During their long sea voyages in the 15th and 16th centuries, a period known as the Age of Discovery, sailors said they had seen great food and verdant fields. The discovery that it was nothing more than an illusion after months at sea. Some sailors wept with longing; others throw themselves too far.
The cure for these nasty wounds turned out to be not a concoction of complex chemicals, as was once suspected, but a simple antidote of lemon juice. These sailors suffered from scurvy, a disease caused by a lack of vitamin C, an essential micronutrient that humans get from eating fruits and vegetables.
Vitamin C is important for the production and release of neurotransmitters, the brain’s chemical messengers. Without it, brain cells don’t communicate effectively with each other, which can lead to hallucinations.
As this famous example of early explorers illustrates, there is a close connection between food and the brain, a connection that researchers like myself are working to unravel. As a scientist nutrition neuroscientist at the University of Michigan, I am primarily interested in how the components of food and their breakdown products can change the genetic instructions that control our physiology.
In addition, my research is also focused on understanding how food can affect our thoughts, moods and behaviours. While we still can’t prevent or treat brain diseases with diet, researchers like me are learning a lot about the role nutrition plays in the everyday brain processes that make us human. our.
It’s perhaps not surprising that 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 a negative or positive way.
As with vitamin C, deficiencies in other vitamins and minerals can also lead to nutritional diseases that adversely affect the brain in humans. For example, low levels of dietary vitamin B3/niacin – commonly found in meat and fish – cause pellagra, a disease in which people develop dementia.
Niacin is needed to turn food into energy and building blocks, protect the genetic blueprint from environmental damage, and control the amount of certain gene products produced. In the absence of these important processes, brain cells, also known as neurons, misbehave 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. In contrast, boosting 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 niacin intake may protect against these diseases, but the results are inconclusive.
Interestingly, a niacin deficiency caused by drinking too much alcohol can lead to effects similar to those found with pellagra.
Another example of how nutrient deficiencies affect brain function can be found in elemental iodine, which, like niacin, must be obtained from a person’s diet. Iodine, found in seafood and seaweed, is an essential building block for thyroid hormones – signaling molecules important for many aspects of human biology, including development, metabolism, appetite and sleep. Low iodine levels prevent adequate production of thyroid hormone, impairing these essential physiological processes.
Iodine is especially important for the developing human brain; Before table salt was fortified with this mineral in the 1920s, iodine deficiency was a major cause of cognitive disability worldwide. The introduction of iodized salt is believed to have contributed to the gradual increase in IQ scores over the past century.
Not all dietary deficiencies are harmful to the brain. In fact, studies show that people with drug-resistant epilepsy – a condition in which brain cells function uncontrollably – can reduce the number of seizures by adopting a carbohydrate-free, well-balanced diet. called a ketogenic diet, in which 80% to 90% of calories are obtained from fat.
A high-fat, ketogenic diet is helpful for epilepsy.
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Carbohydrates are the body’s preferred source of energy. When they’re not available – either by fasting or by a ketogenic diet – cells get fuel by breaking down fats into compounds called ketones. The use of ketones for energy leads to profound changes 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.
The researchers suggest that these diet-dependent changes, particularly a higher production of brain chemicals, 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 a ketogenic state — through dieting or fasting — on cognitive function and mood.
Excess levels of certain nutrients can also have adverse effects on the brain. In humans and animal models, high consumption of refined sugars and saturated fats — a combination commonly found in ultra-processed foods — promotes eating by entertaining the brain to internal signals. hormones that regulate satiety.
Interestingly, this high-food diet also desensitized the taste system, causing animals and humans to perceive foods as less sweet. These sensory changes can affect our food choices as well as the rewards we get from food. For example, research showed that people’s responses to ice cream in brain areas important for taste and reward were reduced when they ate it daily for two weeks. Some researchers suggest that this reduction in food reward cues can increase cravings for even more fat and sugar, similar to how smokers crave cigarettes.
Diets high in fat and processed foods 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 if these effects are due to these foods or to the weight gain and insulin resistance that develop when eating these diets for long periods of time.
Which brings us to an important aspect of diet’s impact on the brain: timing. Some foods can profoundly affect brain function and behavior — hours or days, for example — while others take weeks, months, or even years to have an effect. use. For example, eating a slice of cake would rapidly switch the fat-burning, ketone metabolism of someone with drug-resistant epilepsy into a carbohydrate-burning metabolism, increasing the risk of seizures. In contrast, it took weeks of sugar consumption to induce taste and brain reward pathways to change, and months of vitamin C deficiency to develop scurvy. Finally, when it comes to diseases like Alzheimer’s and Parkinson’s, 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 like subtle Goldilocks: We don’t need too little, not too much, just enough of each nutrient.
Monica Dus is an associate professor of molecular, cellular, and developmental biology at the University of Michigan
