Nutrigenetics – nutrition compatible with genes

Nutrigenetics is a field of science that studies the relationship between genes and human nutrition. Nutrigenetics assumes that nutritional recommendations can not be the same for the entire population because we are different in genetic terms. What exactly is nutrigenetics and is it worth to feed in accordance with your own genes?

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Nutrigenetics is a new field of science that studies the effect of genetic differences (polymorphisms) on the body’s response to nutrients and the risk of diet-related diseases.

Recommendations concerning the daily intake of nutrients such as vitamins, for example, are based on research on the general population and do not actually take into account the individual needs of each organism resulting, among others, from genetic differences. Therefore, the main assumption of nutrigenetics is individualization of the diet in such a way as to treat and prevent diet-related diseases. 

Genetic polymorphisms are small changes in the genome, which results in the occurrence of different genetic variants in the human population, which in turn affects the phenotype, that is how each of us looks and responds to environmental factors. Genetic polymorphisms may affect the metabolism of proteins, carbohydrates, fats, vitamins and the risk of disease development. 

The most common in the human genome are single nucleotide polymorphisms (SNPs), and more than 11 million have been described. 

Searching for genes responsible for diseases such as obesity or cardiovascular diseases is like looking for the proverbial needle in a haystack.

The human genome contains about 25,000 genes, and it is very rare that information in one gene affects only one feature. In addition, complicated processes of gene expression regulation depend on, among others from environmental factors do not allow to clearly indicate that, for example, gene A affects the metabolism of vitamin D. 

Therefore, in genetic studies, the so-called candidate genes, which are then studied in detail by scientists. The candidate genes for nutrigenetic research are selected using genome-wide association study (GWAS ). They consist in the study of very large populations (eg 200,000 people) with the selected feature (disease) and the control group without the examined feature (disease). Then, the genome of the subjects is searched for genetic polymorphisms and compared to the control group. Of course, the genes found in such studies can only potentially be related to a given trait (disease) and to demonstrate their cause and effect relationship, further basic and clinical research is needed. 

The nutrigenetic test is carried out similarly to other genetic tests.

To make it, the person’s DNA is needed, taken from a cheek swab or a saliva sample. Also, venous blood is taken from which lymphocytes are separated in the laboratory. The DNA is then isolated from the collected cells. For direct detection of genetic polymorphisms with DNA, molecular biology methods such as polymerase chain reaction (PCR) and Sanger sequencing are used. The test result is obtained after approx. 3 weeks. 

The nutrigenetic study detects genetic polymorphisms in selected genes.

In order to facilitate the identification of polymorphisms, each of them has been given an identification number, which starts with the letters rs, e.g. rs4988235 for the LCT gene polymorphism (the gene coding for lactase – the enzyme that breaks down lactose). If the nutrigenetic study studies this gene, the result should be information about the number of the polymorphism studied and the patient’s variant of risk. For example, a person with a C / C risk variant has decreased lactase activity and has several times higher risk of lactose intolerance than a person without a risk variant (C / T or T / T). If after drinking a person’s milk, symptoms of lactose intolerance occur, such as flatulence, or diarrhea, it should eliminate products containing lactose from the diet. 

Nutrition in accordance with genes has been known in medicine for a long time.

In addition to the mentioned lactose intolerance, another classic example is phenylketonuria. This disease is associated with a genetic deficiency of the enzyme phenylalanine hydroxylase, which results in the accumulation of phenylalanine in the body. Therefore, in patients with phenylketonuria a low phenylalanine diet is used.

Celiac disease – celiac disease.

It has been shown that people with celiac disease are carriers of specific polymorphisms in the genes coding for the histocompatibility complex (HLA-DQ2 and HLA-DQ8) proteins that predispose their immune system to recognize gluten as something foreign. This results in the activation of T lymphocytes and B lymphocytes that produce antibodies against their own tissues. In the case of celiac disease, the triggering factor is food containing gluten, and its elimination from the diet causes reemission of the disease. 

Folate metabolism and MTHFR gene polymorphisms. The MTHFR gene encodes the enzyme 5,10-methylenetetrahydrofolate reductase involved in the metabolism of folates. Folate, on the other hand, is necessary in the toxic transformation of homocysteine ​​to methionine, which in turn is converted to S-adenosylmethionine (SAM). SAM is an important source of methyl groups for various biochemical pathways. Therefore, folate deficiency may have an omni-directional adverse effect on the body. 

Studies have shown

Some polymorphisms of the MTHFR gene like rs1801133 can reduce the enzymatic activity of the MTHFR protein by up to 70%, thus affecting the bioavailability of folates for biochemical pathways. In the last few years, there have been many publications linking the MTHFR gene polymorphisms with chronic diseases. For this reason, we have recently been able to observe the fashion for binding polymorphisms of the MTHFR gene with such diseases as depression, myocardial infarction or problems with getting pregnant. Due to this, in 2017, the experts of the Polish Society of Human Genetics and the Polish Society of Gynecologists and Gynecologists issued a position in which they found that the evaluation of polymorphisms variants of the MTHFR gene has a small predictive value in terms of the reasons for recurrent miscarriages, the risk of childbirth with central nervous system malformation, chromosomal aberrations, including Down’s syndrome, risk of venous thrombosis, including deep veins, ischemic strokes, coronary heart disease, selected types of affective disorders, psychosomatic development disorders and intellectual disability or some diseases cancer. 

Nevertheless, the Polish Society of Gynecologists and Obstetricians in women planning pregnancy and pregnant women with reduced MTHFR enzyme activity (among others due to polymorphisms of the MTHFR gene) recommends intake of folates at a dose of 0.4 mg / day increased by another 0.4 mg, preferably in form of active folates. 

Summing up

Unfavorable variants of the MTHFR gene will not directly affect the risk of diseases such as ischemic stroke, but on the bioavailability of folates in the body and their possible deficiency. Individual nutrition is based on the additional risk of active forms of folates (preferably together with vitamin B12) and possibly monitoring their level in the blood.

The above example also shows that we can not extrapolate the results of studies on the metabolism of a single nutrient (in this case, folic acid) to the risk of diseases associated with its deficiency. 

Obesity and the FTO gene. The use of nutrigenetic research in diseases with a much more complex etiopathogenesis, such as obesity, for example, is more complicated, although we know that 70% of differences in body mass measured by body mass index (BMI) may be determined by genes. It is much easier to treat diseases dependent on a single gene as the previously mentioned phenylketonuria. Of course, the so-called monogenous obesity, which results in obesity is enormous already in early childhood. However, it occurs only in a few percent of the population. 

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You can read also: How to lower cholesterol?

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