How diet affects mood, behavior, and more

How diet affects mood, behavior, and more

During the long sea voyages of the 15th and 16th centuries, a period known as the Age of Discovery, sailors reported experiencing visions of sumptuous foods and green fields. The discovery that these were nothing more than hallucinations after months at sea was heart-wrenching. Some sailors cried in longing. The others threw themselves into the sea.

The cure for this horrific mirage turned out not to be a mixture of complex chemicals, as previously suspected, but a simple antidote to lemon juice. These sailors suffered from scurvy, a disease caused by a deficiency of vitamin C, an essential micronutrient that people gain from eating fruits and vegetables.

Vitamin C is important for the production and release of neurotransmitters, the brain’s chemical transmitters. In its absence, brain cells do not communicate effectively with each other, which can lead to hallucinations.

As this famous example of early explorers demonstrates, there is an intimate relationship between food and the brain, which researchers like myself are working to unravel. As a scientist who studies the neuroscience of nutrition at the University of Michigan, I am primarily interested in how food components and the products of their breakdown alter the genetic instructions that control our functions.

Beyond that, my research also focuses on understanding how food can influence our thoughts, moods, and behaviors. While we can’t yet prevent or treat brain conditions through diet, researchers like myself are learning a lot about the role that nutrition plays in the everyday brain processes that make us who we are.

Perhaps not surprisingly, a delicate balance of nutrients is key to brain health: A deficiency or excess of vitamins, sugars, fats, and amino acids can affect the brain and behavior in either negative or positive ways.

Nutritional Diseases

As with vitamin C, deficiencies in other vitamins and minerals can lead to nutritional diseases that negatively affect the brain in humans. For example, low dietary levels of vitamin B3/niacin – commonly found in meat and fish – cause pellagra, a disease in which people develop dementia.

Niacin is necessary for converting food into energy and building blocks, protecting the genetic blueprint from environmental damage and controlling the amount of certain genetic products that are manufactured. In the absence of these critical processes, brain cells, also known as neurons, malfunction and die prematurely, leading to dementia.

In animal models, reducing or blocking niacin production in the brain leads to neuronal damage and cell death. Conversely, improving niacin levels has been shown to mitigate the effects of neurodegenerative diseases such as Alzheimer’s, Huntington’s, and Parkinson’s. Observational studies in humans suggest that adequate levels of niacin may protect against these diseases, but the results are still inconclusive.

Interestingly, niacin deficiency caused by consuming large amounts of alcohol can lead to effects similar to those with pellagra.

Another example of how nutrient deficiencies affect brain function can be found in iodine, which, like niacin, must be obtained from an individual’s diet. Iodine, found in seafood and seaweed, is an essential building block for thyroid hormones — signaling molecules important to many aspects of human biology, including growth, metabolism, appetite and sleep. Low iodine levels prevent the production of adequate amounts of thyroid hormones, impairing these basic physiological processes.

Iodine is especially important for human brain development. Before table salt was supplemented with this mineral in the 1920s, iodine deficiency was a major cause of cognitive impairment worldwide. The introduction of iodized salt is thought to have contributed to the gradual rise in IQ scores in the last century.

keto for epilepsy

Not all nutritional deficiencies are harmful to the brain. In fact, studies show that people with drug-resistant epilepsy — a condition in which brain cells fire uncontrollably — can reduce the number of seizures by following a very low-carb diet, known as the ketogenic diet, in which 80 % to 90% of calories are obtained from fat.

Carbohydrates are the body’s preferred source of energy. When it’s not available — either because of fasting or because of a ketogenic diet — cells get fuel by breaking down fats into compounds called ketones. Using ketones for energy leads to profound shifts in metabolism and physiology, including the levels of hormones circulating in the body, the amount of neurotransmitters produced by the brain and the types of bacteria that live in the gut.

Researchers believe that these diet-dependent changes, particularly the higher production of chemicals in the brain that can calm nerve cells and reduce levels of inflammatory molecules, may play a role in the ketogenic diet’s ability to reduce the number of seizures. These changes may also explain the benefits of ketosis — whether through diet or fasting — on cognitive function and mood.

Desensitizing taste

Certain foods can negatively affect your memory and mood.

Excess levels of some nutrients can have harmful effects on the brain. In human and animal models, high consumption of refined sugars and saturated fats — a common combination in ultra-processed foods — encourages binge eating by desensitizing the brain to hormonal signals known to regulate satiety.

Interestingly, a diet rich in these foods also reduces the sensitivity of the taste system, causing animals and humans to perceive food as less sweet. These sensory changes may affect food choice as well as the reward we get from food. For example, research shows that people’s responses to ice cream in areas of the brain important for taste and reward are dulled when they eat it every day for two weeks. Some researchers believe that this decrease in food reward signals may promote cravings for more fatty and sugary foods, similar to the way smokers crave cigarettes.

Diets high in fat and processed foods are also associated with decreased cognitive function and memory in humans and animals, as well as a higher incidence of neurodegenerative diseases. However, researchers still do not know whether these effects are due to these foods or to the weight gain and insulin resistance that develops with long-term consumption of these diets.

This brings us to an important aspect of diet’s effect on the brain: time. Some foods can affect brain function and behavior acutely – for example over hours or days – while others take weeks, months or even years to have an effect. For example, eating a slice of cake quickly shifts the fat-burning ketogenic metabolism of an individual with drug-resistant epilepsy into a carbohydrate-burning metabolism, increasing the risk of seizures. In contrast, it takes weeks of sugar consumption for tasting and altering reward pathways in the brain, and months of vitamin C deficiency to develop scurvy. Finally, when it comes to diseases like Alzheimer’s and Parkinson’s, the risk is influenced by years of exposure to food along with genetics or other lifestyle factors like smoking.

In the end, the relationship between food and the brain is a bit like a thin moderate: we don’t need too little, not too much, but just enough of each nutrient.

This article is republished from The Conversation, an independent, non-profit source for news, analysis, and commentary from academic experts, under a Creative Commons license.

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