Welcome to Energy and Nutrients!
Have you ever wondered why you feel sluggish when you skip a meal, or why athletes eat large plates of pasta before a big race? Just like a car needs fuel to run, your body needs dietary energy from food to keep you alive, warm, growing, and moving.
In this chapter for CCEA GCSE Home Economics: Food and Nutrition (Component 1), we will explore:
• Where our energy comes from (macronutrients)
• How much energy different nutrients provide
• How your body burns energy (BMR and PAL)
• What affects your daily energy needs
• How to keep your energy in balance
Don't worry if nutrition facts seem a bit confusing at first—we will break everything down step-by-step with clear examples!
---1. Energy in Food: The Macronutrients
Energy is measured in two units on food labels: kilocalories (kcal) and kilojoules (kJ). The body gets energy from three main nutrients called macronutrients (plus alcohol, though alcohol is not an essential nutrient).
Energy Values per Gram (Energy Density)
Different nutrients provide different amounts of energy. Energy density refers to how much energy is packed into a specific weight of food.
• Fat: Provides \(9\text{ kcal}\) or \(37\text{ kJ}\) per gram. Fat is the most energy-dense nutrient!
• Protein: Provides \(4\text{ kcal}\) or \(17\text{ kJ}\) per gram.
• Carbohydrate: Provides \(3.75\text{ to } 4\text{ kcal}\) or \(16\text{ to } 17\text{ kJ}\) per gram (standardised to \(4\text{ kcal} / 17\text{ kJ}\) for calculations).
• Reference value: Alcohol provides \(7\text{ kcal}\) or \(29\text{ kJ}\) per gram.
Top Tip to Remember: Think of fat as the heavyweight champion of energy—1 gram of fat gives you more than double the energy of 1 gram of carbohydrate or protein!
Important Examiner Warning: What about Vitamins and Minerals?
A very common mistake in exams is writing that vitamins and minerals provide energy. Vitamins and minerals provide \(0\text{ kcal}\) and \(0\text{ kJ}\)! They are vital helper nutrients that assist enzymes in releasing energy from macronutrients, but they do not contain any energy themselves.
Key Takeaway: Only carbohydrates (\(4\text{ kcal}/17\text{ kJ}\)), proteins (\(4\text{ kcal}/17\text{ kJ}\)), and fats (\(9\text{ kcal}/37\text{ kJ}\)) provide the body with energy.
---2. Dietary Recommendations for Daily Energy
UK Dietary Reference Values (DRVs) give us targets for how our daily energy intake should be divided among the macronutrients.
• Carbohydrates: Should make up approximately 50% of your total daily energy intake.
Sub-target: Free sugars (added sugars and sugars in fruit juices/honey) should make up no more than 5% of daily energy.
• Fats: Should make up no more than 35% of your total daily energy intake.
Sub-target: Saturated fats should make up no more than 11% of daily energy.
• Protein: Should make up approximately 15% of your total daily energy intake.
Common Pitfall: Percentage vs Grams
Do not confuse the percentage of daily energy with the weight in grams. For example, 50% carbohydrate means half of your daily calories should come from carbohydrates, not that you should eat only 50 grams of carbs!
Key Takeaway: Aim for roughly 50% energy from carbs (max 5% free sugars), 35% from fats (max 11% saturates), and 15% from protein.
---3. How the Body Uses Energy (Total Energy Expenditure)
Every single day, your body uses up energy in two main ways. Together, they make up your Total Energy Expenditure (TEE).
A. Basal Metabolic Rate (BMR)
Definition: BMR is the minimum amount of energy required to maintain essential, involuntary life-sustaining bodily functions at complete rest.
Even when you are fast asleep, your body is hard at work keeping your heart beating, lungs breathing, cells repairing, and body temperature stable. BMR accounts for the largest portion of your daily energy output—around 60% to 75% of all the energy you burn in a day!
B. Physical Activity Level (PAL)
Definition: PAL is the energy required above your BMR for physical movement and muscular work.
This includes everything from walking to school, cleaning your room, and fidgeting, to intense sports like swimming or football. A person with a sedentary desk job has a low PAL, while a professional athlete or construction worker has a high PAL.
The Energy Calculation Formula:
\(\text{Total Energy Expenditure (TEE)} = \text{BMR} \times \text{PAL}\)
Key Takeaway: BMR is the energy needed just to stay alive at rest; PAL is the energy used for moving around. Multiplying them gives your total daily energy output.
---4. Factors Influencing Energy Requirements
Not everyone needs the exact same amount of energy. Your daily needs depend on several important factors:
• 1. Age:
Babies, children, and teenagers have high energy needs relative to their body size because they are growing rapidly. In older adulthood, energy requirements decrease because the metabolic rate slows down and muscle mass naturally declines.
• 2. Gender / Biological Sex:
Males generally require more energy than females. This is because males typically have a higher proportion of lean muscle tissue (which burns more calories at rest than body fat) and a larger average body size.
• 3. Body Size and Composition:
Larger individuals require more energy to move their body mass. People with more muscle tissue have a higher BMR than people of the same weight with more body fat.
• 4. Physical Activity Level (PAL):
Someone who does heavy manual labour or trains for sports burns significantly more energy each day than someone who sits at a desk.
• 5. Special Physiological States / Life Stages:
Pregnancy: Energy needs increase slightly, especially during the third trimester (\(+200\text{ kcal/day}\)) to support the growing baby.
Lactation (Breastfeeding): Producing breast milk takes a lot of energy, requiring an extra \(+450\text{ to } 500\text{ kcal/day}\).
Illness & Recovery: Having a fever or healing from surgery/burns speeds up metabolism and increases the body's energy needs.
Key Takeaway: Age, gender, body size, activity level, and life stages like pregnancy all change how much fuel your body needs each day.
---5. Energy Balance
Think of energy balance like a set of weighing scales. On one side, you have Energy Intake (food and drink consumed). On the other side, you have Energy Expenditure (BMR + PAL).
1. Neutral Energy Balance (Weight Stays the Same)
• \(\text{Energy Intake} = \text{Energy Expenditure}\)
• The calories you eat equal the calories you burn. Your body weight remains stable.
2. Positive Energy Balance (Weight Gain)
• \(\text{Energy Intake} > \text{Energy Expenditure}\)
• You consume more energy than your body burns. The unused surplus energy is stored in the body as adipose tissue (body fat), leading to weight gain and increasing the risk of overweight and obesity over time.
3. Negative Energy Balance (Weight Loss)
• \(\text{Energy Intake} < \text{Energy Expenditure}\)
• You consume less energy than your body burns. The body must break down its stored fat and glycogen to supply energy, resulting in weight loss.
Key Takeaway: Balancing the energy you eat with the energy you burn keeps your weight steady. Eating more leads to fat storage, while eating less leads to weight loss.
---Quick Revision Checklist
Before your exam, make sure you can answer these key questions:
• Can you state the energy values per gram for fat (\(9\text{ kcal}/37\text{ kJ}\)), protein (\(4\text{ kcal}/17\text{ kJ}\)), and carbohydrate (\(4\text{ kcal}/17\text{ kJ}\))?
• Can you recall the daily percentage targets for carbohydrates (\(50\%\)), fats (\(35\%\)), and protein (\(15\%\))?
• Can you clearly define BMR and explain how it is different from PAL?
• Can you state the formula: \(\text{TEE} = \text{BMR} \times \text{PAL}\)?
• Can you explain what happens during positive and negative energy balance?