What is Consistency(Stool)?

Stool consistency is evaluated mainly in reference to indirect indicators such as water content or the appearance of stool forms using the Bristol Stool Form Scale (BSFS). Methods of measurement are limited. We thus aimed to develop a simple protocol for direct measurement of stool consistency using the TA.XTExpress Texture Analyser (Stable Micro Systems Ltd.). We developed a protocol that enables mechanical quantification of the gram force against a cylindrical probe pushed into the stool surface at 2.0 mm/s to 5 mm depth. The consistency of 252 stools collected from 40 healthy Belgians was evaluated by the direct method and by the indirect indicators (water content and BSFS) for comparison. The log-transformed stool consistency values measured by the texture analyzer had a negative linear correlation with the stool water contents with homoscedastic variance, suggesting the appropriateness of the new protocol. They showed a similar correlation with the BSFS, but with a large variance in the consistency values of normal stool forms. This correlation was much smaller for BSFS scored by subjects than by experts, collectively indicating BSFS as a rough indicator of stool consistency susceptible to subjective bias despite its effectiveness in clinical use. The optimized direct method using the texture analyzer enables the accurate quantification of stool consistency, which facilitates understanding of the intestinal environment and function and thus may enhance the value of the stool as a predictor of human health.

Introduction

Having regular bowel movements is considered to be a sign of a healthy digestive system. Stool consistency strongly relates to stool transit time and defecation frequency and therefore is regarded as a suitable indicator of bowel function. Irregular bowel movements (too frequent or infrequent) and repeated passages of hard or loose stools reduce the quality of life and can indicate functional constipation (FC) or irritable bowel syndrome (IBS). Therefore, regular bowel movements with normal stool conditions are desirable for good health.

Stool consistency is evaluated by indirect measurements which evaluate stool form visually; the Bristol Stool Form Scale (BSFS) is the one most widely used in both clinical and research settings. The BSFS is a Likert scale used to classify stool forms into seven categories and has been validated as a surrogate measure for gastrointestinal transit time. The Rome Foundation recommends the use of the BSFS for diagnosing FC and IBS according to the Rome IV criteria, and the European Food Safety Authority regards it as a validated questionnaire for measuring stool consistency in their guideline for health claims. Although the BSFS can be easily evaluated by subjects themselves, this indirect method involves a degree of inter-and intra-rater variance, and modifications to the BSFS or training in its use should be explored to improve its validity and reliability.

Stool consistency generally refers to the rheology and viscosity of the stool, which can be measured directly with a penetrometer and a viscometer. Besides these technologies, a texture analyzer, which is used to measure multiple characteristics of foods and other consumer products, such as hardness, crispness, fracturability, adhesiveness, and extensibility, has been used to analyze stool consistency. Physical stool hardness measured by a texture analyzer strongly correlates well with stool water content and thus accurately reflects stool consistency. However, the method was validated mainly in constipated people and requires complicated procedures: e.g. stools must be measured just within a few hours after defecation and must be measured in multiple lumps throughout the length of the specimen to calculate the median value.

Here, we optimized methods for the direct measurement of stool consistency by a texture analyzer (TA.XTExpress Texture Analyser: TAXT; Stable Micro Systems Ltd.) to increase its operational convenience. The validity of the method was evaluated against stool water content and BSFS score. We analyzed differences in stool consistency according to gender, stool symptoms, and the defecation time period in the general Belgian population.