LipidsFunctions, structure and sourcesPreliminary Food Technology - Nutrition

Links to Syllabus

As part of this course, students learn about the structure, sources and function of lipids. They learn to identify lipids in given recipes and meals (composition), and also identify common food

sources of lipids.

● What are lipids?

● Why does the body need them?

● What is their structure?

● What are dietary sources of lipids?

● What are the different types?

● How much does the body need?

Introduction

What are lipids?

● Lipids are groups of substances that include fats, oils, fatty acids, phospholipids, sterols, glycolipids and waxes.

● They provide 37kj/g which is double the energy of carbohydrates and proteins.

Functions of LipidsThe lipid or fat cells (adipose tissue) in the body are an important source of stored energy which can be converted to glucose in times of starvation. Other functions include;

● Surrounds and protects vital organs (Eg. kidneys, glands)

● Forms an insulating layer (adipose tissue) beneath the skin to help preserve body heat and protect the skeleton and organs

● Forms part of cell membranes in each cell throughout the body (phospholipid bilayer) .

● Provide essential fatty acids required for brain and nerve function as well as hormone structure.

Functions of Lipids

● Carries fat soluble vitamins A, D, E and K in the blood. They also regulate chemical reactions in the body (Eg. cholesterol & vitamin D).

● Provides texture and flavour in foods to increase their palatability.

● Foods containing fat provide feelings of fullness (satiety) after a meal, as fat digestion is slow.

● Keep the skin, hair and nails soft and smooth

Review Questions

1. List four functions of lipids in the body.

2. Explain the relationship between lipids and fat-soluble vitamins in the body.

List= State (no explanation needed)Explain = Give a detailed account of

Review Questions

1. List four functions of lipids in the body.

2. Explain the relationship between lipids and fat-soluble vitamins in the body.

List= State (no explanation needed)Explain = Give a detailed account of

Explain the relationship between lipids and fat-soluble vitamins in the body

Explain = Give a detailed account of

Review Questions

1. List four functions of lipids in the body.

● Protection of internal organs and body surface● Carry fat-soluble vitamins in the blood (ADEK)● Part of the structure of bodily cells ● Keep skin, hair and nails soft and smooth● Reserve source of energy in times of starvation/low energy● Form the structure of hormones ● Part of body’s messenger system (nervous system)

2. Explain the relationship between lipids and fat-soluble vitamins in the body. Lipids are vital nutrients which are a necessary source for carrying fat-soluble vitamins A,D, E and K in the bloodstream. They are therefore required in the diet to ensure such vitamins can be transported around the body and used when required. Without lipids, fat-soluble vitamins would not be absorbed which highlights the importance of lipids in the absorption of fat soluble vitamins.

List= State succinctly (no explanation needed)

Explain: Give a detailed account of

Fats and Oils

Fats and oils are used to describe lipids and although they have the same basic chemical structure, their physical appearances differ at normal room temperature. The characteristics of

fats and oils are outlined in the table below;

Fats Oils

Remain solid at room temperature Remain liquid at room temperature

Relatively more saturated Relatively more unsaturated

Relatively higher melting point Lower melting point

More stable chemical structure Less stable

Structure of Lipids

● The term ‘lipid’ is a scientific term used to describe all types of fats and oils.

● Lipids are composed of the elements carbon, hydrogen and oxygen.

● These elements make up molecules of glycerol and fatty acids which combine to form fat molecules on the following way;

● The scientific name for a lipid molecule is a triglyceride

● Triglycerides include one glycerol backbone and three fatty acids chains.

Chemical Structure

Saturated vs Unsaturated Fatty Acids

Lipids can be categorised as saturated or unsaturated depending on how the carbon and hydrogen atoms are arranged.

Saturated fatty acids (or saturated fats) are saturated with hydrogen atoms and cannot accept any more.

Eg. Milk, butter, animal fats, dairy foods, coconut oil, beef fat

Fats that are solid at room temperature are usually saturated fats.

Saturated vs Unsaturated Fatty Acids

Unsaturated fatty acids (or unsaturated fats) are not saturated with the maximum maximum number of hydrogen atoms. Instead, some places have a double bond.

The double bonds can be broken down so that more hydrogen atoms can be inserted in their place, a process called hydrogenation.

Unsaturated Fatty Acids

Unsaturated fatty acids can be monounsaturated (with one double bond) or polyunsaturated (with multiple double bonds).

Monounsaturated = Avocado, olive oil, brazil nuts etc.

Polyunsaturated = Salmon, dairy, eggs, nuts

https://www.youtube.com/watch?v=3Gqo3Y6WFYA

Review Questions

1. Identify the three elements which make up lipids.

2. Describe the basic structure of a lipid molecule.

3. Contrast saturated and unsaturated fatty acids.

Identify= State (no explanation needed)Describe = Outline key characteristics ofContrast = Identify and describe features

which make them different,

Review Questions

1. Identify the three elements which make up lipids.

Carbon, hydrogen and oxygen

2. Describe the basic structure of a lipid molecule.

Lipid molecules are comprised of a single glycerol backbone, connected to 3 fatty acid chains.

3. Contrast saturated and unsaturated fatty acids. Saturated fatty acids are completely saturated or filled with hydrogen atoms (Eg. usually bad fats and include high fat meats, butter, lard). In contrast, unsaturated fatty acids, including polyunsaturated and monounsaturated fatty acids, are not completely saturated with hydrogen atoms due to the presence of double bonds (Eg. usually good fats and include avocado, olive oil, nuts and seeds).

Identify= State (no explanation needed)Describe = Outline key characteristics ofContrast = Identify and describe features

which make them different,

Essential Fatty Acids - Omega 3 and Omega 6

● Needed for normal growth but cannot be synthesized by the body.

● These include omega 3 and omega 6 fatty acids.

● The omega fatty acids are polyunsaturated fatty acids.

Foods high in omega 3

Foods high in omega 6

Non-Essential Fatty Acids - Cholesterol

● Cholesterol is a non-essential fatty acid as it can by produced by the body.

● It is needed in the body for:

○ Making bile acids to break down food in the stomach○ Absorb and use lipids from foods○ Make important hormones○ Acts as a precursor for the absorption and metabolism

of vitmain D (on the skin)

● The body produces cholesterol in the liver. Other animals also make their own cholesterol which is found in foods high in saturated fats.

Over Consumption of Cholesterol

● If you eat too much cholesterol in the diet, the amount your body makes usually decreases.

● A high intake of saturated fats in the diet can lead to higher levels of cholesterol on the blood.

● As a result, cholesterol can line the walls of arteries and restrict blood flow (atherosclerosis) and may even cause a heart attack.

● It is therefore important to ensure saturated foods are consumed in moderation.

How much do we need?

Dietitians Association Australia, 2015

Lipids are found in a variety of foods, both animal and plant sources as seen through the

table of examples.

Limiting Lipids in the Diet

● Lipids should account for no more than 35% of total dietary energy.

● Therefore, a person with an RDI of 8700kj can ingest approximately 3000kj from lipids, or approximately 80g.

(Remember, each gram of fat contains 37kj of energy)

● Also, only 10% of the total kilojoules should be sourced from saturated fat sources.

● For people with high blood pressure, coronary heart disease and atherosclerosis, they need to be mindful of how many lipids they consume.

How can we limit lipids in the diet?

Limiting Lipids in the Diet

● Cutting excess visible fat off meat

● Swapping full fat dairy to low fat dairy

● Seasoning foods with herbs and spices rather than butters and creams to add flavour

● Steaming and stir-frying rather than deep and shallow frying in oil

● Swapping saturated (bad) fats for unsaturated (good) fats. (Eg. Instead of mayonnaise on a sandwich, use an avocado spread. In a salad, adds walnuts instead of cheese)

Review Questions

1. Identify the essential and nonessential fatty acids.

2. Explain why the over consumption of cholesterol has negative effects on health.

3. Outline how much fat is recommended daily.

Identify= State (no explanation needed)Explain = Give a detailed account of

Outline = provide a general description for

Review Questions

1. Identify the essential and nonessential fatty acids.

Essential = Omega 3, Omega 6Non-essential = Cholesterol

2. Explain why the over consumption of cholesterol has negative effects on health.

Cholesterol is a non-essential fat which means it can be produced by the body. If it is over consumed, the body stores it in the bloodstream which lines the arteries forming a plaque. Over time, as more cholesterol is deposited onto the walls of the arteries, blood flow is restricted causing atherosclerosis. Eventually, blood flow is restricted completely leading to a heart attack.

3. Outline how much fat is recommended daily. The recommended daily intake (RDI) of fa is 20 - 35% of the diet which is approximately 70g. The saturated fat content should also remain below 10% of the total energy provided through the diet.

Identify= State (no explanation needed)Explain = Give a detailed account of

Outline = provide a general description for