Inflammatory bowel diseases (IBDs) are chronic, progressive, immune-mediated diseases of the intestinal tract. The main subtypes of IBDs are Chron’s disease (CD) and ulcerative colitis (UC). The etiology is still unclear, but there are genetic, environmental and host-related factors that contribute to the development of these diseases. Recent literature has shown that dietary therapy is the cornerstone of IBD treatment in terms of management of symptoms, relapse and care of the pathology. IBD patients show that microbiota dysbiosis and diet, especially dietary fiber, can modulate its composition. These patients are more at risk of energy protein malnutrition than the general population and are deficient in micronutrients. So far, no dietary component is considered responsible for IBD and there is not a specific therapeutic diet for it.
Etiopathogenetic Factors | Effects | |
---|---|---|
Genetic factors | NOD2 gene mutation [5][6][7][8][9][10][11] | Alteration of intestinal immune homeostasis and components which maintain the mucus layer |
ATG16L1 gene mutation [5][6][12][13][14][15] | Paneth cell function in autophagy mechanisms is compromised, so protection against infection removing many intracellular microbes is reduced | |
Locus IBD5 alteration [16][17] | Wrong codification of a group of cationic organic transporters, OCTN1 and OCTN2. Reduction in cells and tissues from oxidative and/or inflammatory damage | |
Locus IBD3 alteration [16] | Wrong codification of Major Histocompatibility Complex (MHC) | |
Host-related factors | Microbiota alteration [18][19] | Lower production of anti-inflammatory and immunoregulatory metabolites, in particular butyrate—a lack of which may contribute to increased intestinal inflammation |
Immune response [18][20][21][22] | Hyperactivity of T cells with excessive production of cytokines, among which IL-12, il-23 and IFN-γ promote a TH1 and TH17 lymphocytic phenotype. The inhibition of the effector cytokines, such as TNF-α | |
Environmental factors | Diet [19][23] | Red meat consumption has a pro-inflammatory effect. A high consumption of total fatty acids, polyunsaturated fatty acids (PUFAs), especially omega 6 fatty acids, increases the risk of developing both UC and CD |
Cigarette smoking [16] | Formation of fistulas and intestinal strictures increases the frequency of exacerbations and favors post-surgical relapses in CD. On the contrary, in UC, it seems to have a protective action and it is associated with less frequent flare-ups of the disease |
Symptoms and Signs | CD | UC | ||
---|---|---|---|---|
Presence/Absence | Frequency | Presence/Absence | Frequency | |
Abdominal pain | ✔ | + | ✔ | + |
Diarrhea | ✔ | + | ✔ | + |
Hematochezia | ✔/✗ | +/− | ✔/✗ | + |
Abdominal mass | ✔ | + | ✔ | +/− |
Malnutrition | ✔ | + | ✔/✗ | +/− |
Abdominal distension | ✔/✗ | +/− | ✔/✗ | +/− |
Sub occlusive symptoms | ✔ | + | ✗ | - |
Perianal disease | ✔ | +/− | ✗ | - |
Fistulas | ✔ | +/− | ✗ | - |
Anemia | ✔ | + | ✔/✗ | +/− |
Iron deficiency | ✔ | + | ✔/✗ | +/− |
Low vitamin D | ✔ | + | ✔/✗ | +/− |
Elevated inflammatory markers | ✔ | + | ✔/✗ | +/− |
Although current dietary guidelines are not so clear on the amount and the type of fiber that should be consumed in IBD [48][48], in the literature, several studies evaluated the effects of fermentable and non-fermentable fibers in IBD patients.
It is clear that some fermentable fibers such as resistant starch (that is not digested in the small intestine) and inulin are metabolized by intestinal bacteria to SCFAs [55][55], acetate, butyrate and propionate, and they have immunomodulatory properties, promote the regeneration of the intestinal epithelium, lower the pH of the colon and inhibit the growth of pathogens [78][78].
The IBD-altered microbiota composition results in a lower production of anti-inflammatory and immunoregulatory metabolites, in particular butyrate, a lack of which may contribute to increase intestinal inflammation [19]. Butyrate plays a central role in the development of IBD because it represents the main energy substrate for colonocytes [79] and the alteration of its metabolism is linked with mucosal damage and inflammation [80]. In fact, the integration of some types of fibers (especially fermentable fibers) produces SCFAs capable of maintaining remission and reducing mucosal lesions [78]. In addiction, SFCAs, partic- ularly acetate and butyrate, balance mucus production and secretion. Mucus production at the level of the epithelium is a form of host protection to prevent microbial invasion and susceptibility to infection. A diet low in fiber produces less SFCAs and results in an increase in harmful metabolites that increases susceptibility of infections by deterio- ration of the mucus layer and contribute to the development of chronic disease and colorectal cancer (CRC) [80][81][82].chanism of Action of Dietary Fibers in IBD
Although current dietary guidelines are not so clear on the amount and the type of fiber that should be consumed in IBD [48], in the literature, several studies evaluated the effects of fermentable and non-fermentable fibers in IBD patients.
It is clear that some fermentable fibers such as resistant starch (that is not digested in the small intestine) and inulin are metabolized by intestinal bacteria to SCFAs [55], acetate, butyrate and propionate, and they have immunomodulatory properties, promote the regeneration of the intestinal epithelium, lower the pH of the colon and inhibit the growth of pathogens [78].
The IBD-altered microbiota composition results in a lower production of anti-inflammatory and immunoregulatory metabolites, in particular butyrate, a lack of which may contribute to increase intestinal inflammation [19]. Butyrate plays a central role in the development of IBD because it represents the main energy substrate for colonocytes [79] and the alteration of its metabolism is linked with mucosal damage and inflammation [80]. In fact, the integration of some types of fibers (especially fermentable fibers) produces SCFAs capable of maintaining remission and reducing mucosal lesions [78]. In addiction, SFCAs, partic- ularly acetate and butyrate, balance mucus production and secretion. Mucus production at the level of the epithelium is a form of host protection to prevent microbial invasion and susceptibility to infection. A diet low in fiber produces less SFCAs and results in an increase in harmful metabolites that increases susceptibility of infections by deterio- ration of the mucus layer and contribute to the development of chronic disease and colorectal cancer (CRC) [80][81][82].
Although current dietary guidelines are not so clear on the amount and the type of fiber that should be consumed in IBD , in the literature, several studies evaluated the effects of fermentable and non-fermentable fibers in IBD patients.
It is clear that some fermentable fibers such as resistant starch (that is not digested in the small intestine) and inulin are metabolized by intestinal bacteria to SCFAs , acetate, butyrate and propionate, and they have immunomodulatory properties, promote the regeneration of the intestinal epithelium, lower the pH of the colon and inhibit the growth of pathogens .
The IBD-altered microbiota composition results in a lower production of anti-inflammatory and immunoregulatory metabolites, in particular butyrate, a lack of which may contribute to increase intestinal inflammation [19]. Butyrate plays a central role in the development of IBD because it represents the main energy substrate for colonocytes [79] and the alteration of its metabolism is linked with mucosal damage and inflammation [80]. In fact, the integration of some types of fibers (especially fermentable fibers) produces SCFAs capable of maintaining remission and reducing mucosal lesions [78]. In addiction, SFCAs, partic- ularly acetate and butyrate, balance mucus production and secretion. Mucus production at the level of the epithelium is a form of host protection to prevent microbial invasion and susceptibility to infection. A diet low in fiber produces less SFCAs and results in an increase in harmful metabolites that increases susceptibility of infections by deterio- ration of the mucus layer and contribute to the development of chronic disease and colorectal cancer (CRC) [80][81][82].
Diet plays a crucial role in the treatment of IBD; however, no dietary compo- nent is considered responsible for the disease [45]. Thus, patients with IBD should be advised to eat a varied diet that meets their energetic and nutrients requirements, including dietary fibers [45]. In the literature, it is clear that IBD subjects tend to consume less fiber than healthy controls [45]. Studies have shown that fiber supplementation alone is unlikely to restore IBD patients’ microbiota to a healthy state. IBD patients are more at risk of protein-energy malnutrition than the general popula- tion. They have difficulty in gaining weight and, especially those affected by CD, could have deficiencies in micronutrients such as iron, vitamin B12 and vitamin D [83][84] [85][86][87][88].
All of these nutritional problems also have a serious psychosocial repercussion and worsen patients’ quality of life [89]. In fact, a majority of individuals with IBD believe that specific foods trigger their disease flares, although this belief is not supported by any study [90].
This research evaluated the effects of dietary fibers in the two different types of IBD, Crohn’s disease and ulcerative colitis. Actually, there is no consensus on the type and the amount of dietary fibers to suggest in these two cases even when taking into consideration the phase of the disease. Further studies are necessary to determine the appropriate amount and type of fiber to suggest in the case of IBD.