Four reasons BGLs fluctuate

Monday, 4 March 2019

There are four common causes that make our blood glucose levels fluctuate and each can have an impact on the management of your diabetes. Find out just how food, physical activity, medication and illness can impact your BGL’s.

Food intake

The type and quantity of food you eat (particularly carbohydrates) affect your blood glucose levels. All carbohydrates are broken down into glucose in the body. The effect of a meal on blood glucose levels will depend on the quality (type) and the quantity (amount) of the carbohydrates in the meal.

  • Quality: Nutrient-rich carbohydrate foods (e.g. fibre-rich chickpeas) break down into glucose more slowly so blood glucose levels rise slowly, keeping you feeling fuller for longer. These foods are referred to as lower glycaemic index (GI) foods. Highly processed, high GI foods digest and absorb into the bloodstream quickly, which causes large, rapid changes in blood glucose levels.
  • Quantity: If you can keep the amount of carbohydrates you eat at meals and snacks consistent throughout the day, you may find your blood glucose levels become steadier and easier to manage.

A general guide would be two to four serves of carbohydrate (30-60 grams of carbohydrate) at main meals and one to two serves (15-30 grams of carbohydrate) for snacks.

Physical activity

There are many benefits to being physically active such as helping to manage your blood glucose levels, reducing the risk of diseases such as stroke and heart attack, assisting with weight management, increasing strength and helping to keep you happy.

When you exercise your muscles need glucose for energy.  This energy comes from glucose in the blood and stored glucose (in muscles and the liver). Physical activity can lower your blood glucose levels for up to 48 hours after exercise as your body become more sensitive to insulin. If you are on insulin or other glucose lowering medications check your blood glucose levels before, during and after exercise to ensure they are not dropping too low. It is important to always carry hypo treatment with you.

Some types of exercise can temporarily increase blood glucose levels for one to two hours before they settle again and are not a cause of concern. The increase is due to a stress response in the body which often happens during short and intense exercise, or team sports.


When you are sick, even with a simple cold, your blood glucose levels can fluctuate quite a lot. Sickness causes stress hormones to be released by your body. These hormones trigger the liver to increase the amount of glucose in your blood and your body’s insulin becomes more resistant. Both of these things can make it more difficult to control your blood glucose levels. Some illness such as vomiting and diarrhoea can cause blood glucose levels to drop. See your doctor if this happens as your blood glucose levels may become too low.

If you are sick it is important to see your doctor to treat the underlying sickness that is causing the blood glucose level fluctuations. Also if you have a sickness plan, start to follow it. Keep eating and drinking to avoid dehydration and low blood glucose levels

Some medications

One of the most common medications which affect blood glucose levels are steroids. These medications typically increase blood glucose levels as they reduce the action of insulin and also cause the liver to release stored glucose into the blood stream. Steroid medications are often used to treat asthma, arthritis and dermatitis. Sometimes a person undergoing chemotherapy may be prescribed steroids to reduce nausea.

If you are given steroid medications make sure that you discuss with your doctor how to manage the effect they may have on your blood glucose levels. Similarly if you start on any new medication and you notice changes in your blood glucose levels speak with your doctor.

Beta blockers may mask some signs of hypoglycaemia such as a rapid heartbeat so blood glucose levels should be checked regularly if you are taking beta blockers. Discuss this side effect with your doctor if you have concerns.

For more information on any of these topics, please call the Helpline on 1800 637 700 and ask to speak with a health professional – dietitian, exercise physiologist or diabetes educator.

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