Gene-nutrient interactions

Related Terms

Diet, DNA, gene-nutrient interactions, genes, genome, human genome, metabolome, metabolomics, nutrigenetics, nutrition, nutritional genetics, nutritional genomics, nutritional guidelines, PCR, phenotype, polymerase chain reaction, polymorphisms, proteome, proteomics, single nucleotide polymorphisms, SNP.

Background

The incidence of obesity, heart disease, and type 2 diabetes has dramatically increased in recent years. Because both diet and genetics are factors in these diseases, scientists are now examining the relationship between nutrients and gene expression.
Nutrigenomics is a new field of research that examines how diet affects gene expression across an individual's entire genome. Nutrigenetics is an overlapping field that focuses on individual genes, rather than the entire genome, and how they relate to dietary requirements. A genome is the complete set of genetic material contained in an organism. Genes are the individual units that provide the instructions for proteins that perform all of the functions in the organism.
Some diseases are "monogenic" and involve only one gene while others are "polygenic" and involve several genes. Changes in gene sequence, or mutations, may cause disease by changing gene expression levels. Because gene expression can also be affected by diet, scientists use both nutrigenomic and nutrigenetic approaches to understand the dietary basis of certain diseases.
In nutrigenomics, nutrients are viewed as signals that tell the body how to behave. Cells respond to these signals by changing gene expression, which can in turn change protein expression and alter metabolism. The field of nutrigenomics seeks to identify the changes in gene expression that are elicited by nutrients. These changes are measured and analyzed and may then be used to determine how susceptible an individual is to certain diseases. Because genetic makeup can determine unique nutritional requirements and responses to different foods, dietary advice may then be tailored to an individual's needs.
Nutrigenomics also seeks to identify certain foods and single nutrients that can be consumed for an intended effect. These "nutraceuticals" may potentially be used to prevent or treat a number of diseases.

Methods

Single nucleotide polymorphism (SNP): DNA is made up of sequences of four different nucleotides or "bases." These are adenosine (A), cytosine (C), guanine (G), and thymine (T). Each base has a complement. A is complementary to T and vice versa. C is complementary to G and vice versa. The entire human genome is made up of a string of three billion base pairs. Sometimes there is a variation in sequence of bases or nucleotides. This is called a single nucleotide polymorphism (SNP). Studies have found that some SNPs tend to occur with certain traits or diseases. In some cases, these SNPs can affect gene expression or the ways in which humans respond to nutrients and foods.
Population studies: The genetic makeup of all humans is about 99.9% identical. Because the human genome is so large, however, even that 0.1% allows for many differences. Since differences between individuals are greater than differences between populations, researchers use populations to study genetic influences on disease. By studying the DNA of populations, researchers can pick out what makes them different.
Polymerase chain reaction (PCR): Real time polymerase chain reaction (RT-PCR) quantitation of genes analyzes one gene at a time. This process allows scientists to detect and quantify specific DNA sequences. When genes are expressed, the DNA sequence is transcribed into RNA. Gene expression can be quantified using RT-PCR, which converts the RNA back to DNA.
Microarrays: Gene expression microarrays can analyze the expression of many genes at once. This genetic method has been used to identify new genes associated with certain diseases, to classify cancerous tumors, and to predict patient outcomes.

Research

General: Nutrigenomics aims to identify a broad range of gene variants and their significance in health status. With this information, researchers may create individualized strategies for health promotion and disease prevention.
Because diet is a modifiable risk factor, one that can be changed to alter health outcomes, it has become the focus of much attention and research. Current research focuses on individual nutrients (such as vitamin C), individual foods (such as broccoli sprouts or fish), and/or dietary patterns (for example, the Mediterranean diet). Scientists hope that an understanding of the interaction between genes and diet will help identify targets for the prevention or delay of chronic diseases and/or a reduction of disease symptoms.
Diet: The recognition that certain diets can promote health has prompted research into what substances are responsible for these positive effects. The Mediterranean diet, which is rich in fruits and vegetables and high in monounsaturated fat (mostly from olive oil) is associated with low rates of obesity and heart disease. Research on the Mediterranean diet has focused on the relationships between individual dietary components and the diet as a whole and improved disease rates. To ensure that improved disease rates are directly related to nutrient consumption, and not to other factors, such as lower stress levels and active lifestyles, researchers have studied the effects of this diet on disease rates while controlling for other potential factors.
Disease: Because common variations in sequences of genes produce differences in traits, such as potential to gain weight, rate of metabolism, and tendency to develop certain diseases, research has focused on the genetic makeup and dietary habits of individuals with certain diseases. There is much interest, for example, in understanding individual risk and the contribution of diet in the development and worsening of type 2 diabetes.

Implications

Ethical: The field of nutrigenomics raises several potential ethical concerns. These include who has access to the results of nutrigenetic tests, how individuals will access these results, and how people will receive nutrition-related advice. In addition, the regulation of direct-to-consumer marketing of nutrigenetic tests and protection of consumers from unreliable tests, false claims, and unproven therapies will be of concern. Ethical implications for researchers include how different fields of study should collaborate to contribute to a better understanding of this field and its capabilities.
The acquisition, storage, and use of genetic information will likely pose difficult ethical questions. These include maintenance of confidentiality and the right to privacy. It is also possible that health insurance companies and employers may discriminate against people on the basis of this information.
Information that comes from the study of nutrigenomics may cause individuals and societies to develop new social values, norms, and responsibilities. It may change the way people perceive human health and disease and shift the focus of medical care from treatment of patients to disease prevention among individuals. Ethical considerations may also include the extent to which nutrigenomics can alter people's relationships with food, the boundaries between health and disease, and beliefs about the practice of medicine.
Legal: Nutrigenomics raises several legal issues. These are related to who will have access to the results of nutrigenetic tests; how this information will be accessed; how direct-to-consumer marketing of nutrigenetic tests is regulated; and how consumers will be protected from unreliable nutrigenetic tests, false claims, and unproven therapies. Laws specific to these issues will need to be created and enforced.
The acquisition, storage, and use of genetic information will pose difficult legal questions involving the maintenance of confidentiality, the right to privacy, and the risk of discrimination based on this information. In addition, genetic analysis of children will bring up new questions about the limits of parental authority.
Medical education: While practical applications of nutrigenomics are currently limited, there is a need to educate clinicians who will have an impact on these applications. Currently, primary care physicians have minimal training in nutrition and genetics. Medical geneticists are few and far between. Registered dietitians are nutrition experts who have a growing interest in and knowledge about nutrigenomics, but they also require considerable training to bring nutrigenomics into their practice.
Insufficient or lack of timely medical education has the potential to restrict consumer access to nutrigenomics. In addition to the need for education about the practical applications of nutrigenomics, there will be a need for education regarding the ethical and legal implications of this field.
Once practical applications of nutrigenomics information become available, time will be required to accumulate population data, understand the significance of a given gene mutation in disease, and develop suitable diagnostic tests.
Nutritional: The control of food intake is strongly affected by genes that determine taste receptors and a number of peripheral signaling peptides, such as insulin, leptin, ghrelin, and cholecystokinin. Total dietary intake, individual nutrient intake, and how satisfying various foods are will influence the effects of these genes.
Currently, most nutrition studies are created with the assumption that all persons have average dietary requirements. These studies often do not plan for the large subset of people who have requirements that are different from average. If nutrition studies could identify the differences between those who respond to certain nutrients and those who do not based on nutrigenomic information, the ability to detect differences between groups could be greatly increased. In turn, dietary recommendations could be appropriately tailored to individual needs.
The ultimate aim of this field is to provide "personalized nutrition." The study of nutrigenomics may allow researchers to develop individual foods and/or whole diets that are targeted to individual genetic makeup. In this way, specific nutrients, foods, or diets may prevent and manage conditions to which an individual with a particular genetic makeup is susceptible.

Limitations

Because of the complex nature of foods, including nutrient variability, nutrient-nutrient interactions, and the genetic variations among individuals who consume a certain diet, it will be difficult to determine cause and effect with certainty.
The field of nutrigenomics has the potential to generate overwhelming quantities of data. How to classify and interpret this data will inevitably present unique challenges.

Future research

Currently, most nutrition studies are created with the assumption that all persons have average dietary requirements. These studies often do not plan for the large subset of people who have requirements that are different from average. If nutrition studies could identify the differences between those who respond to certain nutrients and those who do not based on nutrigenomic information, the ability to detect differences among groups could be greatly increased. In turn, dietary recommendations could be appropriately tailored to individual needs.
The field of nutrigenomics recognizes that current nutritional guidelines may be ideal for only a relatively small percent of the population. Future research efforts may focus on how to provide population-based guidelines while taking individual variability into account.
Identifying key genetic information that is likely to influence the health of an individual provides an approach to optimizing nutrition at both the population and the individual level.
A significant number of human studies focus on the interactions between genetic mutations and response to diet, including the risk of obesity. Many of the same genetic characteristics and dietary patterns that have an effect on obesity or heart disease also have an effect on cancer. Future research may use this information to better understand such areas of overlap.
Despite the growing body of information about gene-nutrient interactions, the translation of this information into medical practice has been slow. This is due to the time required to accumulate population data, understand the significance of a given gene mutation in disease, and develop suitable diagnostic tests.

Author information

This information has been edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com).

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