The brain is one of the most undervalued organs.
True, people know that the brain is the hub of life. It oversees pretty much everything.
Its most primitive parts control the basic functions for life: breathing, heartbeat, eating, regulating thirst, and more.
Outside of the medical world, the brain has largely been underappreciated by the general public. Only when traumatic brain injury or a brain disease like dementia, Alzheimer’s or Parkinson’s appears, do we sit up and take notice.
The fact of the matter is, like any organ, the brain needs as much care to be and to function its best.
Many so-called lifestyle choices impact the brain either positively or negatively. Working in a mental health and addictions hospital, I see the impact that these choices have on brain health EVERY DAY.
Alzheimer’s and other types of dementia risk are influenced by diet. Anxiety, ADD, and mood disorders like depression respond to nutrition, as do disorders like Bipolar. Nourishing your brain is crucial but so is avoiding, or greatly limiting, other dietary ‘brain robbers’.
8 worst foods for your brain
Many brain health issues are not resigned to your genetic makeup alone. It’s estimated that about 90% of our genes are mutable. What we expose them to influences their function and this includes foods.
What we eat and drink impacts brain structure and function and, in turn, influences how we feel, our long term risk for dementia, and the degree to which we can prevent cognitive decline.
Fish high in mercury and low in selenium
Mercury is a heavy metal found throughout the environment, all over the world. It’s true that mercury (methylmercury) can accumulate in the tissues of animals where concentrations are highest in large predatory fish (1, 2). This is why many people ask me about mercury in fish and if they should avoid their favourite tuna or salmon salad sandwich.
Mercury toxicity can result in damage to the central nervous system (brain and spinal cord), liver, and kidneys. There’s also no denying that in very large concentrations, mercury is a neurotoxin (2). Outside of mercury spills or other occupational exposure, the true clinical impact of infinitely smaller mercury exposure remains controversial (2).
Because mercury can pass through the placenta and lodge in the fetal brain, guidelines for pregnant women to reduce mercury exposure, including avoiding certain fish species have been developed (3). Unfortunately, this message has been inappropriately extrapolated to include the entire human race.
Should you worry about fish?
While high intakes of mercury are toxic to the brain, fish remains to be very healthy food, including being healthy for your brain (4). Most fish and seafood ARE NOT a significant source of mercury (5).
Not only that, the fish that most people eat are also a good source of selenium; a mineral that protects against mercury toxicity. Selenium binds to mercury and sequesters it (6). This reduces mercury accumulation.
It turns out, the very fish that are restricted for both pregnant women and the general population such as marlin, orange roughy, swordfish, tilefish, shark, and fresh or frozen tuna, are fish that are low in selenium. To be clear, the benefits of eating fish and seafood, where mercury content is concerned, FAR outweigh any risk of mercury exposure (2).
Alcohol
No one likes to talk about alcohol’s dark side. It is, after all, the most normalized and sanctioned drug in most societies.
The fact of the matter is, alcohol is a potent neurotoxin. For most people, it’s hard to conceptualize the negative impact of alcohol outside of the cliched example of an ‘alcoholic’. The stereotype of the inebriated, disheveled, abusive, and/or a neglectful person who can’t hold it together.
Alcohol can be enjoyed in ‘moderation’ but it doesn’t take much for it to have a negative impact on brain health and function. Alcohol’s effect on the brain is two-fold: 1) it leads to various forms of malnutrition (even chronic low intake of nutrients over time takes its toll), and 2) neurotoxicity.
Chronic alcohol consumption can lead to a reduction in brain volume, e.g. mass. Just like muscles, your brain can atrophy too with poor nutrition. Alcohol use can also lead to changes in brain function by messing with its metabolic processes and neurotransmitter function (7, 8, 9, 10).
FUN FACT: Smaller brain size (volume) is no bueno.
Alcohol also interferes with sleep which has detrimental, long term effects on brain health and cognition (11). I’m not talking about zonking out. Of course, you sleep, I’m talking about the objective measure of sleep quality, brain wave activity, etc.
Alcohol is known to deplete protective brain nutrients like omega 3 fats, magnesium, and B vitamins. In particular, vitamin B1 (thiamin or thiamine) is hugely important.
Alcohol use can lead to a vitamin B1 deficiency resulting in Wernicke encephalopathy (general term for alcohol-related brain damage). If left untreated, it can progress to Korsakoff syndrome, a severe form of brain damage characterized by anterograde amnesia. This kind of amnesia is the inability to form new memories (12, 13, 14).
Lower-grade brain damage can also occur with habitual alcohol intake. Low grade (functional deficiencies) of nutrients, including thiamine can increase the risk for alcohol-related brain damage (ARBD) (15, 16).
Highly processed foods and junk foods
This isn’t much different than foods high in sugar, trans fat or refined carbs. Highly processed foods can be anything that’s made from ingredients that are isolated from whole food sources, like sugar from beets. They can also include an ingredient that’s been refined to remove many of the healthy parts, e.g. turning a whole grain into white flour, etc.
They are what’s referred to as nutrient-poor; high in calories and low in nutrients. They can negatively affect your brain by promoting weight gain, increasing oxidation and inflammation, and promoting insulin resistance. Metabolic syndrome alone has been shown to cause brain tissue damage (17, 18, 19).
A lot of the calories that most people consume in the so-called modern, Western diet come from processed ingredients and this dietary pattern negatively impacts the brain including reasoning, learning, and memory (20, 21, 22).
A little known player in brain health is brain-derived neurotrophic factor (BDNF). A molecule that is needed for long-term memory, learning, and the growth of new neurons. Yes, we keep growing new neurons throughout life, under the ideal conditions of course. A highly refined and processed diet decreases the production of BDNF (23, 24).
Sugary drinks
Not sure this should be a surprise to anyone.
High sugar drinks include the obvious like soft drinks (a.k.a. pop), as well as, sports drinks, energy drinks, fruit juice, sweetened iced tea, lemonade, etc.
Everyone knows that too much sugar isn’t healthy but specifically for your brain? It’s true, but not only because excess liquid calories can lead to metabolic syndrome, insulin resistance, and diabetes which all negatively affect the brain (25, 26, 27).
High sugar intakes also increase the risk for a common form of dementia, Alzheimer’s. How? Alzheimer’s is marked by insulin resistance of the brain. That’s why Alzheimer’s disease is informally called Type 3 diabetes, or diabetes of the brain (28, 29, 30).
Even without being insulin resistant or having diabetes, elevated blood sugar levels can increase the risk of dementia (31). Large increases, or spikes, in blood sugar after eating are not great for the brain and sugary drinks can be a significant contributing factor for this.
Refined carbs
In a nutshell, this is the white stuff. It can also include refined sugars (table sugar, brown sugar, cane sugar, syrups, etc) but mostly refers to refined grains. The largest amount of which are foods based on white flour (bread, bagels, pasta, crackers, buns, etc).
Foods with concentrated amounts of refined carbs, either as sugars or starch, when consumed in large amounts (either at one sitting or over the course of a day) may impact brain function (32).
The amount of carbohydrate in a diet (pattern of eating) has been associated with poorer cognitive performance (33, 34, 35)
Higher intakes of carbohydrates, especially from refined foods, lead to higher blood sugar levels. This results in more insulin being released and temporarily increases inflammation after eating. Inflammation is a known risk factor for degenerative brain disease (36).
Over time, these mini ‘hits’ can increase the risk for oxidative damage to your neurons which can increase the risk for brain-related disorders and impaired cognitive performance.
Foods high in trans fats
In Canada, like the US, trans fats have been officially banned from the food supply as of Sept 1, 2018. Well, almost.
The catch is that foods produced (formulated) before the ban came into effect will be exempt. Therefore it will likely be three years before trans fats are fully off store shelves.
New food formulations since the ban will not be able to manufacture partially hydrogenated oils from seed and grain oils. It also means that’s it’s illegal for food manufacturers to add artificial trans fats to their products as of Sept 1, 2018.
From a physiology point of view, artificial trans fats don’t work well or play well with others. Brain research has found conflicting results though. Some have shown them to be detrimental to the brain. This includes increased risk for Alzheimer’s, poor memory, early cognitive decline and decrease brain mass (37, 38, 39, 40).
Like with all things research, other studies haven’t found trans fats to be problematic (41, 42, 43, 44). It may be that trans fats don’t directly exert their negative effects on the brain, even when the brain incorporates them into the membrane (structure) of the neurons.
Trans fats are known to increase systemic inflammation (whole-body) which may influence brain health (45, 46, 47). Trans fats and inflammation are known to detrimentally impact the cardiovascular system. The brain needs healthy vessels to bring it nutrients and oxygen while taking away carbon dioxide.
Vegetable oils
This may seem counter-intuitive because we’ve been told that vegetable oil is good for us. This has been the message ever since the 1960s when the anti saturated fat movement started, Since then, we’ve been told to consumed more oils from grains and seeds. These include soybean, corn, safflower, peanut, sunflower, and canola, a.k.a. “vegetable oils”.
One of the ways that vegetable oil can be bad for your brain is that ALL grain and seed oils contain trans fats. This is because, during the refining, bleaching, and deodorizing stages of vegetable oil production, small amounts of trans fat are produced (48).
The trans fat content of these oils can range from 0.2 to 3.6% of the total fat content. Studies have found as much as 4.2% of the total fatty acid content to be trans fat (49).
Health organizations like Health Canada have always known this and make allowances for trans fats to be present in vegetable oils and their products such as margarine. While no longer on their website, this information is captured with this screenshot. This is of course curious since their, and other health organizations’ stances have been that trans fats have no place in a healthy diet.
While not a human study, mouse models of Alzheimer’s found that canola oil consumption was associated with worsened memory and learning ability (50). New research shows lowering omega 6 fats may help the brain (51, 52). This is important because the human brain contains more omega 6 fats than ever before in our evolutionary history.
Vegetable oils are also very high in omega 6 fats. Because they are used so much in food production, we are consuming way more than we should. The ideal ratio of omega 6 to omega 3 should be around 1:1 to 1:4. Some estimates are that it’s closer to 1:15-20. Why does this matter? Consuming more omega 6 may increase systemic inflammation.
This high intake has been associated with non-alcoholic fatty liver disease (NAFLD), inflammatory bowel disease (IBD), cardiovascular disease and total mortality (deaths) and Alzheimer’s disease (53, 54, 55).
Deep fried foods
Most focus on the role that sugar, added fats, and calories have on weight gain which, can contribute to poorer brain health but there are other nuanced ways as well.
Cooking oils, primarily vegetable oils, are structurally changed when heated to high temperatures. When heated, these oils produce aldehydes, toxic compounds that have been associated with increased risk for dementia (56, 57). This doesn’t include concerns for increased cancer or heart disease.
The oils most susceptible to heat-induced structural changes are the polyunsaturated fatty acids found in soybean, corn safflower, peanut, sunflower, and canola oil (58)
Not to rain on your parade but a typical meal of fish and chips (one of my fav) fried in vegetable oil contains between 100 to 200 times more aldehydes than what’s considered safe by the World Health Organization.
Bottom line
Make no mistake, the foods you eat, and the beverages you drink have a significant impact on your brain.
Your diet affects both the structure and function of your brain and the evidence is clear: inflammatory dietary patterns that are low in brain health-protective nutrients and high in brain-robbing foods contribute to poorer brain health.
This is of concern as we are seeing the impact of modern living, including a dietary pattern that is, in many ways, at odds with our biology and it’s taking its toll on our collective anatomy.
“the human brain is changing in a way that is as serious as climate change threatens to be”
Professor John Stein, Oxford University’s emeritus professor of neuroscience
Doug Cook RDN is a Toronto based integrative and functional nutritionist and dietitian a focus on digestive, gut, mental health. Follow me on Facebook, Instagram and Twitter.