Specific carbohydrate diet

Specific Carbohydrate Diet (SCD) is an exclusion diet to treat a variety of conditions with primary use in inflammatory bowel disease (IBD), (categorized as Crohn’s disease or ulcerative colitis), irritable bowel syndrome (IBS), diverticulitis and celiac disease (CD). The diet eliminates all grains (wheat, barley, rye, rice), soy, starchy vegetables like potatoes, sugar, and processed foods.  A complete list of accepted foods can be found on the breaking the viscous cycle website under "legal/illegal".  To achieve the end result, fanatical adherence is considered necessary for a prolonged period at this time, but studies evaluating a broader array of foods and slightly expanded diets with their roots in SCD like the Crohn's Disease Exclusion Diet (CDED) and modified SCD are ongoing. The SCD is one of the most widely studied diets for the treatment of IBD.^[1]

The Specific Carbohydrate Diet was developed by Sydney Haas, MD who along with John Howland, MD served as assistants at Vanderbilt Clinic to L. Emmett Holt, Sr, MD, a physician at the turn of the twentieth century taking a lead role in the US studying celiac disease. Holt, together with Christian Herter, MD, a physician and pathologist from Columbia University, reported that the condition is associated with abnormal forms of bacteria and “may confidently be ascribed to the action of putrefactive products”. Howland reports “that of all the elements of food, carbohydrates is the one which must be excluded rigorously”. Howland’s treatment was successful, but the need for some tolerable carbohydrate remained. Haas discovered a paper on “The value of Banana in the Treatment of Celiac Disease” and began incorporating carefully specific carbohydrates into the diet to determine the tolerability. The SCD, also known at the time in the 1940s’ as the “banana diet”, was successful in treating patients with gastrointestinal conditions diagnosed at the time as celiac disease based on symptoms, as no laboratory tests specific to celiac disease existed. ^[2][3][4]

SCD was popularized by Elaine Gotschall with the publication of her book, Food and the Gut Reaction: Intestinal Health through diet first edition published in 1987, with name change and now 15^th edition, Breaking the Vicious Cycle: Intestinal Health through diet. ^[5] 

The postulated mechanism of benefit from the diet is that the condition of IBS or IBD is due to an overgrowth or imbalance of gut bacteria that can be corrected by the avoidance of specific carbohydrates that feed the overgrowth, hence the name Specific Carbohydrate Diet. The technology at the time of the development of this diet was not able to evaluate this hypothesis.  However, with the current technology of gene sequencing combined with the improvements in data software analysis, the bacterial, viral, and fungal components encompassing the human microbiome are now analyzable and this is among the most active area of research for human diseases and in particular IBD.^[6]

It is now commonly accepted that dysbiosis (disruption of gut bacterial balance from normal) is the hallmark of IBD. ^{[7] [8][9]} Overall richness of the bacterial community is decreased with certain species found to be commonly overgrown in particular the phylum of Proteobacteria and members of the family of Enterobacteriaceae, and fungus including candida tropicalis and candida albicans, while other species tend to be either absent or under represented such as faecalibacterium prausnitzii of the Clostridium clade. ^{[10] [11][12][13][14]}The SCD has been shown to alter this balance of bacteria and shift it more toward that found in healthy population without disease. ^[15][16]

The SCD has been shown to induce remission of Crohn’s disease, with reduction or elimination of symptoms, normalization of serum inflammatory markers and evidence of improved mucosal tissue by endoscopy ,including remission in seven children with active Crohn’s disease without the use of concomitant medications.  These positive findings are considered a result of shifts in the microbiome due to dietary changes.^[1][17]

Patient reports of improvements ^{[18] [19]} have prompted the renewed interest of dietary therapy for IBD.  Two large scale ongoing trials of over 100 patients each are currently underway, PRODUCE (comparing SCD with modified SCD in pediatric patients),^[20] and DINE-CD (comparing SCD with the Mediterranean diet in adult patients).^[21] Additionally, there are over twenty smaller ongoing interventional trials evaluating aspects of diet, microbiome and IBD, many of which are utilizing SCD. ^[22]

As current research documents the role of diet in the pathogenesis and treatment of IBD, there are five ongoing large epidemiologic studies evaluating the relationship to diet and IBD, including the Prognostic Effect of Environmental Factors in Crohn’s and Colitis (PREdiCCT), Inflammation, Microbiome and Alimentation: Gastrointestinal and Neuropsychiatric Effects (IMAGINE), Chronic Inflammatory Disease, Lifestyle and Treatment Response (BELIEVE). ^[22]

The interest in dietary therapy for IBD is growing with the increased focus on the microbiome and the implications of it in the pathogenesis of IBD and the potential to manipulate it. There is a paucity of data for use of diet in IBD, as the evidence to date is from small patient populations, and large clinical trials are needed to validate these findings. Dietary therapy is considered an option to treat IBD in conjunction with medical therapy.^[17][1]