Gene in Focus – GSTM1 & GSTT1 or DETOX Gene

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Gene in Focus – GSTM1 & GSTT1 or DETOX Gene

This week, we turn our attention not to a single gene, but two that play a role in determining our requirements of cruciferous vegetables, which include broccoli, cabbage, cauliflower, kale, and everyone’s favourite, Brussels sprouts. These foods contain plenty of compounds that are beneficial for our health, but one that we are most interested in for these genes are glucosinolates, which have been researched for their effects on cancers.
This week, we turn our attention not to a single gene, but two that play a role in determining our requirements of cruciferous vegetables, which include broccoli, cabbage, cauliflower, kale, and everyone’s favourite, Brussels sprouts. These foods contain plenty of compounds that are beneficial for our health, but one that we are most interested in for these genes are glucosinolates, which have been researched for their effects on cancers.
Within the body, these glucosinolates are metabolised to something called isothiocyanates, and it is this substance which potentially has cancer reducing effects. These genes are called GSTM1 and GSTT1, and they form enzymes that are part of the phase-II detoxification pathway – the way our body gets rids of various toxins, including medications and pesticides found in food. These genes are subject to something called an insertion/deletion polymorphism, similar to a gene we met earlier, ACE. Individuals with the inserted genotype have good function of these enzymes, and those with the deleted genotype have a reduced function, which could be problematic if cruciferous vegetable intake was low. It’s estimated that about 50% of people have the deleted form of GSTM1, and about 25% of people have the deleted form of GSTT1.
A study from 2003 looked at the impact of these genes on markers of DNA damage in 634 subjects, taken from the European Prospective Investigation into Cancer and Nutrition (EPIC) study. Blood tests were carried out to test for DNA damage, and the subjects were genotyped for a number of genes, including GSTM1 and GSTT1. When looking at the impact of diet and GSTM1 on DNA adducts (a segment of DNA bound to a cancer-causing chemical), there was found to be a very strong relationship between those who ate the greatest amount of leafy vegetables – including cruciferous vegetables – and DNA adducts; those eating the most of these vegetables had the lowest amount of adducts. An interesting finding occurs when you compare those with the GSTM1 insertion genotype with those who have the GSTM1 deletion genotype; in the lowest two tertiles for green leafy vegetable intake, those with the deletion genotype have greater amounts of DNA adducts, whilst in the highest tertile, they actually have lower amounts of adducts compared to the insertion group. This effect could well be because both GSTM1 and GSTT1 enzymes metabolise Isothiocyanates, those healthful compounds found in cruciferous vegetables, and so having the deletion genotype means that a person metabolises them slower, allowing them to have their effect for longer. This is a great example of how the environment has a big role to play in the risk associated with certain genes; the same genotype can be “good” or “bad” depending on the environment. r
Based on these two genes, DNAFit can make some general recommendations. If you have the inserted (I) version of both genes, we would recommend that you consume the normal amount of cruciferous vegetables; around 1-2 servings per week as a minimum. However, if you have at least one deleted (D) version, we recommend a higher amount of cruciferous vegetable intake – a minimum of 3-4 servings per week.
GSTM1/GSTT1 Genotype Effect
I The I allele indicates that these enzymes work well, and the standard intake of cruciferous vegetables is recommended.
D The D allele indicates that these enzymes aren’t produced well by the body, and an increased intake of cruciferous vegetables (3-4 portions per week) is recommended.

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