Folate is found in foods such as green leafy vegetables (uncooked best), legumes, eggs and some fruits. Folate from food can be easily destroyed by UV rays, preparation and cooking methods. This readily becomes dihydrofolatereductase (DHFR) which is the next part of its metabolism process.
Folic acid is not found in nature, it is synthesized and added to some foods such as bread. Folic acid does not readily become DHFR. It is oxidised which is why it is stable, cheap and ideal for adding to supplements and foods such as commercially produced bread.
To become biologically active in the body, folic acid requires conversion via the dihydrofolatereductase enzyme (DHFR) to tetrahydrofolate (THF) and then to 5-MTHFR with the help of the enzyme methlytetrahydrofolate reductase. THF plays an important role in our DNA and RNA manufacture and synthesis, hence those with reduced 5 MTHFR activity will not affect their DNA replication. Circulating folic acid that has not been converted through the stages of metabolism is referred to as ‘unmetabolised folic acid’ or UMFA and the jury is still out as to whether this causes a problem to health. One camp suggests UMFA can lead to cancer, the other, that the body reabsorbs it.
Folinic acid is the most stable natural form of folate found naturally in some foods. Folinic acid readily converts to THF without causing UMFA. It is not dependent on dihydrofolate reductase (DHFR) and bypasses steps required for the utilisation of folic acid
Folinic acid has a greater ability to cross the blood brain barrier, as it is not dependent on specific folinic acid receptors to facilitate transport. Calcium folinate is the form usually used but it can be unstable, is easily disturbed by cooking methods and gastric acid within the stomach.