Journal of Neurogastroenterology and Motility 2019; 25(3): 475-477
Modulatory Effects of Gut Microbiota on Constipation: The Commercial Beverage Yakult Shapes Stool Consistency
Min Chen,* Xujun Ye, Dan Shen, and Chunwei Ma
Geriatric Department, Zhongnan Hospital, Wuhan University, China
Published online: July 1, 2019.
© The Korean Society of Neurogastroenterology and Motility. All rights reserved.

cc This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

TO THE EDITOR: It is becoming increasingly recognized that the presence of healthy and diverse gut microbiota is important to achieve or maintain a regular normal bowel movement. It is well known that patients with constipation could be expected to alleviation from the symptoms by the intake of fermented foods such as yogurt, kimchi, and sauerkraut.1Lactobacillus and Bifidobacterium are especially known to support digestive health by generating short-chain fatty acids (SCFAs). The major SCFA in humans are butyrate, propionate, and acetate, where butyrate is the major energy source for colonocytes, propionate is destined for uptake by the liver, and acetate enters the peripheral circulation to be metabolized by peripheral tissues.2

Dietary supplementation with fibers, such as oligofructose, oat bran, and apple pectin, is known to promote a significant production of SCFA upon fermentation by saccharolytic bacteria (capable of hydrolyzing or otherwise breaking down a sugar molecule) in the gut lumen.3 Therefore, there are at least two common ways proposed to increase gut SCFA ie, probiotics (live bacteria such as yogurt containing Lactobacillus and Bifidobacterium) and prebiotics (fiber fermented food containing supplement for bacteria), as well synbiotics (mixtures of prebiotics and probiotics).

Yakult is a dairy beverage that contains Yakult’s exclusive probiotic Lactobacillus casei strain Shirota (LcS), discovered by a Japanese scientist Dr. Minoru Shirota in 1930. Daily consumption of Yakult helps improve digestion and helps build immunity.4 Chen et al5 recently published a study “Differential effects of Lactobacillus casei strain Shirota on patients with constipation regarding stool Consistency in China.”

The study performed by Chen et al5 was based on a subjective survey and a series of laboratory analyses, without comparative design (placebo-controlled, double-blind, parallel-group). Sixty-two adults who had constipation were recruited and divided into 3 groups upon stool consistency classification, ie, hard stool (HS), normal stool (NS), soft stool (SS). A 4-week consumption of Yakult (100 mL containing 1 × 1010 living LcS cells) was evaluated for the efficacy of constipation symptoms, defecation frequency, stool SCFA concentrations, abundancy of the intestinal microbiota and the intestinal environment of each subgroup were evaluated.

The survey shows all the constipation symptoms statistically significant improved conclusively in favor of Yakult beverage in improving all constipation symptoms. Especially, the stool quality improvement is featured in both watery and hard stools which all shifted to a normal consistency when compared before and after Yakult intervention.

Stool SCFA levels, measured by gas chromatography, were shown a sequential distribution as SS > NS > HS in the baseline. Differently, after the ingestion of Yakult, the levels of SCFA were elevated only in HS (35.1% in acetate, 36.8% in propionate, and 39.7% in butyrate). Whereas, the levels of SCFA were decreased only in SS after ingestion of Yakult (28.3% in acetate, 19.3% in propionate and 18.6% in butyrate).

Bacterial 16S ribosomal RNA V3–V4 region was analyzed by using Illumina MiSeq Sequencing in comparison of the abundances of different genera among 3 subgroups. Yakult, compared to baseline, increased the abundances of Pseudobutyrivibrio and Roseburia in HS and decreased the Pseudobutyrivibrio abundance in SS, and decreased Firmicutes in all patients.

This is enriched informative research, however, there are some concerns on the article and the data raised as below:

Firstly, part of this study was a subjective survey and the Yakult probiotic effect in constipation was well known. Therefore, the “true pharmacological effect” was inevitably acknowledged to all participants including observers and observees, which may introduce a bias into the study. Secondly, all recruited subjects were aged 18–45 with the best range of body mass index (Table 1) indicating participants generally in a healthier population category. In other words, this current study was excluded from the highest risk constipation populations such as the elderly, children and obese. Thus, caution is urged for participants who may not be in true constipation, hence, the conceit of assuming that any intervention of gut bacteria has strong “healing” powers may have existed in the study.

Not much information on the subjects provided in the article leads the audience to be suspicious of whether the participants were healthier, occasional constipation, constipation-predominant irritable bowel syndrome, etc. It is indicated that the “diagnosis” was from a qualified hospital, however, no accountable evidence supports those participants who were constipation patients, no constipation history (length) and no pelvic floor condition was provided. Adversely, as seen in Table 2, an average of about 4 times/week defecation frequency was diagnosed as “functional constipation,” which is unfulfilled with Rome III criteria.6 Here, we have to restate functional constipation that defecation frequency occurs less than 3 times per week for a 3 months’ period.

Stool consistency is what focused in this article as seen in Table 3, which shows the effect of drinking Yakult on stool consistency: kept on “normal” in NS, changed toward “normal” in HS, and reversed “loose” to “normal” in SS. However, there is a difference when comparing the calculations, wherein Table 2 there was an average scale of 3.19 in follow-up, whereas, in follow-up in Table 3, those numbers seem not identical while there were scored 3 in HS (n = 23), 3.25 in NS (n = 27), and 4.02 in SS (n = 12). Nevertheless, it is interesting since these changes are accordingly explained by an alternation of SCFA level, furthermore, the gut microbiota adjustment.

Although the authors claimed that all constipation symptoms were significantly improved, there is some confusion in Table 4. For example, NS had more severe pain in the defection effort versus SS, and SS had less straining during defection. Clinically, constipation causes a blockage and the bowel begins to leak out watery stools around the blockage from higher up. The leak from the bowel can look like diarrhea which was always rectal tenesmus.

Lastly, this study was sponsored by Yakult. Does industry sponsorship bias research findings? Funding bias has been associated with research into chemical toxicity, tobacco, and pharmaceutical drugs. It concerns the tendency of a scientific study to support the interests of the study’s financial sponsor.

Anyhow, this study suggests that probiotic beverage has an intestine-conditioning effect by improving the stool quality and rebalancing the intrinsic SCFA and Bacteroides in stool consistency.


Subject Demographics (Adapted From Chen et al5)


HS (n = 23)NS (n = 27)SS (n = 12)
Sex (% of females)8385100> 0.999a
Age (yr)27.5 (10.8)24.0 (7.0)23.0 (3.8)0.007b
Height (m)1.63 (0.13)1.63 (0.10)1.64 (0.06)0.851b
Weight (kg)57.5 (7.8)55.0 (15.0)52.5 (8.3)0.503b
BMI (kg/m2)21.0 (2.4)20.7 (3.5)19.6 (1.7)0.448b

BSFS, Bristol Stool Form Scale; HS, hard stool; NS, normal stool; SS, soft stool; BMI, body mass index.

P-value was calculated by aChi-squared test and bKruskal Wallis test.

Data are presented as median (interquartile range).

Effects of Lactobacillus casei Strain Shirota on Constipation Symptoms and Defecation Frequency (Adapted From Chen et al5)

SymptomBaselineIntake 1Intake 2Follow-up
Painful effort during defecation1.67 (1.29)1.45 (1.14)a1.15 (0.97)a1.16 (0.88)a
Feeling of incomplete evacuation2.27 (1.03)2.01 (1.31)a1.61 (1.28)a1.53 (1.32)a
Straining during defecation2.38 (0.83)2.00 (0.67)a1.75 (1.19)a1.71 (1.17)a
Minutes spent in lavatory per attempt1.90 (1.06)1.68 (0.90)1.68 (0.80)a1.66 (0.94)a
Unsuccessful defecation attempt1.13 (0.40)1.08 (0.43)1.09 (0.28)1.00 (0.14)a
Abdominal discomfort1.97 (1.03)1.92 (1.10)1.60 (1.03)a1.30 (1.08)a
Defecation frequency (times/wk)4.00 (2.50)4.50 (2.50)5.00 (2.50)a5.25 (2.63)a
Stool consistency3.18 (1.02)3.44 (1.41)a3.55 (1.02)a3.19 (1.21)

aP < 0.05, vs baseline.

Intake 1, 2-week Lactobacillus casei strain Shirota (LcS) intake; intake 2, 4-week LcS intake; follow-up, 2-week following LcS intake.

Data are presented as median (interquartile range).

Effects of Lactobacillus casei Strain Shirota on Stool Consistency (Adapted From Chen et al5)

GroupBaselineIntake 1Intake 2Follow-up
HS2.50 (1.13)2.75 (0.84)a3.04 (1.30)a3.00 (1.43)a
NS3.25 (0.39)b3.63 (1.00)3.63 (0.82)3.25 (1.00)
SS4.46 (0.39)b,c4.50 (1.10)4.14 (1.40)a4.02 (1.76)a

aP < 0.05, vs baseline.

bP < 0.05, vs HS.

cP < 0.05, vs NS.

HS, hard stool; NS, normal stool; SS, soft stool; intake 1, 2-week Lactobacillus casei strain Shirota (LcS) intake; intake 2, 4-week LcS intake; follow-up, 2-week following LcS intake.

Data are presented as median (interquartile range).

Effect of Lactobacillus casei Strain Shirota on Constipation Symptoms of Each Group (Adapted From Chen et al5)

SymptomGroupBaselineIntake 1Intake 2Follow-up
Painful effort during defecationHS1.75 (0.99)1.14 (0.88)a1.00 (0.57)a1.00 (0.46)a
NS1.69 (1.29)1.71 (1.14)a1.25 (1.14)a1.29 (0.9)a
SS1.44 (1.30)1.86 (1.35)1.66 (1.63)1.69 (1.20)
Feeling of incomplete evacuationHS2.50 (1.09)2.00 (0.99)a1.46 (0.73)a1.22 (1.12)a
NS2.20 (0.84)1.86 (1.33)1.50 (1.72)c1.36 (1.50)a
SS2.37 (1.31)2.55 (1.21)2.23 (1.04)1.73 (0.75)
Straining during defecationHS2.76 (1.00)2.00 (0.62)a1.56 (0.79)a1.56 (0.92)a
NS2.25 (0.54)b2.00 (1.04)2.00 (1.22)a1.90 (1.10)a
SS1.97 (0.9)b,c2.00 (0.59)1.84 (1.32)1.52 (1.20)a

aP < 0.05, vs baseline.

bP < 0.05, vs HS.

cP < 0.05, vs NS.

HS, hard stool; NS, normal stool; SS, soft stool; intake 1, 2-week Lactobacillus casei strain Shirota (LcS) intake; intake 2, 4-week LcS intake; follow-up, 2-week following LcS intake.

Data are presented as median (interquartile range).


Financial support: None.

Conflicts of interest: None.

Author contributions: Min Chen: designed the study and wrote the manuscript; and Xujun Ye, Dan Shen, and Chunwei Ma: performed data analysis.

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