Fasting blood sugar levels give vital clues about how a person’s body is managing blood sugar. Blood sugar tends to peak about an hour after eating and declines after that.
High fasting blood sugar levels point to insulin resistance or diabetes, while abnormally low fasting blood sugar could be due to diabetes medications.
Knowing when to test and what to look for can help keep people stay healthy, especially if they have diabetes or are at risk of developing the condition.
The body needs glucose for energy, and glucose comes from the food we eat. However, the body does not use all of this energy at once. Insulin makes it possible to store and release it as necessary.
Following a meal, blood sugar levels rise, usually peaking about an hour after eating.
How high blood sugar rises, and the precise timing of the peak depends on the person’s diet.
Factors relating to food that can trigger significant rises include:
As blood sugar rises, the pancreas releases insulin. Insulin lowers blood sugar, breaking it down so that the body can use it for energy or store it for later.
However, people who have diabetes have difficulties with insulin in one of two ways:
In both cases, the result is the same, with people experiencing high blood sugar levels and difficulty using glucose, or blood sugar.
This means that fasting blood sugar depends on three factors:
Blood sugar levels between meals offer a window into how the body manages sugar. High levels of fasting blood sugar suggest that the body has been unable to lower the levels of sugar in the blood.
This points to either insulin resistance or inadequate insulin production and, in some cases, both.
When blood sugar is very low, diabetes medications may be lowering blood sugar too much.
There are two methods that individuals or healthcare professionals use for assessing fasting blood sugar levels:
The HbA1c test measures how the body is managing blood sugar over time, usually the last 2–3 months.
The person will undertake this test at the doctor’s office or in a lab. If levels are very high, the individual may need a second test. The results show as a percentage.
HbA1c is the main test that doctors use to manage diabetes.
A person can test their blood sugar levels at home.
In most cases, doctors ask people to measure fasting blood sugar immediately upon waking and before they have anything to eat or drink. It may also be appropriate to test blood sugar before eating or sometimes 2 hours after a meal when blood sugar has returned to normal levels.
The right time to test is dependant on treatment goals and other factors. For example, most people with diabetes do not need to test between meals unless they are using a diabetes drug that can lower blood sugar. Other people may test between meals if they feel their sugar levels may be low.
Since they do not make any insulin, some people with type 1 diabetes need to test several times a day. They do this because they need to check their levels regularly in order to adjust their insulin dose at that time.
To do the blood sugar test, a person will:
Target blood sugar numbers are as follows, in milligrams per deciliter (mg/dl):
However, the target numbers will vary between individuals. A healthcare professional will help a person identify their own target levels.
It is vital to follow a healthful diet to keep fasting blood sugar from rising too high. Strategies include:
People who are taking diabetes drugs and who are at risk of dangerous blood sugar dips should follow a similar diet. They also need to take proactive steps to prevent blood sugar from dropping. Those include:
People are likely to experience symptoms if their blood sugar levels are too low or too high.
Symptoms of unhealthy fasting blood sugar may include low energy, tiredness, and headaches.
Blood sugar that is too low can cause symptoms such as:
In extreme cases, low blood sugar can trigger seizures, loss of consciousness, confusion, and the inability to drink or eat.
High blood sugar levels
Very high blood sugar, or hyperglycemia, can cause the following symptoms:
As with low blood sugar, high blood sugar may cause loss of consciousness or seizures if people leave them untreated. Persistent high levels can increase the risk of serious complications that doctors relate to diabetes, such as cardiovascular disease.
If a person’s blood sugar levels are high more than three times in a 2-week period without an apparent reason, the National Institute for Diabetes and Digestive and Kidney Diseases (NIDDK) recommend that they seek medical help.
Any significant change in blood sugar patterns warrants a visit to a doctor. People with diabetes and those at risk of diabetes should also consult a doctor if:
Diabetes needs ongoing monitoring, and the treatment can change over time. Information about diet and exercise is vital to enable a doctor to outline a proper treatment plan for each person individually.
People with diabetes can assist their doctor by keeping detailed logs and being transparent and accurate about dietary or lifestyle changes.