Table 1.

Impact of diet patterns/types (A), nutrients (B) other nutritional factors (C) and food preparation/production (D) on gut barrier function, inflammation and the microbiome.

(A) Diet Patterns/Types
Gut Barrier Function	Inflammation	Microbiome
		Overall diet can affect production of inflammatory/anti-inflammatory metabolites by microbiome [14] A “tolerant” gut microbiome may reduce expression of IL-33 and TSLP and may protect against sensitization to food allergens [15]. (mainly murine models)
Western type diet: high saturated/trans fat and protein; low fiber: may affect goblet cell function and reduce mucus layer [16] in murine models		Western-type diet: high saturated/trans fat and protein; low fiber: Can lead to low microbial diversity. Reduces populations in the phylum Bacteroidetes and increases Firmicutes and Proteobacteria in murine models Reduces populations in the phylum Bacteroidetes and increases Firmicutes and Proteobacteria in human studies [17,18,19,20]
		Higher diet diversity is associated with a more diverse gut microbiome in human studies. Diet diversity has been reported to prevent allergic disease [21], but it’s direct role in the management of food allergy has not been investigated [22,23,24] High levels of butyrate and proprioate and a diet high in fermented foods, fruit and vegetables and fish infancy is also associated with reduced allergy outcomes [25].
(B) Nutrients
Gut Barrier Function	Inflammation	Microbiome
	Vitamins–particularly Vitamin A and B9, affect T-regulatory cell function and act as ligands [26,27] as demonstrated in murine models.
Omega-6 fatty acids: enhance tight junctions [28] in murine models	Long chain poly-unsaturated fatty acids particularly omega-3 fatty acids: suppress allergic inflammation via its effect on resolvin D1 and peroxisome proliferator-activated receptors (PPAR) in murine models [29] Can also affect the FADS1 genotype (rs174550) [18,19]
Acid; Docosahexaenoic Acid (long chain omega 3 fatty acids) [30,31]	hsCRP, IL-6, TNF-alpha [30,31]
Dietary Sodium [32,33,34,35]	Increased Th-17/T-regulatory ratio
Dietary Genistein and Daidzein (soy isoflavones) [36]	Decreased CRP
	Amino acids: play and important role in cell wall structures in murine models [37]	Amino acids: Certain amino acids such as D-tryptophan may affect the production of bacterial products that can positively affect immune mediated diseases as shown in murine [37].
(C) Other Nutritional Factors
Gut Barrier Function	Inflammation	Microbiome
Advanced glycosylated end products (AGEs): may affect epithelial cell function as shown in murine models [38,39]	AGEs may affect inflammatory processes, particularly via its effect on IL-33 and TSLP as shown in mice [40]	AGEs: may negatively affect the microbiome composition as shown in a rodent model [41].
AGE content of foods may be affected by sugar content, grilling or roasting meats, high fat content, highly processed foods, fruit juices [42], high fructose corn syrup [43,44] and fizzy drinks [45]. Steaming, boiling, slow-cooking and using acids when cooking can reduce the amounts of AGEs produced [40].
		Prebiotics: selectively stimulate the growth of beneficial bacteria and might offer protection against effects of AGEs as shown in a human trial [46]
Fiber: Short chain fatty acids (SCFAs) are produced through the fermentation of polysaccharides and improve gut barrier function via its effect on IL-22 (promoting mucus production) as shown in murine models [47,48]	Fiber: Short chain fatty acids (SCFAs) are produced through the fermentation of polysaccharides and reduce allergic inflammation as shown in murine models [47,48]
		Polyphenols: Increase gut microbial diversity [49,50] indicated by human studies
Emulsifiers e.g., polysorbate 80 and carboxymethylcellulose may destroy the epithelial mucous layer in the gut as shown in mice [51]	Emulsifiers e.g., polysorbate 80 and carboxymethylcellulose, promote inflammation as shown in mice [51]	Emulsifiers e.g., polysorbate 80 and carboxymethylcellulose, alter gut microbial composition as shown in mice [51]
(D) Food Preparation/Production
Gut Barrier Function	Inflammatory Processes	Microbiome
		Uncooked foods, cooking methods and processing can affect the natural microbial load of foods—Fresh foods contain their own microbiome, including nonpathogenic bacteria (e.g., Lactobacillus plantarum on fruits and vegetables) [52,53]
		Phthalates (a chemical compound from packaging) found in fast foods [54] and some initial data from murine models indicate that it may reduce microbioal diversity in the gut [55]

AGEs: advanced glycytion end products; CRP: C-reactive Protein; IL: interleukin; FADS1, fatty acid desaturase 1; TNF: tumor necrosis factor; Th: T helper cell; TSLP: thymic stromal lymphopoietin; SCFAs: short-chain fatty acids. Bold indicates the particular nutrient factor studied.