Cysteine is a non-essential amino acid. It can be obtained from food or synthesized in the body from the essential amino acid methionine. Methionine is found in many protein-rich foods. Initially, methionine is converted to homocysteine. Subsequently, homocysteine is converted to cystathionine through enzymatic reactions and finally converted to cysteine. Vitamin B6 is required as a cofactor (⇒ foods high in vitamin B6). Our cysteine table shows you foods with high cysteine content.

One of the main functions of cysteine is to support the body in the production of glutathione. Glutathione is a powerful antioxidant that fights free radicals and protects the body from oxidative stress. It aids in the detoxification of pollutants and supports liver function.

By participating in the regulation of the immune system, cysteine supports the production of antibodies and strengthens the immune response against pathogens. This enables the body to effectively respond to invading pathogens.

Cysteine is also important for the structure and protection of proteins. It forms disulfide bonds that maintain the structure and stability of proteins. These bonds are particularly relevant for proteins such as keratin. These structural proteins, in turn, are crucial for the health and strength of hair, nails, and skin.

Cysteine also serves as a precursor for the synthesis of the organic acid taurine. Taurine is an amino sulfonic acid involved in various physiological processes, particularly necessary for the development and function of the nervous system, heart health, and the visual cells in the eye.

Differences between Cysteine and L-Cysteine?

Cysteine and L-cysteine are generally used synonymously. L-cysteine is the bioactive form of cysteine. The letter "L" denotes the left-handed configuration of the molecule. This configuration is the natural form of cysteine found in proteins and the human body.

There is another form of cysteine called D-cysteine, which is right-handed. D-cysteine is less common in nature and is usually not used in proteins. However, it is used in some dietary supplements or medications.

In terms of biological activity, L-cysteine is better absorbed and utilized in the body than D-cysteine. L-cysteine is used as a nutrient source for cysteine synthesis, while D-cysteine cannot be incorporated into protein synthesis.

L-cysteine is often available as a dietary supplement in the form of L-cysteine hydrochloride or N-acetyl-L-cysteine (NAC). These forms are used for their stability and bioavailability.

Who has a higher need?

A balanced vegan diet that is rich in protein-rich plant-based foods can easily meet the cysteine requirement. The body uses the essential amino acid methionine as a precursor for cysteine synthesis. However, under certain circumstances, the requirement may be increased even if the body is capable of producing cysteine:

  • During illnesses or injuries, the body may have an increased need to support the healing process and combat oxidative stress. In such cases, additional cysteine intake through food can be beneficial.
  • Intensive training and physical activity can increase the requirement as they can lead to oxidative stress and muscle breakdown. Adequate intake of cysteine and other antioxidant nutrients can help reduce muscle breakdown and promote recovery. Athletes can benefit from cysteine-rich foods as the amino acid is also used as a building block for proteins.
  • In certain liver conditions such as liver cirrhosis or liver inflammation, cysteine synthesis may be impaired. In such cases, additional cysteine intake may be necessary to meet the cysteine requirement.
  • Smoking can increase the demand because it produces free radicals and causes oxidative stress. Cysteine has antioxidant properties that can help reduce oxidative damage.

Cysteine Foods / Sources

A vegan diet typically provides sufficient cysteine as there are numerous plant-based foods with high cysteine content. The following list reveals good sources of cysteine in each food group:

Sulfur for Cysteine Synthesis

Naturally occurring sulfur in food can contribute to cysteine synthesis in the body. Sulfur is an essential component of cysteine, as cysteine is a sulfur-containing amino acid. The body requires sulfur to produce cysteine. By consuming sulfur-rich foods, the body obtains additional sulfur that can be used in the synthesis of cysteine.

Vegan Cysteine Diet

The following list shows recipe examples for vegan dishes that contain cysteine:

  • Red lentil soup with vegetables and spices
  • Quinoa salad with black beans, avocado, and cilantro
  • Sautéed tofu with broccoli and garlic sauce
  • Vegan chili with kidney beans, bell peppers, and tomatoes
  • Chickpea curry with spinach and basmati rice
  • Vegan burritos with pinto beans, rice, and guacamole
  • Sautéed tempeh with stir-fried vegetables and teriyaki sauce
  • Quinoa burger in a whole wheat bun with homemade BBQ sauce
  • Sautéed broccoli with garlic and roasted pine nuts
  • Lentil Bolognese with whole wheat noodles and vegan Parmesan
  • Vegan sushi rolls with avocado, cucumber, and marinated tofu
  • Tofu scramble with bell peppers, onions, and spices
  • Vegan Thai curry with vegetables and coconut milk
  • Smoked tofu sandwich with grilled vegetables and mustard dressing