Lysine (Lys, K, irreversibly transaminated)

A balanced, plant-based diet with few to no industrially processed foods generally provides sufficient macro- and micronutrients, with the exception of vitamin B₁₂. However, phytochemicals are particularly relevant for maintaining health and healing, even though they are not considered essential nutrients – apart from vitamins.

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Definition

Lysine (Lys, K) is one of eight (ten in children, including histidine and arginine) amino acids considered essential (non-dispensable) for the human body. Humans use 21 proteinogenic amino acids, which are the building blocks of proteins. With the exception of two (lysine and threonine), the body can adapt protein production to its needs, even though eight are traditionally considered essential.

Occurrence

Legumes are particularly rich in lysine, but nuts and seeds also contain high amounts of it.

Examples of seeds containing lysine includepumpkin seeds (1200 mg/100 g) and poppy seeds (950 mg). Among nuts, peanuts also contain a lot of lysine, namely about 930 mg.¹

Among vegetables, cauliflower (220), spinach (170), broccoli (140), and potatoes (110) have higher lysine contents. In comparison, the lysine content in grains is low, making it a limiting amino acid in various diets. In some developing countries, L-lysine hydrochloride is used to fortify grains for human consumption and is also used in the production of animal feed.^1,13

A balanced diet with other plant-based protein sources such as legumes, seeds and nuts can compensate well for the low lysine content of grains.

Some important sources of lysine, such as spirulina (3000 mg/100 g), dried parsley (2100 mg, fresh 180 mg), mustard powder (1800 mg), or fenugreek (1700 mg), as well as many spices, are consumed in quantities that are too small for us to include them in the table.

Soybeans contain about one and a half times as much lysine as meat (raw beef 1790), while lupin flour, lentils, and broad beans have a similar lysine content to meat. Eggs (912) contain about one-third and cow's milk (276) only about 10 % of the lysine found in soybeans.¹

A vegan would have to eat a very unbalanced diet to suffer from a persistent protein deficiency.

Storage and Preparation Losses

Heating food denatures proteins, thus altering their properties. A fried egg is one example; it denatures due to the heat in the pan. When an egg is heated, the liquid yolk and the egg white, the main protein source, solidify. The proteins in the egg thicken, a process known as "coagulation" or "flocculation". The egg white coagulates at 60 °C, the yolk at 65°C, and complete coagulation occurs at 70 °C.

The oxidation of an amino acid by reactive oxygen species can significantly affect its function.

Nutrition - Health

Lysine is one of the essential amino acids. Essential amino acids are those that our bodies either cannot synthesize or cannot synthesize in sufficient quantities to maintain growth and nitrogen balance.⁸ In 1955, William Rose and colleagues demonstrated that lysine is required in the human diet to achieve a positive nitrogen balance.¹⁰ The main role of lysine is its participation in protein synthesis.¹³

It is now known that the body only irreversibly transaminates lysine and threonine, and that only these two are truly essential. ^Vegans tend to get slightly above-average amounts of lysine.

Specific eating habits, such as those of fruitarians (fruitarians, fructarians, fruganians) or the 80/10/10 (high-carb diet) and even more extreme diets, can lead to deficiencies over time. This often occurs over a long period without directly noticeable symptoms.

Long-term daily requirement

Estimates of the daily requirement for lysine in healthy adults range from 12 to 45 mg of lysine per kilogram of body weight, depending on the method used. The WHO specifies an average daily requirement of 30 mg/kg body weight.⁶

However, according to scientific tables Geigy, Vol. 2, p. 232, the minimum requirement for lysine, including a 30 % allowance for individual variations, is only 12 mg/kg body weight. For a person weighing 75 kg, this would be 0.9 g/day.

Deficiency symptoms

A deficiency is possible with insufficient dietary intake over a prolonged period. A natural vegan diet more than adequately covers lysine needs, and increased muscle activity naturally leads to increased food intake. Infants are particularly at risk if they are weaned from breast milk too early and receive inappropriate nutrition.

Lysine deficiency can lead to more frequent infections, as well as hair loss and growth disorders in children. The diseases kwashiorkor and marasmus, which result from very prolonged protein and general energy deficiency, are now rarely seen in the Western world.

Other deficiencies resulting from low intake or imbalances in the supply of essential amino acids can lead to insufficient weight gain and lower lean body mass in adults, even with increased energy intake.^8,9

Lysine oversupply

Elevated lysine levels do not occur with a balanced diet. In cases of impaired kidney function, a low-protein diet is recommended to prevent increased production and accumulation of urea in the kidneys due to amino acid breakdown.

The book * The China Study* impressively demonstrates, with strong evidence, that we normally suffer from an excess of protein rather than a deficiency (see detailed book review): Only in recent years have scientists discovered that animal protein, which was considered the best protein quality (biological value), does not produce the best health, but rather the opposite.

Functions in the body

Lysine has the following functions in the body:^2,3,4,5

• Lysine is essential for the stability of collagen, a key building block in connective tissue, hair, teeth, bones, blood vessels, and tendons. In these structures, lysine occurs as hydroxylysine, meaning it is equipped with OH groups at specific locations. These OH groups are linked together via sugar molecules, forming the particularly stable glycoproteins that are characteristic of collagen.
• Within the proteins around which the genetic material wraps, specific lysines are present in a methylated form.
• The body can use other substances to produce carnitine, a vitamin-like compound, from lysine. Carnitine plays an important role in energy production and fat burning.
• Lysine has a positive effect on the absorption of calcium in teeth and bones.
• Furthermore, various studies show a positive effect of lysine on arteriosclerosis and cancer.

Absorption and Metabolism:

Lysine is almost completely absorbed (nearly 100 %). However, there are differences in the rate of absorption. Essential amino acids, such as lysine, isoleucine, valine, phenylalanine, tryptophan, and methionine, are absorbed much faster than non-essential amino acids.

The digestion of ingested proteins begins in the stomach with the action of pepsin. Pepsins break down the proteins into peptides. Further breakdown into individual amino acids occurs in the small intestine through the action of peptidases.⁵

The first step in the lysine degradation pathway is the formation of saccharin and then 2-aminoadipic acid, which occurs in the mitochondria. The breakdown of 2-aminoadipic acid leads, via several steps, to acetyl-CoA. Although the liver is considered the primary organ for lysine metabolism, it is important to know that lysine degradation also takes place in other tissues and organs throughout the body, including the brain.¹²

The gut microbiota can convert urea into ammonia and use nitrogen for amino acid synthesis. Studies show that labeled lysine is produced in the gut and in the body, but the exact amount is difficult to measure. It is important to understand the role of the gut microbiota in lysine metabolism, especially in cases of low lysine intake.¹⁰

Storage - Consumption - Loss

Proteins are subject to constant synthesis and breakdown. 70-80 % of free amino acids are found in skeletal muscle, a smaller proportion in blood plasma. The liver is the central organ for amino acid regulation.⁵ Breakdown also occurs there, for example through deamination and conversion to urea, to prevent harmful effects in the cells. Amino acids can also be lost through sweat and urine.¹¹

Structures

L-Lysine is a basic amino acid characterized by the presence of an amino group at the end of an aliphatic 4-carbon side chain [-(CH2)4-NH3+]. This structure makes lysine a relatively reactive substance in various chemical reactions, including carbonyl-amine interactions.¹³

Other names for lysine: 2,6-diaminohexanoic acid. Molecular formula: C₆H₁₄N₂O₂. Abbreviations : Lys, K (one-letter code).