Now that we have discussed the different categories of food we now need to understand what happens to that food once we have eaten it.
In order for the food that we have eaten to be useful to our body it needs to be broken down into small molecules which can then easily be absorbed. Large food molecules such as starch, protein and fat are insoluble and cannot dissolve, thus they are unable to pass through the gut wall. On the other hand small food molecules such as glucose, amino acids, fatty acids and glycerol are soluble and can dissolve, thus they are able to pass through the gut wall.
The breakdown of large food molecules into small food molecules is called digestion. Once the food has been digested it dissolves and can then be absorbed through the gut wall into the blood stream. The definition of digestion is as follows: