Last updated February 7, 2024.
Edited and medically reviewed by Patrick Alban, DC. Written by Deane Alban.
A diet high in sugar contributes significantly to depression, anxiety, and stress. Learn how sugar affects the brain and what you can do about it.
We are hardwired to like things that taste sweet.
A preference for sweetness is a survival mechanism that humans developed to protect us from eating toxic foods.
But if you’re feeling anxious, depressed, or stressed out, this inborn preference can work against you.
You may crave sweets and find that eating them makes you feel better. Temporarily.
But sugary and carb-rich foods are harmful in the long run.
There’s a complicated relationship between sugar, the brain, and mental health.
Let’s look at how sugar and other sweeteners affect the brain and can fuel both depression and anxiety.
Understanding Sugar’s Role in the Brain
Table sugar is pure white crystalline sucrose that is usually extracted from sugar cane or sugar beets.
It is intensively processed, has no nutritive value, and, in many ways, is more like a drug than a food.
To understand how sucrose impacts you and your mood, we need to take a look at its two components, glucose and fructose.
While glucose and fructose are structurally very similar, they behave very differently in the body.
Glucose — The Brain’s Main Energy Source
Glucose is a simple sugar molecule that’s a building block of mainly plant-based complex carbohydrates such as those found in whole grains, legumes, fruits, and vegetables.
It is essential to life.
It circulates in our blood and provides energy to all of our cells, especially brain cells which use a disproportionate amount of energy.
Since brain cells can’t store energy, they need a steady supply of glucose.
While the liver can break down stored fat to produce ketones to feed the brain in a pinch, most brains run on glucose most of the time.
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Added Fructose — A Health Disaster
Fructose is another simple sugar naturally found in fruit and sweet vegetables like carrots, beets, and yams.
Virtually every cell in the body can metabolize glucose for energy, but only liver cells metabolize fructose.
Refined sugars like white sugar, high fructose corn syrup, and even “healthy” sweeteners like honey and maple syrup are roughly half glucose and half fructose.
The fructose found in fruit and vegetables is easily handled by the body, but a diet high in added fructose from concentrated sweeteners raises blood fructose levels — and this is a health disaster.
" Frequent consumption of fast food and commercial baked goods increase the risk of depression by up to 38%.
Elevated blood fructose contributes to diseases of the heart, liver, and kidneys and increases the risks of obesity and type 2 diabetes.
And it contributes to chronic inflammation, an underlying cause of a wide range of psychiatric and neurodegenerative disorders.
The Link Between Sugar and Depression
You may turn to sugar when you’re feeling down.
It can make you feel better temporarily, but, in fact, sugar fuels depression and anxiety.
Here’s what research shows regarding the link between sugar and depression:
- A study across six countries found a “highly significant” correlation between sugar consumption and the rate of depression.
- Frequent consumption of commercial baked goods and fast food increases the risk of depression by up to 38%.
- Regular consumption of sweetened drinks significantly increases the chances of developing depression.
And most significant is the Women’s Health Initiative Dietary Modification Trial.
This huge 20+ year project followed the dietary habits of over 48,000 women.
One finding of this study was that sugar and processed grains increase the risk of depression, while fruits and vegetables decrease the risk.
One surprise of this study was that following a low-fat diet provided no health benefits.
It did not lower participants’ risks for heart disease or cancer, nor did it help them maintain a normal weight.
This is important to know because the healthy fats missing from the foods in low-fat diets are critical to brain health and function.
How Sugar Can Cause Depression
It’s not fully understood how sugar contributes to depression, but here are the three most widely accepted theories.
Sugar Causes a Serotonin Crash
Serotonin is a major neurotransmitter known as the “happiness molecule” for its important role in maintaining a positive mood.
Sugar and other processed carbs are appealing when you’re feeling down because they give you a serotonin boost.
But this lift is short-lived, lasting only an hour or two before your serotonin level crashes and you feel even worse.
A smarter long-term strategy for increasing serotonin is to regularly eat healthy carbohydrates.
Paradoxically, when carbs and protein are eaten together, the presence of protein blocks serotonin synthesis.
But you can eat carbs on their own without protein to increase serotonin naturally.
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Sugar Increases Brain Inflammation
The medical consensus is that depression is caused by a lack of two neurotransmitters, mainly serotonin and sometimes dopamine.
However, another promising theory is emerging — “cytokine-induced depression.”
The foundation of this theory is that brain inflammation is the root cause of depression.
Cytokines are immune system messengers that regulate inflammation.
Inflammatory cytokines have been linked to:
- Alzheimer’s disease
- anxiety
- bipolar disorder
- brain fog
- depression
- lack of focus
- memory loss
- schizophrenia
- stroke
High sugar intake negatively affects your intestinal microbiome and stimulates inflammation.
Currently, the most widely used antidepressants are selective serotonin reuptake inhibitors (SSRIs) which are thought to work by increasing serotonin levels.
SSRIs don’t always work, but when they do, it may be for an unexpected reason.
There’s now evidence that SSRIs are anti-inflammatory and that this property may be responsible for their antidepressant effect.
Sugar Suppresses BDNF, a Natural Antidepressant
Brain-derived neurotrophic factor (BDNF) is a protein critical for brain health.
BDNF stimulates the formation of new brain cells and helps protect the brain from neurodegenerative diseases.
It also acts as a natural antidepressant.
But sugar, especially when combined with high fat intake, decreases BDNF production.
Low levels of BDNF are associated with numerous brain-related conditions, including:
- addictions
- Alzheimer’s disease
- anxiety disorders
- dementia
- depression
- eating disorders
- epilepsy
- obsessive-compulsive disorder
- post-chemotherapy cognitive impairment
- post-traumatic stress disorder
- schizophrenia
The Link Between Sugar and Anxiety
Just as you may eat sugar to lighten your mood when you’re feeling blue, you may also eat it to relax when you are feeling stressed or anxious.
In the short term, stress can depress appetite, but chronic stress increases appetite by raising levels of stress hormones and the hunger hormone ghrelin.
Stress also affects food preferences, making you crave sugar, fat, or both.
That’s why no one craves a big salad when they’re stressed out!
Here’s how sugar affects blood sugar levels, contributing to anxiety.
The Blood Sugar Roller Coaster
Foods with a high glycemic index like sugar, high fructose corn syrup, or wheat cause blood sugar levels to spike.
The body responds by making insulin which causes the blood sugar level to drop.
Lowered blood sugar then causes the adrenal glands to release the stress hormones cortisol, norepinephrine, and epinephrine.
This prompts the liver to release stored sugar to bring blood sugar levels back to normal.
But these hormones, the same ones released when the body is in fight-or-flight stress mode, also ramp up anxiety.
The Hypoglycemia-Anxiety Connection
There’s evidence that eating sugar can induce anxiety independently of hypoglycemia, but hypoglycemia is undoubtedly a major physical cause of stress and anxiety.
Hypoglycemia occurs when your blood sugar level drops too low.
The symptoms of anxiety and hypoglycemia are so similar that doctors have misdiagnosed hypoglycemia as anxiety for decades.
Common symptoms of both include mood swings, brain fog, shakiness, nervousness, irritability, inability to concentrate, and crying spells.
A low blood sugar attack can leave you feeling jittery, sweating, heart pounding, and confused — very much like an anxiety attack.
If you suspect that your anxiety is related to hypoglycemia, it’s critical that you limit your intake of all refined carbohydrates and sugar, and eat protein, healthy fats, and complex carbohydrates instead.
This is also an excellent time to examine your caffeine intake, since there are over a dozen different ways in which caffeine contributes to anxiety.
Caffeine and sugar often go hand-in-hand in soft drinks, lattes, and energy drinks.
Caffeine stimulates the production of cortisol and other stress hormones, causing symptoms similar to hypoglycemia.
Also, if you have hypoglycemia, consider taking a magnesium supplement.
This relaxing mineral can help stabilize your blood sugar level.
Sugar Substitutes Are No Better for Depression and Anxiety
You might be thinking of trading in sugar for an artificial sweetener, but that comes with its own drawbacks.
Consumers have reported thousands of side effects of aspartame (Nutrasweet, Equal) to the US Food and Drug Administration (FDA).
You can find some of the most commonly reported side effects listed on the US Centers for Disease Control and Prevention website and in this article in Harvard’s digital library.
Mental health conditions reported to be aggravated by aspartame include anxiety, depression, and attention disorders.
One major study on over 250,000 soda drinkers found that drinking artificially sweetened diet soft drinks increased the likelihood of depression by 30%.
Reported side effects linked to sucralose (Splenda) include:
- anxiety
- blurred vision
- depression
- dizziness
- headaches
- mental confusion
- migraines
- panic attacks
How Artificial Sweeteners Harm Your “Second Brain”
One of the latest, and most unexpected, findings about artificial sweeteners is the effect they have on our gut bacteria, collectively known as our microbiome.
A dysfunctional microbiome can be a root cause of anxiety, depression, and many other brain-related disorders.
Artificial sweeteners change the microbiome which can have a profound impact on brain, mood, and mental health.
The intestines are now considered a “second brain” or “backup brain” since they contain over 100 million neurons.
Gut bacteria are responsible for making over 30 neurotransmitters, including serotonin, GABA, dopamine, and acetylcholine.
This gut-brain connection is a relatively recent discovery that we’ll be hearing a lot more about in the future.
There’s an entire class of probiotics called psychobiotics that specifically bestow mental health benefits.
In fact, this exciting discovery is being called “the new frontier” in mental health treatment.
Numerous studies support that taking the right probiotics can alleviate symptoms of stress, anxiety, and depression.
Quitting Sugar: What To Do Next
If you suspect that sugar is fueling your anxiety or depression, you should eliminate it from your diet to see if you notice any improvements in symptoms.
This is not easy since sugar is hidden in most processed foods and goes by over 60 different names on food labels.
You can find a complete list of alternative names for sugar on the University of California’s website Sugarscience.
And if you’ve ever tried to quit eating sugar, you’ve probably found that sugar cravings are strong.
This is to be expected since sugar meets most of the criteria of an addictive substance!
When you quit sugar you can might experience some withdrawal symptoms including depression and anxiety.
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