Causes & effects of fluctuating blood sugar levels

Updated April 17, 2017

If you have ever suddenly felt tired,had palpitations of your heart, been irritable, had blurred vision or found yourself lacking concentration, you may be experiencing drastic fluctuations in your blood sugar.

Glucose, derived from the carbohydrates you eat, is the source of energy for your body's vital processes. Your brain, muscles, digestion and glands are all dependent on this energy for proper function.


Blood sugar refers to the amount of glucose present in the bloodstream which is directly affected by what and when you have eaten.

Your normal blood sugar or blood glucouse (BG) before a meal (fasting BG) is 83 mg/dl (4.6 mmol/L) or less. If you fasting BG is in the range of 90 mg/dl (5 mmol/L), it may indicate diabetes even though you are yet to be diagnosed with the disease.

If you are healthy, your normal after meal BG (postprandial) level is under 120 mg/dl (6.6 mmol/L). "After meal" means one or two hours. A level under 100 mg/dl (5.5 mmol/L) two hours after eating is also normal.


The glycemic index is a measure of the effect of food on your glucose (sugar) levels. 70 or more is considered high, and 55 is low. As an example, most fruits have a low GI of 55 or less, and white rice has a GI of about 70. Compare this to plain sugar which has a GI of 100.

Foods with a high GI quickly elevate your blood sugar levels. Those with a lower GI are considered healthy because a sustained release of energy is better than a quick spike. A quick spike in glucose induces the pancreas to release insulin. This is dangerous for diabetics or those suffering from a high blood sugar condition.

Reasons for Fluctuation

If you are healthy, you blood sugar fluctuates moderately throughout the day. Poor eating habits, missing meals or eating too late will drop your blood sugar levels. This is known as hypoglycaemia.

Hyperglycaemia, or high blood sugar, is due to large amounts of sugar and the consumption of simple carbohydrates (i.e. foods with a high GI). This is dangerous for a diabetic because their bodies don't produce enough insulin to process glucose.

Effects of Fluctuation

Hypoglycaemia (low blood sugar) increases stress and anxiety. In women, it can contribute to an hormonal imbalance causing symptoms such as excessive sweating. Low blood sugar also leads to mood swings, heart palpitations and elevated blood pressures because your body produces of too much adrenalin when your sugar levels fall too low. Other symptoms may include: nervousness, sweating, intense hunger, trembling, weakness and palpitations.

Hyperglycaemia---high blood sugar and as a result high insulin---over an extended period contributes to heart disease and type 2 diabetes because your body cannot maintain high levels of insulin to break down sugars This condition may be referred to pre-diabetes. With this condition, fat accumulates due to insulin resistance and your body's inability to metabolise fat.


Blood sugar is an important nutrient for the brain and other organs, and it fluctuates primarily due to what you eat. With a proper diet, you can control this condition. A high fibre diet slows down the digestion process, giving you a sustained level of sugar. Eat regular meals to maintain blood sugars. If you are prone to swings in your blood sugar, eat smaller meals more often. Natural, healthy foods such as nuts, whole grains and fruits will help regulate your sugars.

Fasting or "starvation" due to missing meals will exacerbate the problem. Avoid caffeine as it lowers blood sugar. Strictly avoid excess salt and refined sugars. Know the GI of foods you regularly consume, and make changes to foods that are high on the index. Follow 'Glycemic Index' in the reference section for GI information.

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About the Author

Asba Lee is a former IT consultant who specialized in network administration and application development. Now a writer and academic instructor, Lee instructs GMAT, GRE and SAT courses. Lee loves to research and writes to learn new things, testing his thoughts and opinions.