Why we need food?

1. To supply us with a fuel for energy

2. To provide materials for growth and repair of tissues

3. To help prevent disease and keep our bodies healthy

• Diet : the food we eat

• Balanced diet : right amount of each substances in correct proportion

• Nutrient deficiency disease : a lack of particular nutrients

Nutrients

1. Carbohydrates

2. Proteins

3. Lipids

4. Minerals

5. Vitamins

6. Dietary fibre

7. Water

Carbohydrates

Elements (Carbon, Hydrogen, Oxygen)

Monosaccharides- glucose, fructose (fruits)

Disaccharides- sucrose ( ordinary table sugar), lactose (milk)

Polysaccharides- starch (plant tissues), glycogen (animal tissues)

Made up 1% of the body mass

Need about 50% of the daily energy needs, less than 5% coming from sugars

Lipids

Elements (Carbon, Hydrogen, Oxygen)

Fat - solids (common in animals)

Oil - liquids (common in plants)

A molecule of glycerol is joined to three fatty acid molecules.

Glycerol (Glycerine) : an oily liquid

Made up about 10% of body mass

Long term store of energy (heart/kidneys)

Fat layer under skin (insulation) reducing heat loss

Fat around organs (kidney, protect from mechanical damage)

Too much cholesterol(saturated fat)(get from meat/eggs) - unhealthy - heart disease

• Unsaturated lipids (plant) are healthier than saturated ones

Need less than 35% of the daily energy needs

Proteins

Elements- Carbon, Hydrogen, Oxygen, Nitrogen, Sulfur (2 amino acids contain)

Made from 20 different amino acids

Essential amino acids

Amino acids are linked together in long chains, which are usually folded up or twisted into spirals

Made up about 18% of the body mass

Need daily 0.75g per kg body weight

• 60kg, 60 × 0.75 = 45g of protein per day

deficiency disease : kwashiorkor

Minerals

Calcium (1000g) making teeth and bones

Phosphorus (650g) making teeth and bones, part of DNA

Magnesium (30g) making bones, found inside cells

Iron (3g) part of haemoglobin in RBCs, helps carry oxygen

Sodium (100g) in body fluids

Chlorine (100g) in body fluids

Mineral deficiency disease

Rickets - the bones become deformed (calcium, vitamin D)

Anaemia - tried, lacks energy, blood doesn’t carry enough oxygen (iron)

Vitamins

A(0.8mg) making a chemical in retina, protects the surface of eye

• deficiency

1. night blindness (long-term - total blindness and death)

2. damage to cornea of eye

B1(1.1 mg) helps with cell respiration

• deficiency: beri-beri (weakening of muscles and paralysis)

B2(1.4mg) helps with cell respiration

• deficiency: poor growth, dry skin

B3(16mg) helps with cell respiration

• deficiency: pellagra (dry red skin, poor growth and digestive disorders)

C(80mg) sticks together cells lining surfaces

• deficiency: scurvy (wounds fail to heal, bleeding, noticeable in gums)

D(5 micrograms) helps bones absorb calcium and phosphate

• deficiency: rickets, poor teeth

Energy from food

The energy content depends on the proportions of carbohydrates, proteins and lipids that a food contains.

You need a supply of energy even you are asleep. To keep warm, to keep the heart beating, to allow messages to be sent through nerves, for other body functions.

The energy requirements vary with age, sex and pregnancy.

The content of diet also vary.

• Younger women need extra iron in their diet (lost blood during menstruation)

• Women who are breast-feeding need larger amounts of calcium (milk production)