The word "Nutrigenomics" is a combination of nutrition and genomics. Nutrition is about the relationship between food and health; genomics is the study of entire genetic makeup of an organism and how they are expressed and regulated. Therefore, nutrigenomics is a field which concerned about the relationship between diet and gene expression by describing the approach to nutrition and human health that studies the implication of genetic differences in human response to food and how food alter the gene expression, biochemistry, metabolism and promotion of health (Elliot R, 2002). In other words, nutrigenomics is the study and application of gene and nutrition interaction. Besides, nutrigenomics also provides a basis for understanding the biological activity of food components (Rawson N, 2008). In addition, nutrigenomics has also been described by the influence of genetic variation on nutrition by correlate the gene expression with a nutrient's absorption, metabolism and how it is eliminated from our body. In nutrigenomics, nutrients are seen as signals that are detected by a sensory system in the cell that tells the body cells about its environment (diet). Once the nutrient interacts with such system, it alters the gene, metabolite production and protein expression in depending on the level of nutrient it detected (Afman and Muller M, 2006). Hence, different diets will elicit different patterns of gene, protein expression and metabolite production. Such patterns of effects have been referred to as dietary signatures, where they are examined to investigate how homeostasis is influenced (Afman and Muller M, 2006).
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There are many ways on how nutrigenomics is useful to improve quality of life. Firstly, nutrigenomics define the causality relationship between specific nutrients and diet on human health by determining the mechanism of the effect of the nutrients or diet to human body. Besides, nutrigenomics helps to facilitate prevention through dietary modification when the diet-related diseases are detected in early stage. Nutrigenomics also allows the examination on how nutrients affect the genes present in the human genome. With all these reasons, nutrigenomics promotes and improves the understanding of people on how nutrition influence metabolic pathways and alter the homeostatic control in our body. Moreover, nutrigenomics is also able to demonstrate the impact of bioactive food compounds and its effect on human health, which should lead to the development of functional foods that will keep people healthy based to their individual needs. Then, this will further prevent development of chronic diet-related disease such as cardiovascular diseases, obesity and Type 2 diabetes mellitus. In addition, nutrigenomics also involve in finding markers of the early phase of diet-related diseases. At this phase, intervention with nutrition approach can restore patient's health. Once a marker has been found and measured in an individual, the stage of susceptibility of the person to develop the diet-related diseases can be quantified and personalized dietary recommendation can be then given to that particular individual and further improve his or her quality of life.
Cardiovascular disease (CVD) is one of the lifestyle diseases and it is the most common cause of death all over the world. In Malaysia, about 30% of deaths are caused by CVD (WHO, 2009). There are many factors that can lead to CVD. For example, elevated low density lipoprotein (LDL) level, low level of high density lipoprotein (HDL) and high level of total cholesterol. Diet has a significant effect on CVD. However, long term health benefits can be obtained from dietary proteins and bioactive non-nutrients, called phytochemicals, which could be either integrated into the diet or be part of the food itself. One of the foods that can be used to reduce the risk of getting CVD is soybean. Soybean contain soy protein and it contains phytoestrogens which bind to estrogen receptors in the body. Besides, soybean also contains high level of Isoflavones. There are three major isoflavones in soybeans which are genistein, daidzein and glycetein. Isoflavones have a non-steroidal structure. However, they possess a phenolic ring that enables them to bind the estrogen receptor and act either as estrogen agonists or antagonists (Makela et al., 1995).
One of the ways to prevent or reduce the risk of getting CVD is by lowering the LDL cholesterol level in our blood. The LDL is the major cholesterol-carrying lipoprotein in plasma and it is the causal agent of CVD and coronary heart disease. The major determinants of LDL cholesterol levels in the blood are depend on the number and activity of low-density lipoprotein receptor (LDLR). These LDLRs are mostly found on the surface of the hepatic cells. The LDLR controls the uptake of LDL from the circulation and its intracellular degradation by a process known as the LDLR pathway (Anne K Sautar, 2010). According to Manzoni et al, 2003, the peptides formed by the digestion of soy protein up-regulate hepatic LDLR in the mechanism for the cholesterol lowering effects of soy protein. Based on several clinical studies and researches, Sirtori et al (1995) suggested that soy protein can up-regulates LDLR in human. By consuming soy protein with isoflavones, LDLR will be stimulated and increase the uptake of LDL from the circulation and reduce the LDL level in the blood. This will further decrease the risk of getting cardiovascular diseases. Furthermore, the number of LDLRs is regulated by a negative-feedback loop. An increase in hepatocyte cholesterol level will suppress the transcription of LDLR genes and retain LDL in the plasma. In contrast, a decline in hepatic cholesterol will stimulates the transcription of LDLR genes and then removes the LDL from the plasma (Elizabeth G, 2003). In addition, Baum et al, 1998, suggested that isoflavones may increase the efficiency to eliminate LDL from the blood by increasing LDLR densities in the liver. Besides, Anderson et al (1995) also suggested that level of total cholesterol and LDL can be lowered by consuming soy protein with isoflavones. A review of 38 controlled studies on soy and CVD concluded that soybean is definitely effective in improving the cholesterol profile. Interestingly, there are some studies shown that with low concentrations of genistein could up-regulate LDL receptor activity and increase LDL receptor gene expression (Kanuck and Ellsworth, 1995). However, there is also some evidence that isoflavones are the active compound in soy in responsible for lowering the LDL in blood and may offer protection against CVD. Therefore, the mechanisms by which soy modulates blood cholesterol and lipoprotein levels in order to prevent or lower the risk of CVD need further research.
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There are many advantages of nutrigenomics. One of the advantages is nutrigenomics helps to improve our quality of life by promotes an increase of understanding on how nutrition affects metabolism, homeostatic control and introducing the prevention of chronic diet-related diseases to the people. Nutrigenomics also helps in preventing or delaying the onset of diet and lifestyle related disease such as obesity, cancer, CVD and diabetes mellitus. Apart from chemical drug treatment and therapy, nutrigenomics also acts as supporting element to fasten recover and prevent further damage caused by disease. For example, an individual that are diagnosed to have CVD, with the knowledge of nutrigenomics, they can change their dietary intake to lower their low density lipoprotein level and increase their high density lipoprotein level in their body to prevent and minimized the impact of CVD to their body. In addition, nutrigenomics also helps a country to save cost in a long-term prospect. This is because with the development of nutrigenomics, it can leads to prevention of diseases and thus reduces the cost of treatment, along with decrease in the country's burden of disease, which then decrease the cost of the government that allocates for health therapy and health services to the community.
When there are advantages, there will be disadvantages. One of the disadvantages of nutrigenomics is costly and time-consuming. Nutrigenomics researches need long-term intervention trials to determine the causal relationship between nutrition and ways of prevention, as well as the outcome of disease which is time-consuming and costly. The methods for measuring dietary intake are much more imprecise when compared to genetic or biochemical measurement. Another disadvantage of nutrigenomics is ethnical implication. Since nutrigenomics include genetic test by the usage of samples from identified populations, ethical and legal implication may appear. The management of genetic information, consent, confidentiality, non-medical uses of information by employers and insurers are some of the ethnical issues that may arise. Furthermore, nutrigenomics might misused by some companies. Recently, the interest of public in this field is increasing. As a result, in United States, some companies are taking this advantage by providing nutrigenomics services to public. These companies may mislead the consumer by making health-related predictions that are medically unproven or asking their customer to buy costly supplement that they claimed to be developed according to an individual's unique DNA. Moreover, nutrigenomics tests and researches require a large study population of patients and controls to investigate combinations of genetic variants and impact of nutrients in relation to a disease. Thus, it is difficult to visualize the combined data and analyzed, and in an integrated manner, how multiple gene and multiple nutrients interact simultaneously.
In conclusion, nutrigenomics has great potential to benefit medical science in the future. However, it is still only in its infant state and there are many uncertainties about its further development.