Blood Glucose

Your body breaks down every carb you ingest into glucose, also known as blood sugar because it travels through your bloodstream.^[1] Glucose is a simple sugar — more precisely, a monosaccharide (mono meaning single and saccharide meaning sugar). To store glucose, your body combines the molecules into a polysaccharide (poly meaning several) called glycogen, which gets stored in your liver and muscles.

Insulin (a hormone produced by your pancreas) rises when blood glucose rises;^[2] it lowers blood sugar by telling various cells to absorb it — for storage in your liver or muscles or for immediate use — and your liver to stop producing new glucose.^[3]

The ability of cells to absorb glucose in response to insulin is called insulin sensitivity, and low insulin sensitivity is called insulin resistance. The more sensitive you are to insulin, the less resistant, and vice versa.

It is also possible to produce too little insulin. If you have type 1 diabetes or are in the late stages of type 2 diabetes, in which case you suffer from insulin deficiency, glucose can’t be removed efficiently from your blood, causing hyperglycemia (overly high glucose levels).^[4]

Insulin resistance paves the way for type 2 diabetes, which can cause your blood sugar levels to consistently remain too high for too long. If not managed, these high blood sugar levels can lead to serious health complications — mostly cardiovascular diseases,^[5] but probably cancer, Alzheimer’s, and Parkinson’s as well.^[6][7][8]

Glycemic control can be tested several ways, each with its own cutoff values indicating impaired glucose regulation.^[9] Of these tests, fasting blood glucose is the most common, followed by hemoglobin A1C (HbA1c).

Methods of glycemic-control measurement

Fasting Plasma Glucose

Fasting plasma glucose (FPG), also known as fasting blood glucose, is simply a measure of how much glucose is floating around in your blood during a fast. After at least 8 hours of not eating (typically in the morning, before breakfast), blood is drawn and analyzed for glucose concentration.

Hemoglobin A1c

Hemoglobin A1c (HbA1c), or glycated hemoglobin, is a marker of blood-glucose metabolism that estimates the average amount of glucose in your blood over the past 3 months.

The protein that carries oxygen throughout your body, called hemoglobin, is in red blood cells, which live for about 4 months. Glycation is when a sugar — in this case, glucose — is linked to a protein or lipid — in this case, hemoglobin. When blood glucose levels rise, the rate of hemoglobin glycation increases, making glycated hemoglobin an estimate of blood glucose levels over months.

Acute glycemia

There are two types of acute glycemia tests, the more common being the oral glucose tolerance test (OGTT). It involves consuming a specially formulated drink that typically contains 75 grams of glucose and then measuring blood glucose levels at regular intervals over 2 hours. The last blood sample taken is the one used to diagnose.

In short, the OGTT measures your ability to clear a whole lot of glucose from your bloodstream. It has the advantage of being standardized and easy to administer, but it doesn't accurately reflect the body's response to typical individual mixed-macronutrient meals, which vary by meal and by day.

The other type of acute glycemia test is a postprandial test, which uses real food. The exact same meal is eaten before each measurement. This test is often used to test pharmaceuticals and supplements that may work by reducing the glycemic index (GI) of a meal. The lower the GI, the less it raises your blood glucose.

Random Plasma Glucose Test

For the random plasma glucose test (RPGT), or causal test, a blood sample is taken if signs of diabetes are present. The test can be done anytime. As with the last blood sample of an OGTT, a value of 200 mg/dL or more (>11.0 mmol/L) is considered high.

Continuous monitoring

Continuous glucose monitoring (CGM) is where a small monitor is kept in a vein and blood glucose levels are sampled every ≈5 minutes. The CGM monitor can be wirelessly connected to a small medical device or cell phone to notify the wearer if their blood sugar falls too low or rises too high. All diabetics can use CGMs, but they’re most commonly used by those with type 1 diabetes.

Notably, a CGM makes it possible to assess glycemic variability. This is important, because research suggests that glucose swings increase oxidative stress, which is a risk factor for diabetic complications, independent of average glucose levels.^[10][11][12]

What are the symptoms of abnormal blood glucose levels?

Symptoms of abnormal glucose levels are different from person to person and may not even be present until the levels are very high or very low. Generally, blood sugar symptoms may show up when levels fall below 70 mg/dL (3.9 mmol/L) or over 180 mg/dL (10 mmol/L).

Supplements

Supplements that have been shown to have a positive effect on blood sugar regulation mostly do so by either improving insulin signaling or insulin sensitivity or decreasing the rate and amount of glucose absorbed into the body. Some notable supplements include fiber, berberine, inositol, and zinc.

The table below displays an analysis of human studies and indicates how supplements may affect blood glucose.

Diets & foods

Across numerous observational studies, grains, vegetables, fruits, and dairy have been consistently associated with decreasing the risk of type 2 diabetes.^[13]

Multiple randomized controlled trials (RCTs) have come to similar conclusions.^[14]

• Nuts, grains, legumes, and dairy provided the greatest fasting blood sugar reductions.

• Grains, legumes, nuts, fish, fruits, and vegetables improved HOMA-IR (a measure of insulin sensitivity) the most.

• Grains, legumes, fruits, vegetables, and nuts provided the greatest blood sugar reductions in HbA1c tests.

Listed from most to less potent, grains, nuts, legumes, fruits, and vegetables had the greatest impact on improving overall blood sugar control.

Lifestyle

The major cause of abnormally high blood glucose is excess calorie intake and the resulting increase in fat mass. Unsurprisingly, weight loss can help. One review found that weight loss from all kinds of interventions — surgery, appetite-suppressing medicines, lifestyle interventions, or a combination — alleviates diabetes.^[15]

Surprisingly, many long-term studies that used diet alone to achieve weight loss reported only modest improvements in diabetes, probably because few achieved substantial long-term weight loss.^[16] Moreover, exercise in itself can help reduce the risk and severity of type 2 diabetes.^[17][18][19]

Exercising regularly and maintaining a healthy weight are the two major pillars of metabolic health, but insulin resistance can be complex. As a result, the basics may not always cut it, and what’s effective for one person may not be for another. Unfortunately, researchers are often unable to explore differences between individuals, leaving diabetics to fight their disease through trial and error based on what’s effective for the majority.

Medical conditions & considerations

Stress, illness, physical trauma, and dehydration can do some strange things to your blood sugar levels. Menstrual cycles and pregnancy may also throw off your blood sugar.

Injury to the pancreas, where insulin is produced, can lead to hyperglycemia, as can hormone disorders such as Cushing’s syndrome (excess cortisol in the body), pheochromocytoma (a usually benign tumor in an adrenal gland), hyperthyroidism (high thyroid levels), and acromegaly (excess growth hormone that causes abnormally large features).

Drugs

Insulin is perhaps the most well-known and widely used drug to regulate blood sugar levels. But even commonly consumed legal drugs, such as alcohol and caffeine, can have an effect.