Carbohydrates

CARBOHYDRATESCARBOHYDRATES

Carbohydrates are the hydrates of carbon Cx(H2O)y as named erlier. These are made of Carbon, Hydrogen and Oxygen

Carbohydrates are often refered as Saccharides (Saccharum = sugar) because of sweet taste of its simpler members.

But higher membranes are not sweet in taste.

MONOSACCHARIDE

• It is the simplest form of carbohydrates which cannot be further hydrolysed to smaller carbohydrates units. They are made up of 2-6 carbon units.

MOLASSES

HONEY

CORN SOUP

Monosaccharide • Glucose is found in sport drinks• Fructose is found in fruit• Glucose & fructose found in honey• Galactose – milk sugar

Glucose

• Mild sweet flavour• Known as blood sugar• Essential energy source• Found in every disaccharide and

polysaccharide

Fructose

• Sweetest sugar• Found in fruits and honey• Added to soft drinks, cereals, deserts

Galactose

• Hardly tastes sweet• Rarely found as a single sugar

Disaccharides • Pairs of the monosaccharides

- glucose is always present- 2nd of the pair could be fructose, galactose or another glucose- taken apart by hydrolysis- put together by condensation- hydrolysis & condensation occur with all energy nutrients- Maltose, Sucrose, Lactose

Hydrolysis

• Breaking a disaccharide- water molecule splits- occurs during digestion

Maltose

• 2 glucose units• Produced when starch breaks down• Not abundant

Sucrose

• Fructose & glucose• Tastes sweet

- fruit, vegetables, grains• Table sugar is refined sugar cane & sugar

beets• Brown, white powdered

Lactose

• Glucose & galactose • Main carbohydrate in milk

- known as milk sugar

Complex Carbohydrates

• Polysaccharides glycogen & starch• Built entirely of glucoseFiber

variety of monosaccharides & other carbohydrate derivatives

Glycogen

• Limited in meat & not found in plants not an important dietary source of

carbohydrate • But all glucose is stored as glycogenLong chains allow for hydrolysis & release of

energy

Starches

• Stored in plant cells• Body hydrolyzes plant starch to glucose

Fiber

• Structural parts of plants- found in all plant derived food

• Bonds of fibers cannot be broken down during the digestive process– Minimal or no energy available

Fiber types

• Cellulose• Pectins• Lignins• Resistant starches– Classified as starches– Escape digestion & absorption

Carbohydrate Digestion

• Break down into glucose– Body is able to absorb & use

• Large starch molecules– Extensive breakdown

• Disaccharides– Broken once

• Monosaccharides– Don’t need to be broken down

Carbohydrate Digestion

• Begins in mouth– Chewing releases saliva– Enzyme amylase hydrolyzes starch to

polysaccharides & maltose• Stomach – No enzymes available to break down starch– Acid does some breakdown– Fibers in starch provide feeling of fullness

• Small intestine–Majority of carbohydrate digestion takes place here–Pancreatic amylase reduces carbs to glucose cains or

disaccharides– Specific enzymes finish the job• Maltase–Maltose into 2 glucose

• Sucrase– Sucrose into glucose & fructose

• Lactase– Lactose into glucose & galactose

• Large intestine– 1-4 hours for sugars & starches to be digested– Only fibers remain• Attract water, which softens stool

– Bacteria ferment some fibers• Water, gas, short-chain fatty acids (used for energy)

Carbohydrate Absorption

• Glucose can be absorbed in the mouth• Majority absorbed in small intestine–Active transport• Glucose & galactic

– Facilitated diffusion• Fructose• Smaller rise in blood glucose

Lactose Intolerance

• More lactose is consumed than can be digested– Lactose molecules attract water• Cause floating, abdominal discomfort,

diarrhoea– Intestinal bacteria feed on undigested

lactose• Produce acid & gas

Carbohydrate Metabolism• 1/3 of body’s glycogen is stored in liver– Released as glucose to blood stream1.Eat – intake glucose2.Liver condenses extra glucose to glycogen3.Blood glucose falls4.Liver hydrolyzes glycogen to glucose

Glycogen is bulky, so we store only so much: short term energy supply

Fat is the long term energy supply

Glucose for energy

• Enzymes break apart glucose – yielding energy• Inadequate supply of carbohydrates– Ketone bodies (fat fragments) are an alternate

energy source during starvation– Excess ketones can lead to ketosis: imbalance of

acids in body• Minimum of 50 – 100 grams of carbs/day are

needed to avoid ketosis

Glucose Homeostasis

• Maintaining an even balance of glucose is controlled by insulin & glucagon–Insulin•Moves glucose into the blood

–Glucagon• Brings glucose out of storage

• Maintaining balance–Balanced meals at regular intervals• Fiber & some fat slow the digestive

process down• Glucose gets into the blood slow &

steady