Fats: Types and Sources

This lesson covers the types and sources of fat (lipids) in the diet, as required by AQA GCSE Food Preparation and Nutrition specification 8585 (section 3.2.1). You will learn the difference between saturated and unsaturated fats, understand the sub-categories of monounsaturated and polyunsaturated fats, and identify the main food sources of each type. Understanding fat types is essential for questions about healthy eating, diet-related diseases, and food choice.

---

What Are Fats?

Fats (also called lipids) are a macronutrient that provides the body with a concentrated source of energy — 9 kcal per gram, more than double the energy provided by protein (4 kcal/g) or carbohydrate (3.75 kcal/g).

Fats are made up of fatty acids and glycerol. A fat molecule (triglyceride) consists of one molecule of glycerol bonded to three fatty acid chains. The type of fatty acid determines whether the fat is classified as saturated or unsaturated.

Key Terminology

Term	Meaning
Lipid	The scientific term for fats and oils
Fatty acid	The building block of fat; a long chain of carbon atoms with hydrogen atoms attached
Glycerol	An alcohol molecule that forms the backbone of a triglyceride
Triglyceride	A fat molecule made of one glycerol and three fatty acids
Saturated	All carbon-carbon bonds are single bonds; the chain is "saturated" with hydrogen
Unsaturated	One or more carbon-carbon double bonds; the chain has fewer hydrogen atoms

Exam Tip: You do not need to draw the chemical structure of fats for GCSE, but you must understand the terms "saturated" (no double bonds) and "unsaturated" (one or more double bonds) and be able to explain the difference.

---

Types of Fat

Fats are classified into two main categories based on their chemical structure:

graph TD
    A["Dietary Fats"] --> B["Saturated Fats"]
    A --> C["Unsaturated Fats"]
    C --> D["Monounsaturated"]
    C --> E["Polyunsaturated"]
    E --> F["Omega-3"]
    E --> G["Omega-6"]
    A --> H["Trans Fats"]

    style A fill:#4a90d9,color:#fff
    style B fill:#c0392b,color:#fff
    style C fill:#27ae60,color:#fff
    style D fill:#2ecc71,color:#fff
    style E fill:#16a085,color:#fff
    style H fill:#e74c3c,color:#fff

---

Saturated Fats

Saturated fats have fatty acid chains where all the carbon atoms are joined by single bonds and each carbon atom is bonded to the maximum number of hydrogen atoms. The chain is "saturated" with hydrogen.

Properties of Saturated Fats

• Usually solid at room temperature (e.g. butter, lard)
• Mainly found in animal sources
• Tend to raise LDL cholesterol ("bad" cholesterol) in the blood
• Associated with increased risk of coronary heart disease (CHD)

Sources of Saturated Fat

Food Source	Details
Butter	Made from cream; approximately 52% saturated fat
Lard	Rendered pork fat; used in pastry making
Cheese	Particularly hard cheeses like Cheddar; high in saturated fat
Fatty meat	Visible fat on beef, lamb, pork; skin on chicken
Cream	Single, double, and clotted cream
Full-fat milk	Contains approximately 2.3% fat (mostly saturated)
Coconut oil	A plant source that is very high in saturated fat (approximately 87%)
Palm oil	Another plant source high in saturated fat; widely used in processed foods
Processed meat	Sausages, bacon, pies, and pâté
Cakes, biscuits, and pastries	Often made with butter or lard
Chocolate	Contains cocoa butter, which is high in saturated fat

Exam Tip: Students often forget that coconut oil and palm oil are plant-based but high in saturated fat. This is a common exam trick — do not assume all plant fats are unsaturated.

Current Guidance on Saturated Fat

The UK government recommends:

• No more than 11% of total energy intake should come from saturated fat
• This is approximately 20 g per day for women and 30 g per day for men
• Saturated fat should be replaced with unsaturated fat where possible

---

Unsaturated Fats

Unsaturated fats have one or more double bonds between carbon atoms in the fatty acid chain. This means fewer hydrogen atoms are attached, so the chain is "unsaturated."

Unsaturated fats are further divided into monounsaturated and polyunsaturated fats.

Monounsaturated Fats

Monounsaturated fats have one double bond in the fatty acid chain.

Food Source	Details
Olive oil	The primary fat in the Mediterranean diet; approximately 73% monounsaturated
Rapeseed oil	Widely used in UK cooking; good balance of monounsaturated and polyunsaturated
Avocado	Rich in monounsaturated fat; also provides vitamin E and potassium
Almonds	Approximately 32% monounsaturated fat
Peanuts and peanut butter	Good source of monounsaturated fat and protein
Cashew nuts	Rich in monounsaturated fat

Properties:

• Usually liquid at room temperature but may thicken when refrigerated (e.g. olive oil goes cloudy in the fridge)
• Associated with lowering LDL cholesterol and maintaining HDL cholesterol
• Part of the Mediterranean diet, which is linked to lower rates of heart disease

Polyunsaturated Fats

Polyunsaturated fats have two or more double bonds in the fatty acid chain.

Food Source	Details
Sunflower oil	Rich in omega-6 (linoleic acid); widely used in UK cooking
Corn oil	Another omega-6-rich vegetable oil
Soya bean oil	Contains both omega-3 and omega-6
Oily fish (salmon, mackerel, sardines, herring, trout)	Rich in omega-3 fatty acids (EPA and DHA)
Walnuts	One of the best nut sources of omega-3 (ALA)
Flaxseeds (linseeds)	Very rich in omega-3 (ALA)
Chia seeds	Another plant source of omega-3
Sesame seeds	Rich in omega-6

Properties:

• Liquid at room temperature
• Generally considered the healthiest type of fat
• Include the essential fatty acids omega-3 and omega-6

---

Essential Fatty Acids

Two families of polyunsaturated fatty acids are classified as essential because the body cannot make them — they must come from food:

Essential Fatty Acid	Chemical Name	Main Sources	Functions
Omega-3	Alpha-linolenic acid (ALA), EPA, DHA	Oily fish, flaxseeds, walnuts, chia seeds, rapeseed oil	Reduces inflammation, supports brain function, lowers risk of heart disease, important for eye and brain development in babies
Omega-6	Linoleic acid (LA)	Sunflower oil, corn oil, soya bean oil, sesame seeds, nuts	Supports immune function, helps blood clot properly, involved in brain function

The UK government recommends eating at least two portions of fish per week, one of which should be oily fish, to ensure adequate omega-3 intake.

Exam Tip: "Essential fatty acid" is a specific term meaning the body cannot make them. Omega-3 and omega-6 are essential fatty acids. Do not confuse this with fat being "essential for health" (a general statement about why we need fat).

---

Trans Fats

Trans fats (also called trans fatty acids) are a type of unsaturated fat that behaves like saturated fat in the body. They are considered the most harmful type of fat.

How Trans Fats Are Formed

• Hydrogenation: When vegetable oils are industrially processed by adding hydrogen atoms to make them more solid (e.g. converting liquid oil into solid margarine). This process creates trans fats as a by-product.
• Natural occurrence: Small amounts of trans fats are found naturally in meat and dairy from ruminant animals (cattle, sheep).

Health Effects of Trans Fats

• Raise LDL cholesterol (bad cholesterol)
• Lower HDL cholesterol (good cholesterol)
• Increase the risk of coronary heart disease, stroke, and type 2 diabetes
• Many food manufacturers have now removed or reduced trans fats from their products

Exam Tip: Trans fats are created during hydrogenation of vegetable oils. They raise LDL and lower HDL cholesterol, making them worse than saturated fats for heart health. Many processed foods in the UK no longer contain trans fats due to health concerns.

---

Comparing Fat Types: Summary Table