1.10 Outline the relationship between energy intake, energy expenditure and weight

This guide will help you answer 1.10 Outline the relationship between energy intake, energy expenditure and weight.

To keep the body healthy, we must balance what we eat and drink against what we use through daily activities. This balance shapes body weight over time. Energy comes from the food and drinks we consume. We use this energy through basic body processes and movement. How these two sides line up determines if we gain, lose, or maintain weight.

Many people want to manage their weight for health, confidence, or quality of life. To do this, it helps to understand how energy intake and energy expenditure work together.

What Is Energy Intake?

Energy intake is simply the total amount of energy you get from food and drink each day. Different foods contain different amounts of energy, usually measured in kilocalories (kcal) or kilojoules (kJ). Kilocalories are often called “calories” in everyday language.

Food contains three main energy-providing nutrients:

• Carbohydrates: Found in bread, potatoes, rice, pasta, fruit, and sweets.
• Fats: Found in butter, oils, cheese, meat, processed foods, and nuts.
• Proteins: Found in meat, fish, eggs, pulses (beans, lentils), dairy, and soy products.

Each gram of these nutrients provides:

• Carbohydrate: 4 kcal (17 kJ)
• Protein: 4 kcal (17 kJ)
• Fat: 9 kcal (37 kJ)

Alcohol also contains energy (7 kcal per gram), even though it is not needed for health.

When you eat or drink, you add to your total daily energy intake. All calories count, not just those in main meals but snacks and drinks too.

What Is Energy Expenditure?

Energy expenditure is the total energy the body uses to keep alive and to move. This is measured over a day and is often called Total Daily Energy Expenditure (TDEE).

There are three main parts to energy expenditure:

• Basal Metabolic Rate (BMR): This is the energy needed for basic body processes when you are resting and awake, like breathing, heartbeat, and digesting food. BMR makes up the largest part of energy use (about 60-75%).
• Physical activity: This is the energy used for all movement, including walking, exercise, housework, and even fidgeting. This amount can vary greatly from person to person.
• Thermic effect of food (TEF): This is the small amount of energy the body needs to digest and absorb food. It is roughly 10% of energy expenditure.

Anyone can influence the second part — activity level — by changing how active they are each day.

The Energy Balance Equation

The connection between intake, output, and weight is called the energy balance equation. The body needs energy to work, grow, and repair. If the energy you consume matches what you use, your weight will likely stay stable.

The equation is simple:

• Energy in (food and drink) = Energy out (used by the body)

This balance is rarely perfect day-to-day but works over weeks and months. Too much or too little on either side leads to weight change.

What Happens When the Balance Changes?

• Positive energy balance: Energy intake is higher than expenditure (eating more than you use). The body stores excess energy, mostly as fat. Over time, this leads to weight gain.
• Negative energy balance: Energy intake is lower than expenditure (using more than you eat). The body uses stored energy (body fat and sometimes muscle) to make up the shortfall. This leads to weight loss.
• Neutral energy balance: Intake equals expenditure (eating what you use). Weight stays the same.

People often notice changes over time, not instantly. For adults, small differences in daily calories add up, leading to change over months.

Factors Affecting Energy Intake

Energy intake depends on:

• Portion sizes: Larger portions have more energy.
• Frequency of eating: More meals, snacks, or drinks mean more intake.
• Type of food or drink: High-fat and sugary foods tend to have more calories.
• Drinks: Alcohol, sugary drinks, and many milky coffees are high in calories.

People may eat more in social situations, when stressed, bored, or distracted. Packaged or restaurant foods can be high in hidden calories, especially from fats and sugars.

Factors Affecting Energy Expenditure

The amount of energy a person uses each day varies. These are some main influences:

• Body size and composition: Larger people and those with more muscle use more energy, even at rest.
• Age: Younger people tend to burn more, as metabolism slows with age.
• Gender: Males often have more muscle mass, so burn more energy.
• Physical activity: Being active increases energy use. Exercise and daily movement (like walking to work) add up.
• Health conditions: Some illnesses or medicines can increase or decrease energy use.

A person who sits most of the day and does not exercise will need less energy than someone who is active.

How Weight Is Affected by Energy Balance

The body can store excess energy as fat if intake is higher than need. This is useful in times of shortage, but in modern life it often leads to weight gain.

Weight gain:

• Occurs if energy intake continues to be higher than expenditure.
• The surplus energy is stored — mainly as body fat.
• Just 100 kcal extra per day (not used) can put on nearly half a stone (3 kg) in a year.

Weight loss:

• Occurs if energy intake is less than what the body uses.
• The body turns to its energy stores (fat, sometimes muscle) for fuel.
• Regularly using more than you eat leads to steady weight loss.

Weight maintenance:

• Achieved when intake matches expenditure.
• The body does not need to access energy stores, nor does it store extra.

People may find it hard to spot small imbalances day-to-day but see changes in body weight or shape over weeks or months.

Monitoring Weight Change

Scales and measurements can help someone check if they are eating the right amount for their needs. Weight is just one measure; body shape and how clothes fit can also help.

People should not stress about small changes. Daily weight can go up or down by a few pounds (kg) because of water, food, or time of day.

Most healthy adults weigh themselves once a week at the same time. This gives a better idea of long-term trends.

Tips to Support a Healthy Weight Through Energy Balance

Here are some steps to keep energy intake and expenditure in sync:

• Learn the amount of energy your body needs each day.
• Eat standard portion sizes and avoid second helpings.
• Base meals on starchy foods such as potatoes, rice, or pasta, but watch toppings and extras.
• Include fruits and vegetables for vitamins, minerals, and fibre.
• Limit high-fat and high-sugar foods.
• Read food labels for energy content.
• Drink water instead of sugary drinks or alcohol.
• Build physical activity into each day. Aim for at least 150 minutes per week, if possible.
• Find small ways to move more (take the stairs, walk to shops).

Focus on long-term habits. Strict diets or quick changes rarely last.

Energy Needs at Different Life Stages

Energy needs change through life. Children and teenagers use extra for growth and are often more active. Pregnant or breastfeeding women need more energy and nutrients. Older adults use less, especially if less active.

Health conditions can affect needs too. Some illnesses increase energy use, while others lower it.

If unsure, consult a health professional or a registered nutritionist.

The Problem of Unintentional Weight Gain

Many people gradually gain weight without realising. This happens because:

• Busy lives mean more eating on-the-go.
• Larger standard portions, especially in restaurants.
• More processed foods that are high in calories.
• Sugar in drinks adds extra energy.
• Less time spent moving and more screen time.

Being aware of habits and making changes to both eating and activity are important steps.

When to Seek Help

Some people need extra help with weight concerns. Unintentional or unexplained weight loss, or sudden gain without a clear cause, should be discussed with a doctor. This can sometimes signal health problems.

For those who struggle with weight, advice from a registered dietitian, nutritionist, or healthcare team can make changes safer and more effective.

Cultural and Environmental Influences

Where we live, family habits, local foods, and social events all affect energy intake and use. Some people have easier access to healthy foods or spaces to be active. Work or school schedules influence meal times and opportunities for movement. Marketing and advertising affect food choices.

Awareness of these factors can help develop personal strategies. Packing a healthy lunch, choosing water, or adding short walks into the day all help maintain a suitable energy balance.

Final Thoughts

Body weight is shaped by a simple equation, but day-to-day life makes it a complex issue. Small changes on either side – extra snacks or missing a walk – matter over time. Eating a healthy, balanced diet and finding enjoyable ways to be active remain key. There is no single ideal weight or approach; everyone is different.

Regular awareness of what and how much you eat, and how much you move, can help you stay in control. Focus on habits you can maintain. Celebrate progress, however small. If you slip, get back on track rather than giving up.

Managing energy balance is not about strict rules or quick fixes. Instead, aim for consistency and kindness to yourself. Over months and years, these choices will help support health, confidence, and wellbeing. If support is needed, many qualified health and nutrition professionals are ready to help. Keep learning, stay active, and make choices that suit your needs and circumstances.