IGCSE Biology / Food and digestion

The seven parts of a balanced diet

Edexcel International GCSE Biology (4BI1), chapter 4: Food and digestion, specification point 2.24, 2.25. Free lesson.

Read the revision notes · IGCSE Biology past papers

A balanced diet contains seven components, each with a different role in the body. You should know what each is used for and be able to name sources and deficiency diseases for the vitamins and minerals covered here.

What are the seven components?

You need all seven components, including water and fibre, which are easy to overlook. Only carbohydrate, protein and lipid provide energy. Carbohydrate is the main source of energy and the body uses it first. Sources include bread, rice, pasta and potatoes. Protein is needed for growth and repair of tissues, and for making enzymes. Sources include meat, fish, eggs and beans. Lipid means fat or oil. It stores energy, insulates the body and forms part of cell membranes. Sources include butter, oils and nuts. Vitamins are needed in small amounts but are essential. Fruit…

How fibre keeps food moving

Although fibre is not digested, it helps food pass through the gut. It gives the gut muscles something to push against, so peristalsis keeps food moving.

Which vitamins and minerals should you know?

For the named vitamins and minerals, learn a source, what each is needed for, and the effect of a deficiency, which means having too little. Vitamin A comes from liver, fish oils and carrots. It is needed for vision in dim light. A deficiency causes night blindness. Vitamin C comes from citrus fruit and fresh vegetables. It is needed for connective tissue. A deficiency causes scurvy. Vitamin D comes from oily fish and dairy, and is made in the skin in sunlight. It helps the body absorb calcium. A deficiency causes rickets. Calcium comes from milk, cheese and green…

Why can low vitamin D weaken bones?

Eating calcium-rich foods is not enough if the body cannot absorb the calcium. Vitamin D is needed for calcium absorption from the gut, so too little vitamin D can weaken bones even when the diet contains plenty of dairy. Vitamin D is made in the skin in sunlight. Without enough vitamin D, calcium passes through the gut instead of being absorbed. A shortage of vitamin D or calcium can lead to rickets.

More lessons in Food and digestion

• Carbohydrates, proteins and lipids
• Testing for starch, sugars, protein and fat
• What changes how much energy you need
• The parts of the digestive system
• Teeth, chewing and peristalsis
• Amylase, protease and lipase
• Bile, the liver and emulsifying fat
• The villus and absorption
• Practical: measuring the energy in a food sample