Modulatory Effects of Salacinol Intake on Intestinal Putrefactive Products: A Double-Blind,Randomized,Parallel-Group Comparative Study

Abstract

Objective

To evaluate the effects of salacinol on stool levels of putrefactive products and intestinal function in healthy adults.

Methods

We conducted a double-blind, randomized, parallel-group comparative study to examine changes in stool characteristics and defecation-related symptoms associated with salacinol intake in healthy adults aged 55 to 70 years living in Japan. The salacinol group received salacinol supplementation (1 mg/day for 28 days), whereas the placebo group received placebo. We collected stool samples before the start of the study, after 14 days of intake, and on designated days or the day after the study completion date. We assessed stool pH and water content, bowel movement frequency, subjective stool odor score, subjective defecation score, stool putrefactive products (ammonia, phenols, paracresol, indole, skatole, 4-ethylphenol, and total putrefactive products) and safety outcomes. We analyzed these data using the chi-square test or Fisher’s exact test for qualitative variables and the Mann–Whitney U test and the Jonckheere–Terpstra test for quantitative variables.

Results

Thirty-nine participants consented to participate. After exclusion of those who met the exclusion criteria or withdrew consent, 24 participants (70.8% female, mean age 60.3 years, 12 in the salacinol group and 12 in the placebo group) were included in the analysis. The salacinol group showed a significant reduction in stool ammonia levels (approximately 40% from baseline), beginning at day 14 and continuing through day 28, and stool water content increased. These results suggest that salacinol may help regulate intestinal levels of ammonia and other putrefactive products.

Conclusions

The observed decrease in putrefactive products is consistent with salacinol’s proposed effect on microbial fermentation, which is thought to occur through inhibition of carbohydrate absorption in the small intestine. These findings suggest that salacinol has potential as a new functional compound that promotes intestinal health through microbiota-mediated mechanisms.

Keywords

salacia salacinol putrefactive products intestinal microbiota double-blind randomized parallel-group comparative study α-glucosidase inhibitor

Introduction

According to the most recent clinical guidelines for chronic constipation, approximately 10–15% of the Japanese population report symptoms of constipation, with a higher prevalence among women and a gradual increase with age.¹ Chronic constipation is a risk factor for a variety of conditions, including colorectal cancer,^2,3 hemorrhoids,⁴ and intestinal obstruction.⁵ In the elderly population, constipation is further associated with reduced quality of life⁶ and has been suggested to contribute to the risk of developing dementia.⁷

To relieve constipation, lifestyle changes are necessary, particularly dietary modifications. Consuming foods that promote intestinal health is one effective strategy. These properties are commonly attributed to probiotics,⁸ prebiotics,⁹ or synbiotics,¹⁰ with the latter being a combination of both. Although salacinol does not fall into these conventional categories, studies have suggested that it has beneficial effects on intestinal function.^11,12 Salacinol is a bioactive compound extracted from Salacia, a plant in the family Hippocrateaceae that has been traditionally used in Ayurvedic medicine to treat diabetes.^13-15 Salacinol acts as an α-glucosidase inhibitor, thereby reducing the absorption of disaccharides in the small intestine.^16-18 Consequently, undigested disaccharides and oligosaccharides reach the large intestine, where they are presumed to promote the proliferation of Bifidobacterium and Lactobacilli species, while concurrently suppressing the growth of Escherichia coli. In studies of the rat intestinal microbiota, salacinol increased the relative abundance of Bacteroides and decreased that of Firmicutes.¹⁹ In human studies, salacinol increased Bifidobacteria levels while decreasing the prevalence of Clostridium species.²⁰

While the health benefits of common functional foods, such as yogurt and probiotics, have been extensively documented, there is a significant lack of human clinical data regarding salacinol, and further additional studies are needed.

Based on these findings, we hypothesized that oral salacinol intake would act as an α-glucosidase inhibitor, thereby reducing stool putrefactive products and improving intestinal function. To test this hypothesis, we conducted a randomized, placebo-controlled study in healthy adults.

Methods

Study Design

This study utilized a double-blind, randomized, parallel-group comparative design and was conducted in Matsumoto City, Nagano Prefecture, Japan. The intervention group received tablets containing salacinol, while the placebo group received placebo tablets without salacinol. The study period was from November 1 to December 4, 2018.

Study Participants

We recruited healthy adults aged 55–70 years through local bulletin-board postings and from members of the Matsumoto Health Lab, a public–private partnership organization that aims to foster a healthy community through resident participation. The recruitment period for this study was from September 1 to October 16, 2018.

Study Allocation

An individual not involved in this study served as the allocation manager and used a stratified permuted block method to generate a random allocation table based on height, weight, age, and sex. Participants were assigned to either the salacinol group or the placebo group. The allocation officer sealed the assignment list and stored it securely. The officer who enrolled and allocated participants to interventions had no access to the random allocation sequence. Participants and outcome assessors were blinded to group assignment, and neither knew whether participants were receiving salacinol or placebo.

Study Criteria

Table 1 shows the study inclusion and exclusion criteria. Participation was discontinued if participants withdrew consent or developed gastrointestinal symptoms such as diarrhea, abdominal pain, or vomiting, or other adverse effects such as rash or allergic reactions.

Table 1.

Inclusion and Exclusion Criteria

Inclusion criteria	Exclusion criteria
1. Japanese men and women aged 55 to 70 years.	1. Hypertension, hyperlipidemia, dyslipidemia, diabetes, rheumatism, cerebrovascular disease, renal disorders, hepatic disorders (especially hepatitis), or other chronic diseases.
2. Provision of written consent given voluntarily after a full explanation of study participation.	2. A history of or treatment for heart failure, myocardial infarction, atrial fibrillation, arrhythmia, or other cardiac diseases.
3. A regular eating schedule that includes three meals a day.	3. Gastrointestinal irritability, including severe constipation or frequent diarrhea.
4. Bowel movements at least three times per week and not currently constipated.	4. Frequent intake of supplements, bowel regulators, fermented foods, or dairy products that influence the intestinal microbiota.
	5. Allergies to test foods or medications.
	6. A smoking habit or excessive alcohol consumption (equivalent to 60 g/day of ethanol).
	7. Limited carbohydrate consumption to once a day or less.
	8. Shift work or other irregular lifestyles.
	9. Current participation in another clinical trial or participation within the past three months.
	10. Cognitive impairment interfering with self-administered assessment.
	11. Any other reason deemed by the chief medical officer to make the subject unsuitable for participation.

Test Foods

We prepared the salacia plant extract powder as follows. The trunk and root parts of the S. reticulata plant were dried and chipped. After thorough drying, the chips were placed in hot water for 1 h to facilitate extraction and then removed by filtration. The liquid was then cooled, and the extract was powdered using an ADL-310 spray dryer (Yamato Science Co., Tokyo) and stored at 4°C. The powder consisted of 61% carbohydrates, 17% polyphenols, 12% ash, 5% moisture, 4% protein and 0.6% fat. The salacinol content of the salacia plant extract powder was 4.20 μg/mg; this confirmed that salacinol content and its contribution to α-glucosidase inhibition were higher than those of the other ingredients. For the salacinol group, the test food contained 60.00 mg S. reticulata extract, 6.00 mg of calcium carbonate, 172.75 mg of crystalline cellulose, 7.50 mg of sucrose fatty acid ester and 3.75 mg of silicon dioxide per 250 mg. For the placebo group, the test food contained 175.00 mg of crystalline cellulose, 2.50 mg of silicon dioxide, 50.00 mg of erythritol, 2.50 mg of calcium stearate, and 20.00 mg of color adjuster per 250 mg. Aliment Industry Co. (Yamanashi, Japan) produced the test foods. Japan Food Research Laboratories (Ibaraki, Japan) analyzed the components of salacia powder and the test foods, and the salacinol content was confirmed by liquid chromatography–mass spectrometry.

We prepared tablets containing 0.25 mg of salacinol for the salacinol group and administered them according to the following schedule: 1 tablet before breakfast, 1 tablet before lunch, and 2 tablets before dinner, for a total daily salacinol dose of 1 mg. In determining the salacinol dosage, we referred to a previous study that evaluated changes in the intestinal microbiota after salacinol intake, because the production of putrefactive products is associated with alterations in the intestinal microbiota. Since a previous study in healthy adults (15 participants per group) showed changes in the intestinal microbiota at the same salacinol dose as in the present study [20], we selected this dose to evaluate its effects on stool putrefactive products and intestinal function. The placebo group followed the same schedule. Excipients that did not affect the intestinal environment were used for tablet manufacturing, along with color and flavor modifiers in the placebo. The test foods were indistinguishable in appearance, taste, and color.

Outcome Measures

The primary outcomes were stool pH, stool water content, subjective stool odor score using a 5-point scale (1: excellent to 5: very poor), and stool putrefactive products, including ammonia, phenols, paracresol, indole, skatole, and 4-ethylphenol. The secondary outcomes were bowel movement frequency, subjective defecation score assessed using a 5-point scale (1: excellent to 5: very poor), and safety assessments. In addition, participants completed a self-administered questionnaire on medication use, carbohydrate intake, and test tablet consumption, all of which could affect the intestinal microbiota or the effects of salacinol.

The following items were assessed via questionnaire at both the beginning and end of the survey period: sex and age (assessed only at baseline), height, weight, allergies, intake of fermented foods, lactic acid bacteria, dietary supplements, alcohol consumption habits, smoking habits, exercise habits, dietary patterns, and carbohydrate intake. The following items were evaluated through a daily questionnaire: tablet intake, carbohydrate intake, subjective stool odor score, and subjective defecation score. No special diets or dietary restrictions were imposed.

Participants were required to maintain a daily diary throughout the study period to record their physical condition, medication use, and any changes in lifestyle. The researchers monitored these diaries to ensure that all participants in both the salacinol and placebo groups maintained their healthy status. To ensure data integrity, participants who showed significant changes in their health or who met the exclusion criteria were excluded from the final analysis.

We defined an adverse event as any unwanted or unintended injury, illness, or related symptom occurring in a study participant, regardless of whether it was causally related to the research. If an adverse event occurred, the principal investigator or co-investigator immediately took appropriate measures, recorded the event in the case report form, and, if necessary, took appropriate action, such as discontinuing the participant’s involvement in the study.

Stool Samples

Before collecting a stool sample, we gave participants the following instructions: (1) Place the special stool collection sheet in the toilet. (2) Scoop the stool into the collection container while preventing contamination from urine. (3) Place the stool in a polystyrene container along with a cooling pack, and record the date and time of collection as well as the intensity of the stool’s odor. (4) Submit the refrigerated stool sample and self-report form promptly.

We collected stool samples before the study began, after 14 days of intake, and on the designated day or the day after the study concluded. The samples were frozen and stored within 24 hours and then analyzed by an external laboratory. We measured stool pH, water content, and levels of putrefactive products (ammonia, phenols, paracresol, indole, skatole, 4-ethylphenol, and the total amount).

Sample Size

We conducted this study as an exploratory investigation to evaluate the preliminary feasibility of salacinol and assess outcome trends. Because of its exploratory nature, we did not perform a formal power analysis to determine the sample size. Instead, we aimed to recruit 30 participants, which we considered sufficient to provide a basis for future larger-scale confirmatory trials and to estimate effect sizes for subsequent power calculations. This sample size was based on a previous randomized placebo-controlled trial showing changes in the gut microbiome and suppression of inflammation with 30 participants.²⁰

Statistical Analysis

In the basic tabulation, percentages were calculated for qualitative variables, and summary statistics were calculated for quantitative variables. As prespecified, the chi-square test or Fisher’s exact test was used for qualitative variables. In addition, because we considered it important to assess between-group differences and temporal changes in quantitative variables, including test food intake, bowel movement frequency, subjective stool odor score, subjective defecation score, and stool analysis results, we performed post-hoc analysis using the Mann–Whitney U test and the Jonckheere–Terpstra trend test within each group. Statistical analyses were conducted using IBM SPSS Statistics for Windows, version 29 (IBM Corp., Armonk, N.Y., USA). Two-tailed tests were used for comparisons between subjects, and p values less than 0.05 were considered statistically significant. Missing data were excluded from the analysis.

Results

Figure 1 shows the flow diagram of this study. Thirty-nine participants consented to participate in the study; 7 were excluded due to hypertension (n=4), diabetes (n=2), or hyperuricemia (n=1), and 1 withdrew informed consent just before participation. This left 31 participants (15 in the salacinol group and 16 in the placebo group), from whom all necessary data for analysis were collected during the intake period, resulting in a 100% follow-up rate. There was no significant difference in the baseline characteristics between the salacinol and placebo groups. Seven participants (3 in the salacinol group and 4 in the placebo group) were excluded from the analysis because they did not regularly consume carbohydrates at least once a day or met other exclusion criteria. The final analysis included 24 participants (12 in the salacinol group and 12 in the placebo group). There were no serious adverse events in this study.

Figure 1.

Flow diagram of this study

Table 2 shows the baseline characteristics of participants in the salacinol and placebo groups. There was no significant difference between the two groups in terms of demographic factors or dietary habits, including the intake of fermented foods, lactic acid bacteria-containing products, and dietary supplements.

Table 2.

Characteristics of the Placebo and Salacinol Groups

	Total	Placebo group	Salacinol group
	( n=24)	( n=12)	( n=12)	p value
Sex, n
Men	7	4	3	1.000
Women	17	8	9
Age, mean±SD, years*	60.3±4.3	60.8±4.8	59.8±3.9	0.702
Height, mean±SD, cm*	161.5±7.4	162.1±8.5	160.8±6.5	0.744
Weight, mean±SD, kg*	56.9±7.3	57.8±8.4	56.0±6.3	0.702
Body Mass Index, mean±SD, kg/m2 *	21.8±1.8	21.9±1.6	21.7±2.1	0.809
Fermented food
Habit of intaking, n	20	9	11	0.590
Average intakes ±SD, times/week *	4.3±2.3	4.3±1.9	4.2±2.7	0.892
Lactic acid bacterial food
Habit of intaking, n	14	5	9	0.214
Average intakes ±SD, times/week *	4.4±2.1	3.5±1.4	4.9±2.3	0.217
Dietary supplement
Habit of intaking, n	8	4	4	1.000
Average intakes ±SD, times/week *	5.9±1.9	6.8±0.5	5.0±2.4	0.429
Alcohol
Habit of intaking, n	14	8	6	0.680
Average amount of alcohol±SD, g/day *	11.7±13.1	13.4±12.1	10.1±14.4	0.398
Smoking
Never, n	21	11	10	1.000
Past, n	3	1	2
Exercise
Habit of exercising, n	17	9	8	1.000

SD: Standard Deviation p values were calculated by Fisher’s exact test for comparisons between the placebo and salacinol groups.

*p values marked with an asterisk were determined using the Mann–Whitney U test for comparisons between the placebo and salacinol groups.

Table 3 shows the average daily tablet intake, carbohydrate consumption, bowel movement frequency, subjective stool odor score, and subjective defecation score in the salacinol and placebo groups. There were no significant differences between the groups in any of the measured variables. Although there was no significant difference in tablet intake between the groups, a significant decreasing trend in tablet intake was observed over the 28 days in the salacinol group (p for trend = 0.047). Other parameters, including dietary intake and bowel habits, remained stable throughout the study in both groups.

Table 3.

Average of Tablet Intake, Carbohydrate Intake, Bowel Movement Frequency, and Subjective Scores

	Total	Placebo group	Salacinol group	p value	p for trend in the placebo group	p for trend in the salacinol group
	( n=24)	( n=12)	( n=12)	p value	p for trend in the placebo group	p for trend in the salacinol group
Tablet intake, mean±SD, tablets/day
7 days	3.9±0.2	3.9±0.3	3.9±0.2	0.743	0.051	0.047
14 days	3.8±0.5	3.8±0.5	3.8±0.5	0.390
21 days	3.8±0.3	3.8±0.2	3.7±0.4	0.529
28 days	3.6±0.5	3.5±0.6	3.6±0.4	0.987
Total	3.7±0.3	3.7±0.3	3.7±0.3	0.696
Carbohydrate intake, mean±SD, times/day
7 days	2.7±0.5	2.8±0.4	2.6±0.5	0.368	0.208	0.383
14 days	2.7±0.5	2.8±0.4	2.5±0.5	0.250
21 days	2.7±0.4	2.8±0.3	2.5±0.5	0.136
28 days	2.6±0.5	2.7±0.5	2.5±0.5	0.167
Total	2.6±0.4	2.8±0.4	2.5±0.5	0.234
Bowel movement frequency, mean±SD, times/day
7 days	1.3±0.6	1.1±0.5	1.4±0.6	0.227	0.629	0.885
14 days	1.2±0.5	1.0±0.5	1.3±0.5	0.151
21 days	1.3±0.6	1.1±0.6	1.4±0.6	0.334
28 days	1.3±0.6	1.3±0.7	1.3±0.5	0.416
Total	1.3±0.5	1.1±0.5	1.4±0.5	0.294
Subjective stool odor score, mean±SD
7 days	2.7±0.6	2.8±0.6	2.6±0.7	0.539	0.603	0.440
14 days	2.6±0.7	2.6±0.7	2.6±0.6	0.809
21 days	2.7±0.6	2.6±0.6	2.7±0.7	0.764
28 days	2.5±0.6	2.7±0.7	2.4±0.6	0.375
Total	2.6±0.6	2.6±0.6	2.6±0.6	0.722
Subjective defecation score, mean±SD
7 days	2.2±0.8	2.0±0.7	2.5±0.9	0.171	0.636	0.440
14 days	2.3±0.7	2.0±0.9	2.5±0.5	0.219
21 days	2.2±0.8	1.9±0.7	2.4±0.8	0.084
28 days	2.1±0.7	1.9±0.6	2.3±0.7	0.146
Total	2.2±0.7	2.0±0.6	2.4±0.6	0.074

SD: Standard Deviation p values were calculated using the Mann–Whitney U test or Fisher’s exact test for comparisons between the placebo and salacinol groups. p for trend:The Jonckheere–Terpstra test was performed in each group.

Table 4 shows the results of stool analyses at the baseline (day 0), midpoint (day 14), and endpoint (day 28) in the salacinol and placebo groups. Notable overall reductions were seen in both total putrefactive products and ammonia levels in the salacinol group compared to the placebo group over the 28 days (p = 0.020 and 0.033, respectively). Despite a significant reduction in tablet intake over the 28 days in the salacinol group (Table 3), total putrefactive products levels decreased significantly from 59,499.5 µmol/kg (day 0) to 36,989.7 µmol/kg (day 14) and 37,157.8 µmol/kg (day 28) (p for trend = 0.020). Ammonia levels of stool samples in the salacinol group decreased significantly from 59,349 μmol/kg (day 0) to 36,409 μmol/kg (day 14) and 36,598 μmol/kg (day 28) (p for trend = 0.019). The reduction was approximately 40% on day 14 compared to day 0, and this effect lasted through day 28. Notably, ammonia accounted for over 95% of the total putrefactive products at all time points. These findings indicate that salacinol supplementation significantly inhibited ammonia production. Additionally, the change of water content of stool was significantly greater in the salacinol group compared to the placebo group (p = 0.045) over the all period and showed an increasing trend in the salacinol group from 72.9% (day 0) to 78.2% (day 14) and 80.3% (day 28) (p for trend = 0.033). In contrast, there were no significant differences in pH.

Table 4.

Stool Analysis in the Placebo and Salacinol Groups

		Total	Placebo group	Salacinol group	p value	p for trend in the placebo group	p for trend in the salacinol group
		( n=24)	( n=12)	( n=12)	p value	p for trend in the placebo group	p for trend in the salacinol group
pH, mean±SD
	0 day	6.6±0.5	6.6±0.4	6.6±0.6	0.831
	14 days	6.4±0.7	6.5±0.6	6.4±0.9	0.921
	28 days	6.6±0.8	6.8±0.8	6.5±0.8	0.468
	Change overall	0.0±0.7	0.2±0.7	-0.1±0.8	0.921	0.692	0.835
Water content, mean±SD, %
	0 day	74.3±9.3	75.7±10.7	72.9±7.8	0.219
	14 days	77.7±8.2	77.1±9.9	78.2±6.4	0.921
	28 days	77.6±7.2	75.0±8.1	80.3±5.2	0.173
	Change overall	3.3±10.0	-0.7±10.8	7.4±7.5	0.045	0.599	0.033
Total putrefactive products, mean±SD, μmol/kg
	0 days	52452.2±22764.8	45404.9±19361.4	59499.5±24502.2	0.101
	14 days	41382.8±25634.4	45775.9±28684.6	36989.7±22562.4	0.378
	28 days	40132.9±17375.9	43108.1±18700.2	37157.8±16195.1	0.378
	Change overall	-12319.3±21306.9	-2296.8±19533.6	-22341.7±18668.6	0.020	0.966	0.020
Ammonia, mean±SD, μmol/kg
	0 days	52340.6±22707.2	45331.6±19317.2	59349.6±24449.3	0.097
	14 days	40678.3±24917.4	44947.0±28188.0	36409.6±21537.7	0.378
	28 days	38875.4±16475.7	41152.9±17461.5	36598.0±15854.2	0.410
	Change overall	-13465.2±20494.5	-4178.7±18270.7	-22751.6±18874.6	0.033	0.984	0.019
Phenols, mean±SD, μmol/kg
	0 days	3.1±5.4	2.5±3.2	3.7±7.0	0.711
	14 days	35.7±66.6	18.4±14.8	52.9±91.8	0.378
	28 days	57.4±111.6	39.0±34.8	75.8±155.1	0.580
	Change overall	54.3±111.4	36.5±34.1	72.1±155.2	0.551	<0.001	<0.001
Paracresol, mean±SD, μmol/kg
	0 days	68.6±85.9	46.8±52.8	90.4±107.8	0.325
	14 days	476.3±1030.8	613.7±1163.6	338.8±909.0	0.138
	28 days	791.0±1541.6	1339.7±2032.8	242.4±424.3	0.140
	Change overall	722.4±1547.6	1292.8±2033.2	152.0±404.7	0.018	0.037	0.461
Indole, mean±SD, μmol/kg
	0 days	29.6±39.8	15.0±13.3	44.2±51.6	0.089
	14 days	130.6±151.2	145.3±117.9	116.0±182.9	0.128
	28 days	350.8±404.9	496.5±515.1	205.2±176.4	0.060
	Change overall	321.2±415.4	481.4±518.4	161.0±189.9	0.039	<0.001	<0.001
Skatole, mean±SD, μmol/kg
	0 days	8.6±17.8	7.2±12.5	10.0±22.4	0.922
	14 days	45.8±126.0	42.0±89.5	49.6±158.6	0.672
	28 days	34.8±109.4	61.2±152.6	8.5±15.8	0.250
	Change overall	26.3±104.2	54.0±144.5	-1.4±13.0	0.029	0.014	0.626
4-ethylphenol, mean±SD, μmol/kg
	0 days	1.7±2.1	1.7±2.9	1.7±1.0	0.100
	14 days	16.1±32.0	9.5±14.4	22.7±42.9	0.781
	28 days	23.5±35.3	18.9±20.8	28.0±46.1	0.642
	Change overall	21.7±35.0	17.2±20.8	26.3±45.7	0.541	0.966	0.856

SD: Standard Deviation p values were determined using the Mann–Whitney U test for comparisons between the placebo and salacinol groups. p for trend showed the trend in each group based on time series.

Discussion

A daily intake of 1 mg of salacinol for 28 days significantly reduced total stool putrefactive products and stool ammonia levels in the salacinol group compared to the placebo group. Quantitatively, the mean stool ammonia concentration in the salacinol group decreased by approximately 40% from baseline and differed significantly from that in the placebo group. This effect was maintained from day 14 through day 28. Although stool water content increased notably in the salacinol group compared with the placebo group, stool pH remained unchanged, with no significant difference between the groups. Additionally, bowel movement frequency, subjective stool odor score, and subjective defecation score did not differ significantly between the groups. These results suggest that salacinol may help improve the intestinal environment and may have potential clinical relevance.

The findings obtained in this study are considered to be attributable to the α-glucosidase inhibitory activity of salacinol. Salacinol inhibits the breakdown and absorption of carbohydrates in the upper small intestine through its α-glucosidase inhibitory effect.^11,12 As a result, undigested oligosaccharides and monosaccharides reach the large intestine, where they serve as fermentable substrates for gut microbiota.²¹ This promotes the proliferation of specific bacterial groups, leading to alterations in the composition and balance of the intestinal microbiota.²² The α-glucosidase inhibitory activity of salacinol may exert its intestinal modulatory effects through a mechanism distinct from that of probiotics and prebiotics.

The observed reduction in ammonia concentration of stool is likely attributable to the fermentation of undigested carbohydrates that reach the colon as a result of α-glucosidase inhibitor administration. These carbohydrates are metabolized by colonic microbiota, leading to increased production of short-chain fatty acids (SCFAs). The accumulation of SCFAs lowers the colonic pH, thereby suppressing the growth and enzymatic activity of bacteria that produce ammonia. This mechanism is consistent with previous findings linking colonic acidification to reduced ammonia levels of stools.^23,24

In addition to reducing ammonia in stool, α-glucosidase inhibitors such as salacinol may increase stool water content. This effect is thought to be due to the osmotic activity of undigested carbohydrates reaching the colon, which helps to retain water within the intestinal lumen.²⁵ Furthermore, enhanced colonic fermentation and shortened transit time may also contribute to a reduction in water reabsorption and softer stools.

In human studies, administration of the α-glucosidase inhibitor acarbose has been shown to increase SCFA-producing bacteria while suppressing ammonia-producing bacterial populations.²⁶ Specifically, acarbose has been reported to increase the abundance of Lactobacillus spp., Faecalibacterium prausnitzii, and Prevotella spp. in humans, suggesting enhanced microbial glycolysis and fermentation and increased SCFA production in the colon.²⁷ In the present study, one participant with frequent diarrhea was excluded from the analysis (Figure 1). Because diarrhea has been reported as a side effect of α-glucosidase inhibitors,²⁸ we cannot rule out the possibility that salacinol intake contributed to this event. Taken together, these findings indicate that salacinol may exert similar modulatory effects on the gut microbiota.

A major strength of this study is its design as a double-blind, randomized controlled trial involving human participants. This approach minimizes bias and ensures a high level of evidence in clinical research. The study also evaluated parameters—specifically putrefactive products, moisture content, and pH—that are presumed to reflect changes in the gut microbiota. Furthermore, the effects of salacinol were explained in comparison with previously reported findings on acarbose, a known α-glucosidase inhibitor.

This study has several limitations. First, the number of participants included in the analysis was small (twenty-four), which limits the generalizability of the findings. As an exploratory study, it may not reflect the broader population, and larger studies including more diverse participants are needed to confirm these preliminary results. Second, diet was not standardized among participants. Because putrefactive products are generated during the breakdown of dietary proteins and diet substantially affects the intestinal microbiota, dietary differences may have influenced the results. Although we attempted to minimize this issue by excluding participants with markedly unbalanced diets and by monitoring diet during the study period, some residual dietary imbalance may have remained. These first two limitations, together with individual differences and lifestyle differences, may have increased variability and reduced our ability to detect the true effects of salacinol. Third, selection bias may have been present because the study population consisted of high-conscious individuals, and the findings may therefore not be fully generalizable to the broader population. Finally, we did not directly analyze gut microbiota composition. Although putrefactive products, stool water content, and pH may indirectly reflect changes in the gut microbiota, direct microbiota analysis would allow a more complete assessment of salacinol’s effects on microbial composition.

Conclusion

In conclusion, this exploratory study suggests that salacinol intake regulates intestinal ammonia-containing putrefactive product levels and stool water content through α-glucosidase inhibition. However, because of the small sample size and exploratory design, these findings should be interpreted cautiously as hypothesis-generating. Further large-scale studies are needed to confirm these effects.

Footnotes

Acknowledgements

The authors wish to thank all participants and the relevant institutions for their cooperation in this study.

ORCID iD

Masaru Mizuki

Ethical Considerations

Participants who indicated willingness to enroll were provided with a full explanation of the study protocol, after which written informed consent was obtained. Our study was CONSORT compliant and well conducted. Participants who indicated willingness to enroll were provided with a full explanation of the study protocol, after which written informed consent was obtained. Our study adhered to the “Ethical Guidelines for Epidemiological Surveys” and the “Ethical Guidelines for Clinical Research.” The methods and measurement items were examined and approved by the Medical Ethics Committee of Shinshu University School of Medicine (#4132) and the Fujifilm Life Science Ethics Review Committee (#130). We conducted the study with the approval of the ethics review committee with no changes made. We registered this study in the UMIN Clinical Trials Registry under the number UMIN000034522 (. Date of registration: Oct 16, 2018.).

Consent to Participate

The study protocol was fully explained to participants who wished to participate, and written informed consent was obtained before the study was conducted. We explained to participants that no personally identifiable information would be released, and written consent was obtained for publication.

Author contributions

The authors’ contributions are as follows:

Masaru Mizuki: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Visualization, Writing – original draft, Writing – review & editing.

Yuriko Oda: Conceptualization, Investigation, Methodology, Resources, Validation, Visualization, Writing – review & editing.

Shinobu Seki: Project administration, Resources, Writing – review & editing.

Teruomi Tsukahara: Conceptualization, Data curation, Formal analysis, Writing – original draft, Writing – review & editing.

Tetsuo Nomiyama: Conceptualization, Funding acquisition, Methodology, Project administration, Supervision, Validation.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The grant was received by the authors, M.M, T.T and T.N. The grant number is GAY123. This study has been funded by FUJIFILM Corporation. (). The funder was involved in the study design and preparation of the manuscript.

Declaration of Conflicting Interests

The authors declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: This study has been funded by the FUJIFILM Corporation.

Data Availability Statement

The dataset supporting the findings of this study is available at Zenodo. DOI: 10.5281/zenodo.20437220

Trial Registration

We registered this study in the UMIN Clinical Trials Registry under the number UMIN000034522 (. Date of registration: Oct 16, 2018).

Statement of Human and Animal Rights

All procedures in this study were carried out according to the protocol described above. The research was a collaborative effort between Matsumoto City, Shinshu University, and FUJIFILM Corporation.

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