have a diet rich in soya products to meet our need for protein.5
0.9 grammes of protein are recommended per kg of body weight. A varied vegan diet provides all the essential amino acids.
Marsh, K. A.; Munn, E. A. & Baines, S. K. (2013) “Protein and vegetarian diets”, Medical Journal of Australia, 199, 4 suppl., S7-S10 [accessed on 10 May 2018].
Norris, J. & Messina, V. (2011) Vegan for life, Philadelphia: Da Capo.
1 Amino acids are organic molecules that are called like that because they consist of what is known as an amino group (-NH2) and a carboxyl group (-COOH).
2 There are those who argue that histidine is only essential for nursing babies as later this amino acid is provided through our intestinal microbiota, although this position is controversial.
3 There are those who have maintained that histidine is essential only for those babies who are breast-fed, given that it is only later in life that this amino acid can be provided through our intestinal microbiome, although this idea has been disputed.
5 Yáñez, E.; Uauy, R.; Zacarías, I. & Barrera, G. (1986) “Long-term validation of 1 g of protein per kilogram body weight from a predominantly vegetable mixed diet to meet the requirements of young adult males”, Journal Nutrition, 116, pp. 865-872. Young, V. R.; Pellett, P. L. (1994) “Plan proteins in relation to human protein and amino acid nutrition”, The American Journal of Clinical Nutrition, 59, pp. S1203-S1212. Haddad, E. H.; Berk, L. S.; Kettering, J. D.; Hubbard, R. W. & Peters, W. R. (1999) “Dietary intake and biochemical, hematologic, and immune status of vegans compared with non-vegetarians”, The American Journal of Clinical Nutrition, 70, pp. 586S-593S [accessed on 23 April 2017]. Caso, G. (2000) “Albumin synthesis is diminished in men consuming a predominantly vegetarian diet”, Journal Nutrition, 130, pp. 528-533. Elango, R.; Humayun, M. A.; Ball, R. O. & Pencharz, P. B. (2010) “Evidence that protein requirements have been significantly underestimated”, Current Opinion in Clinical Nutrition and Metabolic Care, 13, pp. 52-57.