Nutritional epigenetics is a science that studies the effects of nutrition on gene expression and chromatin accessibility. It is a subcategory of nutritional genomics that focuses on the effects of bioactive food components on epigenetic events.

History 
Changes to children’s genetic profiles caused by fetal nutrition have been observed as early as the Dutch famine of 1944-1945. Due to malnutrition in pregnant mothers, children born during this famine were more likely to exhibit health issues such as heart disease, obesity, schizophrenia, depression, and addiction.

Biologists Randy Jirtle and Robert A. Waterland became early pioneers of nutritional epigenetics after publishing their research on the effects of a pregnant mother’s diet on her offspring’s gene functions in the research journal Molecular and Cellular Biology in 2003.

Research 
Researchers in nutritional epigenetics study the interaction between molecules in food and molecules that control gene expression, which leads to areas of focus such as dietary methyl groups and DNA methylation. Nutrients and bioactive food components affect epigenetics by inhibiting enzymatic activity related to DNA methylation and histone modifications. Because methyl groups are used for suppression of undesirable genes, a mother’s level of dietary methyl consumption can significantly alter her child’s gene expression, especially during early development. Furthermore, nutrition can affect methylation as the process continues throughout an individual’s adult life. Because of this, nutritional epigeneticists have studied food as a form of molecular exposure.

Bioactive food components that influence epigenetic processes range from vitamins such as A, B6, and B12 to alcohol and elements such as arsenic, cadmium, and selenium. Dietary methyl supplements such as extra folic acid and choline can also have adverse effects on epigenetic gene regulation.

Researchers have considered dietary exposure to heavy metals such as mercury and lead primary epigenetic factors leading to increased autism and attention deficit hyperactivity disorder. High-fat and low-protein diets during pregnancy can also increase the risk of obesity in infants. The consumption of phytochemicals can also positively affect epigenetic-based mechanisms that inhibit cancer cells. Research has also suggested a link between nutritional epigenetics and the pathophysiology of major depressive disorder.

Epigenetic Stressors 
Evidence of the generational transmission of epigenetic mechanisms in humans was first discussed by Champagne in 2008 in the context of maternal stress with food insecurity being one type of stressor that can impact gene expression via changes in DNA methylation patterns. Another type of stressor is a poor prenatal diet that results in nutritional insufficiency and fetal epigenetic reprogramming that creates the blueprint for the development of diseases later in a child’s life. Depending on geographical region, food quality issues may impact epigenetic inheritance via changes in methylation patterns associated with dietary heavy metal exposures, especially in the case of autism and attention deficit hyperactivity disorders (ADHD).

Food insecurity 
Food insecurity refers to the inability to access enough food to meet basic needs and is associated with an increased risk of birth defects associated with DNA methylation patterns. An expectant mother who is food insecure will likely be under financial stress and unable to secure enough food to meet her nutritional needs. Her geographical location may be in a food desert where she is unable to access enough safe and nutritious food. Food deserts are linked to food insecurity and defined as areas of high-density fast-food restaurants and corner stores offering only unhealthy highly processed foods at low prices.

Poor prenatal diet 
Poor prenatal diet or unhealthy diet has been shown to affect DNA methylation patterns and contribute to the development of type 2 diabetes, ADHD, and early onset conduct problems in children.  Characteristics of an unhealthy prenatal diet leading to changes in DNA methylation patterns include the increased intake of high fat/sugar ultra-processed food products along with the inadequate intake of nutrient rich whole foods (e.g. fruits and vegetables). High-fat and low-protein diets during pregnancy can also increase the risk of obesity in infants. Dietary methyl supplements such as extra folic acid and choline can also have adverse effects on epigenetic gene regulation. The current global food system is plagued by issues that adversely affect human health through multiple pathways with contaminated, unsafe, and altered foods being one of the most common factors associated with unhealthy diet.

Food quality 
Food quality issues vary from one geographic region to the next depending on country, food safety practices, and manufacturing and agricultural regulations regarding heavy metal, pesticide residues, and other hazardous exposures of concern. To reduce exposures to chemical hazards such as pesticide and heavy metal residues, the World Trade Organization (WTO) sponsored agreements between countries to establish codes of best practices, issued by the Codex Alimentarius Commission, that attempt to guarantee the trade of safe food.  Despite the best practices in use, heavy metal and pesticide residues are still found in the food supply.  Pre-natal and post-natal dietary exposures to inorganic mercury and lead residues resulting from unhealthy diets have been shown to consistently impact important gene behaviors in children with autism and ADHD. Prenatal organophosphate pesticide exposure has been shown to impact DNA methylation in genes associated with the development of cardio-metabolic diseases.

References 

Nutritional science
Genetic mapping
Genomics
Nutrition
Medical genetics
Epigenetics