NUTR 120 Lecture Notes - Lecture 12: Dietary Fiber, Short-Chain Fatty Acid, Resistant Starch
L13 Dietary Fibre and Intro to Protein
Name the healthiest cereal!
- It all depends on what is in the cereal and what ingredient should we be paying attention to
- Processed breakfast cereals are one of the most enriched foods
- Having breakfast will be doing better overall in the day for weight management, concentration,
and etc.
- Higher fibre → full longer and can concentrate longer
- Starch is one of the things that you shouldn’t worry about as long as fibre is present in the food
o Starch is what we should be getting most of our CHO from
- Bran flakes is a good choice – high in fibre and low in sugar
**back to last lecture
Resistant starch = when boiling potatoes and then cooling them down, they go through retrogradation
(converts some of the regular starch into a form that we are not able to digest so well)
- It is more like soluble fibre
- Some foods have naturally resistant starch (legumes and lentils have resistant starch already –
it is serving a role like fibre)
Dietary fibre = we do NOT digest them at all
- For example, cellulose (important component of plant cell wall) – insoluble fibre
- Gum and pectin are found in the pulp of the fruit – high in soluble fibres
Dietary Fibre: Indigestible Plant Material
1. Soluble fibre
E.g. pectin, gum
Food sources:
- Whole oats (particularly -glucan)
- Barley
- Insides of legumes
- Fruit pulp
- Psyllium (major ingredient in Metamucil)
*Some of the examples also have insoluble fibre, but they are more abundant in soluble fibre (you
can’t just have one type of fibre – they always come together)
2. Insoluble fibre
E.g. cellulose, lignans (tough woody substances)
Food sources:
- Skin of legumes
- Vegetable and fruit skin
- Psyllium (major ingredient in Metamucil)
- Strawberry seeds (example of a lignan)
Summary:
- Fibre is found in plants
- The less processed, the better
We are interested in fibre for heart health, weight control, prevention of type-2 diabetes and cancer
- In our diet, we usually have 2/3 insoluble fibre to 1/3 soluble fibre
What does Fibre do in the Colon (large intestine)?
1. Soluble fibre (loose-meshwork of fibres)
- Contents from small intestine enter the large intestine, we call the material digesta (since most
of the nutrients have been absorbed)
- Soluble fibre forms a gel (viscous fibre) → it appears to disappear/solubilize in the gut
o It slows the rate at which we absorb nutrients (good for slow rise in blood glucose)
- Colon also has bacteria and they can break down the soluble fibre (fermentation – a LOT)
o Breaks down the bonds in the soluble fibre so it can use it for food
o Product includes gases (CH4, H2) and short chain fatty acids (each have their own
benefits)
o 2:0 acetic acid = it’s so small that it is just absorbed across the mucosal surface
▪ Body uses this for calories (we do get a little bit of calories from fibre)
o 3:0 propionic acid = it’s short and is able to be absorbed across the mucosa
▪ Goes through the bloodstream and shuts down cholesterol synthesis in the liver
o 4:0 butyric acid = preferred energy sources by the colonocytes (cells that line the colon)
▪ Thought to be a substance that reduces the risk of colorectal cancer
- Not much is left in the fecal matter – it has lots of bacteria and some fibre
o Therefore, it is not helpful in regulating bowel movements
2. Insoluble fibre
- Digesta enters the colon w/ insoluble fibre (very tight meshwork of fibres)
- Insoluble is too tough and difficult even for bacteria to breakdown = fermentation
- Therefore, less short chain fatty acids and less gas, but you end up w/ fecal bulk
o So there’s less constipation and it keep regular bowel movement
- Insoluble fibre goes through our GI tract undigested and becomes part of the fecal matter
Wheat Bran: ‘Gold Standard’ for Insoluble Fibre
- We grow it in Saskatchewan! It is in whole grain bread
Parts of a kernel (wheat, rice, etc.):
- Germ = it is like an egg that gives rise to other plants
o Source of B vitamins, iron, fat soluble vitamins (esp. vitamin E), and fat (MUFAs and
PUFAs)
- Bran = outermost layer (looks like shingles)
o Source of insoluble fibre
o Processing of the kernel removes the bran and automatically removes the aleurone
layer (underlies the bran layer)
▪ Aleurone layer is a source of iron and B vitamins
Document Summary
It all depends on what is in the cereal and what ingredient should we be paying attention to. Processed breakfast cereals are one of the most enriched foods. Having breakfast will be doing better overall in the day for weight management, concentration, and etc. Higher fibre full longer and can concentrate longer. Starch is o(cid:374)e of the thi(cid:374)gs that (cid:455)ou should(cid:374)(cid:859)t (cid:449)orr(cid:455) a(cid:271)out as long as fibre is present in the food: starch is what we should be getting most of our cho from. Bran flakes is a good choice high in fibre and low in sugar. Resistant starch = when boiling potatoes and then cooling them down, they go through retrogradation (converts some of the regular starch into a form that we are not able to digest so well) Some foods have naturally resistant starch (legumes and lentils have resistant starch already it is serving a role like fibre) Dietary fibre = we do not digest them at all.
