Carbohydrates

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Carbohydrates
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Definition

• Sugars, starches and fibre we get from food
• Plants make the sugar glucose by photosynthesis
  for own energy and structural needs therefore
  plants are the major sources of CHO
• Made from carbon, hydrogen, oxygen
• Many sugars end in ose eg glucose

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Main function-Energy

• Primary fuel source for some cells eg nervous
  system, red blood cells
• Muscles rely on supply of CHO to support intense
  physical activity
• Readily available source of energy for all cells
  in form of blood glucose and liver glycogen
  (stored glucose), glycogen in muscles used by
  muscles
• Regular intake important as glycogen stores in
  liver only last approx 18 hours

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CARBOHYDRATE

• Can be classified according to chemical structure
  (simple or complex)
• Simple CHOs
• Mono/di/oligosaccharides
• Complex CHOs
• Starch
• Dietary fibre

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Types of CHO

• Simple CHO (1)
• Monosaccharides
• glucose
• fructose
• galactose

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Glucose

• Little found in food as glucose
• Most glucose comes from starches and sucrose
• Sucrose found in fruits and veges
• Sugars and other CHO in foods are eventually
  converted to glucose in the liver
• Sucrose Glucose fructose

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Fructose

• Found in fruit and honey
• Sweetest simple sugar
• But most comes from high-fructose corn syrup used
  in food processing
• Converted to glucose in liver

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Disaccharides (2)

• Sucrose Glucose fructose
• Lactose Glucose galactose
• Maltose Glucose glucose

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Sucrose (table sugar)

• Makes food tasty
• Functional properties for baking and preserving
• High sugar containing foods termed empty
  calorie foods
• Contributes to dental decay mainly chewy sticky
  forms
• No scientific link to hyperactivity
• Not a major health issue if eating balanced diet
  and not overweight

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Lactose

• Sugar found in milk
• Made in mammary glands of lactating mammals
  except whales and hippos
• Accounts for
• 7.5 of the composition of human milk
• 4.5 of the composition of cows milk

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Maltose (malt sugar)

• Not normally found naturally in food
• Formed in the malting of barley
• Or
• Breakdown of starch molecules

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Polysaccharides

• Starch
• Amylose-straight chain
• Amylopectin-branched
• -easier to digest and release glucose, amount
  influences glycaemic index of a food

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Starch

• Foods containing starch usually form large part
  of diet and termed staple foods
• Corn, arrowroot, rice, potatoes, tapioca
• NZ staples are potatoes and bread
• What is staple in other cultures eg Chinese,
  Italian, Pacific?

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Uses of CHOs

• Plants use CHOs to make up their structural
  components
• NRG source for animals
• Storage and NRG source in humans

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Non-starch polysaccharides (fibre)

• Insoluble fibre (roughage)
• cellulose, lignin
• structural part of plants

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Insoluble fibre

• Not soluble in water and not digested by gut
  bacteria
• Speeds intestinal transit time - no other known
  functions
• Food sources wholegrains eg wheat bran, brown
  rice, wholemeal breads and cereals

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Soluble fibres

• Soluble fibre
• pectin in fruit
• gums
• inside plant walls

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Soluble fibre

• Dissolves or swells in water and can be
  metabolised by gut bacteria
• Delays stomach emptying, slows glucose
  absorption, and lowers blood cholesterol
• Food sources fruit, berries, barley, oats,
  carrots, legumes

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Health benefits of starch (including fibre)

• May improve blood Glucose control
• Weight control
• Sports performance
• Filling not fattening
• Starch rich foods are low in fat
• Some slow rate of digestion
• Prevents constipation
• May lower blood lipids
• Protects against some cancers

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Blood glucose

• Blood glucose levels are regulated by release of
  hormones eg insulin, glucagon
• Safeguard against hypoglycaemia and
  hyperglycaemia
• Insulin stimulates glycogen production and uptake
  of glucose by cells
• Glucagon stimulates glycogen breakdown

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Glycaemic index

• Classifies food based on potential to raise blood
  glucose
• High GI foods-break down quickly and blood
  glucose response is fast eg honey
• Low GI foods break down slowly, releasing glucose
  slowly into bloodstream eg apple
• Useful for diabetes diet planning, athletes
• Has limitations eg high fat foods have low GIs

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Digestion/Absorption of Starch and Sugars

• Mouth
• Salivary enzyme amylase hydrolyses starch
• Stomach
• Hydrolysis starch stops. Protein digesting
  enzymes digest amylase
• Small Intestines
• Amylase further hydrolyses starch
• Large Intestines
• Digested and Undigested starch
• Liver
• Stores and provides liver for NRG
• Main source of NRG

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Effect of food processing on fibre content

• Flour ½ cup
• White 2g
• Rice 1 cup cooked
• White 0.4g
• Orange
• Juice 0.3g

• Wholemeal 8g
• Brown 1.6g
• 1 orange 7.5g

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Examples

• Food CHO Sugar Fibre Starch
• JJuice 10.6 10.4 0.1 T
• Coke 10.9 10.9 0 0
• W-Bix 62.2 T 15.2 62.2
• Pasta 24.2 T 3.2 24.2

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Carbohydrate sources

• Difficult to eat so little CHO that body needs
  are not met
• BUT
• Easy to over consume CHOs that can contribute to
  health problems