Lecture 7 Flashcards by Shannon Chowdhury

Modern Diet

Carbs are basis of modern diet

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Intake of Carbs in Today’s Diet

is more refined
13% kCal comes from added sugars in
- Desserts, Beverages, and prepared snack

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CFG recommends

more unrefined carbs like whole grain, veggies, legumes and fruits
1/2 all grains serving be whole grain
Decrease intake of refined carbs and added sugars

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Whole grains contain:

Bran layers: Good source of fiber and vitamin
Germ: Good source of veggie oils and Vita E
Endosperm: Contains starch and some protein

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Refined Grains

Are largely from endosperm

Mostly starch

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Refined Grains sold in Canada

may be enriched with thiamin, riboflavin, niacin, iron and fortified with folate
Do not have Mg, Vita E, B6 or other nutrients lost during processing
12 grains not whole wheat, refined with added

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Major dietary Monosaccharides

Glucose/Fructose - Fruits, Veggies, HFCS (sticking agent)

Galactose -Bonded to Glu to make lactose

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Major dietary Diasaccharides

Sucrose - Fru+Glu - Fruits, veggies, table sugar
Maltose - Glu+Glu - Germinating seeds, starch digestion
Lactose - Glu+Gal - Milk and milk products

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Polysaccharides

Glycogen
Starches - Amylose and Amlyopectin (branched)
Cellulose

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Glycogen

Carb storage in animals
Liver (100-200g) released in blood
Muscle (200-300G) for muscle use
Stored with water - 1g glycogen = 5-10g water
Not found in foods

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Raw Starch

In plants
Packed in Granules
Semi-crystalline structures
Resistant to digestion

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Starch - Cooking in moist heat

Gelatinization
– Starch granules swell with water
– Crystalline structure disrupted
– Molecules disperse and become entagled (viscous)
– Gelatinized starch is rapidly digested

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Starch - Cooling cooked starch

Retrogradation
– Molecules partially re-associate
– Formation of resistant starch

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Dietary fibre

Polysaccharides and lignin not digested by human
enzymes
Insoluble and Soluble fiber

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Funtional fibre

Indigestible carbs have beneficial physiological effects

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Total fibre

Sum of dietary fibre and functional fibre

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Soluble fibre

Dissolves in water or absorbs water to form viscous
solutions.
Fermented by colonic bacteria
Includes pectins, gums and some hemicelluloses.

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Insoluble fibre

Does not dissolve in water.
Incompletely fermented in colon.
Includes cellulose, some hemicelluloses and lignin

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Physiological Impact of Carbohydrates - Digestibility

Available CHO - absorbed in small intestine

Unavailable CHO - enters the colon

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Physiological Impact of Carbohydrates - Glycaemic Index

How much available CHO raises blood

glucose relative to an equal amount of glucose

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Digestion & Absorption of CHO - Mouth

Chewing
Salivary amylase - Enzyme that begins carbs digestion in the mouth
Breaks carbs in to maltose

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Digestion & Absorption of CHO - Stomach

Acid inactivates salivary amylase

No Carb digestion

Digestion & Absorption of CHO - Pancreas

Amylase is made in the pancreas
Secreted into small intestine
Digests starch to oligosaccharides and maltose

Digestion & Absorption of CHO - Small Intestine

Oligo- & di-saccharides broken down to monosaccharides by brush border enzymes
Monosaccharides absorbed into enterocytes and then enter the blood

Brush-border enzymes

Sucrase, Lactase, | Maltase, Others

Lactose Intolerance

Low levels of intestinal lactase lactose not digested passes to large intestine → gas, pain, diarrhoea More common in non-Caucasian populations Treatment: reduce / eliminate dietary lactose  Cheese low in lactose  Lactose-free milk / non-dairy milk substitutes

Digestion & Absorption of CHO - Large Intestine (Colon)

Unavailable CHO | Breakdown carbohydrates via fermentation to produce gases and short-chain fatty acids

Colonic Fermentation

Short chain Fatty Acids - Acetate, Propionate, Butyrate Gases -H2, CO2, Methane

Dietary Fibre

AI of fiber is 14 grams for every 1000 kcal -38 g for male, 25g for female Most Canadian get 14-21g Eat whole grain foods, fruits, vegetables, and legumes to increase intake

Key Properties of Fibres - Viscosity

``` pectin, guar, psyllium Absorb water Create bulk Slow gastric emptying, decreased glucose absorption CVD, GI, Diabetes ```

Key Properties of Fibres - Fermentability

bran, inulin | create SCFA in colon, depends on microflora (GI)

Actions of Fibre in GI Tract

ADD PIC

Impact of Fiber in Diet

Lowers plasma cholesterol (-glucans) (sol) Modifies glycemic response (sol) Improves function of large bowel (insol/insol)

Impact of Fiber in Diet (2)

May reduce risk of colorectal cancer, diverticulitus, heart disease, type II diabetes May compromise nutrient availability (sol)

Medical Uses of Fibre

``` Laxative Irritable bowel syndrome Constipation Diverticular Disease Lowering Cholesterol Lowering Blood Glucose ```

Effect of 15g Fibre per Day

Lowers cholesterol

Fibre and Health - Soluble Fiber

- Pectin, Gums, mucilages Found in legumes, fruits, oats, and barley +/- metabolic effects

Fibre and Health - Insoluble Fiber

- Lignin, Cellulose, Hemicellulose Found in fiberous veggies, wheat, rye, and corn +/- Stool Bulking

Glycaemic Index

Glucose from food entering blood / Gluouse x 100%

Blood Glucose Response Elicited by Carbs

Depends on - Nature of monosaccharide - Amount consumed - Rate of Absorption

Nature of monosaccharide

Glucose causes response Sucrose causes less response Fructose causes no response

Amount consumed

More glucose causes bigger response

Rate of Absorption

Fat, Fiber, protein slows down absorption

Glycaemic Load

GL= g x GI/100

Glycaemic Index vs Glycaemic Load

Index: qualitative, independent of amount of CHO Load: Depends on CHO quality and quanitity - Quantitative: 1 unit = glycameic impact of 1g glucose

Health Implications of GI

Foods with a low GI: Role in HEALTH Role in DISEASE

Role in HEALTH

``` Weight management Acne Physical and mental performance Reduce risk for diabetes, heart disease and other conditions ```

Role in DISEASE

Management of diabetes

Nutritive sweeteners

Have 4Kcal/g | Sucrose, fructose, honey, brown sugar, sugar alcohol and HFCS

Non-nutritive sweeteners

Little or no energy | Stevia

Sugar Alcohols

Less absorption, impact on insulin | Can cause diarrhea when not absorbed

Artificial Sweeteners

Aspartame Sucralose Saccharine

Sugars have no UL

Evidence suggests: - Behaviour not altered - Cancer- insufficient evidence - Dental Caries- relationship is complex - Diabetes- no evidence - Hyperlipidemia-unclear - Obesity-relationship is complex

CHO Recommendations

``` RDA is 130g/day for adults and kids - min needed by brain AMDR is 45-65% Carbs should be unrefined No more than 25% from refined added CHO CFG recommends little or no added sugar ```