Effect of Resistant Starch on Symptom Improvement and Intestinal Microbiome in Patients With Functional Constipation

Human intestinal microbiota is one of the densest microbial communities on earth, including highly diverse microbial communities, which provide metabolic, immune and protective functions and play a vital role in human health. Gastrointestinal microflora is affected by many factors, including genetics, host physiology (host age, disease, stress, etc.) and environmental factors, such as living conditions and drug use. At the same time, diet is considered to be a key environmental factor mediating gastrointestinal microflora composition and metabolic function . In view of the fact that it is difficult to be digested and absorbed by the human body, probiotics can enter the intestinal tract through the digestive tract, so as to improve intestinal microecology and promote lipid, protein and mineral metabolism.

Food rich in anti-digestible starch has many functions, such as controlling body weight, reducing blood lipids and blood sugar, regulating intestinal flora and so on, which has attracted the interest of many scholars and become a new field of international food research in recent years. Resistant starch (RS) is the anti-digestion part of compound polysaccharide starch. According to the conditions of enzymatic hydrolysis resistance and starch source, the digestible resistant starch was mainly divided into four types, namely RS1, RS2, RS3 and RS4. From the cause of resistance, RS1 and RS2 have natural resistance to amylase, and the resistance can disappear after gelatinization, while the resistance of RS3 and RS4 is formed by the transformation of starch in the process of food processing or food production. RS1 can coexist with RS2 or RS3 in the same kind of food, and the existence of RS4 can increase the food intake of RS3.

Only a small part of the digestible starch can be digested and absorbed in the small intestine, providing a very low utilization rate of glucose. When most of the rest of the undigested components enter the colon, they are fermented by the intestinal microflora, mainly producing short-chain fatty acids (SCFAs): acetate, propionate and butyrate. Although both acetate and propionate have health effects, butyrate is particularly thought to improve health and is the SCFA with the largest increase in RS intake. Butyrate plays an important role in human intestinal health, including reducing inflammation, reducing the risk of colon cancer and improving intestinal barrier function. In vivo and in vitro, resistant starch diet and butyrate significantly increased the proportion of ChAT immunoreactive intermuscular neurons, intestinal neurons expressed monocarboxylic acid transporter 2 (MCT2), small interference with RNA silenced MCT2, and prevented butyrate-induced increase in the proportion of ChAT immunoreactive neurons. Butyrate and trichostatin An increased the acetylation of histone H3 in intestinal neurons. Src signal pathway inhibitors can block the effect of butyrate. Resistant starch diet increased colonic transport, and butyrate increased cholinergic-mediated contraction of colonic circular muscles in vitro. Although RS has been shown to be one of the best fibers to increase butyrate levels in the population, it is clear that not everyone can get the same benefits, and some people do not respond to RS supplementation. This suggests that differences in individual microflora play an important role in determining the outcome of RS consumption, and we need to explore more deeply the mechanism of RS digestion and how it leads to the production of butyrate. In addition, more needs to be done to understand the health effects that may be affected by RS consumption beyond butyrate levels.

Due to the complex structure of RS, certain bacteria are required to initiate the degradation of this semi-crystalline material. R. bromii and Bifidobacterium juvenis are the only known human intestinal microorganisms with RS degrading ability.

R. bromii has received attention for its role as a keystone species for RS metabolism, feeding, and/or enabling other members of the gut microbiome to access this substrate. The starch-breaking enzyme of R. bromii has a unique organizational structure and forms a multi-enzyme complex, which is attached to the cell surface through the scaffold protein in the fibrinosomes through the adhesion protein and dockerin modules, so it is called amylasome. This system has been found in a variety of human rumenococcus, and the key enzyme structure of its amylasome is highly conserved across strains. Despite its incredible ability to degrade RS, R. bromii itself does not seem to outcompete or dominate other species, but rather serves a beneficial purpose by cross-feeding other species by releasing different lengths of sugars and acetate. One study found that median fecal butyrate increased by 50% after treatment with potato starch (RS2), but further examination of individual responses revealed different changes in butyrate. A follow-up study by the same group found that those with increased R. bromii abundance in their microbiota were more likely to have a higher butyrate response to potato starch, suggesting that the right combination of primary degrading bacteria and resistant starch is needed to increase butyrate production.