dietary fibre Flashcards
what is dietary fiber?
dietary fiber is the fraction of the edible parts of plants or carbohydrates which are resistant to digestion and absorption (in the small intestine) and which can be partially or completely fermented (in the large intestine)
where do dietary fibers come from
largely from the plant cells often in the cell walls.
how is total dietary fiber determined
it is the residue of plant materials remaining after removal of lipids, proteins,
and starches. lipids are removed through solvent organic extraction, proteins are removed by protease digestion, and starch is removed by amylo-glucosidase digestion.
what are some examples of dietary fibers
cellulose, mixed linkage glucans, pectin, xyloglucan, and arabinoxylan.
how are dietary fibers classified
solubility, viscosity, and fermentability. if it is insoluble, it will not be viscous, as it cannot hold the water to change viscosity. if not soluble, it will only be partially fermentable. fermentation is important as it improves gut health. also, some small molecules are not viscous despite solubility as they cannot hold enough water.
what are prebiotics?
they are particular dietary fibers which contribute to improving host health. they stimulate growth, increase activity, and change the composition of the intestinal microflora.
how does bacterial fermentation occur?
colonic bacteria use a range of carbohydrate hydrolysing enzymes to break down starch and dietary fiber into absorbable monosaccharides.
what are the roles of the intestinal microflora
contributed to the barrier that protects pathogenic bacteria from invading the gastrointestinal tract. Salvages energy from carbohydrates not digested in the upper gut, released as metabolic useful products for host. Contribute to stool bulking.
what product of dietary fiber fermentation can be absorbed in the colon?
short chain fatty acids: acetic acid, propionic acid; butyric acid, lactic acid.
what does the fermentation pattern depend on
size, structure (sugars and linkages), and solubility of the fiber.
what are the benefits of SCFAs to the body?
Epithelial cells directly use them for fuel, and they are also absorbed into the blood from the colon for the rest of the body to use. they also contribute to colon health, promoting acidity, suppressing pathogenic organisms, reducing bacteria peptide degradation and therefore resultant toxic compounds, and also suppress colonic inflammation. SCFA contribute to host health like preventing and attacking cancerous cells, and decreasing ammonia absorption. (fuel for colon, promote acidity, reducing bacteria peptide degradation and resultant compounds, prevent and attack cancerous cells, reduce ammonia absorption)
what happens partially digested proteins in the body?
they are fermented by gut bacteria, releasing ammonia (harmful)
what are the products of protein fermentation, and what are the impacts for the body
branched chain fatty acids (BCFAs) which are metabolised differently in the body, and can have severe consequences for the body. BCFAs are BAD. And ammonia is released
what are difficulties with dietary fiber research?
much information is based off in vitro research, animal studies only provide clues, epidemiological studies can provide causal links, but are very large and hard to coordinate.
what are the health effects of dietary fiber?
prevents constapation (adding bulk to stool). helps to provide satiation and satiety (increase bulk to stomach and can delay gastric emptying, making food stay in stomach longer. also dietary fibers impact release of satiety hormones like ghrelin), lowers cholesterol absorption, and reduces circulating cholesterol
how do dietary fibers limit body cholesterol, and which specific DF is an example.
beta glucan, for example lowers cholesterol absorption from foods by forming a viscous gel which traps bile-cholesterol micelles, eliminating them from the body. this also forces the body to produce more bile from cholesterol, therefore reducing the circulating body cholesterol.
What enzymes are involved in starch digestion?
- Pancreatic alpha amylase which polymerises large starch molecules like amylose and amylopectin into oligosaccharides, which are too large to be absorbed. Then mucosal alpha-glucosidases of which each are specialised to break particular bonds (e.g. alpha 1,4), producing absorbable glucose units.
what is the glycemic index
a measure of the carbohydrate’s postprandial glucose response of food (the response of the blood sugar, or therefore how fast it is digested). the lower the GI value, the slower glucose is released.
what are the benefits of low GI foods
high-GI is associated with diabetes-2 and cardiovascular disease. Can be used for blood sugar control in diabetics. could be used for reducing body weight
how does dietary fibre help with diabetes management
It delays gastric emptying, slowing down digestion and absorption, while also modifying release of digestion-related gut hormones. It delays amylolysis (starch digestion) and delays sugar diffusion and absorption. all this improves glycemic control (blood sugar control).
What occurs in non-diabetics
- In non-diabetics, the pancreatic beta-cell synthesises insulin when blood glucose levels increase, binding to receptors and increasing glucose uptake in the skeletal muscles and adipose tissue. It is also insoluble (think cotton made of cellulose doesn’t dissolve in the washing machine).
What occurs in type 1 diabetes
- In type 1 diabetes, there is an absolute lack of insulin due to destruction of pancreatic beta-cells. This results in persistent hyperglycaemia.
What occurs in type 2 diabetes
- In type 2 diabetes, the insulin receptors are damaged, meaning that there is less uptake into skeletal muscles and adipose tissue, and the liver increases glucose production.
How does diabetes cause blood vessel damage
The increase in blood Glc levels increases glycation of proteins, making the blood vessels less healthy.
