During the long maritime voyages of the 15th and 16th centuries, the period known as the age of discoverysailors said they suffered visions of sublime food and green fields. The discovery that they were only hallucinations after months at sea was agonizing. Some sailors wept with nostalgia; others threw themselves overboard.
The cure for these harrowing mirages turned out to be not a concoction of complex chemicals, as once suspected, but rather the simple antidote of lemon juice. These sailors suffered from scurvya disease caused by a deficiency in vitamin C, an essential micronutrient that people acquire by eating fruits and vegetables.
Vitamin C is important for the production and release of neurotransmitters, the chemical messengers of the brain. Without it, 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 striving to unravel. As a scientist who studies the neurosciences of nutrition At the University of Michigan, I’m primarily interested in how components of foods and their breakdown products can alter the genetic instructions that control our physiology.
Beyond that, my research also aims to understand how food can influence our thoughts, moods and behaviors. Although we can’t yet prevent or treat brain conditions with diet, researchers like me are learning a lot about the role nutrition plays in the daily brain processes that make us who we are.
It is perhaps unsurprising that a delicate balance of nutrients is essential for brain health: deficiencies or excesses of vitamins, sugars, fats and amino acids can influence the brain and the behavior of negative or positive way.
Vitamin and mineral deficiencies
As with vitamin C, deficiencies of other vitamins and minerals can also precipitate nutritional diseases that negatively impact the brain in humans. For example, low dietary levels of vitamin B3/niacin – usually found in meat and fish – cause pellagraa disease in which people develop dementia.
Niacin is essential for converting food into energy and building blocks, protecting the genetic imprint from environmental damage, and controlling the amount of certain genetic products produced. In the absence of these critical processes, brain cells, also called neurons, malfunction and die prematurelyleading to dementia.
In animal models, decreasing or blocking niacin production in the brain promotes neuronal damage and cell death. Conversely, increasing niacin levels has been shown to lessen the effects of neurodegenerative diseases such as Alzheimer’s, Huntington’s and Parkinson’s. Observational studies in humans suggest that sufficient levels of niacin can protect against these diseasesbut the results are still inconclusive.
Interestingly, niacin deficiency caused by excessive alcohol consumption can lead to effects similar to those seen with pellagra.
Another example of how nutrient deficiency affects brain function can be found in the element iodine, which, like niacin, must be acquired from one’s diet. Iodine, found in seafood and seaweed, is an essential building block of thyroid hormones – signaling molecules important for many aspects of human biology, including development, metabolism, appetite and sleep. . Low levels of iodine prevent the production of adequate amounts of thyroid hormones, impairing these essential physiological processes.
Iodine is particularly important for the development of the human brain; before table salt was supplemented with this mineral in the 1920s, iodine deficiency was a major cause of cognitive impairment in the world. It is believed that the introduction of iodized salt contributed to the gradual increase in IQ scores over the past century.
Ketogenic diet for epilepsy
Not all nutritional deficiencies harm 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 a very low carbohydrate diet, known as ketogenic dietin which 80 to 90% of calories come from fat.
Carbohydrates are the body’s preferred source of energy. When it’s not available — either because of fasting or a ketogenic diet — cells get fuel by breaking down fat into compounds called ketones. Using ketones for energy leads to profound changes in metabolism and physiologyincluding the levels of hormones circulating in the body, the amount of neurotransmitters produced by the brain, and the types of bacteria living in the gut.
Researchers think that these diet-related changes, in particular the higher production of brain chemicals that can calm neurons and reduce levels of inflammatory molecules, may play a role in the ability of the ketogenic diet to reduce the number of seizures. 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 certain nutrients can also have adverse effects on the brain. In humans and animal models, high consumption of refined products sugars and saturated fats – a combination commonly found in ultra-processed foods – promotes healthy eating desensitizing the brain to hormonal signals known to regulate satiety.
Interestingly, a diet high in these foods desensitizes the taste system, which causes animals and humans to perceive foods as less sweet. These sensory alterations can affect food choice 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 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 cues may increase cravings for even more fatty and sugary foods, similar to how smokers crave cigarettes.
Diets high in fat and processed foods are also associated with reduced cognitive function and memory in man 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.
Time scales
This brings us to a critical aspect of the effect of food on the brain: time. Some foods can have an acute influence on brain function and behavior – 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 rapidly changes the fat-burning ketogenic metabolism of an individual with drug-resistant epilepsy to a carbohydrate-burning metabolism, thereby increasing the risk of seizures. In contrast, it takes weeks of sugar consumption for 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 disease and Parkinson’s disease, the risk is influenced by years of dietary exposure in combination with other genetic factors or lifestyle factors such as smoking.
Ultimately, the relationship between food and the brain is a bit like the delicate Goldilocks: we don’t need too little or too much, but just enough of each nutrient.
