*2.3. Nutrigenomics and Nutri-Epigenetics*

The nutrigenomics-impact of dietary components starts early in life and can influence health and disease across life. Dietary components are used to produce metabolites that can impact gene expression directly or through epigenetic mechanisms. Functional groups (i.e., methyl-, acetyl-, phosphate-group, etc.) able to modulate gene expression without any changes in DNA sequence, can be synthesized by dietary components [36]. Folate, vitamins (B12, B2, B6) betaine and choline are necessary to synthesize S-adenosine methionine (SAM), the universal methyl group donor, by one carbon cycle. The availability of methyl groups depends on a folate-rich diet (i.e., green leaves, peas, beans, lentils, liver, etc.) and on folic acid supplementation during pregnancy. B12 is present only in animal food (i.e., eggs, meat, fish), so vegans need oral sublingual treatment (to avoid its hydrolysis by the liver). Reduced level of substrates required for one carbon cycle during pregnancy, has been associated to impaired DNA methylation at promoter level of genes that regulate growth and metabolic diseases (i.e., IL10, LEP, ABCA1, GNASAS and MEG3) in siblings [37]. Differences in DNA promoter methylation (i.e., INSIGF, LEP and GNASAS) were measured also according to sibling gender and gestational timing of the malnutrition, and were associated with increased risk in developing obesity in men and glucose intolerance in women later in life. DNA methylation has a key role in the cell differentiation and the methylation of carbon 5 at the cytosine of CpG island of promoter region is associated to gene silencing [38]. Furthermore, an epigenetic memory of multiple environmental conditions (i.e., diet, air pollution, noise pollution, life style, work, family, education, physical activities, etc.) acquired during early life, remains longer and it can influence adult phenotype as well as be epigenetically inherited from generation to generation [39].

High fat diet, low or high protein intake can address epigenetic responses associated to metabolic diseases (i.e., cardiovascular diseases (CVD), T2DM, obesity, HTN, etc.) in adulthood [40]. The nutrigenomic impact of dietary lipids has been extensively studied [41]. Longitudinal analysis shows that chronic uses of high dietary saturated fatty acids (SFAs) or/and sugars increase the risk to develop CVD [42]. Exposure to palmitic acid, a SFA contained in several types of food (i.e., meat, eggs, butter, palm and coconut oils etc.,) is able to activate inflammatory responses by inflammasome activation (i.e., NLRP3, IL-1β, IL-18), while this effect was not observed after monounsaturated fatty acid exposure with oleic acid [43]. Overall, the consumption of ultra-processed food, rich in fats and sugars, low in fiber and antioxidant/anti-inflammatory bioactive compounds, was associated with a rise of caloric intake (about 500 Kcal/day) [44] and with an increase of risk of CVD and all-causes mortality [45]. These findings should serve as an incentive for limiting consumption of ultra-processed food, and encouraging natural or minimally processed foods, as several national policies recommend.

Furthermore, nutrigenomic impact of high protein intake has been investigated; high protein intake (more than the recommended daily intake (RDI) of 0.8 g/Kg per day) increases the risk of prediabetes and T2DM [46]. In addition, the source of proteins is important; Mediterranean, vegan or whole-food plant-based diets significantly increase high-density lipoprotein cholesterol (HDL-C) and may reduce incidence and mortality of CVD. Adherence to the Mediterranean diet has been associated with a metabolic signature useful to predict CVD risk [47], and new epigenetic biomarkers have been identified to predict the risk and the severity of CVD [48].

Additionally, not only strict vegetarian diets, but also a less strict plant-based diets with limited animal products have been associated with low systolic and diastolic BP [49]. A large prospective cohort study has demonstrated that the replacement of animal protein with plant protein (3% of the energy) decreases the CVD mortality (risk reduction 11% in men and 12% in women) [50]. The positive effect of plant-based food is associated to the nutrigenomic activity (i.e., antioxidant, anti-inflammatory, etc.) of polyphenols contained in plants, the positive impact of fiber on gut microbiota richness and diversity, the folic acid and the essential fatty acid content [51].

In summary, nutrigenomics and nutri-epigenetics outcomes have demonstrated how and when animal and plant-based food contribute to influence molecular responses (with beneficial or detrimental effects), supporting the positive role of high adherence to the Mediterranean and/or plant-based diet to reduce the risk to develop CVD. Strategies for prevention should take into account also the inheritance of epigenetic biomarkers across generations.
