Carbohydrates intestinal bacteria

Metabolism via normal metabolic pathways or fast excretion without metabolism are desirable characteristics. Some intense sweeteners are excreted unchanged while others are metabolised. Bulk sweetener absorption is lower and slower than for carbohydrates and results in reduced caloric availability which is partly due to metabolites formed by intestinal bacteria. Such metabolites and osmotic effects of not fully absorbed bulk sweeteners can cause laxative effects. Generally, the calorific value of bulk sweeteners is lower than for carbohydrates. Intense and bulk sweeteners are, as far as they are metabolised, not dependent on insulin. They are therefore acceptable for diabetics as part of a suitable diet. 

Saline laxatives like MgS04, Mg(OH)2, Mg2 Citrate and Na+ Phosphates act via their osmotic pressure to retain water in the colon. Other osmotic laxatives are carbohydrates such as lactulose, glycerin, sorbitol, and mannitol. They are not absorbed and are resistant to digestion in the small intestine. Most agents are orally administered. It should be noted however that glycerin, sodium phosphates and sorbitol are formulated for rectal use. From lactulose lactic and acetic acids are formed by intestinal bacteria and apart from its osmotic effects it thus acidifies the content of the colon. The reduction of the pH stimulates motility and secretion. 

Biotin (vitamin B ) is widespread in foods and is also synthesized by intestinal bacteria. It is a coenzyme for the carboxylation of pyruvate, acetyl-coenzyme-A (CoA), propionyl CoA, and /1-methyl-crotonyl CoA and is involved in fatty acid formation and in energy release from carbohydrates. In humans deficiencies only occur in patients with an abnormal gut flora and manifests itself as exfoliative dermatitis and alopecia. 

Intestinal microflora are capable of impacting xenobiotic metabolism by causing enterohepatic circulation and delayed excretion and by catalyzing many of the reactions that also occur as a result of detoxication and bioactivation reactions by phase I and II enzymes. The carbohydrate amygdalin, which contains a cyanide substituent, is found in the kernels of various fruits including plum, cherry, peach, and apricot as well as in almonds. Hydrolysis by the [f-glucosidases in intestinal bacteria yields reactive intermediates capable of releasing cyanide. 

Carbohydrate malabsorption plays a major role in diarrhea associated with SBS. Unabsorbed carbohydrates are broken down by intestinal bacteria to short-chain fatty acids (SCFAs), producing an osmotic load in the distal small intestine and colon that can lead to protracted diarrhea. However, the colon is able to use these SCFAs as a source of energy, thus complex carbohydrates may provide a significant caloric source for patients with a massive resection and a preserved colon. ... 

Maillard products, associated with the browning of foods, could also provide some carbohydrate for intestinal bacteria. 

Crittenden, R., Karppinen, S., Ojanen, S., Tenkanen, M., Fagerstrom, R., Mattb, J., et al. (2002). In vitro fermentation of cereal dietary fibre carbohydrates by probiotic and intestinal bacteria. Journal of the Science of Food and Agriculture, 82, 781-789. 

In order to be considered as prebiotics, carbohydrates must fulfill three criteria, namely (1) resistance to gastric acidity, hydrolysis by mammalian enzymes and gastrointestinal absorption (2) fermentation by intestinal microflora and (3) selective stimulation of the growth and/or activity of those intestinal bacteria that contribute to health and well-being. ... 

A considerable amount of biotin is synthesized by human intestinal bacteria, as evidenced by the fact that 3 to 6 times more biotin is excreted in the urine and feces than is ingested. But synthesis in the gut may occur too late in the intestinal passage to be absorbed well and play much of a direct role as a biotin source. Also, several variables affect the microbial synthesis in the intestines, including the carbohydrate source of the diet (starch, glucose, sucrose, etc.), the presence of other B vitamins, and the presence or absence of antimicrobial drugs and antibiotics. 

Saponins and phenolics also have anti-microbial properties (Chung et ah, 1998) and have been associated with reduced rumen functions (Klita et al., 1996 Reed, 1995), thereby limiting the nutrient quality of forages. Also, carbohydrate complexes with hgnins and other compounds reduce carbohydrate utilization by rumen bacteria (Cornu et al., 1994). The influence of such anti-microbials on rumen functions can affect small intestine characteristics by altering nutrient concentrations (Barry and McNabb, 1999). 

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