Glucose is the primary energy source in the body, especially for the brain and red blood cells. Before the body can make use of the food that is eaten, it must be ‘digested’, meaning it must be broken down into its basic parts. The digestive system works like a giant food processor. This system is made up of a group of body parts called organs that work to break food down both mechanically and chemically. This breaks down food into 'nutrients', which are building blocks that the cells can use for growth, repair, and energy. These simple units can then easily cross from the intestine into the blood stream by a process called 'absorption'. From here they can be distributed all around the body. Here is how we track the digestion of carbohydrates through the human body:

Human Digestive System diagram

Mouth

  • Carbohydrates are eaten as sugars and starches
  • Teeth tear and chop food and saliva moistens it for easy swallowing
  • Saliva contains a digestive enzyme called amylase, which begins to break down some of the carbohydrates
  • Waves of muscle contractions called peristalsis push food down through a muscular tube called the esophagus into the stomach

Stomach

  • Chewed carbohydrate mixes with stomach juices
  • The stomach processes food into a thick liquid called chyme
  • Chyme empties into the small intestine

Pancreas

  • The pancreas releases digestive juice into the small intestine 
  • Different types of enzymes in the digestive juice break down starches and sugars into single molecules such as glucose that are then absorbed by the small intestine 
  • Releases insulin into the blood to inform different parts of the body (like muscles) to take up glucose from the blood for energy 

Small Intestine

  • Enzymes in the small intestine complete the breakdown of starches into sugars. All sugars break down into 3 simple sugars: glucose, fructose and galactose
  • Glucose, fructose, and galactose are absorbed into the blood and carried to the liver

Liver

  • The liver releases glucose into the blood to provide immediate energy to the body (cells)
  • Stores sugars for future use, usually as glycogen in liver or muscle or when in excess, as fat, as a secondary fuel source
  • Helps regulate blood glucose and makes glucose from fat, protein, fructose, and other molecules when glucose supply is short

Large Intestine

  • The large intestine receives waste from the small intestine
  • Absorbs water and some vitamins and minerals
  • Processes fibre and stores waste before it is excreted

For more detail on the digestive system, visit the Human Anatomy Online

The Science of Taste

We are connected to the world around us through our five senses. One of their primary jobs is to help us tell if our environment is safe or not. Taste, for example, can help to detect if a food is fresh and good to eat or spoiled and dangerous to our health. A natural liking for foods rich in carbohydrates (starches and sugars) was inherited from our ancestors. These foods not only taste great, they are also full of energy. Primitive people needed a lot of energy to survive in cold weather, on long walks and to get away from animals. Our ancestors were more careful with foods with a bitter or sour taste, like some poisonous plants.

Discovering different flavours in foods is part of what makes eating fun. The tongue contains many bumps, and around the base of these bumps are taste buds. We have about 10,000 taste buds and inside them are special cells that sense taste.

There are different kinds of taste buds, each designed to help taste different sensations. These taste sensations include sweet, salty, bitter, sour, and umami ("savoury" or "meaty"). Some areas of the tongue may be better than other areas in detecting each of these tastes. Taste buds are only activated when food molecules fit the shape of receptors on its surface, much like a key fits into a lock. The taste bud then sends messages to the brain where they are decoded and registered as a 'taste'. Sweet and salty taste buds are the least sensitive, while bitter ones are most sensitive.

With regards to taste, sugars are mostly described in terms of their sweetness. Fructose, one of the sugars found in fruit, is the sweetest. Sucrose or table sugar is less sweet than fructose but sweeter than lactose, a sugar found in milk. Common sugars are listed below in order of sweetness. Keep in mind that sweetness can also vary depending on the form of the sugar (solid or in solution), concentration, temperature, presence of other ingredients, and the taste differences between individuals.

Most Sweet         Least Sweet
Fructose >  Sucrose >  Galactose >  Glucose >  Maltose >  Lactose

Polysaccharides are longer chains of saccharide units. However, starchy foods such as potatoes, pasta, breads and beans, do not taste sweet. This is due to the large structure of the polysaccharides, which do not fit on the tongue’s taste bud receptors, thus resulting in a perceived lack of sweetness. Starchy foods, however, can be broken down into smaller saccharide units, such as sucrose, that can taste as sweet. For example, place a cracker in your mouth for a while. As the digestive process in your mouth begins to break down the starch molecules, you will begin to notice a sweet taste as they become smaller saccharide units.

For more information on Taste buds, visit www.kidshealth.org/kid