Carbohydrates

• What are Macronutrients

  • Humans require nutrients in large quantities each day
  • Macro (means ‘large’)
  • Measured in grams (g) 
  • Provide differing amounts of energy 
  • While water is required in large proportions every day, it does not provide energy and is therefore not considered a true macronutrient
• Structure and Classification of Carbohydrates

  Made from combinations of the elements Carbon, Hydrogen and Oxygen (CHO) 

  Atoms of these elements arrange into a variety of structures called saccharides. 

  The carbohydrate saccharides we consume include: 

  • Monosaccharides (single unit)
  • Disaccharides (double unit of two joined monosaccharides)
  • Oligosaccharides (small number of joined monosaccharides, typically three to ten)
  • Polysaccharides (long linear or highly branched chains of many joined monosaccharides).
• Simple Carbohydrates

  • Monosaccharides and disaccharides are Simple carbohydrates (sugars) 
  • Consist of only one or two sugar units (saccharides) – smaller in size & therefore easily absorbed 
  • Each monosaccharide contains 6 carbon atoms, 12 hydrogen atoms & 6 oxygen atoms, which can be written in shorthand as C6H12O6
  • The monosaccharides include:
  • Glucose
  • Fructose
  • Galactose
  • The disaccharides include:
  • Maltose (glucose + glucose)
  • Sucrose (glucose + fructose)
  • Lactose (glucose + galactose)
• Monosaccharides

  • “Simple” sugars
  • Chemical formula: C6H12O6
  • Simplest forms of carbohydrates
  • Cannot be broken down into another simpler form, contributing to its quick release into the bloodstream
  • Sweet to taste 
  • the difference in arrangement of atoms results in different levels of sweetness 
  • Soluble in water
  • Most common referred to as:
  • Glucose
  • Fructose
  • Galactose
• Glucose

  • “blood sugar”
  • Most carbohydrates are converted into glucose
  • During digestion, carbohydrates are broken down into their simplest sugars to allow for absorption into the bloodstream and transportation to all the body’s tissues.
  • Quick energy source
• fructose

  • “Fruit” sugar
  • Sweetest of sugars
• Galactose

  • Formed from the digestion of lactose (present in milk)
• Disaccharides

  • Formed by the joining of two monosaccharides and removal of a water molecule
  • Double sugars “di”
  • Still considered simple sugars
  • Digestion required only one bond between monosaccharides to be broken
  • How atoms are linked affects its properties
  • Each has its own digestive enzyme to break it down
  • Sucrase 🡪 sucrose
  • Maltase 🡪 maltose
  • Lactase 🡪 lactose
  • Sweet to taste (can vary in strength)
  • Soluble in water

  Chemical formula: C12H22O11
• Most Common Disaccharides

  • Sucrose (glucose + fructose) 
  • Lactose (glucose + galactose) 
  • Maltose (glucose + glucose) 
• Condensation

  • To make a disaccharide, a chemical reaction known as condensation links two monosaccharides together. A hydroxyl (OH) group from one monosaccharide and a hydrogen atom from the other combine to create a molecule of water. The two originally separate monosaccharides link together with a single oxygen.
  • A carbon on one monosaccharide bonds to an oxygen on another, releasing a molecule of water
• Hydrolysis

  • Hydrolysis is the opposite and splits apart a disaccharide through the addition of water and often under activity of an enzyme. Disaccharide bond breaks by adding a hydrogen and hydroxyl group.
  • The disaccharide bond breaks, and a water molecule supplies the H and OH necessary for the existence of two complete monosaccharides
• Complex Carbohydrates

  • Oligosaccharides (3-10) + polysaccharides (many)
  • Larger in size especially the polysaccharides, which may be composed of several hundred thousand joined glucose molecules
  • Breakdown of these saccharides into monosaccharides take longer – therefore absorbed into the bloodstream at a slower rate
• Oligosaccharides include

  • Galacto oligosaccharides: Raffinose and Stachyose
  • Fructo oligosaccharides: ketose and nystose
• Polysaccharides Include

  • Starch 
  • Resistant starch
  • Glycogen 
  • Soluble and Insoluble Fibre
• Oligosaccharides

  • Contains 3-10 singular units 
  • ‘oligo’ means ‘just a few’ 
  • Not relatively abundant in the diet compared to other carbohydrates
• Polysaccharides

  • less than singular sugar units 
  • ‘poly’ means ‘many’
  • Most complex CHO due to their length and most abundant in CHO found in food
• Glycogen

  • Your body mainly uses the store of glycogen in your liver to help regulate your blood glucose (sugar) levels. 
  • Your body normally carefully regulates your blood glucose primarily with the hormones, glucagon and insulin. When your blood glucose levels fall too low (hypoglycaemia), your pancreas releases more glucagon.
• Liver Glycogen

  • Use as a short term energy source for the organism by providing a means to store and release glucose in response to blood glucose levels; liver cells do not use this glucose for their own energy needs
• Muscle Glycogen

  • Provides a readily available source of glucose during exercise to support anaerobic and aerobic energy conversion pathways within muscle cells; muscle cells lack the enzyme glucose 6 phosphate and therefore cannot release glucose into the blood
• Fructose

  Fruit, fruit juices, sweet wines and honey
• Sucrose

  Cane sugar, sugar beets
• Glucose

  Honey, sweets, syrups, foods with added glucose such as soft drinks, chocolate, desserts 
• Galactose

  Milk, seaweed
• Maltose

  Some cereals and sweets, when foods high in starch undergo processing such as cooking the starch can end up being broken down into maltose
• Oligosaccharides

  Found naturally in onion group 

  Can be added to foods such as cereals and yoghurts as inulin
• Lactose

  Found naturally in the dairy group (milk, cheese) making it the only carbohydrate that doesn’t come from plants.
• Starch

  Found naturally in foods such as oats, rice, legumes, corn and root vegetables. It is used as a primary ingredient in cereals, breads and pasta.
• Soluble Fibre

  Found naturally in the pith (flesh of vegetables), oats, legumes and soy products. Can be added to many fibre-enriched/ fortified foods, such as bread.
• Insoluble fibre

  Found naturally in foods such as bran, nuts, seeds, the skin of fruits and vegetables. Can be added to many fibre enriched/ fortified foods such as bread.
• Source of Energy

  • The primary function of simple carbohydrates and starch is to provide energy (16.7kJ/g)
  • Simple carbohydrates and starch are broken down and converted into glucose after consumption. 
  • Once glucose is absorbed into the bloodstream, it is transported to cells and broken down further to create energy in the form of adenosine triphosphate (ATP) through a process of cellular respiration. 
  • The brain can only use glucose (~120g/day) to produce ATP to provide energy – glucose is the body’s preferred glucose
• Simple Carbohydrates

  • Both monosaccharides and disaccharides (need one bond broken down) can enter the blood stream quickly and are associated with a rapid rise in blood glucose levels and therefore a rapid release of energy 
  • Foods or beverages consumed that produce this blood glucose response are known to have a high glycaemic index
• Complex Carbohydrates

  • Starch on the other hand is a larger molecule made of a hundred glucose units bonded together 
  • Takes longer to break down into glucose and therefore longer to be absorbed in the blood stream 
  • This results in a lower and more gradual elevation in blood glucose levels and therefore sustained energy. 
  • Low glycaemic index (low GI) 
• A Component of the Cell Membrane

  • Blood glucose can also be used for a structural role, as part of the cell membrane 
  • Glucose molecules bond together and form short term oligosaccharides on the exterior of the cell membrane 
  • The role of oligosaccharides is cell recognition which is when the body recognises its own cells in contrast to those that are foreign such as bacteria and viruses.
  • Oligosaccharides are 3-10 glucose molecules joined together
• Oligosaccharides

  Carbohydrates that cannot be broken down into glucose and absorbed into the blood stream
• Resistant starch

  Carbohydrates that cannot be broken down into glucose and absorbed into the blood stream
• Soluble fibre

  Carbohydrates that cannot be broken down into glucose and absorbed into the blood stream
• Achieving efficient nutrient absorption and satiety

  1. Carbohydrates bind with water

  2. Partly dissolve to create a gel-like substance in the stomach

  3. Addition of water causes expansion in the stomach

  4. Slows initial digestion

  5. Maximises absorption of nutrients
• Expansion of the stomach

  Slows the rate of food emptying from the stomach into the smaller intestine
• Slowed absorption of monosaccharides

  Provides a gradual release of blood glucose, aiding in blood glucose levels
• Expansion of the stomach

  Keeps the body feeling fuller for longer (satiety)