Threonine - this amino acid is not only important for muscle building!

Amino acids (abbreviated AS) are the building blocks of proteins and are indispensable for the human body, as they are responsible for all the functions of our organism, such as metabolic regulation, the immune system, hair growth and muscle building [1] [2]. Our DNA is also made up of them. AS are responsible for the function of enzymes and hormones, as well as for the transport of blood proteins. One of them is threonine.

We have summarised the most important information about the function of threonine for you here.

What is threonine?

In its natural L-form, threonine (abbreviated Thr or T) is an essential proteinogenic α-amino acid. This AS is broken down in the liver [3]. Vital substances such as vitamin B6, vitamin B3 and magnesium are required for the optimal utilisation of threonine [1].

What are proteins?

Our body obtains essential amino acids from the proteins in our diet. essential amino acids for the body's own protein synthesis, such as creatine, haemoglobin or transferrin, immunoactive proteins (immunoglobulins), nitrogen-containing compounds such as enzymes, peptide hormones such as insulin, as well as DNA and RNA.

Which amino acids are there?

The AS are categorised into the following groups:

Essential amino acids
Non-essential amino acids

Essential amino acids cannot be produced independently by the human body, so the requirement must be covered by food or dietary supplements. These are: L-isoleucine, L-leucine, L-lysine, L-methionine, L-phenylalanine, L-threonine, L-tryptophan, valine and, for infants, histidine (the L- stands for the natural form of the respective amino acid). Without a regular supply of these essential amino acids, deficiency symptoms can occur [4].

The body can produce non-essential amino acids itself. These are: alanine, L-arginine, asparagine, aspartic acid, cysteine, L-glutamine, glutamic acid, glycine, proline, serine and tyrosine [5]. Due to liver diseases, enzyme defects (e.g. phenylketonuria) or a limited enzyme capacity in newborns and infants, some of these amino acids cannot be produced sufficiently by the body. This often affects cysteine, glutamine, tyrosine and arginine.

Amino acids are also precursors in the synthesis of numerous metabolic products such as bile acids, serotonin and histamine [5].

How does an amino acid deficiency develop?

A deficiency of the essential amino acids is caused by an unbalanced diet or the withdrawal of certain amino acids through medication.

What is L-threonine good for?

L-threonine ensures that connective tissue and muscles remain strong and elastic. This also includes the heart, where it is present in large quantities. It also contributes to the formation of strong bones and tooth enamel, can accelerate wound healing and recovery processes and strengthen the immune system. L-threonine is considered one of the most important amino acids, as it is also responsible for tissue formation and growth in addition to the functions mentioned [1] [3].

How does a deficiency of L-threonine occur?

Although threonine (Thr) is found in a wide variety of foods, there may be risk factors for a deficiency:

Diets and unbalanced diets
Vegan diet, unbalanced diet, anorexia, bulimia, low-protein or protein-free diets, fasting cures.

Great stress
Competitive sport, constant stress, mental strain, lack of sleep.

Diseases
Metabolic diseases, chronic inflammatory bowel diseases, long-term stress on the immune system.

Growth
Significantly increased need to build up tendons, ligaments, cartilage, bones, skin and mucous membranes.

Excessive consumption of stimulants
Alcohol, nicotine and caffeine can attack or destroy the mucous membranes of the digestive tract and thus provoke an increased need for L-threonine in order to regenerate them. In addition, the resulting resorption disorders make absorption from food more difficult.

What consequences can a protein deficiency have?

If there is an undersupply of proteins, the body first reduces nitrogen excretion and supplies itself by breaking down the body's own protein from the muscles. This reduction in muscle mass causes a decrease in muscle function, which increases the risk of fractures and frailty in older people. If protein deficiency persists for a longer period of time, the body itself can no longer provide sufficient amino acids due to muscle breakdown, resulting in impaired metabolic and other organ functions [3].

How does a threonine deficiency manifest itself?

A lack of amino acids can have long-term negative consequences for the body. The consequences often include a weak immune system, loss of performance, joint problems, deficits in muscle building, slow wound healing and mood swings through to depression or obsessive-compulsive disorders. Growth disorders in children, accelerated wrinkling in adults, weakening of the tooth substance, impaired fat metabolism and leaky gut syndrome can also be consequences of a threonine deficiency [1] [3] [5] [6].

How much threonine do we need per day?

As there are no guidelines for a recommended daily intake of threonine from either the German Nutrition Society or the World Health Organisation, we can only use the information provided by the United States Department of Agriculture as a guide. This assumes a requirement for adults of 16 mg per kg of body weight per day.
For a person weighing 70 kilograms, this means that 1,120 mg of L-threonine should be consumed daily. This amount can be found in 100 grams of sardines, edamame or lentils. For infants and children, a requirement of 150 mg per kg of body weight per day is specified.

The German Nutrition Society recommends a general protein intake of 800 mg per kg of body weight per day for adults (19 to 65 years), calculated on the basis of a BMI of 22 kg/sqm. For adults aged 65 and over, the general requirement is estimated at 1,000 mg per kg of body weight. The protein requirement during pregnancy is calculated depending on weight gain. Assuming a basic weight gain of 12 kg during pregnancy, a protein requirement of 900 mg to 1,000 mg per kg body weight is assumed. Breastfeeding mothers have an even higher requirement of 1,200 mg per kg of body weight per day [4].

When is the best time to take dietary supplements containing the amino acid threonine?

Our body can best utilise this nutrient as a supplement on an empty stomach. In order to optimally utilise this active ingredient, sufficient magnesium, vitamin B3 and B6 should also be available [1].

Which foods generally contain a lot of protein?

Animal foods with a high protein content (in the order of too little to too much): Cooked pork, cooked trout, quark (at least 20% fat in dry matter), Emmental cheese (at least 20% fat in dry matter), boiled egg, cow's milk with 1.5% fat, yoghurt with 1.5% fat.

Plant-based foods high in protein (in order of way too little): Tofu cooked, wholemeal pasta cooked, lentils cooked, green peas cooked, mushrooms cooked, oatmeal, soya drink, Brussels sprouts cooked, potatoes peeled and cooked, bean greens cooked, walnuts, wholemeal bread.

Which foods contain a lot of threonine?

Meat and sausages:
Beef, pork, goose, duck, ham, salami

Fish and seafood:
Sea fish, carp, trout, prawns, lobster

Pulses, mushrooms and vegetables:
Soy and lima beans, lentils and (chick) peas, savoy cabbage, kale, broccoli and mu-err mushrooms

Nuts and grains:
Peanuts, cashews, almonds, walnuts and hazelnuts, bran, rolled oats, spelt, wheat, barley, millet, corn

Dairy products and egg:
Sliced cheeses such as Edam and Gouda

Baker's yeast:
Baker's yeast not only contains numerous B vitamins, but also plenty of threonine

Is there a difference in protein content between animal and plant-based foods?

Animal and plant proteins have different amino acid compositions. The bioavailability also differs. For example, proteins of animal origin usually contain all essential amino acids in the required quantity with a high level of bioavailability. Plant proteins, on the other hand, usually do not have this.

A purely plant-based diet should therefore be made up of specific combinations, such as lentil vegetables with rice, cereals with pulses or pea stew with bread. Cereals have a low proportion of lysine, threonine and tryptophan, but are rich in methionine. In contrast, pulses are low in methionine but high in threonine and tryptophan. It should also be noted that some food components can limit bioavailability, such as tannins in pulses and cereals.