Table 2 ∣.

Dietary factors influencing the gut microbiome, altering the risk of kidney stone disease

Increased dietary factor	Effects on gut microbiome		Potential implications for urolithiasis	Effect on risk of specific stone types
Fibre	Expands microbial diversity	Increases oxalate degradation capacity of microbial networks; enhances microbial production of short-chain fatty acids	Reduced dietary oxalate absorption and urinary excretiona	↓CaOx stones
Oxalate	Selects for oxalate-degrading bacteria	Increases oxalate degradation and promotes oxalate secretion into the digestive tract160	Reduced dietary oxalate absorption and urinary excretiona
Legumes	Promote colonization of bacteria that produce short-chain fatty acids	Increases gut barrier161 and reduces inflammation	Reduced dietary oxalate absorption and urinary excretiona
Inulin-type fructans		Improves colonic mucosa absorptive capacity	Increased dietary magnesium absorption162 and urinary excretion
Fructo-oligosaccharides	Increase bacterial production of butyrate	Promotes skeletal resistance to parathyroid hormone163	Reduced urinary calcium excretion	↓CaOx stones ↓CaPhos stones
Various polysaccharides and disaccharides (e.g. inulin, lactulose)	Promote colonization of Bifidobacterium longum and other Bifidobacteria164	Reduces bone resorption, potentially by downregulating osteoclast activity164	Reduced urinary calcium excretion
Phytoestrogens	Provide substrate for microbial production of equol	Equol binds to human oestrogen receptor to decrease bone resorption165	Reduced urinary calcium excretion
Animal meat (including fish and seafood)	Selects for sulfidogenic bacteria	Increases bacterial production of sulphuric acid, leading to increased intestinal permeability166	Increased dietary oxalate absorption and urinary excretion	↑CaOx stones
Salt (sodium chloride)	Suppresses colonization of Bifidobacteria and Lactobacillus129	Reduces oxalate degradation capacity of microbiome	Increased dietary oxalate absorption and urinary excretion
Saturated fats	Increase abundance of lipopolysaccharide-bearing bacterial species	Activates Toll-like receptors on immune cells and increased intestinal permeability and inflammation167	Increased dietary oxalate absorption and urinary excretion
	Promote colonization of species associated with decreased insulin sensitivity131	Promotes defect in ammonia genesis leading to lower urinary ammonium excretion132	Overly acidic urine	↑Uric acid stones

The listed effects do not account for synergy between dietary factors; the impact of any one dietary factor is likely to be less important for the gut microbiome than the dietary pattern as a whole. CaOx, calcium oxalate; CaPhos, calcium phosphate. ^aAssumes that higher oxalate consumption promotes concomitant increases in oxalate-degrading bacteria.