7.1 - Balanced Diet

The nutrient groups and water as a solvent

• A balanced diet supplies all the essential nutrients the body needs, in the right proportions.
• There are several groups of nutrients, and each has its own job - so a healthy diet must include all of them in suitable amounts.

The seven nutrient groups

1. Carbohydrates - Found in pasta, rice, bread and sugar; the body's main source of energy.
2. Lipids (fats and oils) - Found in butter and oily fish; provide energy, act as an energy store, insulate the body against heat loss, and protect the internal organs.
3. Proteins - Found in meat, fish and beans; needed for the growth and repair of body tissue, and can also provide energy in emergencies.
4. Vitamins - Needed in small amounts (see below).
5. Mineral ions - Needed in small amounts (see below).
6. Water - From food and drink; needed for almost every process in the body. A constant supply replaces water lost in urine, breathing and sweat.
7. Dietary fibre (roughage) - Found in wholemeal bread and fruit; not digested, but provides bulk that helps food move through the gut and keeps the digestive system working properly.

Vitamins and their functions

• Vitamin A - From foods such as liver; keeps the eyes, skin and hair healthy.
• Vitamin C - From fruit such as oranges; needed for healthy tissue and the repair of body tissue.
• Vitamin D - From eggs and oily fish; needed so the body can absorb calcium. Also made by the skin when exposed to sunlight.

Mineral ions and their functions

• Calcium - From milk and cheese; needed to make strong bones and teeth.
• Iron - From red meat; needed to make haemoglobin, the substance in red blood cells that carries oxygen.

Water as a solvent

Water is the main solvent in living organisms, and much of what the body does depends on substances being dissolved in it.

• Digestion - Food molecules are digested and absorbed in solution, so the products of digestion can pass into the body dissolved in water.
• Excretion - Soluble wastes such as urea dissolve in water and are removed from the body in urine.
• Transport - Substances are carried around the body dissolved in water - in the blood plasma in animals, and in the transport tissues in plants.

Deficiency diseases - Scurvy and rickets

• A deficiency disease develops when the diet is short of a particular nutrient over a long period, so the body can't carry out the processes that depend on it.
• Two examples come directly from missing nutrients.

Scurvy

• Caused by a lack of vitamin C.
• Without enough vitamin C, the body can't repair its tissues properly.
• Symptoms include:
  • Bleeding gums
  • Wounds that heal poorly
  • Pain, especially in the legs

Rickets

• Caused by a lack of vitamin D, or of calcium, or of both.
• Vitamin D is needed for the body to absorb calcium, and calcium is needed to make bones hard and strong - so a shortage of either leads to weak, soft or brittle bones.
• In children: bones can become deformed, along with bone pain.
• In adults: a shortage of vitamin D or calcium can also cause brittle bones and bone pain.