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GI Week 4 > Fiber and Lipids > Flashcards

Fiber and Lipids Flashcards

1
Q

In general, what does the word “fiber” refer to?

A

carbohydrates that are not digestible by human enzymes

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2
Q

Fibers are generally split into what two categories?

A

soluble (mostly viscous, but some non-viscous) and insoluble (non-viscous)

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3
Q

What are the three insoluble fibers we learned?

A

lignins
cellulose
some hemicelluloses

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4
Q

What are some of the soluble fibers we learned?

A 
fructans (this one's non-viscous)
psyllium
B-glucans
pectin
gums
some hemicelluloses
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5
Q

What about the bonds in fiber makes it indigestible?

A

they are glucose polymers with beta1,4 bonds which is not a substrate for amylase, which likes alpha1,4 bonds

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6
Q

What is the simplest insoluble fiber?

A

cellulose - it’s just repeating glucose units in beta1,4 linkages

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7
Q

What determines whether a fiber is soluble or not?

A

the different backbones and side chains affect solubility

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8
Q

Describe the structure of lignin?

A

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

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9
Q

Lignins are found in what foods?

A

stems and seeds of fruits

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10
Q

What foods are high in cellulose?

A

bran, beans, nuts, root veggies and apples

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11
Q

How does hemicellulose differ from cellulose?

A

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

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12
Q

What foods are high in hemicellulose?

A

bran, whole grains and nuts

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13
Q

What are three examples of the side chains that hemicellulose will have?

A

arabinose
glucuronic acid
galactose

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14
Q

Describe the structure of pectin.

A

It is a branched polymer with a galacturonic acid backbone and various side chains including rhamnose, arabinose, xylose, fucose and galactose

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15
Q

What foods have pectins in abundance?

A

apples, strawberries

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16
Q

True or false: pectins are almost completely degraded by gut bacteria.

A

true

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17
Q

How are gums made?

A

they are secreted by plants to close wounds (so cut a tree, wait and collect)

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18
Q

What is the structure of gum arabic?

A

highly branched glucuronic acids

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19
Q

True or false: gut bacteria cannnot ferment gum arabic

A

false - it’s completely fermented by gut bacteria

20
Q

Describe the structure of beta-glucans.

A

homopolymers of glucopyranose subunits

21
Q

What foods have beta-glucans in abundance?

A

oats, barley and mushrooms

22
Q

True or false: beta glucans are broken down by gut bacteria

A

yup - down to short chain fatty acids

23
Q

What’s the structure of fructans?

A

branching polymer of fructose

it’s also called polyfructose…

24
Q

What foods have fructans?

A

asparagus, leeks, onions, garlic, tomatos and bananas

25
Q

Why are fructans considered “prebiotics”? And fibers in general….

A

They are the food for probiotic bacteria like bifidobacteria

26
Q

What is the synthetic fructan used as a fat substitute in salad dressings?

A

inulin

27
Q

What fiber is used in supplements like metamucil? Why?

A

psyllium

it’s quite indigestible and can hold a lot of water, so it works very well in promoting bowel regularity

28
Q

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….

A

plant cell walls
starch granules within cells
retrograde starch (cooked and then cooled pasta)
chemically crosslinked starch

29
Q

What are two insoluble fibers found in the exoskeletons of insects and crustaceans?

A

chitin and chitosan

30
Q

What’s the structure of chitin and chitosan?

A

structure is similar to cellulose but with amino group substitutions on the glucose

31
Q

What is a polymer of glucose and sorbitol used as a food additive to replace sugar?

A

polydextrose

32
Q

What are the gastric effects of the soluble fibers?

A

they delay gastric emptying
increase transit time through the GI
decrease nutrient uptake

33
Q

In particular the viscous fibers….what are the gastric effects?

A
  1. delay gastric emptying
  2. decrease mixing of food with digestive enzymes
  3. decrease nutrient diffusion
  4. increase small intestine transit time
34
Q

What are the gsatric effects of the insoluble fiber?

A
  1. decrease intestinal transit time
  2. increase fecal bulk
  3. also decrease nutrient diffusion
35
Q

What is the glycemic index?

A

a measure of how much/fast blood glucose levels increase after ingestion

36
Q

High fiber foods will have a ____ glycemic index.

A

low

37
Q

What are the benefits of having fiber in the diet in terms of lipid profiles?

A

they decrease lipid absortion b ypreventing micelle formation

so you don’t get fat uptake and lipids go down

38
Q

What are the benefits of fiber in terms of serum cholesterol levels?

A

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

39
Q

What are the benefits of fiber in terms of the gut microbiome?

A

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

40
Q

What are the benefits of fiber in terms of diverticulitis?

A

if you increase fecal bulk, it decreases intraluminal pressure which decreases risk for diverticulitis

41
Q

How can fiber help regulate inflammation in the gut?

A

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

42
Q

How can SCFAs actually alter transcription patterns in immune cells?

A

they can act as histone deacetylases

43
Q

How can GPR43 also suppress fat accumulation?

A

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

44
Q

Does breast milk have fiber? Really?

A

really - it contains non-digestible oligosaccharides

45
Q

What are the potential benefits to having that fiber in breast milk?

A

can be metabolized by gut bacteria and also enter the blood with immunomodulatory effects

46
Q

What effects will breast milk have on the microbiota of the infant’s gut?

A

good things…

increases the proportion of the good bifidobacterium and also increases the variability of the bifidobacterium species

47
Q

How might the human milk oligosaccharides help fight against infections?

A

they can act as decoy receptors so the pathogens bind to the oligosaccharides and not cellular glycolipids or glycoproteins, thus promoting their excretion

GI Week 4 (11 decks)

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