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Transcript
Lecture 4b- 30 September 2016
Fibre
1
Overview of lecture 4b
Fibre
 Fibre structure and classification and effects
 Idatme of fibres
 Fibres in health and disease
 How to get higher fibre in the diet
2
Overview of lecture 4b continued





Recommendations for fibre intake
too much fibre in the diet
Fibres as food additives
What is new in fibre research?
Choosing carbohydrates wisely
Next lecture-5A
Lipids-structure
-function
-IDATME
3
Fibre structure and classification
and effects
Insoluble
Cellulose-bran,vegetables
Hemicellulose-bran, whole grains
Lignins-fruits, mature vegetables, flax
Generally-accelerate gi transit,
-increase fecal weight(promotes bowel movements)
-slow starch digestion,
-delay glucose absorption
-but can be exceptions
4
Fibre structure and classification and
effects continued
Soluble
Pectins-apples, carrots, gums and mucilages- oats, legumes
Generally-delay gi transit,
-delay glucose absorption,
-lower blood cholesterol
-but can be exceptions
5
Other fibre functions (classifications)
- water holding capacity
- viscosity
- cation exchange capacity
- bile binding capacity
- fermentability
6
Fibre ingestion, digestion, absorption
and transport, metabolism, excretion
•
•
mouth for ingestion
fibre not digested in mouth or stomach or by small intestine
enzymes-why?
• bacteria-make short chain fatty acids, water, gas
• short chain fatty acids and water absorbed at large intestine
and transported by blood used for energy (fatty acid metabolism
next week – lecture 5A), water can split molecules to release
energy
• Excretion- gas exits anus, undigested fibre leaves in faeces, water
excreted via faeces, urine, sweat, saliva?, and breathing)
7
Fibre in health and disease
weight control
-bulk-less appetite
-soluble and insoluble fibres
heart disease
-soluble fibres lower cholesterol (bile issue)
-fibre may displace fat in diet
8
Fibre in health and disease continued
Cancer
1) Lower colon cancer-fibre may help by diluting and binding and more
rapid excretion of carcinogens- both soluble and insoluble fibre may
help
2) Breast cancer
-secoisolariciresinol diglucoside (SDG) is a mammalian lignan
pre-cursor that is found in flaxseed-SDG is not a fibre but is
found in the fibre region of flaxseed
-metabolites of SDG are mammalian lignans which are
produced by bacteria in the large intestine- these mammalian
lignans may reduce breast tumour growth in humans)
9
Fibre in health and disease continued
Diabetes
control weight-diabetes
slow glucose absorption-glucose surge
soluble fibres are key here
10
How to get higher fibre in the diet
High
5g
Fibre content
Medium
Low
2g
0.5 g
Breads cereal
Rice Group
Breads
1 slice
Cereal
½ cup
Pasta
½ cup
Whole wheat
bread
All
bran
Shredded
Wheat
whole
wheat pasta
white
bread
Rice
Krispies
macaroni
11
How to get higher fibre in the diet
continued
Fibre content
High
4g
Medium
2g
Low
1g
apple
melon
Fruit group
1 MEDIUM
OR ½ CUP
berries
12
How to get higher fibre in the diet
continued
High
4g
Fibre content
Medium
2g
Low
1g
Vegetable
Group
½ cup
peas
green
beans
asparagus
13
Remember that:
• fibre from natural sources rather than commercially
prepared fibre is better because foods contain vitamins
and minerals as well as the fibre
14
DRI recommendation for fibre intake
follow DRI recommendations for carbohydrate intake and this will
provide sufficient fibre
DRI - 14 grams fibre/1000 kcal (roughly 25-35 grams of fibre/day)
(no distinction between soluble and insoluble but variety is the key to
balance)
15
Too much fibre in the diet gives:
•flatulence
•obstruct gi tract if greater than 50 g fibre /day
•top recommendation is 40 g/d for adults (who)
16
Too much fibre in the diet continued
•insoluble fibre has phytates that can bind minerals- e.g. calcium, iron,
zinc and magnesium
•prevents enzyme contact
17
Too much fibre in the diet continued
•
increases volume of food required to meet energy requirements
•
satiety before adequate nutrition-generally only a problem if diet
low in micronutrients or in small children (small stomachs)
18
Too much fibre in the diet continued
-important to increase water intake with increases in
dietary fibre
-otherwise constipation but if have enough water can get
diarrhea (bacterial breakdown of fibre)
19
Fibres as food additives
pectin -common in fruits and vegetables
-forms gel when sugar and acid added
-commercially from citrus peels and apples
-thickening agent in jams, jellies and tomato paste
20
Fibres as food additives continued
-carbohydrate gums- used and thickeners and stabilizers
because they combine with water to keep solutions from
separating
-used in gravies, pie fillings, jellies and puddings
21
Fibres as food additives continued
 gums derived from gum arabic, gum karaya, guar
gum, locust bean gum, xanthan gum and gum
tragacanth
 gums extracted from shrubs, trees and seed pods
22
Fibres as food additives continued
 pectins and gums are used in reduced fat products
to mimic the texture and viscosity of fat
23
Fibres as food additives continued
 other thickening agents and stabilizers are from seaweeds
( e.g. agar, carrageen and alginates)
24
What’s new in fibre research?
Oligosaccharides now considered fibre (used to be
that fibre was only in polysaccharide form)
Oligosaccharides (e.g. inulin which is found in
chicory and Jerusalem artichoke for example, can
promote growth of good (for health) bacteria in the
large intestine (please note that inulin is a pre-biotic
and the bacteria are called pro-biotics)
Slavin, J. Nutrients 5:1417-35 (2013)
25
How to choose carbohydrates wisely
1)increase intakes of whole grains
2)use whole grain products such as oatmeal,
brown rice and whole wheat bread
3)increase consumption of legumes such as
kidney, black and pinto beans)if fresh fruits
not available, choose frozen or canned fruits
without added sugar
26
How to choose carbohydrates wisely
continued
4)use whole grain flour for
¼ to ½ the amount of flour in the recipe
5)use less sugar in baking
6)use less added sugars in foods
7)eat fewer high sugar foods
8)use food labels to guide one’s choices
27