It is becoming increasingly clear that the food choices we make every day can alter the way we process information about the world around us. Perhaps this shouldn’t be a big surprise. We know now that the human adult brain, which constitutes only about 2% of our body weight, uses 20% of our total oxygen consumption, and hence 20% of the calories, that we take in. This high use of energy is remarkably constant over widely varying mental activity. The brain never shuts off. Even during sleep, it continues to consume approximately the same amount of energy as it does during the waking hours. Our brains are constantly communicating, both between nerve cells within the brain and nervous system, and from the brain to other parts of the body (1). Where does this energy required for the brain come from? The answer is, from the food that we eat. It’s not too big a jump to realize that eating healthy food might, at the very least, support a healthy brain.
The most common diet of today is linked to compromised brain function
The diet that has been predominant in the developed world throughout the last several decades is known as the Western diet or the Standard American Diet (SAD). It is a diet high in meat, dairy products and processed foods. Consequently, this is also a diet high in sugar and fat, especially saturated fat, and low in fiber and phytonutrients. The underlying problems with the Western diet are its richness in calories that results in chronic overnutrition, and its inflammatory components. Augmenting this is the sedentary lifestyle common in Western societies that itself produces a state of chronic metabolic inflammation (2).
The culmination of these two lifestyle factors is a heightened state of inflammation, called metaflammation, that can wreak havoc throughout the body. Ongoing destructive chronic inflammation and constant stimulation of pro-inflammatory immune cells eventually give rise to the development of the prevalent chronic diseases we see today (2). A vast amount of evidence links the Western diet to many diseases including cognitive impairment (loss of the ability to think clearly, remember important information, and to find the right word to use) and neurodegenerative diseases (amyotrophic lateral sclerosis (ALS), Parkinson’s disease, Alzheimer’s disease and Huntington’s disease) as well as cardiovascular disease, cancer, diabetes and autoimmune diseases (3,4).
Can a healthier diet improve the function of our brains?
Continuing research is unearthing connections between a number of aspects of the food we eat and their effects on brain activities.
Abdominal Body fat
A recent study reveals that fat deposited within our bodies appears to age our brains. Individuals of middle age that carry more visceral fat (fat around the abdomen) slowly lose what is known as “fluid intelligence”. Fluid intelligence is the ability to solve new problems for which there is no background knowledge by utilizing problem solving skills and learning. In other words, that bulge around the middle is exacerbating cognitive decline with aging. Conversely, higher lean muscle mass seems to be brain protective. This research illustrated that these effects remain consistent even after accounting for chronological age, level of education and socioeconomic status (5).
Animal studies from January 2020 demonstrate that visceral fat generates chronically high levels of a specific inflammatory protein, called interleukin-1 beta, that can pass across the blood-brain barrier into the brain. Once there it is free to influence microglial cells. Microglial cells are a type of macrophage (an immune cell) that resides in the brain and spinal cord. In fact, microglia account for 10 to 15% of all the cells found in the brain (6).
Microglia can be helpful or harmful, depending on the signals they are exposed to. They are fundamental for proper brain development and function. They also act as the first and main form of active immune defense in the central nervous system (CNS) by functioning as watchdogs, constantly roaming the brain, eliminating disease-causing organisms, dead cells and other debris as well as both forming and eliminating connections between neurons. In a healthy body, microglia release brain-derived neurotrophic factor (BDNF), which helps to regulate synapses (connections between brain cells) and is important for learning and memory. But, in a body compromised by visceral fat that is producing interleukin-1 beta, hyper-stimulation of the microglia results, transforming them into a highly inflammatory state and prompting them to wrap around the synapses, hindering communication between brain cells (6,7). Microglial dysfunction has been shown to be involved in the development and/or the progression of multiple CNS diseases, including Alzheimer’s disease, Parkinson’s disease, autism spectrum disorder and depression (8).
Blood flow within the brain
A study from early 2020 discovered that higher BMI (Body Mass Index) is linked to decreased blood flow in the brain as well as to increased risk of Alzheimer’s disease and mental illness. As weight goes up, the brain begins to experience lower blood flow and reduced brain cell activity. Researchers in this study used brain imaging to analyze the brain scans of over 17,000 individuals. Results elucidate that higher BMI correlates with decreased blood flowing throughout the brain, including those regions influenced by damage that ends up as Alzheimer’s disease. Hence, low cerebral blood flow is a predictor of Alzheimer’s disease development and is also associated with depression, schizophrenia, bipolar disorder, traumatic brain injury, ADHD, suicide and addiction (9).
Omega-3 fatty acids
There are two essential fatty acids for human beings, omega-3 fatty acids and omega-6 fatty acids. The “essential” moniker means that they must be obtained through diet. Humans are not able to manufacture them. The dry weight of the human brain contains about 60% fat and fatty acids are among the most crucial molecules that determine the brain’s integrity and ability to perform. Omega-3 fatty acids, especially the long chain omega-3 fatty acids, DHA and EPA, are critical for normal brain development and function throughout life. These two fats are also abundant in the cell membranes of brain cells (10).
Research has unveiled that long-chain omega-3 fatty acids are involved in protecting neurons from degeneration and other effects of aging (11). The levels of both DHA and EPA in people with dementia and pre-dementia tend to be low (12). Older people with higher levels of DHA and EPA maintain noticeably healthier brains over time as illustrated by MRIs taken five years apart, when compared to the MRIs of individuals who started out with lower levels of omega-3s (13). Another study measured blood levels of DHA and found that people with higher DHA levels have an associated 47% decrease in risk of dementia from any cause as well as an associated 39% decreased risk of Alzheimer’s disease in particular when compared to people with lower DHA blood levels (14). In addition, a randomized double-blind placebo-controlled trial showed that high intake of omega-3 fatty acids in older adults for about 6 ½ months results in about 60% less brain shrinkage along with increases in cognitive function compared to a control group consuming lower amounts of omega-3 fatty acids (15).
Omega-6 fatty acids are also necessary for brain function, however omega-6s are ubiquitous in the modern diet. Their problem is not one of deficiency but one of abundance and the consequence is an imbalance in the relative amounts of omega-3 and omega-6 fatty acids eaten today. The ideal ratio of dietary omega-3 to omega-6 is about 1:4. Today’s standard Western diet is quite high in omega-6s but very light in omega-3s, with most people eating this way having an omega-3 to omega-6 ratio of 1:20 and even higher (16). Current investigations demonstrate that healthy brain size and preservation of cognition and memory is associated with a more balanced ratio of omega-3 to omega-6 fatty acids in the blood (17).
The population of tiny organisms living in our intestines, consisting of a multitude of species of bacteria, fungi, viruses, archaea and protozoa, is known as the gut microbiome. These microorganisms have complex effects on the human body including the ability to alter cognition in aging people in both positive and negative ways. Simply altering the number of species, and thus the genetic diversity, in the microbiome can affect mental state and people with less diverse microbiomes display higher anxiety, stress and sleeplessness (18).
The gut microbiome and the brain are constantly in contact. Their communication is a two-way street and each can affect the other’s functions with consequences on aspects of brain function such as cognition, stress, anxiety and depression. Studies of both animals and human beings provide evidence of this interplay between the microbiome and the brain and its key role in maintaining brain health (19).
Gut microbes are able to affect neuronal function directly and indirectly through multiple mechanisms, including transmissions through nerves, immune modulation, signalling via receptors and stimulation of neurons by bacterial metabolites. Examples of these metabolites are neurotransmitters, vitamins and neuroactive microbial metabolites such as short-chain fatty acids (19). Research is underway now exploring whether microbes might be used to produce therapeutic neurotransmitters for treating neurological disorders (20).
Age is associated with increased oxidative stress and inflammation which inevitably lead to cognitive decline. Oxidative stress is caused by reactive oxygen species (ROS) that, though they are the natural by-products of metabolism in the body, can cause damage to cells and DNA when they are allowed to build up. Recent evidence suggests that gut microbiota are important in regulating these factors through several mechanisms (21);
Gut bacteria can produce antioxidants that protect against ROS.
Butyrate, a short-chain fatty acid that is the product of the fermentation of fiber by beneficial Gut bacteria, directly reduces oxidative stress.
Gut microbiota can modulate the function of mitochondria, the tiny power plants inside cells, reducing oxidative stress.
Gut microorganisms can protect against damage to the lining of the gut, thus preventing toxins and pathogenic microbes from entering the bloodstream. If the gut becomes damaged enough to become permeable to hazardous substances, the immune system can be activated, causing the release of inflammatory proteins called cytokines and boosting inflammation. Prolonged exposure of the brain to inflammation can significantly impair cognition with increasing age.
One very important capability of the microbiota is the regulation of tryptophan levels. From tryptophan, the neurotransmitter serotonin is synthesized. Serotonin plays a significant role in the function of the brain with low brain serotonin levels associated with poor memory and depressed mood (22). However, serotonin does not only alter CNS receptors to directly influence brain function; it is also capable of exerting epigenetic control over gene expression. Epigenetic changes alter the way genes work through effects of behaviour and the environment; epigenetic changes are reversible and do not change the DNA sequence itself but modify how the body reads and expresses the information contained in the DNA. This means that, even though your own genetic code may house genes that increase the risk of diseases such as Alzheimer’s and other types of cognitive decline, those genes may never be expressed. The lifestyle choices you make for your health as well as the environment in which you live can dictate the ultimate effects of the codes hidden within your genes (19,23).
Finally, newly emerging studies are revealing the crucial part that gut bacteria may play in regulating the maturation and function of microglia, the immune cells found throughout the brain and spinal cord that were previously mentioned under the discussion of abdominal fat. Researchers have found indications that gut microbiome activity can alleviate microglial impairment. Ongoing research is needed to provide more details about this role of the gut microbiome. However, studies on the brain are indicating that most CNS diseases affected by the gut microbiome are likely associated with microglial dysfunction. These include Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, depression and autism spectrum disorder (8,19).
FOODS THAT IMPROVE COGNITIVE FUNCTION
Beans, peas, chickpeas, lentils, peanuts May significantly slow Alzheimer’s
disease by preventing amyloid
plaque formation (23)
Brightly coloured fruits and vegetables Contain antioxidant vitamins C and E and the phytonutrient, carotene Delay cognitive decline (24)
Leafy greens Ex; Kale, spinach, arugula, collard greens Slow cognitive aging; increase memory (24,25)
Folate (folic acid) Found in dark green leafy vegetables such as
spinach, asparagus, kale and brussels sprouts; orange juice, nuts, beans, peas with small amounts in meat, poultry and dairy products
Adequate levels are necessary for proper brain function; adequate levels prevent cognitive decline (18,26)
Whole grains Ex; Brown rice, quinoa, whole wheat, oatmeal Lower risk of cognitive decline (27)
Nuts and seeds Ex: Walnuts, cashews, pecans, pumpkin seeds Protect brain cells from oxidative stress and increase cognitive function
Herbs and spices Ex: Turmeric, parsley, thyme, oregano, basil Protect brain from oxidative stress and inflammation; slow cognitive decay in mouse models of Alzheimer’s (24)
Dark chocolate Rich source of flavonoids Improve cognitive processing and cognitive function in the elderly (24,29)
Green tea Contain EGCG and other flavonoids Prevention of beta-amyloid proteins and improvement
of cognitive function (24,30)
Coffee Contains antioxidants Protects brain from
inflammation damage (31)
Blueberries Contain antioxidants Delay cognitive decline (32)
Avocados Contain antioxidants Can prevent neurodegenerative
Flax seeds, chia seeds Contain omega-3 fatty acids Slow cognitive decline (24)
FOODS THAT WORSEN COGNITIVE FUNCTION
Processed foods Contain saturated fats, trans-fats, added sugar, refined carbohydrates Associated with poor cognitive outcomes (24,27)
Processsed meats Ex: Lunch meats, bacon Promote neurodegeneration
Red meat Contains heme iron Increases oxidative stress; toxic to the brain; increases risks for Alzheimer’s disease (35)
Fried food Especially fried meats Associated with worsened memory and cognitive function (36)
Saturated fats Found in meat, dairy products, butter, coconut oil, lard, ghee, cottonseed oil and palm kernel oil
Increased cognitive decline (24,37)
Cheese Contains saturated and trans-fats Increased oxidative stress and poor cognitive outcomes (36)
Pastries and sweets Contain saturated fats, sugar Causes insulin resistance in the
brain and impaired memory and cognitive function (27)
Sugary drinks High sugar content Worsened memory (27)
Excessive alcohol More than 8 alcoholic drinks a week Faster cognitive decline (38)
High zinc levels in the diet Sources are meat, shellfish, eggs, dairy, nuts, seeds
Increased cognitive decay (24)
Lifelong low selenium levels Sources are nuts, cereals, meats, fish, eggs
Associated with lower cognitive
function in humans (24)
Low blood copper levels Sources are brazil nuts, cocoa, black pepper, blackstrap molasses, beef liver and oysters
Associated with cognitive decline in Alzheimer's patients (24)
Summing it all up
Startling evidence is mounting that cognitive impairment may be a lifestyle disease, raising the possibility that it could be prevented through the adoption of healthier diet and exercise habits (9).
Here are some positive steps that can be taken in our own lives to optimize brain health;
Lower oxidative stress in the body
Poor nutrient status throughout the body is associated with inflammation and oxidative stress. Strive to eat foods especially high in anti-inflammatory and antioxidant capacity. This means foods high in fiber, vitamin C, vitamin E and phytonutrients such as carotenoids and polyphenols (including flavonoids). Foods containing these nutrients are almost exclusively derived from plants (39).
Reduce body fat, especially visceral fat, and keep BMI at a healthy level of between 18.5 and 24.9
Lowering body fat can be approached in a number of ways. The key to shrinking body fat is to cut fat-promoting foods such as dairy products, meats, processed foods, pastries, sweets and added oils from the diet. A whole food plant-based diet will diminish body fat. But so will a paleo diet. Indeed, weight can be lost following either of these eating patterns. However, a plant-based diet is the only one that emphasizes intake of foods that will lower inflammation as well as fat and BMI. In addition, the foods that a paleo diet is based upon, animal-sourced proteins, have well-known negative effects on long-term health and are associated with greater risks of cardiovascular disease, coronary heart disease, cancer, diabetes, respiratory disease, infectious disease, and early death from all causes (40,41,42,43,44,45,46).
Balance intake of omega-3 and omega-6 fatty acids
This can be achieved by avoiding foods high in omega-6s and increasing your intake of foods high in omega-3s to bring your omega-3:omega-6 ratio into a level closer to 1:4. Simply put, cutting out animal-sourced fatty foods (meat and dairy products), processed foods and plant-derived oils and increasing whole plant-based foods in the diet should do the trick (17).
Promote genetic diversity in the gut microbiome and encourage the healthiest gut bacteria species to flourish
Undoubtedly nutrition has a major influence on the composition of the gut microbiome and diet may prove to be a critical factor in the prevention and mitigation of brain-related disorders. Short-term consumption of diets composed entirely of either plant or animal products rapidly change the structure and activity of the microorganism population living in the human gut (20). The available literature indicates that high-fiber diets such as plant-based diets promote more diverse, stable and healthful microbe populations. Inflammation is reduced, growth of the beneficial microbe species that ferment fiber into short-chain fatty acids is stimulated, immunity to pathogens improves and integrity of the blood-brain barrier is strengthened. A diverse ecosystem of healthful microbes supports both the health of the human gut microbiome and overall health (47).
Research completed in 2019 found that people who strongly adhered to a plant-based diet pattern during midlife were up to 33% less likely to develop cognitive impairment as they aged than those not following a plant-based diet (48). When we add to this the overwhelming evidence of the many other benefits of eating plant-based such as reductions in heart disease, diabetes, cancer and auto-immune diseases, there really is only one choice to make if you want to add years to your life and life to your years. Simply fill your plate as often as you can with whole plant foods.
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