There are certainly downsides to eating too much sugar, but in itself, sugar isn’t “bad” for us. Far from it, in fact—sugar is crucial for key bodily functions that keep us alive. 

Glucose is a type of sugar that our bodies use as fuel. It’s the main source of energy for all our tissues and cells,[1] and keeps our brains running normally.[2] You could think of it as the battery that powers our regular functioning so that we can meet the demands of our day-to-day lives.

Glucose is the main energy source for all our tissues and cells, and keeps our brains running normally

Physiology - Glucose, Trends Neurosci

But for this battery to work as it should, our glucose levels must be kept stable—not creeping too high and not dropping too low. Being on either side of this fence can have implications for our health. 

To toe this line, it’s important to understand both how glucose affects the body and what keeps its levels in balance. Here’s everything you need to know. 

What is glucose?

There are three main types of nutrients we get from our diet: carbohydrates, protein, and fat. Sugars are a type of carbohydrate molecule, a key source of fuel for the body.[3]

Glucose is a type of sugar known as a monosaccharide. This means that glucose molecules can’t be broken down any further and therefore are digested quickly.[3] Sugars like this are called simple carbohydrates.

The body also converts all other carbs that we eat—except for fibre, which can’t be digested—into glucose in order to use it as energy.[3] These are called complex carbohydrates or starches, and take longer to digest. 

Where do we get glucose from?

We mostly get glucose from our diet but the body can also generate it.[1] This happens if we need to “free up” more glucose to be used as energy, for example, if we haven’t eaten in a while. After all, many tissues need a continuous supply of energy to function, like the brain, eyes, and testes. 

We mostly get glucose from our diet but the body can generate it.

Hantzidiamantis and Lappin, Phsyiology - Glucose

Glucose is produced in two ways: glycogenolysis, which is when carbs that are stored in the liver as reserve energy are broken down into glucose, and gluconeogenesis, when the kidney and liver produce glucose from amino acids and lactate, a by-product of the process of converting glucose to energy.[4] 

If we’re in a fasting state, meaning that all our food has been digested and absorbed, initially our glucose levels are mostly topped up via glycogenolysis.[5] But as our reserve energy stores deplete, gluconeogenesis kicks in to make sure that blood sugar stays stable.[5]

In terms of diet, we can get glucose from carbs (except fibre), honey, fresh fruits, and vegetables. It’s also sometimes added to processed foods.

What role does glucose play in the body?

Just in case we haven’t hammered this home enough: we need glucose to survive. It plays a crucial role in fuelling every single one of our organ systems,[1] plus key processes like cell division and growth; hormone, cell, and membrane creation; muscle contractions; and maintaining nerve function.[4] 

The brain is responsible for 20% of our total energy consumption

Mergenthaker et al., Trends Neurosci

It’s also essential for brain function. While the brain accounts for about 2% of our body weight, it’s responsible for about 20% of our total energy consumption.[2] Glucose is not only required for the formation of neurotransmitters, which are chemical messengers we can’t function without, but helps to maintain tissues, eliminate harmful cells, and provide the energy needed for information processing.[2] 

Our muscles rely on glucose, too, and account for around 70-80% of glucose uptake from the blood.[6] This energy powers all our movements and muscle contractions, as well as our workouts, which are an important part of a healthy lifestyle. 

Muscles account for 70-80% of glucose uptake from the blood

Stepto et al., Endocr Connect

The amount of glucose in our blood also influences how well we’re able to process and store energy. The body notes our blood sugar and prepares its resources accordingly to convert the glucose into fuel. But depending on how much sugar is present, this process can vary and therefore be more or less efficient.[7]

Our blood sugar levels determine how much insulin the body produces,[8] for example, which is a hormone we use to help us absorb glucose for use as energy. 

How does glucose affect our health?

Ideally, glucose levels are kept fairly stable, and various organs and bodily systems work together to keep it that way.[9] But if they fall out of balance, it can affect our metabolism and general health. 

When our blood sugar is high, our body makes more insulin to help process it—but if we make too much insulin over time then its effects can actually start to wear off. We then enter a state called insulin resistance.[10]

At this point, we’re less able to absorb blood sugar, which means that more can remain in the blood. Elevated blood sugar can ultimately develop into type 2 diabetes if left unchecked.[10] Insulin resistance is also linked to high blood pressure, heart disease,[10] and pregnancy complications.[11]

We also go into a kind of “fat storage mode”, where the body takes raised levels of insulin and blood sugar as a signal to prefer storing energy as fat rather than using it as fuel.[7] 

On the other hand, having blood sugar levels that are too low can also be dangerous, as this means that the body doesn’t have the energy to function as normal. This is called hypoglycemia, and if left untreated can affect brain and eye function, cause heart problems, and disrupt our sleep.[12] However, hypoglycemia is rare in folks who don’t have diabetes.[13]

Keeping our blood sugar in line is super important for our health. Diet plays a key role here, but our sleep and exercise habits, plus any underlying metabolic conditions, can also influence our glucose levels. 

For example, one way to prevent surges in blood sugar is by avoiding carbs that break down quickly[14], which are called high glycemic-index (GI) foods. Because they release their energy fast, this translates into a sharp rise in glucose. Processed foods like crisps and soft drinks are generally high-GI, for example. 

Instead, low-GI foods like non-starchy vegetables, whole grains, and pulses, release energy slowly and have a more gradual impact on blood sugar.[14] 

The key thing here is to eat a balanced diet that provides enough sources of glucose but doesn’t overdo it. A generally healthy lifestyle, with enough sleep and regular workouts, can also help keep blood sugar stable. 

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