Diet Revision Notes

A balanced diet is one that supplies all the nutrients the body requires in the right amounts and proportions. It ensures the body functions efficiently, supports growth and repair, and provides sufficient energy for daily activities.

Without a balanced diet, deficiencies or excesses of nutrients can lead to health problems such as malnutrition, obesity, or diseases related to vitamin and mineral shortages.

Maintaining a balanced diet is essential for overall well-being and long-term health.

• Provides energy for bodily functions and activities.
• Supports growth, repair, and maintenance of tissues.
• Prevents nutrient deficiencies and related diseases.
• Promotes a healthy immune system.

A balanced diet includes carbohydrates, proteins, fats, vitamins, minerals, fibre, and water. Each nutrient group has specific roles that contribute to health.

Carbohydrates are the main source of energy. They are broken down into glucose, which cells use to produce energy.

Proteins are vital for growth and repair of body tissues. They provide amino acids necessary for building enzymes and hormones.

• Carbohydrates: energy source, found in bread, rice, pasta.
• Proteins: growth and repair, found in meat, beans, eggs.
• Fats: energy storage, insulation, hormone production, found in oils, butter.
• Vitamins and minerals: regulate body processes, support immune function.
• Fibre: aids digestion and prevents constipation.
• Water: essential for hydration and metabolic reactions.

Carbohydrates provide quick energy. For example, eating a bowl of rice supplies glucose for muscle activity.

Proteins repair damaged tissues and build new cells. For instance, after exercise, protein helps rebuild muscle fibres.

Fats serve as a concentrated energy source and are important for hormone production and protecting organs. An example is the fat stored beneath the skin that insulates the body.

• Carbohydrates yield 4 kcal/g energy.
• Proteins also provide 4 kcal/g and supply amino acids.
• Fats provide 9 kcal/g, more than double carbohydrates and proteins.
• Balanced intake prevents energy imbalance and related health issues.

Vitamins and minerals are micronutrients needed in small amounts but are crucial for processes like immune defence and bone health.

Vitamin C supports healing and immune function, while vitamin D aids calcium absorption for strong bones.

Minerals like calcium and iron are essential for bone strength and oxygen transport respectively. Fibre helps maintain healthy digestion by adding bulk to stools, preventing constipation, and reducing the risk of bowel diseases. Water is vital for hydration, temperature regulation, and as a medium for biochemical reactions.

• Vitamin C found in citrus fruits; prevents scurvy.
• Vitamin D from sunlight and fortified foods; prevents rickets.
• Calcium in dairy products; strengthens bones and teeth.
• Iron in red meat and spinach; essential for haemoglobin.
• Fibre in whole grains and vegetables; promotes gut health.
• Water intake varies but is essential daily.

Eating a variety of foods from different groups ensures all nutrient needs are met. Portion control helps maintain energy balance and healthy body weight.

For example, combining vegetables, lean protein, whole grains, and healthy fats in meals covers multiple nutrient requirements.

Regularly consuming excessive fats or sugars can lead to obesity and related diseases, while insufficient intake of vitamins or minerals can cause deficiency disorders.

• Include diverse food groups in daily meals.
• Limit intake of saturated fats and sugars.
• Consume adequate fibre and water.
• Adjust diet according to age, activity level, and health status.
• Monitor portion sizes to avoid under- or over-nutrition.

Carbohydrates are the body's primary source of energy. They are found abundantly in foods such as bread, rice, pasta, potatoes, and cereals. When consumed, carbohydrates are broken down into glucose, which cells use in respiration to release energy.

For example, eating a bowl of rice provides starch, a complex carbohydrate, which enzymes break down into glucose molecules. This glucose is then transported in the blood to cells where it undergoes aerobic respiration:

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (ATP) (in cells) The energy released powers cellular activities such as muscle contraction and nerve impulses. Without sufficient carbohydrate intake, the body may use proteins or fats for energy, which is less efficient and can impair bodily functions.

• Main sources: bread, rice, pasta, potatoes, cereals
• Broken down into glucose for energy
• Supports all cellular activities requiring energy

Fats and oils are concentrated energy sources, providing more than twice the energy per gram compared to carbohydrates. They are found in butter, oils, nuts, and fatty meats.

Besides energy storage, fats are essential components of cell membranes, contributing to their structure and fluidity. They also provide insulation to maintain body temperature and protect vital organs.

For example, olive oil contains unsaturated fats that help maintain healthy cell membranes. When energy intake exceeds immediate needs, excess fats are stored in adipose tissue for later use.

• Sources: butter, oils, nuts, fatty meats
• Provide long-term energy storage
• Contribute to cell membrane structure
• Insulate and protect organs

Proteins are vital for growth, tissue repair, and the production of enzymes and hormones. Dietary proteins come from meat, fish, eggs, dairy products, beans, and lentils.

Proteins are made of amino acids, which the body uses to build new cells and repair damaged tissues. For example, after a cut, proteins help form new skin cells to heal the wound.

Unlike carbohydrates and fats, proteins are not primarily used for energy unless the diet is deficient in other sources.

• Sources: meat, fish, eggs, dairy, beans, lentils
• Made of amino acids for cell growth and repair
• Essential for enzymes and hormones

Vitamin C is found in citrus fruits, strawberries, and green vegetables. It is crucial for the immune system and helps the body repair tissues by aiding collagen formation, a protein important for skin and blood vessels.

Vitamin D is obtained from oily fish, egg yolks, and is also synthesised in the skin through sunlight exposure. It promotes calcium absorption from the gut, essential for strong bones and teeth.

For example, a lack of vitamin C can cause scurvy, characterised by bleeding gums and poor wound healing, while vitamin D deficiency leads to rickets, causing weak and deformed bones in children.

• Vitamin C sources: citrus fruits, strawberries, green vegetables
• Supports immune function and tissue repair
• Vitamin D sources: oily fish, egg yolks, sunlight
• Promotes calcium absorption for bone strength

Calcium is abundant in milk, cheese, and green leafy vegetables. It is essential for building and maintaining strong bones and teeth, as well as for muscle contraction and blood clotting.

Iron is found in red meat, beans, and fortified cereals. It is a key component of haemoglobin in red blood cells, which transports oxygen from the lungs to body tissues.

For example, insufficient iron intake can cause anaemia, leading to fatigue and shortness of breath due to reduced oxygen delivery.

• Calcium sources: milk, cheese, leafy greens
• Strengthens bones and teeth; aids muscle function
• Iron sources: red meat, beans, fortified cereals
• Essential for oxygen transport in blood

Fibre, or roughage, is found in whole grains, fruits, vegetables, and legumes. It is not digested but adds bulk to the diet, helping food move smoothly through the digestive system and preventing constipation.

Water is vital for all bodily functions, including temperature regulation, nutrient transport, and chemical reactions. It is obtained from drinking fluids and water-rich foods like fruits and vegetables.

For example, drinking adequate water prevents dehydration, which can impair concentration and physical performance. Fibre also supports gut health by promoting regular bowel movements.

• Fibre sources: whole grains, fruits, vegetables, legumes
• Aids digestion and prevents constipation
• Water sources: drinking fluids, fruits, vegetables
• Essential for hydration and metabolic processes