Blood sugar is so important to understand – and not just if you’re diabetic. We asked Rachel Hampson, MA (Cantab) Medicine, MSc, mBANT, chair of trustees at the Institute for Optimum Nutrition, about the basics of blood sugars and how to manage them.

What is blood sugar?

Blood sugar refers to the amount of glucose (the smallest unit of sugar) circulating in the blood.

When we eat, glucose is produced from the digestion of carbohydrates.

It is then taken in by our cells from the blood and used to make energy, which is essential not just for moving muscles, but also for all the biochemical and hormonal pathways in the body.

What controls blood sugar?

In response to glucose in the blood, we produce the hormone insulin which facilitates uptake of glucose into cells.

When there is more glucose in the blood than required, insulin tells the liver to store glucose — first as glycogen (several sugar molecules bonded together), then as fat — so the body has a store of energy to use between meals or in the event of food shortage.

What is low blood sugar?

When blood sugar gets too low, the body tries to compensate quickly to restore energy balance.

This is when we might crave ‘quick fix’ starchy or sugary foods to quickly restore blood sugar.

What is high blood sugar?

High blood sugar is when there is too much glucose in the blood. It can lead to damage in the blood vessels, decreasing their elasticity and impeding blood flow.

This can cause higher blood pressure in order to increase the supply of blood and oxygen to the tissue.

Thus, people with diabetes and elevated blood sugar have a much higher risk of cardiovascular disease and stroke, as well as Alzheimer’s and vascular dementia.

How do stress and sleep affect blood sugar?

Stress of all kinds via cortisol promotes the release of glucose, particularly from glycogen stores in the liver, so this can increase blood sugar regardless of whether it’s needed.

Poor sleep has also been shown to negatively affect how well the body can clear glucose from the blood stream, as well as affecting hunger hormones that may influence appetite and food choices.

Is having steady blood sugar important?

Maintaining steady blood sugar is important for providing energy throughout the day, for physical activity and for mental focus.

When blood sugar is consistently high due to poor diet, stress, lack of sleep, or physical inactivity, insulin is being produced constantly to deal with high circulating levels of glucose.

The result is that insulin works less well — the body loses its sensitivity to the normal action of the hormone (insulin resistance).

Blood sugar becomes less well controlled, which leads to even greater production of insulin. These are the first steps towards developing diabetes.

Which foods affect blood sugar?

It is the carbohydrate component of food that will have the most immediate impact; depending on how much glucose is contained in our food and how quickly it gets released into the bloodstream.

Foods that are obviously sugary, like sweets, cakes, biscuits, sugary drinks, and even some fruits, contain large amounts of sugar that is released quickly. They cause high blood sugar.

Starches in bread, rice, pasta, potato and beans are also broken down to release glucose into the blood. The speed at which this happens depends on whether the glucose is also wrapped in lots of fibre.

White bread and wholegrain brown bread may contain similar amounts of starch (which gets broken down to glucose) but the brown bread also has more fibre, which makes the carbohydrates harder to get at — it is ‘slow release’.

This is what we want because it provides a steady source of energy and avoids blood sugar spikes.

It is best to eat carbohydrates when the body is likely to require more energy; earlier in the day, or just after exercise (to replace glycogen stores).

What should I eat for breakfast?

Breakfast has become one of the most carbohydrate-heavy meals, with fruit juices, cereals, granolas and mueslis, bread, bagels, pastries, pancakes, sweetened yoghurts, fruit, and jam.

Starting the day with a spike in blood sugar is likely to lead to low energy levels, hunger or coffee cravings by mid-morning.

For those who prefer a sweeter breakfast, choose natural yoghurt with lower-sugar fruits such as berries, with ground flaxseed to add healthy fibre and fats.

Alternatively, choose overnight oats or porridge made with rolled or jumbo oats that still require some chewing (rather than overly processed instant oats) topped with mixed seeds, nuts and berries.

Which foods balance blood sugars?

Including protein in each meal and snack can help maintain steadier blood sugar, and may help reduce cravings and snacking.

For some people, including diabetics, snacking can help regulate blood sugar levels.

For others, it is better to separate meals and snacks by at least three or four hours to give the gut and the hormone systems a ‘rest’.

How to test blood sugar

You might conclude that eating very few carbohydrates and sticking to high-fat foods and protein would be a sensible approach to maintaining steady blood sugar.

However, knowing how your body responds is probably a more informed approach.

Blood sugar responses to different types of carbohydrate can vary quite significantly depending on a person’s metabolism, genetic makeup, stress levels, sleep patterns and even gut microbes.

There are affordable ways to monitor your blood sugar using a sensor that is attached to your skin and an app on your phone such as the Freestyle Libre.

Alternatively, you can ask your GP to check your glycosylated haemoglobin (HbA1c).

This does not directly measure the level of blood glucose, but reflects how blood glucose levels have tended to be over a period of two to three months so you can see how well you have been controlling your blood sugar.

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