Nutritional Psychology Answers Why Diet Impacts How We Think and Feel

The waitress of the fast food joint asks, “Would you like fries with that?” The customer quickly requests a super-sized meal, while the woman at the neighboring orders a grilled chicken salad. Whichever dietary choice resembles your own, nutrition has a vast impact on how we think, feel, and behave. Why? Nutritional psychology explains how nutrition determines cognitive skills, mood disorders, and intelligence.

What is Nutritional Psychology?

Nutritional psychology is the study of nutrition and how it pertains to mood, behavior, and mental health. The foods we eat influence psychological, behavioral, cognitive, perceptual, sensory, and psychosocial patterns. This area of study has the goal to implement education and nutrition to connect diet with mental health.

Nutritional Psychology: The Enteric Nervous System

The nervous system is known to describe the brain and spinal cord; however, most are surprised to learn that a large portion of the nervous system is in our gastrointestinal tracts. From chewing food to absorption and even elimination, the gut is home to millions of nerve cells, hormones, and enzymes that perform a variety of functions. This is why it is commonly referred to as our second brain. Together, the gastrointestinal tract and all it entails is called the enteric nervous system.

Nutritional Psychology: Hormones

Gut bacteria line the stomach and intestines to facilitate digestion. These bacteria manufacture neurotransmitters not only to regulate digestion, but to control key cognitive processes like memory, mood, and learning. Serotonin is a particular prominent neurotransmitter in the gut. Bacteria create nearly 95 percent of the body’s serotonin—a neurotransmitter imperative to stabilize mood and trigger peristalsis (i.e. contractions of the stomach and intestines to digest food). When serotonin is off, it can cause symptoms of nausea, vomiting, and constipation. But serotonin is not the sole neurotransmitter, GABA and dopamine are also relevant. Studies have allowed experts to document observations like mood changes in the presence of functional gastrointestinal disorders such as irritable bowel syndrome. It was once thought that emotions and disorders like anxiety and depression result in bowel symptoms, but scholars at John Hopkins now believe that an unhealthy gastrointestinal tract leads to anxiety and depression.

Nutritional Psychology: Food and Brain Structure

The food we consume literally has the power to alter brain structure. A 2018 study published in the Journal of Neuroscience reveals an increased volume of grey matter in the prefrontal cortex shown on brain imagine in patients who made food choices based on whether a food item is healthy rather than on taste or indulgence. Judging grey matter volume in these areas is a helpful predictor of various eating disorders including obesity and anorexia nervosa.

Neurons, nerve cells in the brain, are also affected by food. Diets with a high fat and sugar content have fewer synapses in the brain’s hippocampus—the connections that transmit signals to other cells in the body. The brain is less efficient at neuroplasticity. It cannot adapt as quickly. Instead, the hippocampus becomes inflamed as the cells respond to harm.

Nutritional Psychology: Obesity

The term obesity is described as having a body mass index (BMI) of 30 or greater. There are more than 400 million obese adults worldwide. Being overweight has a vast impact on the body. Although someone who is obese is prone to developing heart disease, diabetes, and hypertension, the brain is particularly effected. Scientists have attributed multiple cases of cognitive impairment with obesity.   

The brain of obese individuals is vulnerable to cerebral atrophy. The brain literally shrinks. As the brain volume decreases in size, the likelihood of memory impairment increases with age. A lack of brain volume makes it difficult to refrain from excessive eating, which fuels the cycle.

Nutritional Psychology: Caloric Intake

The first line of defense against the obesity epidemic is to adopt a healthy diet and lifestyle. Diet and exercise are key to shedding the extra pounds because it burns more calories than one expends. However, restricting caloric intake is potentially detrimental to psychological health.

Studies show that caloric restriction is linked to depression—a mental health disorder characterized by feeling unexplained sadness, anxiety, loss of interest, low motivation, and interrupted sleeping and eating patterns for more than 2-weeks. Male subjects went from consuming 3,200 calories to 1,600 calories of foods such as potatoes, turnips macaroni, milk, bread, chicken, and rutabagas. These men reported a multitude of symptoms: dizziness, cold intolerance, fatigue, muscle aches, edema, reduced sex drive, low attention spans, poor concentration, and psychological distress. Some were even sent to a psychiatric hospital for self-mutualization and suicide attempts.

Contrarily, other studies conclude that the risk for dementia and cognitive decline is lessened by a lower caloric intake. The combination of studies supports that the quality of food choices are important. For our brains to thrive, we require a range of foods from all food groups to avoid nutritional deficiencies.

Nutritional Psychology: Carbohydrates and Cognition

Carbohydrates are the body’s main source of fuel. As carbs are consumed, the body breaks the carbohydrates down into glucose. The nerve cells utilize the glucose in the bloodstream for energy. Restricting carbohydrates, like so many of modern day dieters do, is depriving the body of its main source of fuel. Thus, cognitive skills are affected. Researchers at Tufts University tested this hypothesis. Women were placed into groups based on “low-carb” and “low calorie” diets. Their cognitive skills were tested before the study, during, and after. Those on low carbohydrate diets presented with poor memory performance within a week of their diet.

In the average Western diet, the type of carbohydrates has an impact too. Refined, processed carbohydrates result in repeated spikes in blood glucose levels which triggers the rapid release of stress hormones that increase anxiety and mood disorders.

Nutritional Psychology: Fatty Acids and Cognition

70 percent of the human brain is comprised of fat. Fats are critical for brain development. When the body does not have sufficient carbohydrates available, it uses fat to perform necessary functions. Psychiatrists at Harvard University discovered that the amount of fat an individual consumes has little impact on brain function; however, the form of fat does.

Omega-3 fatty acids are beneficial dietary fats. They are found in fish, walnuts, and chia seeds. Other fats, like saturated fats, are good in moderation and come from meat, coconut, and dairy products. Hydrogenated fats (i.e. trans fats) are best avoided in foods that are processed or deep-fried.

Nutritional Psychology: Vitamins and Minerals and Cognition

Vitamins and minerals are also related to brain function. The body is exposed to free radicals. Free radicals are unstable cells that damage healthy cells. The result is disease, aging, and illness. Vitamins and minerals contain radical fighting substances known as antioxidants.

The following vitamins and minerals are essential:

• Iron—Adults and children who are anemic score lower on cognitive tests.
• B Vitamins—B vitamins for the brain include B12, B6, and B9 (folate). When B vitamins are lacking, the body cannot convert homocysteine into protein. As homocysteine accumulates, cognitive performance suffers.  
• Vitamin C—Vitamin C aids in iron absorption, but it does affect the brain directly. It is responsible for building the myelin sheath that allows the nerves to communicate. Vitamin C partakes in manufacturing neurotransmitters like dopamine and serotonin.
• Vitamin D—Vitamin D is absorbed from both dietary sources and sunlight. Similar to vitamin C, vitamin D facilitates nerve growth. Experts claim vitamin D activates certain enzymes to produce neurotransmitters and reduce inflammation.
• Vitamin E—Vitamin E is the main vitamin that combats neurodegeneration in the brain by reducing oxidative stress. When compounded with other vitamins, it improves memory and cognitive thinking processes.
• Zinc—Deficiencies in zinc reflect issues with language and numbers. Patients with Alzheimer’s disease tend to have a zinc deficiency, which provides evidence that zinc aids in cognitive function.
• Magnesium—Unrefined grains (i.e. buckwheat), green leafy vegetables, and nuts (i.e. almonds, cashews) are sources of magnesium. This deficiency is common in third-world countries and vegetarians.

Dietary Psychology: Can Your Diet Lower Your Risk of Dementia?

Dementia is an umbrella term for neurodegenerative illnesses that cause impaired cognitive skills. Those with dementia experience memory loss, confusion, difficulties with language, and problem-solving abilities that inhibit normal daily functioning. The most common form of dementia is Alzheimer’s disease.

Published in April 2020’s edition of American Academy of Neurology, people who primarily eat snack foods (i.e. cookies, cakes), processed meats, and starchy foods such as potatoes have a higher risk of dementia than individuals who consume foods from a diverse range of food groups. Additionally, previous studies confirm that greater caloric intake is associated with Alzheimer’s.  

Abiding by dietary guidelines proposed by the Alzheimer’s Association is actually a treatment for the condition. Patients have an increase in memory and an overall reduction in the progression of the disease. Two diets are recommended to fight dementia:

• DASH Diet—DASH stands for The Dietary Approaches to Stop Hypertension. It promotes a diet to lower blood pressure, which reduces stress on the nervous system. Someone following the DASH diet is encouraged to reduce their intake of excessive amounts of sodium, fats, red meats, full-fat dairy products, sweets, sugary beverages and to consume lean meats (i.e. poultry, fish), whole grains, nuts, fruits, and vegetables.
• The Mediterranean Diet—The Mediterranean diet limits red meat, replaces butter with healthy alternatives and focuses on a diet of fruits, fresh vegetables, nuts, and whole grains. Fish and poultry are eaten twice weekly and spices replace salt.

Nutritional Psychology: Foods That Are Harmful To Your Brain

Much like a diet of fruits, green leafy vegetables, whole grains, lean meats, nuts, and seeds are healthy for the brain, there are many foods that have the opposite effect. The chemicals in the foods we eat are stored throughout the body, including the brain and nervous system.

Soft Drinks

Sugary soft drinks include high fructose corn syrup. High fructose corn syrup is 55 percent fructose and 45 percent glucose. The inflammatory substance incorporated into our favorite beverages is known to impair memory. For example, high fructose corn syrup affects brain function because of it leads to insulin resistance. When the body is unable to bring blood glucose levels to normal ranges, the increase levels are damaging to the brain.

Refined Carbohydrates

Refined carbohydrates are processed grains like white flour. They have a high glycemic index in which the body responds with a spike in blood sugar levels. Studies of the elderly population proved that the risk of dementia and mild cognitive impairment is nearly doubled in the population who received over half of their dietary caloric intake from unhealthy carbohydrates. Whole, unrefined grains, fruits, and vegetables are healthier alternatives.

Trans Fats

While naturally occurring trans fats in meat and dairy products are not dangerous in controlled amounts, hydrogenated vegetable oil, margarine, pre-packaged desserts, frosting, and shortening are foods hiding the brain’s silent killer. Synthetic trans fats are harmful to cognitive function, as well as cardiac health. It advances inflammation.

Artificial Sweeteners

“Sugar free” is not always the healthier option. Aspartame and artificial sweeteners are in sugar free products. Aspartame is made from the amino acids aspartic acid and phenylalanine. If aspartame is consumed, the body breaks it down into methanol which is toxic in large amounts.

Studies show artificial sweeteners provoke behavioral changes, depression, and learning difficulties. Participants consumed 11 mg of aspartame for every pound of body weight. After eight days, they scored lower on cognitive tests, were irritable, and had increased rates of depression in comparison to control subjects.

Alcohol

Alcohol impairs the way in which the brain communicates and decreases brain volume. Those who frequently consume alcohol typically develop a B vitamin deficiency, which is connected to poor cognitive functioning. While the majority of detrimental effects stem from episodes of binge drinking, it is recommended that young people avid alcohol because it interferes with brain development. Teenagers who drink are susceptible to risky behaviors and alcohol dependence into adulthood.

Nutritional Psychology: Which Diet Is Best For Your Brain?

So, what diet is best for your brain? Low carb, high carb, high fat, low fat, calorie restriction? Optimal eating habits are not any single diet. It is learning to be intuitive with your body’s nutritional needs, consuming a diet as colorful as the rainbow, and incorporating a variety of foods from all food groups. It is about establishing a balance that allows your body and brain to thrive.

References

American Academy of Neurology. (2020, April 22). Which foods do you eat together? How you combine them may raise dementia risk: Study finds ‘food networks’ centered on processed meats, starches may raise risk. ScienceDaily. Retrieved November 22, 2020 from www.sciencedaily.com/releases/2020/04/200422214038.htm

Harvard University. Protect your brain with “good fat.” Retrieved from https://www.health.harvard.edu/mind-and-mood/protect-your-brain-with-good-fat

Cheyanne Perry

Cheyanne is currently studying psychology at North Greenville University. As an avid patient advocate living with Ehlers Danlos Syndrome, she is interested in the biological processes that connect physical illness and mental health. In her spare time, she enjoys immersing herself in a good book, creating for her Etsy shop, or writing for her own blog.