Table 1.

Methods available for gut transit measurements and examples of their application in human gut microbiome research

Method		Region	Subjects	Gut microbiome and/or transit time-related findings	References
Direct transit time measures	Radio-opaque markers	CTT WGTT	48 healthy subjects	Distal CTT was associated with increased microbial α-diversity, rectosigmoid CTT was negatively associated with faecal SCFA and distal CTT was negatively associated with plasma acetate	18
			98 subjects	CTT positively associated with microbial community structure, microbial richness and microbial protein catabolism	10
			48 healthy subjects with slow WGTT*	RCT with arabinoxylan-oligosaccharide increased faecal Bifidobacterium and softened stool consistency without changing the WGTT	46
			14 healthy subjects†	WGTT positively correlated with urinary sulphate, faecal methanogens and negatively with total faecal SCFA, sulphate and bile salts	134
	Scintigraphy	WGTT GET SITT CTT	50 healthy and constipated patients	Colonic mucosal microbiota was not associated with CTT and was significantly different between the two groups, faecal microbiota was associated with CTT and breath methane	88
			36 healthy and 20 patients with liver cirrhosis	SITT was negatively correlated with B:F ratio and microbial dysbiosis index	215
	SmartPill	WGTT GET SITT CTT	11 obese and 11 normal weight subjects	Shorter SITT was associated with Bact2-enterotype, longer CTT was associated with Rum-enterotype	12
			33 healthy and 114 IBS-C patients	Colonic intraluminal pH levels were significantly lower in IBS patients compared with HC, and total faecal SCFA levels correlated negatively with CTT	216
			19 healthy and 9 constipated subjects	Rectosigmoid pH negatively correlated with Bifidobacterium spp and positively with Coprococcus spp	108
	Gas-sensing capsules	WGTT GET SITT CTT	4 healthy volunteers	SITT was slower with a diet high in fermentable fibre (~34 g/day) compared with a diet low in fermentable fibre (~22 g/day)	217
	Blue dye	WGTT	1102 subjects	Gut microbiome composition predicted WGTT, longer WGTT was linked with Akkermansia muciniphila, Bacteroides and Alistipes spp.	11
	Sweet corn	WGTT	31 healthy subjects	WGTT positively correlated with faecal BCFA and Coprococcus	107
Indirect transit time measures	Stool frequency	WGTT	69 subjects	B:F ratio and Bacteroides:unclassified_Ruminococcacea positively associated with stool frequency	218
			60 healthy subjects	B:F ratio was higher in a group with stool frequency of ≤2 times/week compared with one time/day or one time/2 day and ≥2–3 times/day	219
	Stool consistency (BSS)	CTT	53 healthy subjects	Stool consistency was positively correlated with species richness, Akkermansia and Methanobrevibacter abundances, and negatively associated with the B:F ratio,	17
			1126 subjects	BSS was associated with the B:F ratio, high BSS score positively correlated with F. prausnitzii	220
	Faecal water (stool moisture)	CTT	31 healthy subjects	Faecal water positively correlated with WGTT	107
			40 subjects	Stool moisture accounted for 4.3% of interindividual microbiota variation (absolute abundances)	79
			12 IBS patients and 12 controls	Association between stool consistency and microbial community structure/microbial richness	31
	Stool crosslinking	CTT	170 samples	Faecal acetate and methionine were predictive of stool consistency	221
	Breath test	Oro-caecal	14 healthy subjects	Oro-caecal transit time was positively correlated with WGTT	134

*Transit time also measured by BSS, faecal water content and breath test.

†Transit time also measured by the breath test.

BCFA, branched-chain fatty acids; B:F, Bacteroidetes:Firmicutes; BSS, Bristol Stool Scale; CTT, colonic transit time; GET, gastric emptying time; IBS, irritable bowel syndrome; RCT, randomised controlled trial; SCFA, short-chain fatty acids; SITT, small bowel transit time; WGTT, whole gut transit time.