Glossary: Glycaemia

Glucose is the main sugar found in the blood and the body's main source of energy. Blood glucose, sometimes called blood sugar, is particularly important for the brain, which cannot use any other form of energy. Therefore, the body tries to keep blood glucose at a relatively constant level. Blood glucose concentration is the amount of glucose in a given amount of blood. It is most commonly measured as millimoles per litre (mmol/L) or milligrams per decilitre (mg/dL).

Fasting blood glucose 

Blood glucose often rises slightly after eating, the amount it rises by depends on the food eaten and the body’s insulin response. As such, measuring blood glucose after food can give quite varied results. Therefore, to assess whether an individual has a healthy blood glucose level, measurements are often taken after fasting. Fasting is defined as 8 hours or more without food or drink (other than water). A normal fasting blood glucose level is ≤5.6 mmol/l; fasting glucose of 6.1 mmol/l or higher may indicate insulin resistance or type 2 diabetes mellitus. 

Postprandial blood glucose 

Plasma glucose concentration following a meal. This is often measured to assess how a particular food or meal affects blood glucose or to help diagnose insulin resistance or diabetes mellitus.

Type 1 and Type 2 diabetes mellitus

• Type 1 diabetes mellitus: an auto-immune disease whereby the body’s natural defence system attacks the pancreas. As a result, the β-cells in the pancreas which produce insulin are destroyed. Without enough insulin, the body is unable to control blood glucose levels. Type 1 diabetes mellitus is managed by injections of insulin. 
• Type 2 diabetes mellitus (T2DM): In the early stages of T2DM, the body’s cells become less sensitive to the action of insulin (called insulin resistance) and so blood glucose levels remain high after eating carbohydrates. As a result, the pancreas produces more insulin to help lower blood glucose. However, over-time this increased demand for insulin can damage the insulin-producing β-cells in the pancreas. The pancreas is unable to maintain enough insulin production. Consequently, blood glucose levels are not controlled and can become too high. The cause of this disease is complex and is often a mix of genetic, diet and lifestyle factors.

Gestational diabetes 

Gestational diabetes is high blood glucose that develops during pregnancy and usually disappears after giving birth. It can happen at any stage of pregnancy but is more common in the second or third trimester. It happens when the body cannot produce enough insulin to meet the extra needs in pregnancy. Gestational diabetes can cause problems for mother and baby during pregnancy and after birth. However, the risks can be reduced if the condition is detected early and well managed. 

Impaired glucose tolerance 

Sometimes called pre-diabetes or impaired fasting glucose. It is a condition in which blood glucose levels are higher than normal, but are not high enough for a diagnosis of diabetes. People with impaired glucose tolerance are at increased risk of developing diabetes, heart disease and stroke.

Fructosamine is a glycated protein, formed when glucose combines with protein in the blood. It can reflect the average blood glucose concentration of the past 2–3 weeks. A high fructosamine level means the average blood glucose over the previous 2 to 3 weeks has been elevated above normal levels.

A hormone produced by the cells in the pancreas, called alpha cells. It helps to break down glycogen, raising blood glucose.

The presence, or the level, of glucose in the blood.

Hyperglycaemia 

A physiologically high concentration of glucose in the blood. Clinically this is defined as: Blood glucose levels greater than 7.0 mmol/L when fasting, and blood glucose levels greater than 11.0 mmol/L two hours after a meal. Regularly having hyperglycaemia can damage the vessels and increase the risk of heart disease, kidney disease, nerve and eye damage. 

Hypoglycaemia 

A physiologically low concentration of glucose in the blood. Clinically this is defined as: Blood glucose levels below 4 mmol/L. Hypoglycaemia most often occurs in people with diabetes mellitus, especially if they use insulin. If left untreated, it can affect the functioning of the brain and lead to an individual collapsing or having a seizure.

Glycaemic index (GI) is a rating system for foods containing carbohydrates. It represents how quickly a food affects blood glucose levels when that food is eaten on its own. Carbohydrate foods that are broken down quickly by the body, and that cause a rapid increase in blood glucose, have a high GI rating.

High GI and low GI foods

High GI foods include white bread, potatoes, and white rice. Lower GI foods include wholegrain foods, most fruits and vegetables, beans, and lentils. Sugar has a medium GI.

To assess dietary GI, foods from an individual’s dietary assessment (e.g. food diary) are assigned a GI rating to provide an overall score.

Standard method for a GI test to calculate the GI value of a food 

At least ten healthy participants are tested. The test food and a standard food are consumed on separate occasions. The portion of available carbohydrate in both should be the same (often set at 50 g). The standard food is typically glucose in water, or white bread. Blood sampling times should be at 0 min (baseline sample), followed by measurements at 15, 30, 45, 60, 90 and 120 min after the consumption of the test or standard food. Data from all participants is averaged, and the incremental area-under the curve (IAUC) is calculated, which indicates how much the food increased blood glucose. GI is then calculated using the IAUC values.

Research has shown that it is the amount of carbohydrate, rather than its GI rating, that has the biggest influence on blood glucose levels after meals. Therefore, glycaemic load (GL) is often used. GL is a measure that considers the amount of carbohydrate in a portion of food together with how quickly it raises blood glucose levels (GI). GL is calculated from the GI value of a food as follows: GL = [GI × total available carbohydrate in a standard portion of the test food]/100 To assess dietary GL, foods from an individual’s dietary assessment (e.g. food diary) are assigned a GL rating to provide an overall score.

Glycated haemoglobin is formed when the glucose combines with red blood cells. High blood glucose causes more glycated haemoglobin to form. Therefore, a high glycated haemoglobin level means the average blood glucose over the past 8–10 weeks has been elevated.

Glucose in stored in the body in the form of glycogen. It is large multi-branched polymer of glucose which is accumulated in response to the hormone insulin and broken down into glucose in response to the hormone glucagon. Glycogen is mainly stored in the liver and the muscles and provides the body with a readily available source of glucose, for energy production, if blood glucose levels decrease.

The presence of glucose in the urine. Normally, glucose filtered through the kidney is reabsorbed into the blood and doesn’t appear in the urine. However, when blood glucose is particularly high or when the kidneys aren’t working properly (kidney disease) glucose can appear in the urine.

A hormone secreted by the pancreas that plays a key role in the regulation of blood glucose levels. Insulin regulates how the body uses and stores glucose and fat.

Hyperinsulinemia
A higher than normal level of insulin in the blood.

Insulin resistance & insulin sensitivity 
Insulin sensitivity describes how sensitive the body is to the effects of insulin. People with low insulin sensitivity, also referred to as insulin resistance, will require larger amounts of insulin either from their own pancreas or from injections in order to keep their blood glucose stable.

Ketones are compounds that are produced by the liver from fatty acids. They are produced during periods of low food intake (fasting), carbohydrate restrictive diets, starvation, prolonged intense exercise, or in untreated (or inadequately treated) type 1 diabetes mellitus.

Ketonemia 

The presence of ketone bodies in the blood. An abnormally high level of ketones indicates that the body lacks insulin and/or carbohydrates. Ketonemia often occurs when a person is hypoglycaemic or fasting. 

Ketonuria 

The presence of ketone bodies in the urine. An abnormally high level of ketones indicates that the body lacks insulin and/or carbohydrates. This can occur when a person is hypoglycaemic or fasting.