Your brain is the most important organ in your body.
It keeps your heart beating, lungs breathing and all the systems in your body functioning.
That’s why it’s essential to keep your brain working in optimum condition with a healthy diet.
Some foods have negative effects on the brain, impacting your memory and mood and increasing your risk of dementia.
Estimates predict that dementia will affect more than 65 million people worldwide by 2030.
Luckily, you can help reduce your risk of the disease by cutting certain foods out of your diet.
This article reveals the 7 worst foods for your brain.
1. Sugary Drinks
Sugary drinks include beverages like soda, sports drinks, energy drinks and fruit juice.
A high intake of sugary drinks not only expands your waistline and boosts your risk of type 2 diabetes and heart disease — it also has a negative effect on your brain (1Trusted Source, 2Trusted Source, 3Trusted Source).
An excessive intake of sugary drinks increases the odds of developing type 2 diabetes, which has been shown to increase the risk of Alzheimer’s disease (4Trusted Source).
In addition, higher sugar levels in the blood can increase the risk of dementia, even in people without diabetes (5).
A primary component of many sugary drinks is high-fructose corn syrup (HFCS), which consists of 55% fructose and 45% glucose (1Trusted Source).
A high intake of fructose can lead to obesity, high blood pressure, high blood fats, diabetes and arterial dysfunction. These aspects of metabolic syndrome may lead to an increase in the long-term risk of developing dementia (6).
Animal studies have shown that a high fructose intake can lead to insulin resistance in the brain, as well as a reduction in brain function, memory, learning and the formation of brain neurons (6, 7Trusted Source).
One study in rats found that a diet high in sugar increased brain inflammation and impaired memory. Additionally, rats that consumed a diet consisting of 11% HFCS were worse than those whose diets consisted of 11% regular sugar (8Trusted Source).
Another study found that rats fed a high-fructose diet gained more weight, had worse blood sugar control and a higher risk of metabolic disorders and memory impairments (9Trusted Source).
While further studies in humans are needed, the results suggest that a high intake of fructose from sugary drinks may have additional negative effects on the brain, beyond the effects of sugar.
Some alternatives to sugary drinks include water, unsweetened iced tea, vegetable juice and unsweetened dairy products.
2. Refined Carbs
Refined carbohydrates include sugars and highly processed grains, such as white flour.
These types of carbs generally have a high glycemic index (GI). This means your body digests them quickly, causing a spike in your blood sugar and insulin levels.
Also, when eaten in larger quantities, these foods often have a high glycemic load (GL). The GL refers to how much a food raises your blood sugar levels, based on the serving size.
Foods that are high-GI and high-GL have been found to impair brain function.
Research has shown that just a single meal with a high glycemic load can impair memory in both children and adults (10Trusted Source).
Another study in healthy university students found that those who had a higher intake of fat and refined sugar also had poorer memory (10Trusted Source).
This effect on memory may be due to inflammation of the hippocampus, a part of the brain that affects some aspects of memory, as well as responsiveness to hunger and fullness cues (10Trusted Source).
Inflammation is recognized as a risk factor for degenerative diseases of the brain, including Alzheimer’s disease and dementia (11).
For example, one study looked at elderly people who consumed more than 58% of their daily calories in the form of carbohydrates. The study found they had almost double the risk of mild mental impairment and dementia (12Trusted Source).
Carbohydrates may have other effects on the brain too. For example, one study found that children aged six to seven who consumed diets high in refined carbs also scored lower on nonverbal intelligence (13Trusted Source).
However, this study could not determine whether consuming refined carbs caused these lower scores, or simply whether the two factors were related.
Healthy, lower-GI carbs include foods such as vegetables, fruits, legumes and whole grains. You can use this database to find the GI and GL of common foods.
3. Foods High in Trans Fats
Trans fats are a type of unsaturated fat that can have a detrimental effect on brain health.
While trans fats occur naturally in animal products like meat and dairy, these are not a major concern. It’s industrially produced trans fats, also known as hydrogenated vegetable oils, that are a problem.
These artificial trans fats can be found in shortening, margarine, frosting, snack foods, ready-made cakes and prepackaged cookies.
Studies have found that when people consume higher amounts of trans fats, they tend to have an increased risk of Alzheimer’s disease, poorer memory, lower brain volume and cognitive decline (14, 15Trusted Source, 16Trusted Source, 17Trusted Source).
However, some studies have not found an association between trans-fat intake and brain health. Nonetheless, trans fats should be avoided. They have a negative effect on many other aspects of health, including heart health and inflammation (18Trusted Source, 19Trusted Source, 20Trusted Source, 21Trusted Source).
The evidence on saturated fat is mixed. Three observational studies have found a positive association between saturated fat intake and the risk of Alzheimer’s disease, whereas a fourth study showed the opposite effect (14).
One cause for this may be that a subset of the test populations had a genetic susceptibility to the disease, which is caused by a gene known as ApoE4. However, more research is required on this topic (14).
One study of 38 women found that those who consumed more saturated fat relative to unsaturated fat performed worse on memory and recognition measures (15Trusted Source).
Thus, it may be that the relative ratios of fat in the diet are an important factor, not just the type of fat itself.
For example, diets high in omega-3 fatty acids have been found to help protect against cognitive decline. Omega-3s increase the secretion of anti-inflammatory compounds in the brain and can have a protective effect, especially in older adults (22, 23Trusted Source).
You can increase the amount of omega-3 fats in your diet by eating foods like fish, chia seeds, flax seeds and walnuts.
4. Highly Processed Foods
Highly processed foods tend to be high in sugar, added fats and salt.
They include foods such as chips, sweets, instant noodles, microwave popcorn, store-bought sauces and ready-made meals.
These foods are usually high in calories and low in other nutrients. They’re exactly the kinds of foods that cause weight gain, which can have a negative effect on your brain health.
A study in 243 people found increased fat around the organs, or visceral fat, is associated with brain tissue damage. Another study in 130 people found there’s a measurable decrease in brain tissue even in the early stages of metabolic syndrome (24Trusted Source, 25).
The nutrient composition of processed foods in the Western diet can also negatively affect the brain and contribute to the development of degenerative diseases (26, 27).
A study including 52 people found that a diet high in unhealthy ingredients resulted in lower levels of sugar metabolism in the brain and a decrease in brain tissue. These factors are thought to be markers for Alzheimer’s disease (28).
Another study including 18,080 people found that a diet high in fried foods and processed meats is associated with lower scores in learning and memory (29).
Similar results were found in another large-scale study in 5,038 people. A diet high in red meat, processed meat, baked beans and fried food was associated with inflammation and a faster decline in reasoning over 10 years (11).
In animal studies, rats fed a high-fat, high-sugar diet for eight months showed impaired learning ability and negative changes to brain plasticity. Another study found that rats fed a high-calorie diet experienced disruptions to the blood-brain barrier (30Trusted Source, 31Trusted Source, 32Trusted Source).
The blood-brain barrier is a membrane between the brain and blood supply for the rest of the body. It helps protect the brain by preventing some substances from entering.
One of the ways processed foods may negatively impact the brain is by reducing the production of a molecule called brain-derived neurotrophic factor (BDNF) (10Trusted Source, 33).
This molecule is found in various parts of the brain, including the hippocampus, and it’s important for long-term memory, learning and the growth of new neurons. Therefore, any reduction can have negative impacts on these functions (33).
You can avoid processed foods by eating mostly fresh, whole foods such as fruits, vegetables, nuts, seeds, legumes, meat and fish. Additionally, a Mediterranean-style diet has been shown to protect against cognitive decline (28, 34).
Aspartame is an artificial sweetener used in many sugar-free products.
People often choose to use it when trying to lose weight or avoid sugar when they have diabetes. It is also found in many commercial products not specifically targeted at people with diabetes.
However, this widely used sweetener has also been linked to behavioral and cognitive problems, though the research has been controversial.
Aspartame is made of phenylalanine, methanol and aspartic acid (35Trusted Source).
Phenylalanine can cross the blood-brain barrier and might disrupt the production of neurotransmitters. Additionally, aspartame is a chemical stressor and may increase the brain’s vulnerability to oxidative stress (35Trusted Source, 36).
Some scientists have suggested these factors may cause negative effects on learning and emotions, which have been observed when aspartame is consumed in excess (35Trusted Source).
One study looked at the effects of a high-aspartame diet. Participants consumed about 11 mg of aspartame for every pound of their body weight (25 mg per kg) for eight days.
By the end of the study, they were more irritable, had a higher rate of depression and performed worse on mental tests (37Trusted Source).
Another study found people who consumed artificially sweetened soft drinks had an increased risk of stroke and dementia, though the exact type of sweetener was not specified (38).
Some experimental research in mice and rats has also supported these findings.
A study of repeated aspartame intake in mice found that it impaired memory and increased oxidative stress in the brain. Another found that long-term intake led to an imbalance in antioxidant status in the brain (39Trusted Source, 40).
Other animal experiments have not found any negative effects, though these were often large, single-dose experiments rather than long-term ones. Additionally, mice and rats are reportedly 60 times less sensitive to phenylalanine than humans (35Trusted Source, 41Trusted Source).
Despite these findings, aspartame is still considered to be a safe sweetener overall if people consume it at about 18–23 mg per pound (40–50 mg per kg) of body weight per day or less (42Trusted Source).
According to these guidelines, a 150-pound (68-kg) person should keep their aspartame intake under about 3,400 mg per day, at the maximum.
For reference, a packet of sweetener contains about 35 mg of aspartame, and a regular 12-ounce (340-ml) can of diet soda contains about 180 mg. Amounts may vary depending on brand (42Trusted Source).
In addition, a number of papers have reported that aspartame has no adverse effects (42Trusted Source).
However, if you’d prefer to avoid it, you could simply cut artificial sweeteners and excess sugar from your diet altogether.
When consumed in moderation, alcohol can be an enjoyable addition to a nice meal. However, excessive consumption can have serious effects on the brain.
Chronic alcohol use results in a reduction in brain volume, metabolic changes and disruption of neurotransmitters, which are chemicals the brain uses to communicate (43Trusted Source).
People with alcoholism often have a deficiency in vitamin B1. This can lead to a brain disorder called Wernicke’s encephalopathy, which in turn can develop into Korsakoff’s syndrome (44Trusted Source).
This syndrome is distinguished by severe damage to the brain, including memory loss, disturbances in eyesight, confusion and unsteadiness (44Trusted Source).
Excessive consumption of alcohol can also have negative effects in non-alcoholics.
Heavy one-off drinking episodes are known as “binge drinking.” These acute episodes can cause the brain to interpret emotional cues differently than normal. For example, people have a reduced sensitivity to sad faces and an increased sensitivity to angry faces (45).
It’s thought that these changes to emotion recognition may be a cause of alcohol-related aggression (45).
Furthermore, alcohol consumption during pregnancy can have devastating effects on the fetus. Given that its brain is still developing, the toxic effects of alcohol can result in developmental disorders like fetal alcohol syndrome (46, 47Trusted Source).
The effect of alcohol abuse in teenagers can also be particularly damaging, as the brain is still developing. Teenagers who drink alcohol have abnormalities in brain structure, function and behavior, compared to those who don’t (48).
Particularly, alcoholic beverages mixed with energy drinks are concerning. They result in increased rates of binge drinking, impaired driving, risky behavior and an increased risk of alcohol dependence (49).
An additional effect of alcohol is the disruption of sleep patterns. Drinking a large amount of alcohol before bed is associated with poor sleep quality, which can lead to chronic sleep deprivation (50).
However, moderate alcohol consumption may have beneficial effects, including improved heart health and a reduced risk of diabetes. These beneficial effects have been particularly noted in moderate wine consumption of one glass per day (51, 52Trusted Source, 53Trusted Source).
Overall, you should avoid excessive alcohol consumption, especially if you’re a teenager or young adult, and avoid binge drinking entirely.
If you are pregnant, it is safest to avoid drinking alcohol altogether.
7. Fish High in Mercury
Mercury is a heavy metal contaminant and neurological poison that can be stored for a long time in animal tissues (54Trusted Source, 55).
Long-lived, predatory fish are particularly susceptible to accumulating mercury and can carry amounts over 1 million times the concentration of their surrounding water (54Trusted Source).
For this reason, the primary food source of mercury in humans is seafood, particularly wild varieties.
After a person ingests mercury, it spreads all around their body, concentrating in the brain, liver and kidneys. In pregnant women, it also concentrates in the placenta and fetus (56).
The effects of mercury toxicity include disruption of the central nervous system and neurotransmitters and stimulation of neurotoxins, resulting in damage to the brain (56).
For developing fetuses and young children, mercury can disrupt brain development and cause the destruction of cell components. This can lead to cerebral palsy and other developmental delays and deficits (56).
However, most fish are not a significant source of mercury. In fact, fish is a high-quality protein and contains many important nutrients, such as omega-3s, vitamin B12, zinc, iron and magnesium. Therefore, it is important to include fish as part of a healthy diet.
Generally, it is recommended that adults eat two to three servings of fish per week. However, if you’re eating shark or swordfish, only consume one serving, and then no other fish that week (57).
Pregnant women and children should avoid or limit high-mercury fish, including shark, swordfish, tuna, orange roughy, king mackerel and tilefish. However, it’s still safe to have two to three servings of other low-mercury fish per week (57, 58).
Recommendations may differ from country to country, depending on the types of fish in your area, so it’s always best to check with your local food safety agency for the recommendations that are right for you.
Also, if you are catching your own fish, it is a good idea to check with local authorities about the levels of mercury in the water you are fishing from.