Molecules of life

• The major nutrients required for a healthy diet are carbohydrates, proteins and lipids.
• The digestive system breaks down large molecules of food, which are then absorbed into the bloodstream.
• Carbohydrates are a food group consisting of sugars, starch and cellulose, which are vital for energy in humans and are stored as fat if eaten in excess.
• In plants, carbohydrates are important for photosynthesis.
• Proteins are organic compounds made up of amino acid molecules, one of the three main food groups, and are needed by the body for cell growth and repair.
• Fats or oils, composed of fatty acids and glycerol, are major nutrients that we need in large quantities and are obtained by eating them.
• Fats are broken down first and then reassembled into our own carbohydrates, proteins and lipids because most of the molecules in food are too large to pass through the absorbing surface of the gut wall and the carbohydrates, proteins and lipids are reassembled in the form required, rather than other animal or plant versions.
• Carbohydrates are the source of energy, with glucose being the main respiratory substrate.
• Starches are found in potatoes, rice and wheat products, bread, cereals and pasta.
• Sugars are found in fruit, smoothies, fizzy drinks, chocolate and sweets.
• Proteins are needed for growth and repair and are found in meat, eggs, cheese, beans, nuts and seeds.
• Lipids are fats or oils, composed of fatty acids and glycerol, which are essential for normal growth and are found in butter and margarine, meat and processed meat, plant oils, oily fish, nuts and seeds.