Table 2.

The role of dietary components abundant in WD in the gut microbiota, immune system, intestinal barrier, and systemically.

Nutritional Component	Top Food Sources	Maximum Intake Limits Per Day/Week	Immunomodulation	Gut Microbiota Modulation	Intestinal Barrier Damage and Other Pathological Effects	Alternatives/Substitutes and Suggestions	Ref
Added/Free sugars	UPFDs or naturally present in unsweetened fruit juices, honey and syrups	<25 g (↓ 10% of total daily Caloric intake)	Pro-inflammatory environment	↑ Firmicutes/Bacteroidetes ratio, ↓ population of favorable butyrate producers (e.g., Lachnobacterium sp.)	Intestinal barrier disruption, endotoxemia, insulin resistance, visceral adiposity, cognitive dysfunction and addiction	Replacing added sugars consumption by intrinsic sugars (Whole fruits and vegetables) Using healthy sweeteners: Cinamon, vanilla, dates, raisins, banana, pumpkin, sweet potato, etc.	[350,351,352,353,354,355]
Refined grains	White bread, UPFDs, white flours and derivates	______________	↑ IL-6 and CRP levels; negative functioning in memory T cells	Probable effects ↑ Enterobacteriaceae while ↓ SCFA producers (Lachnospira)	Further evidence is needed to determine the possible effects of refined grains on the human body	Substituting refined with whole-grain products. Combining refined grains products consumption with fiber-rich vegetables and fruits may reduce their detrimental effects	[356,357,358]
Unhealthy fats	UPFDs, animal products, fast food	Daily fat recommendations is ≤ 30% of total Caloric intake	↑ pro-inflammatory cytokines IFNγ, TNFα, IL-1β and IL-6	↑Firmicutes/Bacteroidetes ratio	↓ Antimicrobial Paneth cells activity	Limiting the consumption of these fats by previous reported healthy fats (MUFAs, PUFAs) should be the basis of fat intake	[359,360]
Saturated fats	Animal-derived products (Milk, butter, meat, etc.) and plant-based foods (chocolate, nuts, cocoa, coconut and palm oils)	Not superior to 10% of daily intake	______________	______________	______________	Saturated fats are not as dangerous as thought before. It is more important to observe the quality and processing of the food, even if it presents a high content of saturated fats (e.g., high % dark chocholate, nuts or milk)	[361]
ω-6/ ω-3 ratio	Previously reported	ω-6/ ω-3 ratio must not exceed 4/1 proportion	Pro-inflammatory status	↑ Enterobacteriaceae, Segmented Filamentous Bacteria and Clostridia.	↑ Metabolic endotoxemia ↓ Production of PUFAs metabolites	Increase the intake of omega 3-enriched foods and reduce omega 6 foods	[212], [374,375,376]
Trans fats	Naturally in ruminant meats and UPFDs	Less than 1% of daily caloric intake	↑ Low grade chronic inflammation	Promotion of gut dysbiosis, particularly affecting BA producers bacteria	↑ Intestinal permeability, disruption of enteroendocrine cells	As it is prominently associated with ultra-processing, it should be avoided	[182], [362,363,364,365,366,367]
Refined oils	UPFDs, precooked foods	______________	Pro-inflammatory cytokines↑	Refined palm oil ↓ Akkermansia muciniphila, SFB, and Clostridium leptum growth Refined olive oil ↑ Desulfovibrionaceae, Spiroplasmataceae, and Helicobacteraceae along with Erysipelotrichaceae and Sutterellaceae ↓ Sunflower oil ↑ Sphingomonas and Neisseria spp. while ↓ Akkermansia muciniphilla and Bifidobacterium spp. Coconut oil ↓ Akkermansia muciniphilla abundance and ↑ Staphylococcus, Prevotella and Bacteroides sp.	↑ Intestinal permeability	Cooking with EVOO, or non-refined oils; look carefully at nutritional labeling, reduce precooked foods	[368,369,370,371,372,373]
Red and processed meats components over-consumption	Beef, veal, pork, lamb, mutton, horse, or goat meat consumed directly or after further processing (sausages, corned beef, and biltong or beef jerky)	______________	Neu5Gc contained in red meat, N-nitroso compounds TMA produced by red and processed meat precursors under conditions of dysbiosis may exert pro-inflammatory effects	Changes in certain microbial populations like Fusobacterium nucleatum, Streptococcus bovis/gallolyticus, Escherichia coli, and Bacteroides fragilis	Altering intestinal barrier ↑ Hyperproliferation of colonic enterocytes and correlation with colorectal cancer	Red meat is not a central component of the human diet and it could be completely displaced. However, it might be equally included in a healthy diet, although moderately (Not superior to 2 to 3 portions per week or 350–500 g according to AICR guidelines) Avoid or further limit processed meats consumption	[377,378,379,380] [383,384,385]
Salt	UPFDs	<5 g per day	Affecting gut microbiota-Th17 axis	↓ Lactobacillus sp. Oscillibacter, Pseudoflavonifractor, Clos-tridium XIVa Johnsonella and Rothia ↑ Parasutterella spp. Erwinia genus, Christensenellaceae, Corynebacteriaceae Lachnospiraceae and Ruminococcus	Promoting hypertension and CVD risk	Avoid consumption of high-salt foods, particularly ultra-processed. It is possible to cook with salt, but at moderate doses. Maintaining a proper balance of Na+ and K+ should help to avoid systemic defects of salt	[391,392,393,394,395]
Additives	UPFDs Processed foods	______________	Low/non caloric sweeteners are associated with a pro-inflammatory switch	↓ Lactobacillus and Bifidobacteria microorganisms; ↑ pathogenic bacteria Polyalcohols may act favorably in gut microbiota, acting like prebiotics ↑ Bifidobacterium and Lactobacillus	↑ Gut permeability, glucose intolerance, weight gain ↑ Gut integrity, no negative effects at cholesterol, glucose or insulin levels	Additives are a difficult component of diet to study, and most of them are inocuous or necessary for food conserving. However, some of them have provided accumulative evidence of their potential negative effects, so avoiding their consumption should be suitable	[396,397,398,399,400,401]

Maximum intake suggested has been extracted from World Health Organization (WHO) recommendations, although it could be favorable to even reduce these limits. Some alternatives and advice are given to avoid the overconsumption of these detrimental components, in order to progressively replace unhealthy with healthy ingredients.