What are fats made of, what do they do, and why does the type of fat matter?
Fats and lipids as a macronutrient: triglyceride structure, saturated, monounsaturated and polyunsaturated fatty acids, essential fatty acids and cholesterol, the functions and food sources of fat, and the dietary recommendations and health effects of different fats.
A CCEA A-Level Nutrition and Food Science answer on fats and lipids: triglyceride structure, saturated, monounsaturated and polyunsaturated fatty acids, trans fats, essential fatty acids, cholesterol, the functions and sources of fat, and the dietary recommendations.
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What this dot point is asking
CCEA wants you to describe fat (lipid) as a macronutrient: the structure of a triglyceride, the difference between saturated, monounsaturated and polyunsaturated fatty acids, what essential fatty acids and cholesterol are, the functions and sources of fat, and the dietary recommendations and health effects linked to the type of fat eaten.
Structure of fats
The properties of a fat depend on its fatty acids. A saturated fatty acid has no carbon-to-carbon double bonds, so every carbon carries as much hydrogen as possible; the straight chains pack tightly, so saturated fats tend to be solid at room temperature. An unsaturated fatty acid has one or more carbon-to-carbon double bonds, which put kinks in the chain so the molecules cannot pack closely, making unsaturated fats liquid oils at room temperature.
Cholesterol is a lipid made in the liver and also found in some foods. It is needed to make cell membranes, bile and some hormones, but it is carried in the blood as low-density lipoprotein (LDL, the harmful form) and high-density lipoprotein (HDL, the protective form).
Functions, sources and recommendations
UK dietary advice is to keep total fat to about 35 percent of food energy, with saturated fat no more than about 11 percent, and to replace some saturated fat with unsaturated fat. A high saturated and trans fat intake raises blood LDL cholesterol, which is deposited in artery walls and linked to coronary heart disease, the key health connection CCEA tests.
Examples in context
Example 1. Swapping fats to protect the heart. A family that fries in lard, spreads butter thickly and eats processed meat has a high saturated fat intake. Switching to rapeseed oil for cooking, using a small amount of unsaturated spread, and eating oily fish such as mackerel twice a week lowers saturated fat and raises beneficial unsaturated and omega-3 intake. Over time this helps lower blood LDL cholesterol, illustrating the direct diet-to-disease link the module examines.
Example 2. Fat-soluble vitamin absorption. A very low-fat diet can reduce the absorption of vitamins A, D, E and K, because these vitamins dissolve in and travel with dietary fat. Including a little unsaturated fat with vegetables, for example a drizzle of olive oil on a salad containing carrots, improves the uptake of vitamin A from the carotene. This shows that fat has nutritional roles beyond energy.
Try this
Q1. Explain why saturated fats are usually solid and unsaturated fats usually liquid at room temperature. [2 marks]
- Cue. Saturated chains have no double bonds and pack closely (solid); unsaturated chains have kinked double bonds and cannot pack closely (liquid).
Q2. Name the two essential fatty acids and give a food source of each. [2 marks]
- Cue. Omega-3 from oily fish or linseed; omega-6 from sunflower or corn oil.
Q3. State the recommended maximum for saturated fat as a percentage of food energy. [1 mark]
- Cue. About 11 percent of food energy.
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA AS 20196 marksExplain the difference between saturated and unsaturated fatty acids, and discuss the dietary advice given about each.Show worked answer →
A 6-mark answer needs the structural difference and the health-based dietary advice for each type.
A fatty acid is a chain of carbon atoms with a carboxyl group at one end. A saturated fatty acid has no double bonds between its carbon atoms, so each carbon is saturated with hydrogen; these chains pack closely and saturated fats are usually solid at room temperature (butter, lard, fat on meat). An unsaturated fatty acid has one or more carbon-to-carbon double bonds. Monounsaturated fatty acids have one double bond (olive oil, rapeseed oil); polyunsaturated fatty acids have two or more (sunflower oil, oily fish). The double bonds create kinks, so unsaturated fats are usually liquid oils at room temperature.
Dietary advice: a high intake of saturated fat raises blood LDL cholesterol, which is linked to coronary heart disease, so the recommendation is to reduce saturated fat to no more than about 11 percent of food energy. Replacing some saturated fat with unsaturated fat is encouraged because unsaturated fats, especially the omega-3 fatty acids in oily fish, are linked to better heart health. Trans fats from hydrogenation should be kept as low as possible.
Markers reward the double-bond distinction, the solid-versus-liquid consequence, named examples, and the reduce-saturated, replace-with-unsaturated advice with a reason.
CCEA AS 20214 marksDescribe the functions of fat in the diet.Show worked answer →
A 4-mark answer needs four separate functions.
Fat is a concentrated source of energy, providing about 37 kilojoules (9 kilocalories) per gram, more than twice that of carbohydrate or protein. It carries the fat-soluble vitamins A, D, E and K and aids their absorption. Stored fat (adipose tissue) insulates the body against heat loss and forms a protective layer around delicate organs such as the kidneys.
Fat also contributes to the palatability of food, improving flavour, texture and satiety (the feeling of fullness after eating), and it supplies the essential fatty acids the body cannot make.
Markers reward four distinct points from: concentrated energy with its value, carrying fat-soluble vitamins, insulation, protection of organs, palatability or satiety, and supplying essential fatty acids.
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Sources & how we know this
- CCEA GCE Nutrition and Food Science specification — CCEA (2016)
- Saturated fats and health (SACN report) — Scientific Advisory Committee on Nutrition (2019)