Protein oxidation and cysteine
Protein oxidation and cysteine


Protein is required for a paradigm known as “anabolic competence”, the body needs to remain in an anabolically competent state to keep all cells of the body growing, dividing and differentiating as they should.  When this competence is lost or affected by nutritional deficiencies it will lead to the breakdown of cells within the the body as they become an energy source. Anabolic competence is maintained by lean muscle mass and adequate protein intake is a requirement for the maintenance of lean body mass [1].

Cooking protein rich food increases the availability of certain nutrients and simultaneously decreases the availability of certain amino acids within the food we eat.  Specific amino acids important to hair, like methionine and cysteine, with a very reactive sulphydryl groups oxidise easily when exposed to heat or mechanical force.  As the processing and heating of meat contributes to the level of oxidation and availability of amino acids within the protein source, could this typo of food preparation be a link to hair loss?

Essential amino acid content of raw and boiled seeds of Prosopis Africana.

Essential amino acid content is reduced by boiling seeds.

Essential amino acid content of raw and boiled seeds of Prosopis Africana.

Essential amino acid content is reduced by boiling seeds.


Proteins serve many critical functions in the the human body.  They act as antibodies, enzymes, messengers, transporters on the surface of the cell membrane.  Proteins also provide structural integrity to the skin, hair, tissue, organs and muscle.  Proteins are made up of individual amino acids, each individual amino acid has a specific characteristic.

Whilst most individual amino are simply building blocks to make protein, some have a number of specific roles.

Maintaining adequate protein levels within the body is crucial for essential biological activities such as regulation of gene expression, cell signalling and the maintenance of metabolic pathways.

Protein metabolism is a description of the pathways that direct the building up and breaking down of proteins and the amino acids that make them.  Anabolism describes the process of making a protein from amino acids and catabolism describes the process of breaking down proteins into amino acids.  The balance between the making of proteins and the breaking down of proteins directly effects lean muscle mass.

When there is low dietary protein availability due to diet, inflammation of the gut or malabsorption, the muscles will be broken down to release amino acids in to the blood stream for circulation.  A limited availability of specific amino acids will also lead to a stimulation of lean muscle mass breakdown.   If muscles are continuously broken down then there will eventually be a loss of lean body mass.

Protein formation and hair loss

The formation of proteins from amino acids.

A peptide is a molecule composed of two or more amino acids.


Lean muscle mass directly impacts the basal metabolic rate, a higher lean muscle mass equates to a higher metabolism and leads to faster hair growth.  Lean supports immune activity and contributes to strong bones, the Mediterranean Intensive Oxidant Study found that lower levels of skeletal muscle mass (a major component of lean muscle mass) was correlated with thinner bones.

A study of over 13,000 completed over a 6-year timeframe showed low levels of muscle mass also contributes to increased insulin resistance [2].  The research showed showed for every 10% increase in skeletal muscle mass, there was an 11% decrease in insulin resistance.  Insulin resistance has been linked to higher levels of circulating androgen and DHT levels.  Early androgenic alopecia has been shown to be an indicator of insulin resistance [3].

Lean muscle mass and hair growth


The utilisation of proteins refers to the amount of of ingested protein that can be digested and used in the body for protein synthesis.  To maintain adequate levels regular intake of protein is essential.  Protein provides a source of nitrogen and supports essential metabolism.

When a meal containing protein is consumed, the dietary proteins are broken down into amino acids by digestive enzymes, after this point they are available for the building of proteins.

There is no way for the body to store proteins or amino acids, there is a tightly regulated pool of around 100 grams in cells and the blood stream.  This pool is maintained by the continuous breaking down and building of proteins within cells.  This pool can respond quickly to changes in demands of the cell, if the cell needs more protein than is available in the cell.

The cell can also respond to a limited availability of specific amino acids for  the production of all non essential proteins like the keratin needed for hair growth. Keratin is a unique protein due to its high sulphur content,  if sulphur containing amino acids are low in availability will cease.

It is likely there is an inherant hierarchy that allows reduction of keratin formation in the hair fibre before there is a reduction in the keratin fibre that make up the skin and nails.  If the cell does not have enough amino acids to make the protein it need it will instantly halt production until that amino acid is available.

Sulphur is also essential for a process known as sulphonation and sulphurylation, this is a process that allows the addition of a sulphur group to another molecule.  This process allows for transport of hormones in the blood to target tissue, the removal of toxins and the conjugation of bile for the uptake of fat-soluble vitamins.

Hair loss and cysteine sulphur group


The modification of methionine and cysteine leads to protein-to-protein cross linking that eventually leads to protein aggregates.  For a protein to be absorbed it must first be broken down by digestive enzymes into its constituents amino acids.

The strong sulphur-sulphur cross linkages prevent enzyme breakdown and leads to a low absorption or sulphur containing proteins and an increased amount of sulphur entities in the digestive tract which can lead to adverse gastrointestinal symptoms such as:

  • intestinal discomfort and indigestion
  • nausea
  • digestion
  • dehydration
  • diarrhoea
  • bloating

The oxidation of proteins intrinsically lowers the nutritional value and specifically lowers the absorbability of amino acids crucial for detoxification process and the building of keratinous structures like the hair and skin.

Protein oxidation and cysteine linked to hair loss

Protein oxidation and cysteine. Heating foods to temperatures below 100˚C aids in digestion, heating proteins over 100˚C can lead to extensive protein oxidation which decreases protein susceptibility to digestive enzymes.

Protein oxidation and cysteine linked to hair loss

Protein oxidation and cysteine. Heating foods to temperatures below 100˚C aids in digestion, heating proteins over 100˚C can lead to extensive protein oxidation which decreases protein susceptibility to digestive enzymes.


Protein oxidation is defined as the modification of a protein induced either by the direct reactions with reactive oxygen species, lipid reactions or by indirect reactions with by-products of oxidative stress. Reactive oxygen species can cause protein fragmentation or protein-protein cross-linkages.

Although all amino acids can be modified by reactive oxidative species, cysteine and methionine are the most susceptible to oxidative changes due to high reaction susceptibility of the sulphur group in this amino acid. Cysteine and methionine have very reactive sulphydryl group side chains, this puts them in special position that cannot be replaced or substituted by any other amino acid.


Cystiene is the main amino acid in nails, skin, and hair and it is especially important in the creation of collagen and other soft tissue stuctures such as the gut. Cysteine, because of disulphide bridges, plays very important role in stabilization of all protein structures. With cysteine being the most susceptible to strong sulphur to sulphur cross-linking that can not be broken down by digestive enzymes, it naturally follows that there will be a reduced ability to absorb cysteine. In cases of hair loss, adding sulphur to the diet can offset some effect of protein oxidation by providing an alternative source of sulphur that can be incorporated into cysteine during protein manufacture.  For overall health, lowering the intake of proccessed meat would be of great benefit.


  1. Kitada, M., Ogura, Y., Monno, I. and Koya, D., 2019. The impact of dietary protein intake on longevity and metabolic health. EBioMedicine, 43, pp.632-640.
  2. Srikanthan, P. and Karlamangla, A.S., 2011. Relative muscle mass is inversely associated with insulin resistance and prediabetes. Findings from the third National Health and Nutrition Examination Survey. The Journal of Clinical Endocrinology & Metabolism, 96(9), pp.2898-2903.
  3. Matilainen, V., Koskela, P. and Keinänen-Kiukaanniemi, S., 2000. Early androgenetic alopecia as a marker of insulin resistance. The Lancet, 356(9236), pp.1165-1166.