Macronutrients :Carbohydrates

Structure, sources and function

As part of this course, students learn about the structure, sources and

function of carbohydrates. They learn to identify

carbohydrates in given recipes and meals

(composition), and also identify common food

sources of carbohydrates.

Introduction● What are carbohydrates?

● Why does the body need them?

● What is their structure?

● What are dietary sources of carbohydrates?

● What are the different types?

● How much do we need?

What are Carbohydrates?● The term ‘carbohydrate’ refers to

the sugars and starches found in many of the foods that we eat.

● Many people think that rice, potatoes and pasta are the only foods that contain carbohydrates.

● However, all fruits and vegetables, all breads and grain (cereals) products, sugar and sugary foods contain carbohydrates.

Why do we need Carbohydrates?The main role of dietary carbohydrates is to provide energy to the bodily cells, particularly the brain, in the form of glucose.

Other macronutrients (protein and lipids) can provide energy, however they must be converted into glucose first to allow the brain and red blood cells to use it.

Therefore, carbohydrates are the most ideal energy source as they can be readily used by the brain andred blood cells.

Carbohydrates provide 16kj/g.

Why does the body need energy?

All of our cells consume energy, even when we are sleeping. This energy, provided primarily by carbohydrates, is needed for a number of reasons including;

● To work the muscles that we use for breathing● To keep the heart pumping and keep the body warm● To provide energy to muscles during physical activity

Most of the energy we use everyday comes from the sugars that are produced when carbohydrates are broken down in your gut to glucose.

Your blood then carries these sugars around the body to where energy is needed.

Review Questions1. Identify 5 food sources of carbohydrates.

2. Describe the main role of carbohydrates in the body.

3. Explain why carbohydrates are a better energy source than other macronutrients.

Identify = ListDescribe = Outline key characteristics

brieflyExplain = Give a detailed account of

1. Identify 5 food sources of carbohydrates.

Rice, bread, pasta, fruits, vegetables, lollies, cake, ice-cream, pretzels, cereals, legumes etc.

2. Describe the main role of carbohydrates in the body. To provide easily accessible and readily available energy to all cells in the body for daily activities including resting, sleeping, exercising, moving and even breathing.

3. Explain why carbohydrates are a better energy source than other macronutrients.

Carbohydrates are an ideal source of energy compared to the other macronutrients of protein and lipids, because they are readily available sources of energy. The body does not need to metabolize carbohydrates into glucose to be used by the brain and red blood cells which makes them a superior energy source.

Chemical Composition of Carbohydrates

Carbohydrates are molecules made of Carbon (C), Hydrogen (H) and Oxygen (O).

What is their structure?

● Carbohydrates are classified into 3 main groups:

○ Monosaccharides ○ Disaccharides○ Polysaccharides

● “Saccharide” means sugar so this means the terms above mean ‘1 sugar’, ‘2 sugars’ and ‘many sugars’, respectively.

Monosaccharides ● Glucose, fructose and galactose

are all monosaccharides● They are single sugar molecules

and have the structure shown below:

Disaccharides● Maltose, lactose and sucrose are all

disaccharides● They are two- sugar molecules and

have the structure shown below:

Sucrose = glucose +fructoseLactose = glucose + galactoseMaltose = glucose + glucose

Polysaccharides Monosaccharides can be joined into long chains called polysaccharides to make a variety of starches and fibres. There are 3 including:

Starch: A glucose polysaccharide that is found in plants.

Pectin: A polysaccharide found in cells(especially seeds and peel) of fruits and vegetables. It is essential in setting jams.

Glycogen: A glucose polysaccharide found in the bodies liver and muscles. It is stored energy or stored glucose.

Review Questions 1. List the 3 main groups of carbohydrates.

2. Identify the elements that make up carbohydrates.

3. Circle either True (T) or False (F) to agree or disagree with the following statements.

Carbohydrates are made of carbon, helium and oxygen. T F

The three groups of carbohydrates are monosaccharides, disaccharides and polysaccharides.

T F

Disaccharides are and polysaccharides are made from different combinations of monosaccharides joined together.

T F

Polysaccharides include starches and fibres. T F

List= Write down/identify succinctly Identify = State (no explanation needed)

1. List the 3 main groups of carbohydrates.

Monosaccharides, diasacharides and polysaccharires

2. Identify the elements that make up carbohydrates.

Carbon,hydrogen and oxygen

3. Circle either True (T) or False (F) to agree or disagree with the following statements.

Carbohydrates are made of carbon, helium and oxygen - False (hydrogen NOT helium)

The three groups of carbohydrates are monosaccharides, disaccharides and polysaccharides. - True

Disaccharides are and polysaccharides are made from different combinations of monosaccharides joined together. - True (Eg. Galactose = glucose+lactose)

Polysaccharides include starches and fibres - True

Types of Carbohydrates

Review Questions 1. Identify the two main groups of carbohydrate foods?

2. Justify why complex carbohydrates should be consumed in preference to simple carbohydrates. Use examples of these foods to support your answer.

Identify = State (no explanation needed)Justify = To provide an explanation or

rationale to support an idea

1. Identify the two main groups of carbohydrate foods?

● Simple Carbohydrates● Complex Carbohydrates

2. Justify why complex carbohydrates should be consumed in preference to simple carbohydrates. Use examples of these foods to support your answer.

● They provide the body with energy as well as vitamins, minerals and fibre● Fibre is important as it aids in digestion and excretion (the removal of waste from the

body)● They provide sustained energy for longer periods of time (usually low GI)● Reduced the risk for diabetes type 2 as the blood sugar levels remain stable over time,

unlike simple carbohydrates where blood sugar levels spike from the refined and processed foods.

● Food examples: Wholegrain breads and cereals, brown rice, quinoa, cous cous, fibrous vegetables, fresh fruits (particularly those low in sugar including berries)

Glycaemic Index - Milo Case Study

Glycaemic Index● Glycaemic Index (GI) is a scale from 0 - 100 to

represent the impact of foods (particularly glucose) on blood sugar levels.

● Foods which release energy quickly and spike blood sugar levels are high GI.

● Foods which release energy slowly and do not raise blood sugar levels quickly or dramatically are low GI.

● To reduce the risk of diabetes, carbohydrate foods should be low-medium GI to ensure a steady insulin supply which is ensured when blood sugar levels are not rising and dropping continuously after eating.