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Most people have heard that sugar is unhealthy, but how exactly can it work against your good mental health?

When you eat concentrated sources of rapidly-digestible carbohydrates such as sugar, flour, fruit juice, and processed cereal products, your blood sugar (glucose) can rise sharply, triggering an equally strong rise in the hormone insulin in an effort to bring blood glucose back down to normal.

These dramatic fluctuations in glucose occur inside the brain as well, because brain glucose seems to typically rise and fall in proportion to blood glucose.

These steep increases and drops in glucose and insulin levels could potentially negatively affect your brain and body chemistry in three critical ways.

Refined carbohydrates can destabilize hormones and mood

The problem with unstable insulin levels is that insulin isn’t simply a blood sugar regulator; it also acts as a signaling hormone that affects numerous other hormones throughout the body. Every time insulin rises and falls, these hormones may follow suit, which can place you on a hormonal rollercoaster.

Let’s say you start off your morning with a food rich in refined carbohydrates — like orange juice, a bagel, or a bowl of corn flakes. Within a half hour, your blood sugar escalates, and your pancreas immediately releases insulin into your bloodstream to pull the extra sugar (glucose) out of your blood and squirrel it away into your cells. About an hour or so later, as your blood sugar is dropping, you may feel tired, unfocused, and hungry.

The body perceives rapidly falling glucose as a potential emergency, so it releases a mixture of hormones to keep glucose from falling below normal. This mixture includes the stress hormones cortisol and adrenaline — our “fight-or-flight” hormone.

Many people consume refined carbohydrates at every meal and as snacks, which can place their hormones on a seesaw all day long and even well into the night. Age, metabolism, gender, genetics, and activity level can influence what your personal hormonal rollercoaster feels like. Fluctuating energy levels, difficulty concentrating, mood swings, binge eating, irritability, anxiety attacks, and insomnia are all possibilities, depending on the individual.

Yet even if you aren’t aware of any symptoms on the outside, trouble may be brewing on the inside, as normal rhythms are disrupted in ways that can slowly, silently lead to health problems down the road. For more information, including graphs of sugar and hormone rollercoasters on different diets, read “Stabilize your mood with food.”

Refined carbohydrates can promote oxidation and inflammation

Unnaturally high blood sugar may promote oxidation and inflammation, which are features of many chronic diseases, including psychiatric disorders.

What is oxidation?

The chemical reactions our cells rely upon to turn food into energy require oxygen molecules that can break apart into reactive “free radicals” during digestion. Free radicals are like little bulls in a china shop — left unchecked, they bump into and react with neighboring structures and DNA, potentially damaging cells from the inside out (oxidation).

Since some amount of oxidation is normal and necessary, Mother Nature has armed us with a variety of our very own internal antioxidants to mop up excess free radicals. Under normal circumstances, these built-in antioxidants are sufficient to keep oxidation and anti-oxidation forces in balance and prevent cellular damage.

The problem with high-sugar foods and beverages is that they can present chemical pathways with too much glucose at once, generating more free radicals than our internal antioxidants can neutralize. Depression, bipolar disorder, schizophrenia and obsessive-compulsive disorder are all potentially associated with excess oxidation.

We are often told that the solution to our oxidation problem is to consume colorful, antioxidant-rich fruits and vegetables to bring our systems back into balance. Yet most plant antioxidants, when consumed in their natural form, are poorly absorbed by the human body, and it’s still unclear whether or not they are of much use to us.

On the other hand, refined carbohydrates may deplete our natural antioxidants, making it appear as if we need more antioxidant power than we already have. Instead of buying antioxidants, wouldn’t it make a lot more sense to simply stop eating pro-oxidants? For more information about the pros and cons of antioxidants, including “superfood” examples, read the “The antioxidant myth.”

What is inflammation?

Our immune system reacts to oxidative damage by mounting an inflammatory response. This isn’t the kind of inflammation that makes your brain swollen, red, or sore — it’s inflammation on a microscopic level. Multiple lines of evidence point to a connection between inflammation and many cases of depression, bipolar disorder, and schizophrenia.

When cells are in distress, they release tiny cries for help in the form of “inflammatory cytokines” such as IL-6 and TNF-alpha that can be measured in the blood. Levels of these molecules are often higher in people with mood and psychotic disorders.

Inflammatory cytokines may trigger damage to nearby brain cells and cause chemical imbalances in the brain by disrupting normal production of serotonin, dopamine, and glutamate — key neurotransmitters involved in psychiatric disorders. While we don’t yet have clinical studies cementing a causal relationship, paths leading from sugar to oxidation to inflammation may help to connect the dots between modern diets and mental illnesses.

Mechanistic theories suggest that refined vegetable and seed oils like soybean and sunflower oil might also contribute to excess inflammation. However, this is controversial as a systematic review of randomized trials found no evidence that linoleic acid, the main omega-6 fatty acid in vegetable oils, increases inflammation, at least in healthy people. These oils are found in all kinds of processed foods — from high-carbohydrate foods like chips and baked goods to popular low-carb foods like mayonnaise and salad dressings.

Omega-6 fatty acids are responsible for mounting the inflammatory response to oxidative damage, injuries and infections, whereas omega-3 fatty acids are responsible for initiating the healing response.

These two forces likely work best when they are roughly in balance. Unfortunately, modern diets are not only extremely high in omega-6 fatty acids, they are also often low in omega-3 fatty acids compared to our hunger-gatherer predecessors. Imbalances in these essential fatty acids have been seen in many psychiatric disorders.

Numerous studies have tested whether anti-inflammatory drugs can be used to treat mood and psychotic disorders — and they do sometimes help to some extent. But rather than taking drugs to simply mask symptoms — drugs which cost money and can cause side effects — why not start by eliminating processed foods instead?

Too much sugar contributes to insulin resistance

Insulin resistance is emerging as a potentially important factor in the development of most of the mental health problems we fear — from straightforward conditions such as depression to complex brain degeneration disorders like schizophrenia and Alzheimer’s disease. As tragic as this may seem, understanding that insulin resistance strongly influences our risk for psychiatric disorders is tremendously empowering, because insulin resistance is a familiar beast we already know how to tame.

High-sugar diets may place too much pressure on the pancreas to produce high amounts of insulin to keep blood glucose under control. Over time, if exposed to elevated insulin levels too often, the receptors that transmit insulin’s instructions can become damaged and dwindle in number, making it increasingly difficult for cells to respond to insulin’s important messages.

In people with insulin resistance, the insulin receptors responsible for escorting insulin from the bloodstream into the brain’s interior can malfunction and shrink in number, restricting insulin flow into the brain. If you have insulin resistance or type 2 diabetes, glucose may continue to easily enter the brain, but insulin will struggle to gain access.

Without adequate insulin, brain cells can’t process glucose properly, and will start to slow down. This sluggish glucose processing problem is called “cerebral glucose hypometabolism” and is a key feature of many brain disorders, particularly Alzheimer’s disease.

How low-carbohydrate diets can improve brain metabolism

If high blood sugar and insulin can jeopardize brain health through inflammation, oxidation, and insulin resistance, then we can hypothesize that reducing blood glucose and insulin levels could help improve brain health. A growing body of scientific literature supports the idea that ketogenic diets have the potential to address all of these underlying biochemical disturbances, and therefore hold great promise for the dietary treatment of psychiatric disorders.

Carbohydrates tend to raise glucose and insulin levels the most, whereas fats raise them the least. So it stands to reason that a low-carb, high-fat diet could be one of the best ways to target these root causes of brain malfunction, improve brain metabolism, and protect the brain from further damage.

It has been known for nearly a century that ketogenic diets have the power to completely eliminate seizures in some children with epilepsy and significantly reduce the frequency of seizures in others. Although the exact mechanism is not know, the findings certainly suggest that low-carbohydrate diets can beneficially impact brain chemistry.

The brain is a highly-active organ that demands a constant supply of high-quality fuel. And while it’s true that some of its fuel must be in the form of glucose, that glucose does not need to come from carbohydrates in the diet.

The US Food and Nutrition Board acknowledges that “the lower limit of dietary carbohydrate compatible with life is apparently zero, provided that adequate amounts of protein and fat are consumed.” Through a natural process called “gluconeogenesis” (making glucose from scratch), the liver can make glucose and release it into the bloodstream for any cells that require it, including brain cells.

When carb intake is reduced, insulin levels decrease. If insulin levels are sufficiently low, your body switches from primarily burning sugar to primarily burning fat. This shift is called ketosis, in which your liver releases fat-like compounds called ketones into the blood to provide fuel for your cells. You can test to see if you are generating ketones with a blood ketone meter.

Although muscle cells and most other cells in the body can use fatty acids for energy, brain cells aren’t equipped to use them. So, they use ketones instead. Ketones are an excellent fuel source for the brain. They seem to burn more efficiently than glucose, producing less oxidation and inflammation.

Although some rapid-fire brain cells always require some glucose (because it burns faster than ketones do), ketones can meet up to a remarkable two-thirds of the brain’s total energy requirements. In fact, some data suggests most brain cells will burn ketones over glucose, making ketones the preferred energy source for large portions of the human brain.

Although insulin resistance of the brain makes it difficult for insulin to cross into the brain, it doesn’t interfere with the flow of ketones. Therefore, the more ketones you have in your blood, the higher your brain ketone levels will be, and the more ketones your brain cells can absorb and use for energy. As an added bonus, it just so happens that ketones burn beautifully in a low-insulin environment, making ketones an ideal fuel source for the insulin-resistant brain.

The food-mood connection

From glucose and insulin oscillations to oxidation, inflammation, and insulin resistance, a modern diet full of sugar and refined carbohydrates can be a potential driver of psychological distress. For more details about how a whole-food, low-carbohydrate diet can help with specific psychiatric disorders, please visit our guide, The food-mood connection.

If you are struggling with mental health issues and taking medication, we have a lot more information on this topic in our guide, Low carb and mental health: Getting started and managing medications. We also have an FAQ that addresses many common questions and concerns about the links between diet and mental health.

/ Dr. Georgia Ede, MD