Fats: Functions, Deficiency and Excess

This lesson covers the functions of fat in the body and the effects of deficiency (not enough fat) and excess (too much fat), as required by AQA GCSE Food Preparation and Nutrition specification 8585 (section 3.2.1). Fat is often portrayed negatively in the media, but it is an essential macronutrient with many vital functions. Understanding both the benefits and risks of fat consumption is critical for the exam.

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Functions of Fat in the Body

Fat performs a wide range of essential functions in the body:

Function	Explanation
Concentrated source of energy	Fat provides 9 kcal per gram, more than double the energy from protein (4 kcal/g) or carbohydrate (3.75 kcal/g). This makes fat an efficient energy store.
Energy reserve	Excess energy is stored as adipose tissue (body fat) beneath the skin and around organs. This reserve can be used when food intake is insufficient.
Insulation	The layer of subcutaneous fat beneath the skin acts as a thermal insulator, helping to maintain body temperature. This is particularly important in cold environments.
Protection of vital organs	Fat surrounds and cushions vital organs such as the kidneys, heart, and liver, protecting them from physical damage.
Absorption of fat-soluble vitamins	Fat is needed for the absorption of vitamins A, D, E, and K. These vitamins dissolve in fat and cannot be absorbed without it. Without adequate fat in the diet, deficiency of these vitamins can develop.
Essential fatty acids	Fat provides the essential fatty acids omega-3 and omega-6, which the body cannot manufacture. These are needed for brain function, cell membranes, inflammation regulation, and growth.
Cell membranes	Every cell in the body has a phospholipid bilayer membrane made partly of fat. Fat is essential for building and maintaining cell structure.
Satiety	Fat takes longer to digest than carbohydrate, so it helps you feel full for longer after a meal. This is called satiety.
Flavour and texture	Fat carries flavour molecules and contributes to the texture and mouthfeel of food (e.g. the richness of butter, the creaminess of cheese).

Exam Tip: When listing the functions of fat, try to give at least four or five distinct functions. The most commonly tested are: concentrated energy, insulation, organ protection, and absorption of fat-soluble vitamins A, D, E, K. Use the mnemonic ADEK to remember the fat-soluble vitamins.

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Fat-Soluble Vitamins: A, D, E, K

Since fat is required for the absorption of these vitamins, a diet very low in fat can lead to deficiencies:

Vitamin	Key Functions	Sources
Vitamin A	Vision (especially night vision), immune function, skin health	Liver, eggs, dairy, orange/yellow vegetables (beta-carotene)
Vitamin D	Absorption of calcium and phosphorus, bone health	Oily fish, eggs, fortified cereals, sunlight on skin
Vitamin E	Antioxidant, protects cell membranes from damage	Vegetable oils, nuts, seeds, spinach
Vitamin K	Blood clotting, bone metabolism	Green leafy vegetables, vegetable oils, meat

graph TD
    A["Fat in Diet"] --> B["Absorption of Fat-Soluble Vitamins"]
    B --> C["Vitamin A — Vision, immunity"]
    B --> D["Vitamin D — Calcium absorption, bones"]
    B --> E["Vitamin E — Antioxidant, cell protection"]
    B --> F["Vitamin K — Blood clotting"]

    style A fill:#e67e22,color:#fff
    style B fill:#4a90d9,color:#fff
    style C fill:#27ae60,color:#fff
    style D fill:#27ae60,color:#fff
    style E fill:#27ae60,color:#fff
    style F fill:#27ae60,color:#fff

Exam Tip: If asked "Why is fat needed in the diet?", always include the absorption of fat-soluble vitamins A, D, E, K as one of your points. Examiners specifically look for this.

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Fat Deficiency

Fat deficiency is relatively rare in the UK but can occur in people on very low-fat diets, those with eating disorders, or those with conditions affecting fat absorption (e.g. cystic fibrosis, Crohn's disease).

Effects of Fat Deficiency

Effect	Explanation
Deficiency of fat-soluble vitamins	Without adequate fat, vitamins A, D, E, and K cannot be absorbed. This can lead to night blindness (vitamin A), rickets or osteomalacia (vitamin D), cell membrane damage (vitamin E), and poor blood clotting (vitamin K).
Lack of essential fatty acids	Deficiency of omega-3 and omega-6 can cause dry, flaky skin, poor wound healing, impaired brain function, and inflammation.
Poor growth in children	Fat is needed for brain development and overall growth. Children on very low-fat diets may not develop properly.
Feeling cold	Reduced subcutaneous fat means less insulation, leading to greater sensitivity to cold temperatures.
Lack of energy	Fat is the most concentrated energy source. Without it, the body may struggle to meet its energy requirements.
Dry skin and hair	Fat helps maintain healthy skin and hair. Deficiency can cause dryness and brittleness.
Hormonal disruption	Fat is involved in the production of certain hormones. Very low body fat can disrupt menstrual cycles in women and affect reproductive health.

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Fat Excess

In the UK, many people consume more fat than recommended, particularly saturated fat. Excess fat intake has significant health consequences.

Effects of Fat Excess

Effect	Explanation
Obesity	Fat provides 9 kcal per gram. Consuming more energy than the body uses leads to excess energy being stored as adipose tissue, resulting in weight gain and eventually obesity.
Coronary heart disease (CHD)	Excess saturated fat raises blood levels of LDL cholesterol. This cholesterol can build up in the walls of coronary arteries, forming atheroma (fatty deposits). This narrows the arteries (atherosclerosis), reducing blood flow to the heart and increasing the risk of heart attacks and angina.
High blood cholesterol	Saturated and trans fats raise total blood cholesterol and LDL cholesterol. High cholesterol is a major risk factor for heart disease and stroke.
Type 2 diabetes	Obesity (caused partly by excess fat intake) is a major risk factor for type 2 diabetes. Excess body fat, particularly around the abdomen, reduces the body's sensitivity to insulin.
Stroke	Atherosclerosis can also affect the arteries supplying the brain. If a blood clot blocks a narrowed artery in the brain, a stroke occurs.
High blood pressure	Excess weight and fatty deposits in blood vessels increase the workload on the heart, raising blood pressure (hypertension).
Some cancers	Obesity is linked to an increased risk of certain cancers, including bowel, breast, and kidney cancer.

The Process of Atherosclerosis

graph LR
    A["High saturated fat intake"] --> B["Raised LDL cholesterol"]
    B --> C["Cholesterol deposits in artery walls"]
    C --> D["Atheroma forms"]
    D --> E["Artery narrows — atherosclerosis"]
    E --> F["Reduced blood flow"]
    F --> G["Angina / Heart attack"]
    E --> H["Blood clot may form"]
    H --> I["Stroke or heart attack"]

    style A fill:#c0392b,color:#fff
    style D fill:#e67e22,color:#fff
    style G fill:#8e44ad,color:#fff
    style I fill:#8e44ad,color:#fff

Exam Tip: When discussing excess fat and heart disease, use the correct sequence: excess saturated fat → raised LDL cholesterol → atheroma in arteries → atherosclerosis → reduced blood flow → CHD. This chain of events is worth multiple marks in extended-answer questions.

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Current UK Guidelines on Fat Intake

Guideline	Recommendation
Total fat	No more than 35% of total energy intake
Saturated fat	No more than 11% of total energy intake (approximately 20 g/day for women, 30 g/day for men)
Trans fat	As low as possible; ideally no more than 2% of total energy
Oily fish	Eat at least two portions of fish per week, one of which should be oily fish
Replace, don't just reduce	Replace saturated fats with unsaturated fats where possible