7.5 Food and Gut Flashcards
What is the food matrix effect
The food matrix is the interactions in the gut between the different nutrients in digestion and absorption. These interactions can impact digestibility.
Describe the effect of soluble dietary fibres on glucose absorption in the gut
The presence of dietary fibres slows down the absorption of glucose. It does this by slowing gastric emptying (by forming a gel like matrix that increases viscosity). Additionally it reduces enzyme access to starch, reduces receptor signalling molecule interactions and the general adsorption. This lowers the glycaemic response.
What is the glycaemic index and glycaemic response
The glycaemic index is an index of how much blood glucose goes up after eating a food. The GI is measured on a scale from 0 to 100, with 100 representing the reference food, typically glucose or white bread. The glycaemic response is extent of the rise in blood glucose levels after consuming carbohydrates.
How can the processing and cooking of the food alter it’s glycaemic index
-is it eaten raw
-is it eaten hot or cold
-does retrogradation (structural changes upon heating and then recooling) of the starch occur in cooking or processing
-how is it cooked
How can chewing have effects on the glycaemic response
When chewing, mechanoreceptors under your teeth send signals to stomach and pancreas to get ready for food intake, hence chewing can increase the rate of digestion and absorption.
Swallowing small pieces of food without chewing them leads to lower glucose responses as they take longer to digest
So the more chewing, the greater the glycaemic response
Describe how the chemical structure of the nutrient can impact digestibility using carbohydrates as an example.
Chemical structures such as primary structure (what components and types of bonds), secondary structure (how the bonds turn the shape of the polysacharide chain) and tertiary structure (the 3D bonding between chains and their associations with water). Carbohydrates made from glucose alone include starch, cellulose and beta glucans. Different bonds (e.g a 1-4 glycosidic, a 1-6 glycosidic, b 1-4 glycosidic etc) give different primary and secondary structure. Amylose has a helix shape, amylopectin has a branched helix shape and cellulose has a pleated sheet shape. Then the same bonds can interact to give different tertiary structures, e.g a type A starch in wheat gives a lattice structure and type B starch in potatoes gives a super helix structure. All these factors lead to differences in digestibility.
Describe how differences in starch granules alter digestibility
Different starches have different starch granules, these are coated granules that store the starch to make sure they dont just sit in the cell and alter osmolarity. There is variability in granule surface area to volume ratio. This causes altered impact of amylase digestion on starch granules of different types.
How can processing alter structure and thus digestibility of starch.
As a starch granule is heated, it bursts, releasing the starch, the helical structure becomes disorganised and the starch gelatinises. When the starch cools it starts to recrystallise, some forming a tighter structure like B type starch, this is retrogradation. After the retrogradation, some of the starch becomes resistant to digestion and more and more of this happens the more heating and cooling cycles there are
What are the different ways starch can be classified
Starch can be classified as rapidly digestible, slowly digestible or resistant to digestion
What is resistant starch
Resistant starch is the products of starch degradation that can not be absorbed in the small intestine of healthy individuals. This can be because it is physically inaccessible, has naturally resistant starch granules, is retrograded or is modified.
Describe the variations in the structure of proteins that lead to different digestibilities
Proteins can have different tertiary structures such as globular, helical or pleated sheets. There are complex structures such as muscle proteins and proteins can be strengthened by connective tissue. In fungal proteins there are intact hyphal walls and in plant proteins there are intact cell walls
Give an example of a soluble fibre
Pectin
Give some mechanisms that can slow digestion
reduced gastric emptying (e.g from a high fat meal), high luminal viscosity (e.g through soluble dietary fibre) and high particle size (e.g through lack of chewing
How does fat and fibre alter the absorption and metabolism of flavanoids
Fats and fibres entrap flavanoid molecules as part of food matrix and they are not digested in the small intestine, this stimulates and alters colonic bacterial populations and metabolism. This changes the physiochemical environment in the colon and altering gastric emptying.
What happens to food not digested in the small intestine.
It is either fermented by the colonic microflora into short chain fatty acids and gases which are absorbed in the colon or it is excreted in faeces
