Once reserved for diabetics, CGMs (continuous glucose monitors) are now being pushed as a tool to help balance your energy levels, maximise your training output and even boost weight loss. But do fluctuations in blood sugar really matter that much? We asked an expert.

What Causes a Spike

Within a few minutes of tucking into a high-carb, low-fibre treat – think a white bagel with strawberry jam – your body reacts with an ‘immediate spike in blood sugar’, says Charlotte Norton, chief medical officer at doctor-led weight loss service The Slimming Clinic. Your digestive system makes short work of those simple sugars, allowing them to enter the bloodstream quickly, triggering a burst of energy and brain activity along with a temporary mood boost. ‘With little-to-no protein in a meal, the simple carbs are metabolised faster, as protein slows the digestion of carbs.’

Then Comes the Crash

That sugar high doesn’t last. Over the next 90 minutes to two hours, your body releases a flood of insulin to clear the glucose from your bloodstream, moving it into your cells to be stored as glycogen in the liver and muscles. ‘As simple carbs create such a large spike, the resulting decline causes a crash,’ explains Dr Norton. Your energy levels dip, which can leave you craving more sugary foods. ‘Not only can this negatively impact your energy levels, causing lethargy, it also affects mood and brain function.’

Forming a Habit

Other than arousing your desire for an afternoon nap, the occasional blood sugar high won’t do much harm. But make it a habit and it can take its toll. Repeated spikes and dips can trigger hormonal shifts, which could spark anxiety and irritability, says Dr Norton. Then there are the physical effects. Though insulin does a great job at clearing away the sugars from a high-carb meal or snack, it can also stop the body from breaking down its fat stores. This stimulates the creation of more body fat. ‘Eat too many [of these foods] you might gain weight, as well as increasing your risk of type-2 diabetes.’

Rising Risk Factors

For some people, a diet heavy in fast-acting carbs can do more than see them put on a few pounds. Over time, it could lead to insulin resistance. This is where cells no longer respond to the hormone, causing more and more insulin to be released into the blood without sugars being broken down. Those with higher than normal blood sugar (known as prediabetes) can have up to a 50% chance of developing diabetes in the next five to 10 years. But it isn’t only diet that dictates whether or not you’re at risk, points out Dr Norton – sleep, alcohol, fitness and genetics all contribute, too.

Finding a Good Balance

If you’re otherwise healthy, it’s not worth stressing over your Sunday morning cinnamon roll. There are no fixed rules, but ‘if poor eating habits become a daily occurrence over several months and result in weight gain’, then health problems are more likely, says Norton, who also suggests getting no more than 50% of your calories from carb-based foods. ‘Regular exercise can also help to control blood sugar, as muscle cells absorb and store excess sugar.’ Hitting your 30g of fibre a day will benefit you too, she says, as could a chromium supplement, which supports the action of insulin.