How Sugar Affects The Brain
Does Sugar Consumption Hinder Cognitive Performance?
The brain’s relationship with sugar is a complicated one. These days you will find plenty of articles about how sugar is the evil to end all evils. To read some of the most popular blog-cum-news sites today, you’d think they had a quota for sugar-bashing articles.
While the vast majority of these articles focus on sugar’s powerful effect on our body fat levels, more attention is now being given to sugar’s effect on the brain. Some of these concentrate on sugar’s ability to affect brain function (learning, attention span and memory), while others take a look at sugar’s relationship with long-term brain health.
In this article, we are going to try to take a balanced look at both of these aspects.
We won’t be commenting on all of sugar’s effects on the body; that high or frequent sugar intake has a direct correlation with diabetes, obesity, and some cancers is a topic dealt with elsewhere.
Rather, we will restrict ourselves to examining sugar’s relationship with the brain, looking at both its long-term physical health and its ability to function properly. We will look at what happens when someone consumes too much sugar, as well as what happens when someone consumes any sugars of any kind.
Hopefully this will give you a good, rounded understanding of how sugar affects the brain. We will try to give you a good basis of knowledge which will allow you to do further research into a topic that interests you most, while also allowing you to implement your knowledge to improve your own cognitive performance.
The Brain Needs Sugar
We are not being dramatic when we say that the brain needs sugar. In fact, glucose is the primary fuel source for almost every cell in the human body. It is, in a sense, the perfect fuel for your cellular mitochondria.
The brain is far and away the most “energy greedy” organ you have. Each and every day, your brain consumes about 50% of all the sugar in the body. If your blood sugar is too low, then your brain simply can’t function properly. Of course it will still function to a degree, but just as you can’t run a marathon without sufficient energy stores, your brain can’t be expected to be as sharp as it could be if it doesn’t have access to enough glucose.
You will notice this happening if you skip lunch or if your late morning meeting drags on into the early afternoon. As you get hungrier, you become less attentive, drowsy, perhaps irritable.
What’s happening is your brain is running low on fuel, so it is prioritizing functions; it wont cut back on important things like limb movement, but it can cut back on less important things like the ability to take in what Mark is saying about this month’s sales.
And it isn’t protein or fat that the brain is craving; it’s glucose.
Does That Mean You Need To Eat Sugar?
The brain needs glucose to function, as do lots of other organs and cells within your body. But that does not mean that you must make glucose a significant part of your diet.
When you eat any carbohydrate, no matter what it is, your digestive system breaks it down into sugar and releases those sugar molecules into the bloodstream.
All carbohydrates are simply more or less intricately arranged sugar molecules.
Regardless of what your personal trainer might tell you, complex carbohydrates are nothing more than sugar molecules arranged in long, intricate (some might say complex) chains.
So the fact that the brain needs sugar to operate doesn’t mean that you need to start drinking a can of Coca Cola every day. No, not at all. Any carbohydrate you eat will be broken down into its constituent sugars and that fuel will find its way to your brain.
In fact. as far as concentration levels go, eating complex carbohydrates is preferable to eating simple sugars.
Complex Carbs vs Simple Sugar Consumption For Focus
Complex carbohydrates take longer to break down than simple sugars because they’re, well, more complex.
This means that the sugar release is much more gradual. Your blood sugar levels will rise slowly as the sugar molecules are drip fed into your blood stream. This means that while the boost in energy levels is less pronounced, it lasts much longer.
The fall in blood sugar levels is also much less pronounced when consuming complex carbohydrates, or those with a very low glycemic load. This means you wont have a sudden and short loved high followed by a crashing low as the meeting draws to a close an hour or so later.
So when you take a break from your monthly client update and you need a pick-me-up, you’ll be much better off reaching for a bran muffin or some oatmeal or a wholewheat bread sandwich than some soda and a bag of potato chops, even if the latter makes you feel better in the short run.
What Sugar Consumption Does To The Brain
We think that should suffice as an explanation of the brain’s relationship with sugar, how it gets sugar, and what that means for your diet.
Now we can begin looking at the adverse effects of sugar consumption on brain health and brain function. We will break this section down into small chunks, each focusing on a different aspect of brain health or cognitive performance and how sugar affects it.
Learning & Memory
The link between a diet high in simple sugars and impaired cognitive function is remarkably well-established. This is surprising when you consider how few people know about this link, and how fewer still use that information to boost mental performance.
One widely quoted study published in the Journal of Physiology looked at the effect of a high fructose diet on the brain function of rats. The results are fairly unequivocal: a diet with a consistently high fructose content gradually impairs memory function and learning.
As Fernando Gomez-Pinilla, Professor of Neurosurgery at the David Geffen School of Medicine at UCLA, stated: “Our findings illustrate that what you eat affects how you think…Eating a high-fructose diet over the long term alters your brain’s ability to learn and remember information.”
Another study, published in peer-reviewed Nutrients in August 2015 (read here), found that “Hippocampal-dependent memory appears to be particularly vulnerable to the effects of high-energy diets and these deficits can occur rapidly and prior to weight gain.” By high-energy diets, the researchers mean diets high in both fat and sugar. The authors noted that more chronic exposure to a high energy diet seems necessary for other types of memory to be adversely affected.
These results have been replicated in many studies, published in disparate journals, and conducted by researchers around the world.
Take this study for instance, which lays out a literature review and finds that high fat and sugar “intake is associated with cognitive impairment, with a specific emphasis on learning and memory functions that are dependent on the integrity of the hippocampus.”
Perhaps most importantly, this study looked at the effect of a high fat and sugar (HFS) diet on humans. Published in Behavioural Neuroscience in 2011, these researchers found that “the HFS rich diet groups were less accurate in recalling what they had previously eaten and evidenced reduced sensitivity to internal signals of hunger and satiety, relative to a group consuming less HFS rich diets. Together, these findings reveal an association between HFS consumption and poorer hippocampal function in human participants, consistent with findings from animal-based studies.”
So what is going on here?
Well, there seem to be a few mechanisms that are plausible causes of the cognitive impairment observed in these studies.
The main contender seems to be the way that insulin can interfere with signalling in the hippocampus; the part of the brain responsible for certain types of memory (ref).
According to Fernando Gomez-Pinilla, the UCLA Professor mentioned earlier, “Because insulin can penetrate the blood–brain barrier, the hormone may signal neurons to trigger reactions that disrupt learning and cause memory loss.”
This does indeed seem to be borne out by clinical trials.
One paper published in Nutritional Neuroscience in 2015 states that the researcher’s findings “suggested that a high-fructose diet induced peripheral insulin resistance and an abnormal insulin-signaling pathway in the hippocampus which exacerbated memory deficits in the rats.”
Another contender is the effect sugar intake has on brain-derived neurotrophic factor (BDNF).
A good explanation of this view can be found in a 2002 edition of Neuroscience. Researchers looked at a high saturated fat and refined sugar (HFS) diet and how it interacts with brain-derived neurotrophic factor.
“We show that animals that learn a spatial memory task faster have more brain-derived neurotrophic factor (BDNF) mRNA and protein in the hippocampus. Two months on the HFS diet were sufficient to reduce hippocampal level of BDNF and spatial learning performance.”
Whatever the cause, one thing seems fairly clear: consuming a diet high in saturated fat and refined sugars seems to be a reliable way to impair your cognitive function. Specifically, high sugar diets seem quite capable of significantly inhibiting learning and memory abilities. Only some aspects of memory seem to be affected initially, while more chronic consumption of a HFS diet seems to be related to more widespread memory defects.
We’re very skeptical when anybody claims to be able to point to any one cause of a condition like dementia. The most intelligent, experienced, and determined researchers on the planet, those wonderful people who have dedicated their entire lives to beating dementia, are yet to really decide on a decisive cause.
This is because there are always likely to be several contributory factors which differ in importance according to the person in question.
That said, it is certainly possible to identify what those contributory causes are, and to estimate how well they serve as predictors of dementia occurrence. It is here that we see sugar coming to the fore once again.
We recently came across quite an exceptional observational study which looked at the relationship between bloog glucose levels and dementia risk. The study looked at over 2000 participants. They were all patients at Group Health Cooperative; a large health care facility in Washington State.
The findings are really remarkable: “In conclusion, our data provided evidence that higher glucose levels are associated with an increased risk of dementia.”
The results were clear, unambiguous, and significant. This is best explained by one of the researchers in an interview published in the New Old Age blog of New York Times.
In that interview, lead author Dr. Paul Crane made it clear that the correlation between blood glucose levels and dementia risk was a close and direct one:
“We found a steadily increasing risk associated with ever-higher blood glucose levels, even in people who didn’t have diabetes,” Dr. Crane said. Of particular interest: “There’s no threshold, no place where the risk doesn’t go up any further or down any further.”
So as blood glucose levels continued to rise, so did the risk of that patient developing dementia. As blood glucose levels fell, so did dementia risk. In all circumstances, it seems, lower blood glucose levels mean lower risk of dementia, and vice versa.
That inflammation and cognitive decline are linked now seems to be highly likely. More attention is being given to this proposition than ever before, and a recent study published in Therapeutic Advances in Chronic Disease concluded that, while “the mechanism of age-related cognitive decline is not yet known”, we can confidently say that “age-related inflammatory changes are likely to play a role”.
For sure, inflammation is necessary in certain circumstances, such as fighting specific infections or reducing the damage of certain traumas. But chronic inflammation is another story. This is when inflammation becomes fundamentally destructive rather than healing.
The link between high blood sugar levels and brain inflammation is not yet well-established. However, there are many respected health professionals who firmly believe that elevated blood sugar levels lead to increased brain inflammation, and as a result, accelerated cognitive decline.
As Dr. David Perlmutter states in the above linked article: “When a protein becomes glycated, again as a consequence of persistent blood sugar elevation, it dramatically increases the production in the body of inflammatory chemicals, and as such is directly relates to brain decline.”
Dr. Perlmutter states that much research has been done on this subject, although we are struggling to find a substantial library of scholarly articles and clinical trial data affirming this. All the same, we have found plenty of reputable sources claiming that sugar is an inflammatory substance. Clearly more work is desperately needed.
This one is an indirect link, but it is important to discuss it nonetheless as it is a link commonly made by both experts and laymen alike.
People are generally too flippant with the illnesses they ascribe to certain lifestyle choices. Depression is often carelessly thrown into just about any list of ailments or conditions someone is attributing to a certain substance, practice, or whatever.
The reason for that is because depression is a difficult condition to really pin down. Similar to dementia, it doesn’t seem (to our knowledge anyway) to have any one particular cause, any one particular manifestation, or any one particular “cure”. Health care professionals, psychiatrists and psychologists are perpetually torn between genetic, environmental, behavioural, emotional, and even bacterial explanations for the onset of mental illnesses.
Nobody can point to one particular behaviour and say “don’t do that and you wont develop dementia”. The world is seldom so simple.
That said, we are increasing our understanding of depression on an almost daily basis, and many people are now positing a distinctly physical cause for the condition (or rather one potential cause/contributory factor).
Once again, we’re talking about inflammation.
There is mounting evidence which suggests that there is a strong link between inflammation and depression.
A relatively new study carried out by Researchers from the Centre for Addiction and Mental Health’s (CAMH) Campbell Family Mental Health Research Institute in Toronto, Canada, conducted PET scans of the brains with 40 people; 20 with depression, 20 without as a control.
The researchers found significant inflammation in the brains of the people with depression. Interestingly, the more severe the inflammation, the more serious the depression.
Staggeringly, according to the cited article: “the brains of people who were experiencing clinical depression exhibited an inflammatory increase of 30%.”
If, as outlined in our previous section, inflammation is indeed exacerbated by a diet high in simple and refined sugars, then a link can be drawn between high sugar intake and the onset of depression. Of course, we made it clear that this link is not direct; many things appear to be linked, but on closer inspection, the link is only coincidental. Once again, more study is needed here.
This article was not written to be an eternal guide on sugar and how it affects the brain. Rather, we have simply set out a rough introduction to current thinking on sugar’s influence on brain health and cognitive function.
Hopefully, this will serve as a good basis for you to conduct further research.
It should also hopefully give you some extra pause for thought before you reach for the candy bar or the can of soda when you’re feeling tired and un-focused at work. Sugar clearly has a much more immediate impact on our cognitive function that many of us realize, and the long-term effects to your mental capacity may be significant.
What’s more, the health effects clearly extend to some degree beyond the physical. With mounting evidence showing a link between high sugar intake and cognitive decline, depression and even dementia, you may have more to worry about from your daily chocolate bar than diabetes and a bigger waistline.