Dr. Ron’s Research Review – December 19, 2018


This week’s research review focuses on Gibsons Conundrum.

The low-fermentable oligo-, di-, and monosaccharide and polyol (FODMAP) diet is a 2-phased intervention, with strict reduction of all slowly absorbed or indigestible short-chain carbohydrates (ie, FODMAPs) followed by reintroduction of specific FODMAPs according to tolerance. The FODMAP diet includes lactose and most other prebiotics.
Gibsons conundrum involves two mechanisms providing hypothetical benefits. (Fung and Szilagyi, 2012)
Adapting to beneficial prebiotics.
Avoiding of a wide array of carbohydrates, including prebiotics.
In the first instance, carbohydrates bypassing absorption in the small intestine can specifically manipulate metabolism and benefit the commensal bacteria, which in turn help reduce inflammation.
Prebiotics include: inulin, fructooligosaccharides (FOS), galactooligosaccharides (GOS), lactulose. (Gibson et al., 2004)
Traditionally, complex carbohydrates, that is, resistant starch and non-starch polysaccharides, such as cellulose, hemicellulose, lignin, pectin and oligosaccharides, have been the major focus of prebiotic research, because they are resistant to gastric acidity and hydrolysis by mammalian enzymes, escape digestion and reach the large intestine as primary substrates for microbial fermentation. In addition, simple sugars, disaccharides and sugar alcohols (when reaching the colon owing to over- feeding or malabsorption) as well as human milk oligosaccharides in infants can be substrates for colonic microbial fermentation. Proteins, amino acids and certain lipids can also escape digestion and become substrates for the gut microbiota. (Steinert et al., 2016)
Short-chain fatty acids (SCFAs), the principal end products of carbohydrate fermentation, are considered the key metabolites underpinning the physiological benefits of prebiotics. Butyrate is the primary energy source for colonocytes; propionate is thought to regulate liver cholesterol synthesis and acetate controls hepatic lipogenesis and is used to generate ATP in muscle tissue. Moreover, SCFAs reduce intestinal pH, thus antagonizing pathogens, and possess antimicrobial activity. (Steinert et al., 2016)

Dr. Ron



Carbohydrate Elimination or Adaptation Diet for Symptoms of Intestinal Discomfort in IBD: Rationales for "Gibsons' Conundrum".
            (Fung and Szilagyi, 2012) Download
THERAPEUTIC USE OF CARBOHYDRATES IN INFLAMMATORY BOWEL DISEASES (IBDS) IS DISCUSSED FROM TWO THEORETICAL, APPARENT DIAMETRICALLY OPPOSITE PERSPECTIVES: regular ingestion of prebiotics or withdrawal of virtually all carbohydrate components. Pathogenesis of IBD is discussed connecting microbial flora, host immunity, and genetic interactions. The best studied genetic example, NOD2 in Crohn's disease, is highlighted as a model which encompasses these interactions and has been shown to depend on butyrate for normal function. The role of these opposing concepts in management of irritable bowel syndrome (IBS) is contrasted with what is known in IBD. The conclusion reached is that, while both approaches may alleviate symptoms in both IBS and IBD, there is insufficient data yet to determine whether both approaches lead to equivalent bacterial effects in mollifying the immune system. This is particularly relevant in IBD. As such, caution is urged to use long-term carbohydrate withdrawal in IBD in remission to control IBS-like symptoms.

Dietary modulation of the human colonic microbiota: updating the concept of prebiotics.
            (Gibson et al., 2004) Download
Prebiotics are non-digestible (by the host) food ingredients that have a beneficial effect through their selective metabolism in the intestinal tract. Key to this is the specificity of microbial changes. The present paper reviews the concept in terms of three criteria: (a) resistance to gastric acidity, hydrolysis by mammalian enzymes and gastrointestinal absorption; (b) fermentation by intestinal microflora; (c) selective stimulation of the growth and/or activity of intestinal bacteria associated with health and wellbeing. The conclusion is that prebiotics that currently fulfil these three criteria are fructo-oligosaccharides, galacto-oligosaccharides and lactulose, although promise does exist with several other dietary carbohydrates. Given the range of food vehicles that may be fortified by prebiotics, their ability to confer positive microflora changes and the health aspects that may accrue, it is important that robust technologies to assay functionality are used. This would include a molecular-based approach to determine flora changes. The future use of prebiotics may allow species-level changes in the microbiota, an extrapolation into genera other than the bifidobacteria and lactobacilli, and allow preferential use in disease-prone areas of the body.

The prebiotic concept and human health: a changing landscape with riboflavin as a novel prebiotic candidate
            (Steinert et al., 2016) Download
Emerging evidence suggests that the gut microbiota has a critical role in both the maintenance of human health and the pathogenesis of many diseases. Modifying the colonic microbiota using functional foods has attracted significant research effort and product development. The pioneering concept of prebiotics, as introduced by Gibson and Roberfroid in the 1990s, emphasized the importance of diet in the modulation of the gut microbiota and its relationships to human health. Increasing knowledge of the intestinal microbiota now suggests a more comprehensive definition. This paper briefly reviews the basics of the prebiotic concept with a discussion of recent attempts to refine the concept to open the door for novel prebiotic food ingredients, such as polyphenols, minerals and vitamins.



Fung, QM and A Szilagyi (2012), ‘Carbohydrate Elimination or Adaptation Diet for Symptoms of Intestinal Discomfort in IBD: Rationales for “Gibsons’ Conundrum”.’, Int J Inflam, 2012 493717. PubMed: 22518336
Gibson, GR, et al. (2004), ‘Dietary modulation of the human colonic microbiota: updating the concept of prebiotics.’, Nutr Res Rev, 17 (2), 259-75. PubMed: 19079930
Steinert, RE, et al. (2016), ‘The prebiotic concept and human health: a changing landscape with riboflavin as a novel prebiotic candidate’, Eur J Clin Nutr, 70 (12), 1348-53. PubMed: 27380884