Blood sugar: spikes, causes and what you can do

Unstable blood sugar

Often unnoticed, yet important

Unstable blood sugar means your blood sugar fluctuates a lot during the day. A quick rise is often followed by a quick drop, and you notice that in signals like these.

Tiredness after eating
Energy dips during the day
Sudden hunger and cravings for sweets
Difficulty concentrating

The normal course after a meal

Intake of carbohydrates Bread, pasta, fruit or sugar are broken down into glucose in the gut.
Blood sugar rises Glucose enters the blood. The pancreas responds with insulin.
Insulin brings sugar into the cells Muscles, liver and fat tissue take up the glucose as fuel or storage.
Blood sugar falls After a big spike it often drops just as fast, and then hunger and tiredness follow.

From blood sugar spikes to prediabetes

A vicious circle

With insulin resistance your cells respond less well to insulin. Your body compensates by making more insulin, until too much insulin circulates in the blood. Several factors play a part in how it develops.

Epigenetic programming
Chronic stress
Eating too often
Not enough exercise
Sugary, ultra-processed food
Excess weight, though not necessarily

How the circle keeps itself going

Insulin resistance The cells respond less well to insulin.
Fasting blood sugar rises More glucose stays in the blood, also between meals.
More insulin is needed The pancreas makes extra insulin to bring blood sugar down.
Hyperinsulinaemia Too much insulin in the blood in turn makes the cells even less sensitive.

Many people develop prediabetes without knowing it.

Know what you eat

Which foods cause blood sugar spikes

Processed sugars and fast carbohydrates in particular make blood sugar rise sharply. But healthy carbohydrates can cause spikes too, especially when you eat them on their own, in large portions or on an empty stomach.

Sugary drinks: soft drinks, fruit juice, energy drinks, chocolate milk
Heavily processed sugary products and snacks: biscuits, sweets, crisps, granola bars
Ultra-processed carbohydrates: breakfast cereals, cornflakes, industrial bread
Bread, pasta, rice, mashed potato, oats, banana, grapes and dried fruit also cause spikes if you eat them on their own

Limiting blood sugar spikes

Not only what, but also how and when

The same meal can cause a large or a small spike, depending on how you put it together and eat it.

Combine carbohydrates with protein and fats
Eat fruit after a meal rather than on an empty stomach
Smaller portions cause smaller spikes
Walk after a meal: ten minutes already helps

Eat in the right order

Vegetables The fibre slows the absorption of what follows.
Protein and fats They provide satiety and slower stomach emptying.
Carbohydrates Eaten last, they give a flatter curve.

What you can do yourself

Seven habits for steadier blood sugar

Lifestyle is the basis. These habits are the most often recommended and studied.

Eat low-carb or low-GI

1

Limit pasta, bread and rice, and start every meal with a portion of vegetables.

How it was studied

Randomised cross-over study in people with type 2 diabetes: the same meal, eaten in a different order. Measured on glucose and insulin after the meal.

Shukla et al., 2015

Eat enough protein

2

Start the day with a protein-rich meal and eat enough protein at every meal. It flattens the blood sugar spike.

Avoid sugary drinks

3

Skip soft drinks and sweetened beverages. Fruit juice or a smoothie on an empty stomach also causes a spike.

Limit ultra-processed food

4

Biscuits, crisps, soft drinks and ready meals cause sharp spikes and keep insulin resistance going.

Move every day

5

Walking after a meal makes blood sugar fall faster. Strength training at your own level increases insulin sensitivity.

How it was studied

Systematic review and meta-analysis: breaking up long sitting with standing or light walking. Measured on glucose and insulin after the meal.

Buffey et al., 2022

Sleep and relax

6

Poor sleep and chronic stress raise cortisol, and that makes blood sugar less stable.

How it was studied

Study in healthy young men with six nights of four hours’ sleep. Measured on glucose tolerance and hormones.

Spiegel et al., 1999

Eat within a time window

7

An eating window of eight to ten hours a day gives the pancreas rest and reduces the number of insulin peaks.

How it was studied

Randomised cross-over study in men with prediabetes: eating within six hours, early in the day. Measured on insulin sensitivity.

Sutton et al., 2018

Do you have diabetes or take medication for your blood sugar? Do not change your diet or medication without your doctor or pharmacist. They can give you personal advice on food, lifestyle and follow-up.

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Sources (5)

Shukla AP, Iliescu RG, Thomas CE, Aronne LJ. Food Order Has a Significant Impact on Postprandial Glucose and Insulin Levels. Diabetes Care. 2015;38(7):e98–e99.
Buffey AJ, Herring MP, Langley CK, Donnelly AE, Carson BP. The Acute Effects of Interrupting Prolonged Sitting Time in Adults with Standing and Light-Intensity Walking on Biomarkers of Cardiometabolic Health in Adults: A Systematic Review and Meta-analysis. Sports Med. 2022;52(8):1765–1787.
Spiegel K, Leproult R, Van Cauter E. Impact of sleep debt on metabolic and endocrine function. Lancet. 1999;354(9188):1435–1439.
Sutton EF, Beyl R, Early KS, Cefalu WT, Ravussin E, Peterson CM. Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes. Cell Metab. 2018;27(6):1212–1221.
International Diabetes Federation. IDF Diabetes Atlas, 10th edition. Brussels; 2021.

Science