What is protein?

Protein – also called protein – is one of the three main nutrients (along with carbohydrates and fat) and a central building block of life . It consists of amino acids , which are necessary for the structure, repair, and function of all body cells.

Approximately 15–20% of the human body consists of protein – primarily in muscles, skin, organs, enzymes, hormones, and the immune system. Without sufficient protein intake, the body cannot form new cells, maintain muscle mass, or carry out essential metabolic processes.

Structure and types of protein

Proteins consist of amino acids linked together by peptide bonds. There are a total of 20 proteinogenic amino acids , 9 of which are essential – meaning they must be obtained through food, as the body cannot produce them itself.

Essential amino acids:
Leucine, isoleucine, valine, lysine, methionine, phenylalanine, threonine, tryptophan, histidine

Non-essential amino acids:
They can be produced by the body itself (e.g., alanine, glutamine, glycine).

High-quality proteins contain all essential amino acids in optimal ratios (e.g., from animal sources or certain plant combinations).

Important protein sources

Animal sources:

  • Meat, fish, eggs

  • Dairy products (quark, yogurt, cheese)

  • poultry

Plant sources:

  • Legumes (lentils, beans, chickpeas)

  • Soy and tofu

  • Quinoa, Amaranth

  • Nuts, seeds, whole grain products

By cleverly combining foods – e.g., grains + legumes (such as rice with beans or bread with hummus) – the biological value of plant proteins can be significantly increased.

How does protein work in the body?

1. Building and maintaining muscles:
Proteins are the building blocks of muscle. They promote muscle growth, maintenance, and regeneration , especially after physical activity. The amino acid leucine plays a key role in this process, as it activates muscle protein synthesis .

2. Structure and cell organization:
Protein is a component of skin, hair, nails, bones, tendons, and connective tissue . It ensures the firmness, elasticity, and stability of all body structures.

3. Enzymes and hormones:
Many enzymes and hormones are made of proteins. They control vital processes such as digestion, metabolism, cell division, and signal transmission.

4. Immune system:
Antibodies (immunoglobulins) consist of proteins and are crucial for defending against pathogens .

5. Transport and storage:
Proteins transport nutrients (e.g., hemoglobin transports oxygen, transferrin iron) and store important substances.

6. Energy source (in case of emergency):
If energy intake from carbohydrates or fats is insufficient, protein can be used to generate energy – but at the expense of muscle mass.

Benefits of adequate protein intake

  • Promotes muscle growth and regeneration

  • Supports the maintenance of muscle mass during weight loss

  • Provides long-lasting satiety and stable blood sugar levels.

  • Strengthens immune system, skin, hair and nails

  • Supports hormone and enzyme production

  • Contributes to healthy cell formation and wound healing.

Recommended daily protein intake

According to the German Nutrition Society (DGE) :

  • Adults: 0.8 g protein per kg body weight

  • Physically active individuals: 1.2–2.0 g/kg

  • Muscle building or dieting phases: up to 2.2 g/kg

Example:
A person weighing 70 kg needs an average of about 56 g of protein per day , and up to 140 g with regular training.

Possible consequences of deficiency or excess

Protein deficiency:

  • Muscle weakness and decline

  • Delayed wound healing

  • Brittle nails, hair loss

  • Weak immune system

  • Fatigue and concentration problems

Excessive intake:

  • Generally harmless for people with healthy kidneys.

  • Consuming very high amounts over a long period can strain the kidneys if too little fluid is consumed at the same time.

  • A balanced diet remains crucial

Conclusion

Protein is the body's most important building block – essential for muscles, organs, skin, hormones, and the immune system. Adequate protein intake supports performance, regeneration, metabolism, and satiety. Crucially, it's not just the quantity that matters, but also the quality and variety of protein sources . A combination of animal and plant-based proteins ensures optimal supply and long-term health.

Sources

  1. German Nutrition Society (DGE). (2020): Reference values ​​for nutrient intake – Protein.

  2. Phillips SM, et al. (2016): Dietary protein for athletes: from requirements to metabolic advantage. Appl Physiol Nutr Metab , 41(5), 565–572.

  3. Paddon-Jones D, et al. (2008): Role of dietary protein in the sarcopenia of aging. Am J Clin Nutr , 87(5), 1562S–1566S.

  4. Wu G. (2016): Dietary protein intake and human health. Food Funct , 7(3), 1251–1265.