Key nutrients and their functions

A healthy diet provides the essential substances your body needs to function, grow, and perform during physical activity. These substances, known as nutrients, come from various foods and help maintain overall health.

Carbohydrates

Carbohydrates are the sugars, starches, and fibres found in foods like fruits, grains, vegetables, and milk products. They serve as the body's primary source of energy.

Key facts about carbohydrates:

• Sources - Fruits, breads, grains, starchy vegetables (such as potatoes), sugars, pasta, and rice
• Functions - Provide fuel for physical activity and brain function; supply fibre to regulate digestion
• Energy contribution - Make up to 55% of daily energy intake

Fats

Fats are substances in food that provide a rich, concentrated source of energy. One gram of fat contains 9 calories, compared to just 4 calories in a gram of protein or carbohydrate.

Key facts about fats:

• Sources - Red meats, butter, cooking oils, cheese, and bacon
• Functions - Supply stored energy that the body can use when needed
• Energy contribution - Make up to 30% of daily energy intake

Proteins

Proteins are the building blocks of life, found in every cell of the body. They consist of chains of smaller units called amino acids.

Key facts about proteins:

• Sources - Low-fat meats, dairy products, beans, eggs, and fish
• Functions - Help cells grow and repair; support muscle tissue repair after exercise
• Energy contribution - Make up to 15% of daily energy intake

Vitamins and minerals

Vitamins are organic compounds that help regulate body processes, such as immune function and bone health. Minerals are inorganic elements, like calcium and iron, that support functions such as oxygen transport and muscle contraction.

Key facts about vitamins and minerals:

• Sources - Varied foods, including fruits, vegetables, dairy, and meats
• Functions - Support overall body processes; for example, vitamin C aids tissue repair, while iron helps form red blood cells

Water

Water is a vital substance that makes up a large part of the body and is essential for life.

Key facts about water:

• Sources - Drinks, and foods with high water content such as soup and watermelon
• Functions - Transports nutrients to cells; removes waste products; maintains body temperature

Components of a balanced diet and varying nutritional needs

A balanced diet includes all the main nutrients in the right proportions to support health and performance. This means combining carbohydrates, fats, proteins, vitamins, minerals, and water appropriately. Eating a variety of foods ensures you get these nutrients without excess or deficiency.

Why a balanced diet matters

Different people have unique nutritional needs based on factors like age, growth stage, and health status.

Examples of varying nutritional needs:

• Children need more protein than adults because their bodies are still growing and developing tissues.
• Pregnant women require extra iron to support the development of blood cells in their babies.

Reasons for special diets

Some people follow special diets to meet specific requirements or goals. These diets adjust nutrient intake for various reasons.

Common reasons for special diets:

• Health conditions, like diabetes or allergies.
• Weight management, to gain or lose weight through calorie adjustments.
• Religious or cultural reasons.
• Athletic training regimes, to optimise performance in sports.

Energy requirements, balance, and health impacts

Energy is the fuel your body gets from food, measured in kilocalories (kcal) or simply calories. Your daily energy needs depend on age, gender, and lifestyle – more active people require more calories to support their activities.

Daily energy requirements

Typical daily energy needs:

• Teenagers (around 15 years old) typically need about 2,820 kcal for males and 2,390 kcal for females.
• Active adults generally require around 2,500 kcal for males and 2,000 kcal for females.

Energy expenditure by activity

Energy use, or expenditure, varies depending on the intensity of the activity. This is measured in calories per minute and differs by body weight and gender. The table below shows approximate ranges for a 58-kg woman and a 70-kg man.

For context, watching TV uses about 75 calories per hour, while competitive sports can burn over 400 calories per hour.

Maintaining energy balance

Energy balance means matching the calories you consume with those you use. This is crucial for health.

Consequences of energy imbalance:

• If you consume more energy than needed, the excess is stored as fat, which can lead to obesity.
• Obesity increases risks of health problems like high blood pressure, diabetes, liver disease, heart disease, stroke, and cancer.
• If you consume less energy than needed, you may become underweight, leading to a weakened immune system, fragile bones, and fatigue.

Nutrition labels and energy storage in the body

Nutrition labels on packaged foods provide key details to help make healthy choices. They list information on energy (in kJ and kcal), fat, saturates (a type of fat linked to health risks), carbohydrates, sugars, protein, and salt.

Understanding nutrition labels

Many labels use a colour-coded 'traffic light' system:

Traffic light system:

• Green - Low levels (healthier choice)
• Amber - Medium levels
• Red - High levels (consume in moderation)

Foods with mostly green indicators are generally better for a balanced diet.

How the body stores and uses energy

Glucose is a simple carbohydrate transported in the bloodstream to tissues, where it's used for energy. Muscle cells release energy from glucose through respiration (the process of breaking down nutrients with oxygen to produce energy). If not used immediately, glucose is stored as glycogen in the liver and muscles for later use.

Nutritional strategies for athletes

Athletes often adapt their diets to enhance performance, focusing on specific nutrients and timing. These strategies build on a balanced diet but tailor intake to training demands.

Carbohydrate loading

Carbohydrate loading is a method used by endurance athletes to boost energy stores before events. It involves eating excess carbohydrates about one week prior, increasing glycogen levels in muscles and the liver. Athletes on this regime may consume 4,000-5,000 calories daily, helping sustain prolonged activity like marathons.

High-protein diets

Bodybuilders and strength athletes often follow high-protein diets to support muscle repair and growth. While extra protein aids recovery, it doesn't directly build muscle.

Additional strategies athletes use

• Some athletes reduce calories before events to achieve lightness and agility.
• Hydration is critical; water prevents dehydration during exercise.