Lecture 3b- 21 January 2015

CARBOHYDRATES II

Overview of lecture 3b

Carbohydrates

-blood glucose homeostasis

-functions of carbohydratesessential or not?

-fad diets

BLOOD GLUCOSE HOMEOSTASIS P. 106-109

Maintaining blood glucose at normal levels is important

-too low-dizzy and weak

-too high-fatigued, confused and difficulty breathing

Regulating hormones - insulin and glucagon

Balancing in normal range - insulin and glucagon

Blood glucose homeostasis continuedFalling outside normal range-diet does not regulate blood sugar-the body does-diabetes-types 1 and 2 and gestational diabetes-elevated blood glucose-type 1 diabetes -autoimmune attack on pancreatic beta cells -used to be called insulin dependent diabetes mellitus or

juvenile diabetes -no cure at the moment-type 2 diabetes -insulin resistance followed by beta cell failure

-used to be called-non-insulin dependent diabetes mellitus(NIDDM) or adult onset diabetes

-no cure at the moment-gestational diabetes (GDM) -insulin resistance in pregnancy due to excessive

weight gain -resolves with medical management -greater risk of type 2 diabetes later on for mum

and post-partum child who experienced in utero GDM

-hypoglycemia-low blood glucose from too much insulin or not enough to eat

Blood glucose homeostasis continued

Falling outside normal range continued

-but dietary modifications important-

-before and after type 2 diabetes, GDM and hypoglycemia sets in

-for type 2 diabetes and GDM avoid uneccessary weight gain by dietary change-low fat and rich in complex carbohydrate and fibre

-for hypoglycemia-get enough to eat

Blood glucose and diet p. 108-9

glycaemia-blood glucoseglycaemic index of food-ability to provoke a blood glucose response - effects blood sugar rise

-high glycaemic index foods (eg white bread) causes rapid rise in blood glucose followed by quicker drop in blood glucose

-lower glycaemic foods (eg whole grain bread) - causes less rapid rise in blood glucose followed by slower drop in blood glucose - may reduce chances of getting or

worsening type 2 diabetes

-effect of food on blood glucose-if have slow absorption get modest rise in blood glucose and smooth decrease of blood glucose

Blood glucose and diet continued P.108-9

-blood glucose dependent on whether carbohydrate eaten alone or as part of a mixed meal

-eating small meals often is same as low glycemic index-why?

Blood glucose and diet continued

page 108

-however, glycemic index is controversial

- inadequate science? - determined for relatively few foods - when determined it is based on average of multiple

tests with a great deal of variability

Blood glucose and diet continued

Fad diets

-no apples or oranges but bacon and eggs alright-this is notgood why?

Carbohydrates - essential or not?

yes- why?

Healthy roles for carbohydrates

1) neural function 2) give structure to molecules 3) metabolically 4) impact on nutrient absorption

Carbohydrate functions- healthy

Neural function

•brain and nerves really only set up to use glucose

•lipids/proteins cannot be used

Carbohydrate functions-healthy continued

give structure to molecules

carbohydrate e.g. glycogen

disaccharides oligosaccharides

non-carbohydrate e.g. some proteins (i.e. glycoproteins)

Carbohydrate functions-healthy continued

metabolically

-energy-heat/fuel -sparing protein -burning fat

Carbohydrate functions healthy continued

metabolically continued

make other compounds - glycogen - fat - protein (non-essential amino acids) - DNA/RNA

Carbohydrate functions-healthy continued

Impact on nutrient handling

• non-absorbable oligosaccharides impair carbohydrase activity

• starch granules exposed to moist heat and then cooling are less dense and hence less available to enzyme action

Unhealthy roles for carbohydrate

glycation (glycosylation) of proteins

proteins-albumin -hemoglobin

lipoproteins

blood vessels

Unhealthy roles for carbohydrate glycation (glycosylation) of proteins continued

albumin glycation or glycosylation

can cause tissue breakdown via stimulating chemical messengers

Unhealthy roles for carbohydrate glycation (glycosylation) of proteins continued

Haemoglobin

may set up a chemical reaction that leads to blood vessel breakdown

Unhealthy roles for carbohydrate-glycation (glycosylation) of proteins continued

Lipoproteins

low good cholesterol

higher bad cholesterol

Unhealthy roles for carbohydrate glycation (glycosylation) of proteins continued

Blood vessels

glucose itself binds to protein in blood vessels-leaky

Next lecture - carbohydrates in health and disease

Influence of:

•the diet

•nutraceuticals

•functional foods