The gut, or digestive tract, is where the food we eat is broken down (digested) and absorbed into the blood. The key food groups are fats, carbohydrates and proteins; vitamins and minerals are also required for a healthy diet and of course we need water too.
Examples of foods that are mainly protein are meat, fish, pulses and soya products. Fats, including butter and oil, are found in a range of foods, such as cheese and cream. Carbohydrates are found in bread, potatoes, rice and pasta, as well as within sugary foods and drinks. Vitamins and minerals are found in many foods, especially fruit and vegetables.
Within the gut, chemicals known as enzymes break down food into smaller components. Fats are broken down into fatty acids, carbohydrates into glucose, and proteins into amino acids. These smaller components can then be absorbed through the wall of the small intestine and transported in the blood to various parts of the body to provide energy or to be used as building blocks for growth (Figure 3). The level of glucose in the blood is altered by what and how much we eat.
Question: Which do you think will result in more glucose in the gut: a carbohydrate-rich meal, or a protein-rich meal?
If you eat a meal that is mainly carbohydrate you will produce more glucose in the gut to be absorbed than if you eat a meal that is mainly protein.
When you read food labels you will find that some foods list sugars as glucose or fructose. Fructose is a sugar, like glucose. Unlike complex carbohydrates, these simple sugars do not need breaking down as they are already in the required small units and so can be absorbed easily and quickly.
The speed with which food is broken down and absorbed depends on the combinations of food eaten and their exact composition. People with diabetes often notice that eating a mixed meal that includes protein, fat and carbohydrate has a different effect on their blood glucose levels compared with a meal that consists of carbohydrate alone. Try Activity 2 below in order to think about this further.
Activity 2: The effect of drinking a sugary drink
Make brief notes on the effect that a drink containing a lot of sugar such as glucose might have on the blood glucose level of an individual without diabetes. Examples of high-sugar drinks that you may know are Lucozade® and non-diet Coca-Cola®.
In people without diabetes the blood glucose levels are kept tightly controlled. Before a meal the blood glucose level is between 4 and 7 mmol/l. (Pronounced milly-moles per leeter, mmol/l is a unit of measurement, often used for substances within the blood. It represents the amount of substance per litre of blood.) After a meal the blood glucose usually peaks at less than 11 mmol/l. Drinking a sugary drink causes glucose to enter the blood quickly as it does not need to be broken down in the gut. The glucose makes the pancreas produce insulin, which will control the blood glucose level. Without diabetes the level of blood glucose usually remains less than 11 mmol/l and drops back to its baseline level of about 4–7 mmol/l within a couple of hours.
In people who are diagnosed with diabetes, the term hypoglycaemia refers to the condition where the blood glucose level falls below 4 mmol/l and hyperglycaemia to the condition where the blood glucose level rises above 11 mmol/l.