WARNING!
This is an older article that may not reflect Dr. Mercola’s current view on this topic. Use our search engine to find Dr. Mercola’s latest position on any health topic.
By Dr. Mercola
Compelling research shows that your brain has great plasticity, which you control through your diet and lifestyle choices. Unfortunately, the American public has been grossly brainwashed by the sugar and processed food industries into believing that sugar is a perfectly reasonable "nutrient" that belongs in a healthy diet.
A piece of fruit, or even a treat like ice cream, isn’t going to cause you too much trouble… provided it truly is just that – a treat and not something that you overindulge in.
Most Americans, however, are overindulging – and that’s putting it mildly. The average American consumes one-third of a pound of sugar per day, half of which is processed fructose.
Other statistics found in Dr. Richard Johnson’s book, The Sugar Fix, suggest about 50 percent of Americans consume as much as half a pound, more than 225 grams, per day!1
Talk surrounding excess sugar consumption is often centered on obesity, to which it does contribute. However, this is an issue of far more than weight gain alone. When you consume too much sugar, it leads to serious imbalances in your body, including microbial changes that have far-reaching effects on your health.
Eating Too Much Sugar Is Detrimental to Your Brain
Obesity, type 2 diabetes, and even heart disease are commonly known to be caused, in part, by a poor diet with excess sugar (including fructose). But brain troubles? These, too, are strongly linked to eating sugar, unbeknownst to many Americans.
A study in mice, published in the journal Neuroscience, revealed that a high-sugar diet lead to changes in gut bacteria that were in turn related to a significant loss of cognitive flexibility, which is a measure of your brain’s ability to adapt to changing situations.2
Impairments in both long-term and short-term memory were also noted.3 After four weeks of consuming excess amounts of sugar, the mice performed poorly on a variety of tests related to mental and physical function when compared to mice fed a normal diet.
Further, an analysis of the mice microbiome revealed that an imbalance of bacteria in the guts of the high-sugar mice directly correlated with their poor performance on tests of cognitive flexibility.
Kathy Magnusson, a professor in the OSU College of Veterinary Medicine and principal investigator with the Linus Pauling Institute, said in an Oregon State University news release:4
“It’s increasingly clear that our gut bacteria, or microbiota, can communicate with the human brain… Bacteria can release compounds that act as neurotransmitters, stimulate sensory nerves or the immune system, and affect a wide range of biological functions…
We’re not sure just what messages are being sent, but we are tracking down the pathways and the effects.”
Too Much Sugar Makes You Stupid…
This isn’t the first time sugar has been linked to declines in brain function. In 2012, researchers investigated the effects of high-fructose syrup, similar to high-fructose corn syrup (HFCS), a cheap sweetener six times sweeter than cane sugar, which is used in many soft drinks, processed foods, condiments, and even some baby foods.
The team sought to study the effects of a steady intake of this super-processed, concentrated form of fructose. They fed rats a fructose solution as drinking water for six weeks, then tested their ability to remember their way out of a maze.5
The rats fed fructose syrup showed significant impairment in their cognitive abilities—they struggled to remember their way out of the maze. They were slower, and their brains showed a decline in synaptic activity. Their brain cells had trouble signaling each other, disrupting the rats' ability to think clearly and recall the route they'd learned six weeks earlier.
Additionally, the fructose-fed rats showed signs of resistance to insulin, a hormone that controls your blood sugar and synaptic function in your brain. Because insulin is able to pass through your blood-brain barrier, it can trigger neurological processes that are important for learning and memory.
Consuming large amounts of fructose may block insulin's ability to regulate how your brain cells store and use sugar for the energy needed to fuel thoughts and emotions.6
In this case, a second group of rats was given omega-3 fats in the form of flaxseed oil and DHA (docosahexaenoic acid), in addition to the high-fructose diet. After six weeks, this group of rats was able to navigate the maze better and faster than the rats in the non-DHA group.
The researchers concluded that DHA is protective against fructose's harmful effects on your brain. DHA is essential for synaptic function—it helps your brain cells transmit signals to one another, which is the mechanism that makes learning and memory possible.
Your body can't produce enough DHA, so it must be supplemented through your diet in wild-caught seafood or a supplement like krill oil. Many Americans are seriously deficient in omega-3 fats, which means they may be especially vulnerable to the harmful effects of excess fructose.
Elevated ‘Normal’ Blood Sugar Levels Linked to Memory Loss
Remember how the fructose-fed rats showed signs of insulin resistance, which could play a role in its negative effects on brain health? Even if you don’t have type 2 diabetes or pre-diabetes suggestive of insulin resistance, higher blood sugar levels appear to have a negative influence on cognition.
One study involved people (with an average age of 63) who were free from diabetes and pre-diabetes (or impaired glucose intolerance). Yet, even among this group, those with higher blood sugar levels scored lower on memory tests.
For each 7-mmol/mol increase in HbA1c (a measure of blood glucose), participants recalled two fewer words on memory tests.7 Those with higher blood sugar levels also had lower volume of the hippocampus, a brain region linked to memory. As one of the study’s authors said:
"Clinically, even if your blood sugar levels are 'normal,' lower blood sugar levels are better for your brain in the long run with regard to memory functions as well as memory-relevant brain structures like the hippocampus.
Scientifically, we were able to shed further light on the mechanisms mediating these effects. DTI-based (diffusion tensor imaging) measurements demonstrated that not only volume of the hippocampus, but also microstructural integrity is lower if blood sugar levels are higher."
If You Become Desensitized to Insulin, Your Whole Body Suffers
Most likely, this effect has to do with the increased levels of insulin being released in response to the chronically elevated blood sugar levels… Any meal or snack high in grain and sugar carbohydrates typically generates a rapid rise in blood glucose.
To compensate for this, your pancreas secretes insulin into your bloodstream, which lowers your blood sugar to keep you from dying. Insulin, however, is also very efficient at lowering blood sugar by turning it into fat – so the more you secrete, the fatter you become.
Unfortunately, If you consume a diet consistently high in sugar and grains, your blood glucose levels will be correspondingly high and over time your body becomes "desensitized" to insulin and requires more and more of it to get the job done.
Eventually, you become insulin resistant, and then full-blown diabetic. But as the new study showed, health effects of this elevated blood sugar/insulin cycle begin to occur even before insulin resistance sets in.
Even Dementia Has Been Linked to a Poor Diet
It's becoming increasingly clear that the same pathological process that leads to insulin resistance and type 2 diabetes may also hold true for your brain.
As you over-indulge on sugar and grains, your brain becomes overwhelmed by the consistently high levels of insulin and eventually shuts down its insulin signaling, leading to impairments in your thinking and memory abilities, and eventually causing permanent brain damage, among other health issues.
Research has even shown that higher glucose levels are associated with a higher perceived age;8 in other words, the higher your glucose levels, the older you’ll tend to look!
Even Alzheimer's disease was tentatively dubbed "type 3 diabetes" in early 2005 when researchers discovered that in addition to your pancreas, your brain also produces insulin, and this brain insulin is necessary for the survival of brain cells. Studies have found that people with lower levels of insulin and insulin receptors in their brain often have Alzheimer's disease.
Neurologist Dr. David Perlmutter, MD insists that being very strict in limiting your consumption of sugar and non-vegetable carbs is one of THE most important steps you can take to prevent Alzheimer's disease for this very reason. He cites research from the Mayo Clinic, which found that diets rich in carbohydrates are associated with an 89 percent increased risk for dementia.
Sugar Decimates Your Gut Health, Which in Turn Decimates Your Brain…
Getting back to the featured study, the impairments in memory were directly linked to changes in gut microbiota caused by excess sugar consumption. This isn’t entirely surprising since your gut, which is teeming with microbial life, also communicates with your brain, via what’s known as the “gut-brain axis.” Embedded in the wall of your gut is actually your enteric nervous system (ENS), which works both independently of and in conjunction with the brain in your head.
This communication between your "two brains" runs both ways and is the pathway for how foods affect your mood or why anxiety can make you stick to your stomach, for instance. However, this gut-brain connection is about far more than just comfort food or butterflies in your stomach. According to Scientific American:9
"The gut-brain axis seems to be bidirectional—the brain acts on gastrointestinal and immune functions that help to shape the gut's microbial makeup, and gut microbes make neuroactive compounds, including neurotransmitters and metabolites that also act on the brain."
Changes in Your Gut Bacteria May Lead to Brain Disorders
Download Interview Transcript
The close connection between your microbiome and your brain also explains why changes in your gut bacteria are linked to brain disorders and more, including depression. Jane Foster, PhD, an associate professor of Psychiatry and Behavioral Neurosciences at McMaster University, described to Medicine Net the multiple ways your gut microbes communicate with your brain:10
“One is via the enteric nervous system, the part of the nervous system that governs the digestive tract. Also, gut bacteria can alter how the immune system works, which can affect the brain. The gut bacteria are involved in digestion, too, and the substances they make when they break down food can affect the brain. And under certain conditions, such as stress or infection, potentially disease-causing gut bacteria, or bad bugs, can leak through the bowel wall and enter the bloodstream, enabling them and the chemicals they make to talk with the brain through cells in blood vessel walls.
Bacteria could also communicate directly with cells in certain regions of the brain, including those located near areas involved in stress and mood…”
Dr. Perlmutter also explains that one of the primary mechanisms of action that explains how a healthy diet "works" for preventing disease, including neurological disorders, is that it upregulates, modifies, and improves the quality of your gut microbiome.
"We're now recognizing from research at our most well-respected institutions from around the globe that the gut bacteria are wielding this very powerful sword of Damocles… They determine whether we're going to have a healthy brain or not, whether our brain is going to function well or not, and whether our brain is going to become diseased or not. Who knew that we'd be referring back to the gut?"
How to Keep Your Gut (and Brain) Healthy
A healthy gut may therefore be the key to a healthy brain, and one of the key strategies toward this end is limiting excess sugar, including fructose. There is no question in my mind that regularly consuming more than 25 grams of fructose per day will dramatically increase your risk of dementia, including Alzheimer's disease. So you’ll want to limit your intake to 25 grams per day (or less), and 15 grams or less if you are overweight or have diabetes, pre-diabetes, high cholesterol, or high blood pressure.
Further, consuming naturally fermented foods, such as sauerkraut, naturally fermented pickles, miso, tempeh, and fermented dairy made from raw, unpasteurized grass-fed milk (yogurt, kefir, etc.), is one of the best ways to optimize your microbiome, which in turn may optimize the health of your brain. Fermented vegetables are particularly easy to make in your own kitchen.
They are also the most cost-effective way to get high-quality probiotics in your diet. Your goal should be to consume one-quarter to one-half cup of fermented veggies with each meal, but you may need to work up to this amount. In the long run, making sure you’re eating a healthy diet is the key to a healthy gut and stellar brain health alike.