Overview: Researchers are evaluating how our food choices can affect our moods and behavior, explaining how specific diets can help manage certain neurological disorders.
Source: The conversation
During the long seafaring voyages of the 15th and 16th centuries, a period known as the Age of Discovery, sailors reported seeing visions of sublime food and green fields. The discovery that this was nothing more than hallucinations after months at sea was painful. Some sailors wept with longing; others threw themselves overboard.
The cure for these harrowing mirages turned out not to be a mixture of complex chemicals, as was once suspected, but rather the simple antidote of lemon juice. These sailors suffered from scurvy, a disease caused by a deficiency of vitamin C, an essential micronutrient that humans ingest from eating fruits and vegetables.
Vitamin C is important for the production and release of neurotransmitters, the brain’s chemical messengers. In its absence, brain cells do not communicate effectively with each other, which can lead to hallucinations.
As this famous example from early explorers illustrates, there is an intimate connection between food and the brain, one that researchers like me are trying to unravel. As a scientist studying the neuroscience of nutrition at the University of Michigan, I am particularly interested in how components of food and their breakdown products can alter the genetic instructions that govern our physiology.
In addition, my research also focuses on understanding how food can influence our thoughts, moods and behavior. While we can’t yet prevent or treat brain disorders with diet, researchers like me are learning a lot about the role food plays in the everyday brain processes that make us who we are.
Perhaps unsurprisingly, a delicate balance of nutrients is key to brain health: Deficiencies or excesses in vitamins, sugars, fats and amino acids can affect the brain and behavior in a negative or positive way.
Vitamin and mineral deficiencies
As with vitamin C, deficiencies in other vitamins and minerals can also cause nutritional diseases that negatively affect the brain in humans. For example, a low dietary level of vitamin B3/niacin, which is usually found in meat and fish, causes pellagra, a disease in which people develop dementia.
Niacin is essential to convert food into energy and building blocks, protect the genetic blueprint from environmental damage and control how much of certain gene products is made. In the absence of these critical processes, brain cells, known as neurons, malfunction and die prematurely, leading to dementia.
In animal models, reducing or blocking the production of niacin in the brain promotes neuronal damage and cell death. Conversely, increasing niacin levels has been shown to reduce the effects of neurodegenerative diseases such as Alzheimer’s, Huntington’s and Parkinson’s disease. Observational studies in humans suggest that adequate levels of niacin may protect against these diseases, but the results are still inconclusive.
Interestingly, a deficiency in niacin, caused by the consumption of excessive amounts of alcohol, can lead to effects similar to those of pellagra.
Another example of how a nutrient deficiency affects brain function can be found in the element iodine, which, like niacin, must be obtained from the diet. Iodine, which is present in seafood and seaweed, is an essential building block for thyroid hormones – signaling molecules important to many aspects of human biology, including development, metabolism, appetite and sleep. Low iodine levels prevent the production of sufficient thyroid hormones, affecting these essential physiological processes.
Iodine is especially important for the developing human brain; 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 over the past century.
Ketogenic Diet 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 adopting an ultra-low-carb regimen known as a ketogenic diet, where 80% to 90% of calories are obtained from Fat.
Carbohydrates are the body’s preferred source of energy. When unavailable — either because of fasting or on a ketogenic diet — cells obtain 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 think these diet-dependent changes, specifically the higher production of brain chemicals that can calm neurons and lower levels of inflammatory molecules, may play a role in the ketogenic diet’s ability to reduce seizure numbers. These changes may also explain the benefits of a ketogenic state — either through diet or fasting — on cognitive function and mood.
Sugar, saturated fats and ultra-processed foods
Excessive levels of some nutrients can also have adverse effects on the brain. In humans and animal models, increased consumption of refined sugars and saturated fats — a combination often found in ultra-processed foods — promotes eating by desensitizing the brain to the hormonal signals known to regulate satiety.
Interestingly, a diet high in these foods also desensitizes the taste system, causing animals and humans to perceive food as less sweet. These sensory changes can affect food choices, as well as the reward we get from food.
For example, research shows that people’s reactions to ice cream in areas of the brain that are important for taste and reward are dulled if they eat it every day for two weeks. Some researchers think this decrease in food reward signals may amplify cravings for even more fatty and sugary foods, similar to the way smokers crave cigarettes.
High-fat and processed diets are also associated with lower cognitive function and memory in humans and animal models, as well as a higher incidence of neurodegenerative diseases. However, researchers still don’t know whether these effects are due to these foods or to the weight gain and insulin resistance that develop with long-term consumption of these diets.
This brings us to a crucial aspect of how food affects the brain: time. Some foods can affect brain function and behavior acutely, such as hours or days, while others take weeks, months, or even years to take effect.
For example, eating a slice of cake quickly shifts the fat-burning, ketogenic metabolism of a person with drug-resistant epilepsy into a carbohydrate-burning metabolism, increasing the risk of seizures.
In contrast, it takes weeks of sugar consumption to alter the brain’s taste and reward pathways, and months of vitamin C deficiency to develop scurvy.
Finally, when it comes to diseases such as Alzheimer’s and Parkinson’s, the risk is influenced by years of dietary exposure combined with other genetic or lifestyle factors such as smoking.
Ultimately, the relationship between food and the brain is a bit like the delicate Goldilocks: we don’t have too little, not too much, but just enough of each nutrient.
About this nutrition and psychology research news
Author: Monica Dus
Source: The conversation
Contact: Monica So – The Conversation
Image: The image is in the public domain