Human Nurition

• All living organisms need food
• Balanced diet


  A diet that contains all the essential nutrients in the correct proportions to maintain good health
• Nutrients needed in a balanced diet

  • Carbohydrate
  • Lipid
  • Protein
  • Vitamins
  • Mineral salts
  • Fibre (roughage)
  • Water
• Carbohydrates and lipids


  Provide energy
• Protein


  Provides essential amino acids to make new cells and tissues for growth or repair
• Food samples


  • whole-meat
  • white fish meal
  • bread
  • baked beans
• The percentage of water includes any salts and vitamins. There are wide variations in the composition of any given food sample according to its source and the method of preservation and cooking
• Energy requirements


  Enough to keep internal body processes working, maintain body temperature, and allow work and other activities
• One gram of carbohydrate or protein can provide 16 or 17 kJ (kilojoules). A gram of lipid can give 37 kJ
• We need to obtain about 12000 kJ of energy each day from our food
• Energy requirements


  • Depend on age, occupation and activity
  • Females usually have lower energy requirements than males
  • Metabolism tends to slow down with age
• Classes of food


  • Carbohydrates
  • Proteins
  • Lipids
• Carbohydrates


  Sugar and starch are important carbohydrates in our diet. They are a cheap and readily available source of energy
• Cellulose


  A carbohydrate in plant cell walls that we cannot digest but is important as fibre (roughage)
• Lipids


  Used in cells to make part of the cell membrane and other membrane systems. Can be oxidised in respiration to provide energy
• Proteins


  Supply the amino acids needed to build up our own body structures
• Proteins are chemically different from carbohydrates and lipids because they contain nitrogen and sometimes sulfur
• Vitamins


  Organic substances that are vital in small quantities for health, work with enzymes in chemical reactions in cells
• Plants can make vitamins in their leaves, but humans have to eat plants or animals to get them ready-made
• At least 15 vitamins have been identified, grouped into water-soluble and fat-soluble
• Falafel


  A food made of chickpeas, fava beans or both, becoming increasingly popular in vegetarian and vegan diets. It can contain 13.0 g protein per 100 g.
• Use of lipids in the body


  • Storage; source of energy
  • Source of energy (twice as much as carbohydrate)
  • Insulation against heat loss
  • Some hormones
  • Cell membranes
  • Insulation of nerve fibres
• Use of proteins in the body

  • Growth
  • Tissue repair
  • Enzymes
  • Some hormones
  • Cell membranes
  • Hair
  • Nails
  • Can be broken down to provide energy
• Nucleic acids are not digested or broken down for energy, usually they are not built into the body structures, but they are vital in small quantities for health and are needed for chemical reactions in the cells, working with enzymes.
• Plants can make vitamins in their leaves, but humans have to eat plants or animals to get them ready-made.
• Classes of vitamins


  • Water-soluble
  • Fat-soluble
• If any one of the vitamins is missing or deficient in the diet, a vitamin-deficiency disease may develop. The disease can be cured, at least in the early stages, simply by adding the vitamin to the diet.
• Vitamin C


  Present in citrus fruits, blackcurrants, guava, mango and cabbage. Needed to maintain healthy skin and gums. Deficiency results in scurvy.
• Vitamin D


  The only vitamin the body can make when the skin is exposed to sunlight. Helps in the absorption of calcium and phosphorus through the gut wall. Deficiency can lead to rickets in children and increased risk of fractures in adults.
• Mineral ions are sometimes called mineral salts or minerals. They are present in the food we eat and provide elements the body needs in addition to carbon, hydrogen, oxygen, nitrogen, sulfur and phosphorus.
• Iron


  Part of the haemoglobin molecule in red blood cells, needed to carry oxygen around the body. Lack of iron can lead to iron-deficiency anaemia.
• Calcium


  Deposited in bones and teeth, also needed for blood clotting, muscle contraction and nerve impulse transmission. Lack of calcium can lead to rickets and weak, brittle nails and muscle cramps.
• Dietary fibre (roughage)


  • Plant cell walls made of cellulose that we cannot digest, but they help prevent constipation and keep the colon healthy.
• Water


  Makes up about 70% of most tissue, is a vital part of cytoplasm, and is a solvent and transport medium for digested food, salts, vitamins and excretory products.
• We lose water by evaporation, sweating, urinating and breathing, so we have to replace this by taking in water with the diet.
• Calories


  Obsolete unit
• To calculate the energy from 1 g of nut

  1. Divide your answer by the mass of nut you used

  2. This gives a value in J g-¹
• The experiment is not very accurate
• Feeding involves taking food into the mouth, chewing it and swallowing it down into the stomach
• For food to be of any use to the whole body it needs to be digested