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Our blood sugar level fluctuates during the day. But it rarely dips low enough to bother people who do not have diabetes.

Do you often get low blood sugar? No, you probably don't

ASK A RESEARCHER: You feel tired, nauseous, and irritable. Low blood sugar, maybe?

“You’re probably just hungry. We can become irritable, stressed, weak, and dizzy if there’s too much time between meals,” says Jøran Hjelmesæth.

He heads the Morbid Obesity Centre at Vestfold Hospital Trust and is a professor at the University of Oslo.

“Having low blood sugar has entered our daily speech as a way of saying we need to eat now. I might say it myself, but it doesn't mean my blood sugar is actually low,” says Hjelmesæth.

When healthy people think they have low blood sugar, they usually haven’t measured it.

“So they don't know if it’s actually low,” says Elisabeth Qvigstad. 

She is an associate professor of medicine at the University of Oslo and senior physician at Oslo University Hospital.

“As long as blood sugar hasn’t been measured and other illnesses are excluded, these are just common symptoms that people experience from time to time,” she says.

She compares the feeling to athletes who have exhausted themselves.

“It could be that your activity level isn’t in sync with when you last ate, and you're starting to run out of energy,” says Qvigstad.

Sugar courses through the bloodstream

Blood sugar, also called blood glucose, is just that: sugar floating around in your blood. The sugar provides energy for our brains, muscles, liver, red blood cells, and fat cells.

Too much or too little sugar in the blood is not good, but the pancreas regulates it with the hormone insulin. It releases more insulin after a meal, and blood sugar levels drops. Insulin also ensures that the energy from the sugar is stored in muscle tissue and the liver or converted into fat.

Blood sugar is measured in millimoles per litre of blood – expressed as mmol/l. Normal levels range from 4 to 6 mmol/l, which is less than one gram. If you eat food high in carbohydrates, it is not uncommon to reach between 7 and 10.

“We consider levels between 3 and 4 to be slightly low blood sugar. This can – but doesn’t always – cause symptoms like heart palpitations, sweating, and feeling hungry,” says Hjelmesæth.

Running without food

Blood sugar well below level 3 can affect the brain and cause confusion or loss of consciousness.

“It’s rare for healthy people to drop that low,” says Hjelmesæth.

He tested a blood glucose monitor on himself.

“I ate too little that day, and then I went for a run. Under those conditions, I managed to push my blood sugar level below a 3,” says Hjelmesæth.

He felt really unwell.

“But it’s not dangerous for healthy people to have slightly low blood sugar, even if you experience heart palpitations and feel stressed. This reaction is simply the body telling you it’s time to eat,” he says.

Weekend without food

A few years ago, Elisabeth Qvigstad conducted a study on insulin sensitivity, which measured how well the body uses insulin to regulate blood sugar. A group of students fasted for a weekend.

Elisabeth Qvigstad studies insulin and diabetes.

“Some of the girls had blood sugar levels between 2.6 and 2.9 mmol/l on Monday. They were tired, but they hadn't eaten all weekend,” says Qvigstad.

“If we’re healthy, we can tolerate having our blood sugar dip down to 2.8 mmol/l during fasting because the body can burn fat or amino acids as a substitute,” she says.

The body has very effective systems that protect against low blood sugar in healthy individuals, such as the hormones glucagon, adrenaline, growth hormone, and cortisol. As a result, very few people are at risk of getting blood sugar levels lower than 3.5 mmol/l.

“But here we observe a huge variation between people – this is biology after all,” says Qvigstad.

Different for people with diabetes

For those with diabetes, however, it can be dangerous for blood sugar levels to get too low. They either produce no insulin at all or their insulin is ineffective. Therefore, diabetics can take artificially produced insulin. Occasionally, a little too much is taken, resulting in low blood sugar.

When non-diabetics say they have low blood sugar, they often describe the same symptoms that people with diabetes experience when their blood sugar levels become too low.

But in healthy people, the body is able to quickly regulate the level itself. It takes a lot to dip so low that the feeling of discomfort is actually due to low blood sugar.

The condition where blood sugar levels fall below normal values is called hypoglycaemia.

It is rare in people who do not have diabetes, according to several studies, including a study in the journal Diagnostics last year. This most often occurs in older individuals, and doctors usually find one or more causes.

“A lot of conditions and diseases can cause low blood sugar in people who aren’t being treated for diabetes or using medications that lower blood sugar. For example, low blood sugar can occur with infections, liver failure, kidney failure, low metabolism, and in individuals who have undergone bariatric surgery,” says Elisabeth Qvigstad.

Blood sugar issues with a shorter intestine

Those who have undergone bariatric surgery for obesity end up with a shorter intestine. Additionally, the hormones in their intestines may react differently to food.

“It usually stabilises in the first period after the surgery. Small and frequent meals are important for this group of people. Fast carbohydrates are not beneficial for them,” says Qvigstad.

Jøran Hjelmesæth and the research group at Vestfold Hospital Trust will soon be starting a study on bariatric patients. Some people who have undergone gastric bypass surgery have problems with low blood sugar after meals.

Some non-operated individuals also experience large fluctuations in their blood sugar levels after meals high in carbohydrates. First, the pancreas secretes a lot of insulin because of all the sugar in the food. The blood sugar spikes, and then it plummets quite quickly for some people.

“This is a natural reaction, but it’s usually not dangerous. If it's bothersome, it might be a good idea to talk to your GP. They usually advise eating more frequent meals and fewer fast carbohydrates,” says Jøran Hjelmesæth.

Some fluctuate more than others

Hjelmesæth points to a 2021 study in Nature Metabolism that shows the relationship between blood sugar and obesity.

Researchers served standardised meals to 1,000 study participants for two weeks. Their blood sugar levels were measured regularly. The results showed individual differences in how much blood sugar fluctuated from low to high levels. Some participants had significant drops in blood sugar two to four hours after eating.

“This study was an eye-opener. Those predisposed to having blood sugar drop a bit too much and too quickly after a meal can develop an increased appetite and a higher risk of obesity,” says Hjelmesæth.

The researchers behind the study found that the participants with significant blood sugar drops after meals consumed an average of 300 calories more per day than those with less fluctuation in blood sugar levels. Over time, this can lead to obesity if they are not more active than others.

Alcohol interferes

Alcohol is another disrupter of blood sugar levels, in addition to diseases and bariatric surgery, according to Elisabeth Qvigstad. The liver produces and stores blood sugar.

But if the liver is busy breaking down alcohol, it may neglect other functions. A lot of alcohol can thus lead to low blood sugar.

“What happens in the liver depends on how much sugar was in the alcohol, how much you drank and ate, how active you have been, whether you are taking glucose-lowering medications, and how quickly you metabolise alcohol,” says Qvigstad.

“But if you drink yourself into a stupor, you can expect problems.”


Elghobashy et al. Investigation and Causes of Spontaneous (Non-Diabetic) Hypoglycaemia in Adults: Pitfalls to Avoid, Diagnostics, vol. 13, 2023. DOI: 10.3390/diagnostics13203275

Wyatt et al. Postprandial glycaemic dips predict appetite and energy intake in healthy individuals, Nature Metabolism, vol. 3, 2021. DOI: 10.1038/s42255-021-00383-x


Translated by Ingrid P. Nuse

Read the Norwegian version of this article on forskning.no

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