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How Does Sugar Affect Your Brain?

What impact does sugar have on your brain? You’ve likely heard the advice to keep your sugar intake to a minimum, or at least cutback, but what exactly happens to your brain when you consume too much sugar?

In this article, you’ll learn the difference between dietary sugar and blood sugar (glucose), how each impacts your brain, and why watching your sugar intake is an essential part of maintaining healthy cognitive function. 

Sugar, Glucose, and Blood Sugar

Before we dive into how sugar affects your brain, it’s essential to understand the difference between dietary sugar and the broken-down form of carbohydrates, referred to as glucose. 

While these two are often used interchangeably, some significant differences must be highlighted for you to understand how one impacts the production of the other in your body. 

Sugar

When you look at a food label, you see “added sugars,” which is typically referring to table sugar or cane sugar but may also refer to added sources of sugar like honey or maple syrup. Put simply, added sugars refer to what you likely picture when someone says the word “sugar.” 

Chemically, sugar is the simplest form of dietary carbohydrate and is made up of two units – glucose and fructose.

Glucose

Glucose is the term used to describe the fuel that your body uses on a cellular level for energy. When you consume carbohydrates, either simple or complex, they will eventually get broken down into glucose. Even fructose must first be converted to glucose before your body can use it. 

When someone refers to “blood sugar,” they are actually referring to the amount of glucose in your blood – not the whole sugar molecules you get from dietary sources. 

Complex Carbohydrates 

Complex carbohydrates refer to sources of glucose that are more complex in their chemical structure. While sugar contains only two molecules (fructose and glucose), complex carbohydrates like whole grains and vegetables contain three or more (often many more). 

Blood Sugar

Carbohydrates’ impact on your blood sugar depends on whether it is simple or complex. Simple carbohydrates (AKA sugar) are broken down and absorbed rapidly by your digestive tract, creating a spike in blood sugar (glucose). Complex carbohydrates often come packaged with fiber and other macromolecules, making them harder to break down and, therefore, slower to get digested and absorbed. This produces a steadier increase in blood sugar.

At the end of the day, all of the carbohydrates you consume will eventually convert into glucose to fuel your body (or be stored as fat). But the key is keeping your blood sugar within a healthy range so that your cells can take up what they need and not have to deal with an overload. This is where the issues concerning sugar (simple carbs) come in. 

How Sugar Affects Your Brain

The Good

Glucose is your brain and body’s primary source of fuel. When you have a steady stream of glucose flowing through your body, your brain can pick it up and use it to fuel the many vital processes that take place, which allow you to think, remember, learn, self-regulate, and more. 

Glucose provides the fuel that allows your neurons to fire and communicate with one another, sending messages throughout your nervous system and entire body. 

When glucose is low, your brain turns to a secondary form of fuel called ketones, energy molecules made from fat. However, as long as there is sufficient glucose available in your body, glucose will be your brain’s preferred fuel source.

In fact, it’s estimated that your brain is so energy-hungry that it uses half of all the glucose produced by your body.[1]https://hms.harvard.edu/news-events/publications-archive/brain/sugar-brain 

The Bad

When you consume too much dietary (simple) sugars, it can create an overload of glucose in your body. When there is too much glucose in your blood (high blood sugar), your cells fill up with what you need for fuel, and the excess sugar has no place to go. This is where the benefits of glucose to your cells start to fade, and detrimental impacts begin to appear:

Brain Aging

Research shows a direct correlation between the consumption of sugar and cellular aging. This may be the most pronounced for people with type 2 diabetes, as they cannot control the glucose levels in their blood. Consistently high glucose levels affect the brain’s functional connectivity and may lead to atrophy (cell death).[2]https://hms.harvard.edu/news-events/publications-archive/brain/sugar-brain 

Furthermore, excess glucose in the brain stimulates an inflammatory response, creating neuroinflammation. Among the serious side effects of inflammation in your brain is an increased risk of neurological diseases like Alzheimer’s.[3]https://pubmed.ncbi.nlm.nih.gov/28124586/ 

Memory and Other Cognitive Functions

The presence of excess glucose in the blood may harm the delicate blood vessels in your brain, leading to damage and reduced blood flow. When blood flow is inhibited in your brain, it can cause shrinkage of brain tissue and a disruption in the connectivity, which links specific brain regions together. 

Research suggests that this is one of the reasons that people with diabetes tend to experience cognitive impairment and memory issues. Consistently high blood glucose creates changes in the brain structure and inflammation, leading to disruption of cognitive processes.[4]https://link.springer.com/article/10.1007%2Fs11892-016-0775-x 

What’s more, animal studies show that a diet high in refined sugars impacts the production of brain-derived neurotrophic factor (BDNF). BDNF plays a crucial role in the health and functionality of your brain cells. For example, it enhances neuroplasticity, your brain’s ability to change and adapt to new information, and assists in the growth and maturation of neurons. 

Low levels of BDNF may inhibit your brain’s ability to form new connections, directly impacting memory and learning.[5]https://www.sciencedirect.com/science/article/abs/pii/S0306452202001239?via%3Dihub 

Mood

The inflammatory model of depression states that it’s not a chemical imbalance but rather inflammation in the brain that’s at the root of depressive symptoms. 

As mentioned, sugar is known to increase neuroinflammation.

In a research study involving over 23,000 participants, investigators found that higher rates of sugar consumption in the form of sweet food, sugar-sweetened beverages, and added sugars, increased the incidence of common mental disorders like depression 23%.[6]https://www.nature.com/articles/s41598-017-05649-7 

Another study found that when diabetics experienced high blood sugar, they not only showed cognitive deficits but also reported feelings of sadness and anxiety.[7]https://care.diabetesjournals.org/content/27/10/2335 

This research underlines the importance of steady blood sugar levels for optimal brain function, where too little or too much glucose may disrupt the natural flow of energy to the brain, with downstream effects in cognition and mood.

Reward Response and Sugar Addiction 

Perhaps one of the most frustrating effects that sugar has on the brain is its impact on your reward system. 

Logically, if consuming too much simple sugar is bad for neurological health, why don’t we all just stop? The reason is that sugar is intrinsically addicting. Research shows that foods higher in sugar activate your brain’s reward system, stimulating your desire for more and more.[8]https://academic.oup.com/ajcn/article/98/3/641/4577039 

Animal studies even show that sugar may be more addicting than cocaine.[9]https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0000698 

From an ancestral perspective, this makes a lot of sense. Sugar is the quickest fuel source for the human body and always has been. However, your ancient ancestors would never come across the amount of sugar that you do today. In fact, the only sugar sources they would have access to would be berries that they spent hours picking by hand. But you can bet that once they sat down to enjoy their fruity feast, it would light up their brain, sending signals of pleasure throughout their body.

Takeaway

It’s fair to say that the human body was never meant to ingest the amount of sugar that many people consume today. As a result, when blood sugar becomes too high, your body becomes confused, fighting back with inflammation, which only makes matters worse. 

This is not to say that you should never consume sugar. However, for optimal brain health, it’s crucial that you only do so in moderation. Your body is perfectly capable of handling a cookie now and then. However, when high sugar becomes a daily habit, both your brain and body will suffer. 

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