Topic 4: Carbohydrates, sugars, starches, glycogen, and fibre

carbohydrates (CHO)

* main source of energy for people throughout the world
* staple foods: pasta, rice, cassava, beans, and bread
* about ==50% of total calories== consumed by North Americans come from carbohydrates

two categories of carbohydrates:

1. simple carbohydrates
2. complex carbohydrates

* starches and glycogen
* fibre

primary role of carbohydrates

* supply energy to ==spare protein== (4kcal/g) (except fibre 0kcal/g)
* alcohol sugars and alcohol are ==chemical relatives== of carbohydrates

simple carbohydrates (sugars)

* Small molecules (require ==little to no digestion== to be absorbed)
* two types: ==monosaccharides and disaccharides==
* including both ==single sugar units== and ==linked pairs of sugar units==
* the basic sugar unit is a molecule containing six carbon atoms, together with oxygen and hydrogen atoms

monosaccharides

* glucose (“blood sugar” or “dextrose”)
* fructose (“fruit sugar”) sweetest
* galactose

disaccharides

* consist of two lined molecules
* glucose + galactose = ==lactose== (milk sugar)
* glucose + fructose = ==sucrose== (found in sugar cane, honey and sugar beets)
* glucose + glucose = ==maltose:== join in food to form starch molecules

disaccharides (continued)

* broken down during digestion
* only ==glucose, fructose, and galactose==, are absorbed into the bloodstream
* high-fructose corn syrup and alcohol sugars are also simple sugars

complex carbohydrates (polysaccharides)

* polysaccharides are composed of: @@starches, glycogen, and dietary fibre@@
* @@starches@@ = plant storage form of carbs
* @@glycogen@@ = human and animal form of carbs
* ==fibre== = indigestible part of plant food; humans do not have the enzymes to digest fibre. It passes through the @@GI tract unchanged@@

complex carbohydrate SOURCES

* they can be found in: @@whole grain@@ and @@refined breads, cereals, pastas and crackers@@
* \* plant foods such as @@vegetables, legumes,@@ are rich sources of complex carbohydrates

carbohydrate for energy

* the body uses @@glucose for energy@@
* fructose and galactose are @@converted to glucose@@

@@glycogenesis:@@ the liver and muscles store glucose as the polymer glycogen

* glycogen is chains of linked glucose units

when the body needs energy

* glycogen @@cleaved to provide@@ glucose
* glucose can be @@derived from amino acids@@ (glyconeogenesis) and to add an insignificant level of glycerol


* glucose is the preferred energy source for brain cells, other nerve cells, and red blood cells
* excess glucose is @@converted to fat@@

CHO rich foods: source of fibre

* human digestive enzymes cannot break the bond between glucose molecules in fibre (cellulose)
* bacteria in the colon ferment some fibre for their energy needs

types of fibre

1. @@soluble or viscous fibre:@@ form gels, fermented by gut microflora
2. @@insoluble fibre:@@ non-viscous, non-fermented, structural part of plant

health benefits of fibre

* lowers @@blood cholesterol@@ = lowers risk of heart disease
* modulates @@blood glucose levels@@ = lower risk of diabetes
* maintains healthy bowel function
* prevent constipation
* alleviate haemorrhoids
* prevent appendicitis
* prevent diverticulosis
* fosters weight control

fibre and blood cholesterol control

* role of soluble or viscous fibre
* traps glucose
* delays transit of chyme in upper GI tract
* delays glucose absorption
* blunts post meal increase in blood glucose

fibre and bowel health

* insoluble fibre
* adds volume & softens the stool
* speeds up transit time through colon
* reduces pressure needed to evacuate rectum
* strengthens muscles of colon wall

fibre and weight control

high Fibre foods are:

* low fat
* low added sugar
* less energy dense

insoluble fibre

* add bulk and feeling of fullness (satiety)

soluble fibre

* slow transit through upper GI tract enhance satiety

recommended CHO intake

1. Total carbohydrate DRI

* minimum: @@130g/day@@ for adults and children

AMDR@@: 45-65% of total calories from CHO


2. Fibre DRI

* Al: Men 19-50 year @@38g/day@@
* Al": Women 19-50 year @@25g/day@@

added sugars (WHO)

* @@less than 10%@@ of calories from sugar

current intake reports

* about 50% of total calories CHO
* @@14-15g/day of fibre intake@@
* North Americans consume less than recommended

simple sugar and added sugar

* according to the canadian community health survey nutrition (CCHS-Nutrition) data, simple sugar intake accounts for @@17-25%@@ of the canadian diet
* children between @@2-8 years@@ consume the highest percentage

sugar in processed foods

* most teenagers consume soft drinks daily
* @@soft drinks@@ account for the largest component of adolescent sugar intake
* 14% of sugar intake

cons of consuming sugar

* foods with simple sugars are p@@oor sources of nutrients@@
* simple sugars @@provide only calories@@
* many foods high in sugars are @@also high in fat@@
* sugar intake likelihood diet will be @@insufficient in vitamins and minerals@@

highly processed sugar added foods have

• high energy density • low nutrient density

does sugar increase risk of CVD?

* moderate sugar = not much effect
* @@saturated + trans fat@@ = main culprit
* higher sugar intake, higher blood levels of saturated fat