19 May 2021 Article

This article contains information about the important qualities of protein and about the quantities of protein we need. This post is not meant exclusively for vegans. I hope it is also interesting for non-vegetarians who want to cut out animal protein.

One of the potential dangers of long-term strict vegetarian diets is a chronic lack of protein. This can lead to weakening of the immune system, the destruction of muscle and bone tissue, and in severe cases to diseases such as senility and degeneration.

What is a complete protein?

The utility of a protein is determined by two factors – its digestibility and its amino acid content. Generally, animal proteins have a digestibility index of 90-99%, plant proteins – 70-90%. Corn protein, for example, is absorbed very poorly, but the digestibility of soybeans is very close to that of an animal protein.

All proteins are composed of amino acids. You can imagine amino acids like little building blocks. To construct a protein in the human body, 20 different building blocks or amino acids must be used. Nine of them are essential. This means that they must be ingested through food. Our body cannot produce them. The essential amino acids are phenylalanine, valine, threonine, tryptophan, methionine, leucine, isoleucine, lysine and histidine.

Protein synthesis in the human body occurs in an interesting way. First, a protein that we get from food is split into amino acids. Then, as a result of complex chemical reactions, these separate amino acids are arranged into proteins needed by the body.

All animal proteins are complete, that is, they contain a complete set of essential amino acids necessary for optimal maintenance of protein synthesis in the human body. Plant proteins are generally lacking one or more essential amino acids. For example, cereals lack lysine and isoleucine, and legumes lack methionine and tryptophan. However, if you combine cereals and legumes, you get a set of amino acids, which complement each other. In combination, they can become a valuable source for the synthesis of proteins that we need. Therefore, vegans are recommended to consume foods that combine complementary proteins.

To determine the quality of a protein, the so-called protein digestibility-corrected amino acid score (PDCAAS) is used world-wide. The score takes into account the amino acid composition of proteins and protein digestibility, i.e. both parameters described above. Eggs, milk and soybeans have the highest score of 1. Interestingly, meat has a lower score of about 0.9.

Soybeans contain more protein than other legumes (and this protein is well absorbed by the human body), and they provide all nine of the essential amino acids. Soybean products such as tofu, soy drinks, soy yogurt alternative, tempeh and edamame are therefore the number one choice for strict vegetarians.

Other good sources of plant protein are:

  • Seitan
  • Lupine
  • Beans
  • Lentils
  • Industrially made plant-based burgers meat alternatives.

Nuts and seeds contain a lot of protein per 100 grams (20-25 grams), but they are also very high in fat (and calories), therefore it is not recommended to use them as a main source of protein.

Smart combinations

If combined properly, plant foods can deliver all the essential amino acids, making sure that the protein synthesis in the human body is optimal. In principle, the main rule of the combination of plant proteins is simple: cereals are combined with legumes or nuts or seeds. Some examples of classic combinations include:

  • Pita and falafel (chickpea croquettes)
  • Sandwich with hummus (chickpea dip) or peanut/nut butter
  • Rice with lentils or beans
  • Porridge with nuts
  • Lentil soup with bread

Recent research shows, however, that it is not absolutely necessary to consume complementary proteins in the same meal. What this means is that you don’t have to become obsessed with the complementarity of the proteins you consume. Just make sure you don’t skip any essential food categories (grains, legumes, nuts and seeds).

How much protein does an omnivore, vegetarian and vegan need?

Under normal circumstances, a healthy omnivore (or flexitarian) should consume around 0.83 grams of protein per 1 kg of body mass per day. For example, if you weigh 60 kg, you need 60 × 0,83 = 50 grams of protein per day. However, if you’re vegetarian, you need approximately 20% more, which makes it roughly 1 g of protein per 1 kg of body mass. Therefore, if you are a 60 kg vegetarian, you need 60 g of protein per day. The guideline for vegans is 30% more than for omnivores, or 1,08 g/kg/d. This guideline is based on the fact that plant protein, on average, is digested more poorly. Thus, if you are a vegan and weigh 60 kg, you need 65 grams of protein per day.

If you doubt whether you eat enough protein, a food diary can help you make a good estimate. Nowadays, there are plenty of apps that do all the calculations for you, so you might want to try one out. Otherwise, you can consult a registered dietitian in your area.