Fiber and Lipids Flashcards
In general, what does the word “fiber” refer to?
carbohydrates that are not digestible by human enzymes
Fibers are generally split into what two categories?
soluble (mostly viscous, but some non-viscous) and insoluble (non-viscous)
What are the three insoluble fibers we learned?
lignins
cellulose
some hemicelluloses
What are some of the soluble fibers we learned?
fructans (this one's non-viscous) psyllium B-glucans pectin gums some hemicelluloses
What about the bonds in fiber makes it indigestible?
they are glucose polymers with beta1,4 bonds which is not a substrate for amylase, which likes alpha1,4 bonds
What is the simplest insoluble fiber?
cellulose - it’s just repeating glucose units in beta1,4 linkages
What determines whether a fiber is soluble or not?
the different backbones and side chains affect solubility
Describe the structure of lignin?
a branched polymer of phenolic subunits, so there are phenol groups, which is somewhat odd for a carb
makes them undigestible by us AND bacteria
Lignins are found in what foods?
stems and seeds of fruits
What foods are high in cellulose?
bran, beans, nuts, root veggies and apples
How does hemicellulose differ from cellulose?
hemicellulose has the similar string of glucose molecules in beta1,4 linkages, but will also have various sugars on the backbone which cellulose doesn’t have
What foods are high in hemicellulose?
bran, whole grains and nuts
What are three examples of the side chains that hemicellulose will have?
arabinose
glucuronic acid
galactose
Describe the structure of pectin.
It is a branched polymer with a galacturonic acid backbone and various side chains including rhamnose, arabinose, xylose, fucose and galactose
What foods have pectins in abundance?
apples, strawberries
True or false: pectins are almost completely degraded by gut bacteria.
true
How are gums made?
they are secreted by plants to close wounds (so cut a tree, wait and collect)
What is the structure of gum arabic?
highly branched glucuronic acids
True or false: gut bacteria cannnot ferment gum arabic
false - it’s completely fermented by gut bacteria
Describe the structure of beta-glucans.
homopolymers of glucopyranose subunits
What foods have beta-glucans in abundance?
oats, barley and mushrooms
True or false: beta glucans are broken down by gut bacteria
yup - down to short chain fatty acids
What’s the structure of fructans?
branching polymer of fructose
it’s also called polyfructose…
What foods have fructans?
asparagus, leeks, onions, garlic, tomatos and bananas
Why are fructans considered “prebiotics”? And fibers in general….
They are the food for probiotic bacteria like bifidobacteria
What is the synthetic fructan used as a fat substitute in salad dressings?
inulin
What fiber is used in supplements like metamucil? Why?
psyllium
it’s quite indigestible and can hold a lot of water, so it works very well in promoting bowel regularity
What are some examples of resistant starches?
which are carbs that have bond confiurations that could be broken down, but for some reason are inaccessible to the enzymes….
plant cell walls
starch granules within cells
retrograde starch (cooked and then cooled pasta)
chemically crosslinked starch
What are two insoluble fibers found in the exoskeletons of insects and crustaceans?
chitin and chitosan
What’s the structure of chitin and chitosan?
structure is similar to cellulose but with amino group substitutions on the glucose
What is a polymer of glucose and sorbitol used as a food additive to replace sugar?
polydextrose
What are the gastric effects of the soluble fibers?
they delay gastric emptying
increase transit time through the GI
decrease nutrient uptake
In particular the viscous fibers….what are the gastric effects?
- delay gastric emptying
- decrease mixing of food with digestive enzymes
- decrease nutrient diffusion
- increase small intestine transit time
What are the gsatric effects of the insoluble fiber?
- decrease intestinal transit time
- increase fecal bulk
- also decrease nutrient diffusion
What is the glycemic index?
a measure of how much/fast blood glucose levels increase after ingestion
High fiber foods will have a ____ glycemic index.
low
What are the benefits of having fiber in the diet in terms of lipid profiles?
they decrease lipid absortion b ypreventing micelle formation
so you don’t get fat uptake and lipids go down
What are the benefits of fiber in terms of serum cholesterol levels?
fiber increases the excretion of bile acids by reducing uptake in the ileum
this means you need to use your cholesterol to make more bile acids and serum cholesterol goes down
What are the benefits of fiber in terms of the gut microbiome?
fiber promotes growth of the good guys - lactobacilli and bifidobacteria
it’s basically food for them and we get the short chain fatty acids out of the deal
What are the benefits of fiber in terms of diverticulitis?
if you increase fecal bulk, it decreases intraluminal pressure which decreases risk for diverticulitis
How can fiber help regulate inflammation in the gut?
the fiber will be broken down by bacteria to SCFAs
the SCFAs act as a ligand for GRP4 which acts as an anti-inflammatory signal on the immune system and thus helps keep the immune system tolerant to good microbiota
How can SCFAs actually alter transcription patterns in immune cells?
they can act as histone deacetylases
How can GPR43 also suppress fat accumulation?
It’s expressed on adipocytes
activation by short chain fatty acids in the blood will inhibit insulin-dependent storage of fatty acids in the adipocytes, increases their use by other tissues like muscle and liver
essentially a monitor for excessive dietary energy
Does breast milk have fiber? Really?
really - it contains non-digestible oligosaccharides
What are the potential benefits to having that fiber in breast milk?
can be metabolized by gut bacteria and also enter the blood with immunomodulatory effects
What effects will breast milk have on the microbiota of the infant’s gut?
good things…
increases the proportion of the good bifidobacterium and also increases the variability of the bifidobacterium species
How might the human milk oligosaccharides help fight against infections?
they can act as decoy receptors so the pathogens bind to the oligosaccharides and not cellular glycolipids or glycoproteins, thus promoting their excretion
