Why a blood sugar crash may be to blame for that dreaded mid-afternoon slump

July 7, 2020

What is a ‘blood sugar crash’? Why do they happen? And how can you eat to avoid them?

Many of us will have experienced those mid-afternoon funks that leave you feeling tired, sluggish and desperately craving chocolate and caffeine. The cause? A classic blood sugar crash.

In this post, we explore the science behind the blood sugar crashes. We find out why they happen, why they make you feel so bad, why some people seem to suffer from them more than others, and how to eat in the way that best maintains your energy and health.

What is a blood sugar crash?

Before we dive into the science behind a blood sugar crash, here’s a quick recap of what happens when you eat something containing carbohydrates

Your body breaks down the carbohydrates in your food into its glucose (sugar) building blocks, which pass into your bloodstream. Your blood sugar levels begin to rise, prompting your body to release insulin. In turn, this triggers your cells to take up the glucose to use for generating energy, swiftly returning your blood sugar levels to normal. 

This is a perfectly normal process that happens in all of us, whatever we eat, and protects your body from the harmful effects of high blood sugar (hyperglycaemia).  

But when your blood sugar increases very steeply after eating, your body can release too much insulin, making your blood sugar plummet below normal levels. This is technically referred to as postprandial hypoglycemia or reactive hypoglycemia, but it’s commonly called a blood sugar ‘crash’.

Are blood sugar crashes bad for you?

A blood sugar crash is medically defined as a blood glucose level below 70 mg/dL (3.9 mmol/L). But even if you don’t have a way of monitoring your blood glucose, you can recognize when you are experiencing a blood sugar crash by simply observing how you feel. 

The glucose in our blood is the primary source of energy for our body and brain. So when you have low blood sugar, the cells in your body aren’t receiving enough energy. This causes tell-tale symptoms including hunger, irritability, fatigue, anxiety, headaches, difficulty concentrating, shakiness, and dizziness

A blood sugar crash leaves you hungry - even if it wasn’t that long since you ate. Our PREDICT study showed that blood sugar dips after eating were linked to increased hunger, suggesting that curbing sugar crashes might be a good weight control strategy but cutting the urge to snack.

Besides making you feel lousy and hungry, unhealthy blood sugar responses after eating, such as spikes and crashes, have been linked to a myriad of health problems, including chronic diseases like obesity, diabetes, and heart disease. Repeated reactive hypoglycemia (frequent blood sugar crashes) can lead to prediabetes and eventually type 2 diabetes if left untreated. 

Are some people more susceptible to blood sugar crashes than others?

Have you ever noticed that you’re suffering from a terrible afternoon slump, when your lunch companion who ate exactly the same meal seems just fine?

We saw blood sugar crashes in plenty of our PREDICT participants, who underwent continuous glucose monitoring for two weeks. But they were more common in some people than others. And even identical twins, who share all their genes, could have different glucose responses after eating the same foods.

The mechanism behind blood sugar crashes isn’t fully understood, and it may vary between people. One theory is that if your blood sugar levels are not well controlled, the insulin-secreting cells in your pancreas can become damaged and don't produce enough insulin as your blood sugar begins to rise after eating. In response, your body ‘panics’ and releases excessive insulin later on, causing a crash. 

Another idea is that your blood sugar responses depend on the microbes that live in your gut. We all have a unique set of microbes, so we all process our food differently, causing unique responses to food, even when we've eaten precisely the same thing.

Avoiding the blood sugar slump

While giving in to your craving for a Snickers might seem like the right thing to do when you’re in the midst of a blood sugar crash, your sugary snack will only give you a temporary fix before leaving you feeling low again. The best way to dodge a sugar slump is to avoid the foods that cause them. Instead, pick foods that keep your blood sugar relatively steady. 

Avoiding sugary drinks and snacks is probably sound advice for everyone seeking better control over their blood sugar. But some experts advise highly restrictive diets that limit all carbohydrates. However, studies have shown that diets high in carbohydrates from plants can improve blood sugar control after eating by increasing the activity of gut microbes, which protect against unhealthy blood sugar reactions. 

Rather than avoiding certain food groups, like carbohydrates, we advise eating a varied diet tailored to your unique biology. After all, our PREDICT-1 study has shown us that the same foods can cause different blood sugar responses in different people, so there is no one-size-fits-all advice for maintaining healthy blood sugar levels.  

To understand what causes your sugar crashes, and how you can avoid them and maintain your energy levels, you need to know how YOUR body responds to food. You are unique, and your diet should be too. 

But how can you know what foods are best for your body? Sign up for early access to our home test kit to be among the first to discover your unique responses to food and get a personalized insights report and action plan tailored to your biology.

Sugar slumps in short

  • Our cells need sugar to function correctly - we get it from breaking down simple and complex carbohydrates in the foods we eat.
  • Our blood sugar levels fluctuate throughout the day.
  • If your blood sugar falls below normal levels (a blood sugar 'crash'), it can make you feel tired, confused and sluggish
  • Uncontrolled blood sugar levels have also been linked to long term health problems.
  • Everyone has different responses to food.
  • To maintain your energy and health, you need to know how your body works and eat in the way that suits you best

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