Nutrition and mental health

Nutrition and the brain

A person's food intake affects mood, behavior, and brain function. A hungry person may feel irritable and restless, whereas a person who has just eaten a meal may feel calm and satisfied. A sleepy person may feel more productive after a cup of coffee and a light snack. A person who has consistently eaten less food or energy than needed over a long period of time may be apathetic and moody.

The human brain has high energy and nutrient needs. Changes in energy or nutrient intake can alter both brain chemistry and the functioning of nerves in the brain. Intake of energy and several different nutrients affect levels of chemicals in the brain called neurotransmitters. Neurotransmitters transmit nerve impulses from one nerve cell to another, and they influence mood, sleep patterns, and thinking. Deficiencies or excesses of certain vitamins or minerals can damage nerves in the brain, causing changes in memory, limiting problem-solving ability, and impairing brain function.

Several nutritional factors can influence mental health, including: overall energy intake, intake of the energy-containing nutrients (proteins, carbohydrates, and fats), alcohol intake, and intake of vitamins and minerals. Often deficiencies of multiple nutrients rather than a single nutrient are responsible for changes in brain functioning.

In the United States and other developed countries, alcoholism is often responsible for nutritional deficiencies that affect mental functioning. Diseases can also cause nutritional deficiencies by affecting absorption of nutrients into the body or increasing nutritional requirements. Poverty, ignorance, and fad diets also contribute to nutritional deficiencies.

Energy intake and mental health

Energy, often referred to as the calorie content of a food, is derived from the carbohydrate, protein, fat, and alcohol found in foods and beverages. Although vitamins and minerals are essential to the body, they provide no energy. The human brain is metabolically very active and uses about 20 to 30% of a person's energy intake at rest. Individuals who do not eat adequate calories from food to meet their energy requirements will experience changes in mental functioning. Simply skipping breakfast is associated with lower fluency and problem-solving ability, especially in individuals who are already slightly malnourished. A hungry person may also experience lack of energy or motivation.

Chronic hunger and energy deprivation profoundly affects mood and responsiveness. The body responds to energy deprivation by shutting or slowing down nonessential functions, altering activity levels, hormonal levels, oxygen and nutrient transport, the body's ability to fight infection, and many other bodily functions that directly or indirectly affect brain function. People with a consistently low energy intake often feel apathetic, sad, or hopeless.

Developing fetuses and young infants are particularly susceptible to brain damage from malnutrition. The extent of the damage depends on the timing of the energy deprivation in relation to stage of development. Malnutrition early in life has been associated with below-normal intelligence, and functional and cognitive defects.

Carbohydrates and mental health

Carbohydrates include starches, naturally occurring and refined sugars, and dietary fiber. Foods rich in starches and dietary fiber include grain products like breads, rice, pasta and cereals, especially whole-grain products; fruits; and vegetables, especially starchy vegetables like potatoes. Foods rich in refined sugars include cakes, cookies, desserts, candy, and soft drinks.

Carbohydrates significantly affect mood and behavior. Eating a meal high in carbohydrates triggers release of a hormone called insulin in the body. Insulin helps let blood sugar into cells where it can be used for energy, but insulin also has other effects in the body. As insulin levels rise, more tryptophan enters the brain. Tryptophan is an amino acid, or a building block of protein, that affects levels of neurotransmitters in the brain. As more tryptophan enters the brain, more of the neurotransmitter serotonin is produced. Higher serotonin levels in the brain enhance mood and have a sedating effect, promoting sleepiness. This effect is partly responsible for the drowsiness some people experience after a large meal.

Some researchers claim that a high sugar intake causes hyperactivity in children. Although carefully controlled studies do not support this conclusion, high sugar intake is associated with dental problems. Further, foods high in refined sugars are often low in other nutrients, making it prudent to limit their use.

Proteins and mental health

Proteins are made up of amino acids linked together in various sequences and amounts. The human body can manufacture some of the amino acids, but there are eight essential amino acids that must be supplied in the diet. A complete or high-quality protein contains all eight of the essential amino acids in the amounts needed by the body. Foods rich in high-quality protein include meats, milk and other dairy products, and eggs. Dried beans and peas, grains, and nuts and seeds also contain protein, although the protein in these plant foods may be low in one or more essential amino acid. Generally, combining any two types of plant protein foods together will yield a complete, high-quality protein. For example, a peanut butter and jelly sandwich combines grain protein from the bread with nut protein from the peanut butter to yield a complete protein. A bean-rice hot dish combines bean and grain protein for another complete protein combination.

Protein intake and intake of individual amino acids can affect brain functioning and mental health. Many of the neurotransmitters in the brain are made from amino acids. The neurotransmitter dopamine is made from the amino acid tyrosine. The neurotransmitter serotonin is made from the amino acid tryptophan. If the needed amino acid is not available, levels of that particular neurotransmitter in the brain will fall, and brain functioning and mood will be affected. For example, if there is a lack of tryptophan in the body, not enough serotonin will be produced, and low brain levels of serotonin are associated with low mood and even aggression in some individuals. Likewise, some diseases can cause a buildup of certain amino acids in the blood, leading to brain damage and mental defects. For example, a buildup of the amino acid phenylalanine in individuals with a disease called pheylketonuria can cause brain damage and mental retardation.

Fats and mental health

Dietary intake of fats may also play a role in regulating mood and brain function. Dietary fats are found in both animal and plant foods. Meats, regular-fat dairy products, butter, margarine, and plant oils are high in fats.

Although numerous studies clearly document the benefits of a cholesterol-lowering diet for the reduction of heart disease risk, some studies suggest that reducing fat and cholesterol in the diet may deplete brain serotonin levels, causing mood changes, anger, and aggressive behavior.

Other studies have looked at the effects of a particular kind of fat, the omega-3 fatty acids found in fish oils, and brain functioning. Although a few studies suggest omega-3 fatty acids are helpful with bipolar affective disorder and stress, results are inconclusive.

High levels of fat and cholesterol in the diet contribute to atherosclerosis, or clogging of the arteries. Atherosclerosis can decrease blood flow to the brain, impairing brain functioning. If blood flow to the brain is blocked, a stroke occurs.

Alcohol and mental health

A high alcohol intake can interfere with normal sleep patterns, and thus can affect mood. Alcoholism is one of the most common causes of nutritional deficiencies in developed countries. Alcoholic beverages provide energy but virtually no vitamins or minerals. A person who consumes large amounts of alcohol will meet their energy needs but not their vitamin and mineral needs. In addition, extra amounts of certain vitamins are needed to break down alcohol in the body, further contributing to nutrient deficiencies.

Thiamin

Thiamin is a B vitamin found in enriched grain products, pork, legumes, nuts, seeds, and organ meats. Thiamin is intricately involved with metabolizing glucose, or blood sugar, in the body. Glucose is the brain's primary energy source. Thiamin is also needed to make several neurotransmitters.

Alcoholism is often associated with thiamin deficiency. Alcohol interferes with thiamin metabolism in the body, and diets high in alcohol are often deficient in vitamins and minerals. Individuals with a thiamin deficiency can develop Wernicke-Korsakoff syndrome, which is characterized by confusion, mental changes, abnormal eye movements, and unsteadiness that can progress to severe memory loss.

Vitamin B-12

Vitamin B-12 is found only in foods of animal origin like milk, meat, or eggs. Strict vegans who consume no animal-based foods need to supplement their diet with vitamin B-12 to meet the body's need for this nutrient.

Vitamin B-12 is needed to maintain the outer coating, called the myelin sheath, on nerve cells. Inadequate myelin results in nerve damage and impaired brain function. Vitamin B-12 deficiency can go undetected in individuals for years, but it eventually causes low blood iron, irreversible nerve damage, dementia, and brain atrophy.

Folic acid

Folic acid is another B vitamin found in foods such as liver, yeast, asparagus, fried beans and peas, wheat, broccoli, and some nuts. Many grain products are also fortified with folic acid. In the United States, alcoholism is a common cause of folic acid deficiency.

Folic acid is involved in protein metabolism in the body and in the metabolism of some amino acids, particularly the amino acid methionine. When folic acid levels in the body are low, methionine cannot be metabolized properly and levels of another chemical, homocysteine, build up in the blood. High blood homocysteine levels increase risk of heart disease and stroke.

Even modest folic acid deficiency in women causes an increased risk of neural tube defects, such as spina bifida, in developing fetuses. Folic acid deficiency also increases risk of stroke. Some studies suggest that folic acid deficiency leads to a range of mental disorders, including depression, but this concept remains controversial. Folic acid deficiency can lower levels of serotonin in the brain.

Niacin

The B vitamin niacin is found in enriched grains, meat, fish, wheat bran, asparagus, and peanuts. The body can also make niacin from the essential amino acid tryptophan, which is found in high-quality animal protein foods like meat and milk. Niacin deficiency used to be common in the southern United States but is now common only in developing countries such as India and China.

Niacin is involved in releasing energy in the body from carbohydrates, proteins, and fats. A deficiency of niacin produces many mental symptoms such as irritability, headaches, loss of memory, inability to sleep, and emotional instability. Severe niacin deficiency progresses to a condition called pellagra, which is characterized by the four D's: dermatitis (a rash resembling a sunburn), diarrhea, dementia, and ultimately, death. The mental symptoms in pellagra can progress to psychosis, delirium, coma, and death.

Vitamin B-6

Vitamin B-6, also known as pyridoxine, is found in many plant and animal foods, including chicken, fish, pork, whole wheat products, brown rice, and some fruits and vegetables. In healthy individuals, deficiency of vitamin B-6 is rare, but certain drugs, including some antidepressant drugs, can induce vitamin B-6 deficiency. Vitamin B-6 is needed by the body to produce most of the brain's neurotransmitters. It is also involved in hormone production. Although rare, vitamin B-6 deficiency is characterized by mental changes such as fatigue, nervousness, irritability, depression, insomnia, dizziness, and nerve changes. These mental changes are related to the body's decreased ability to manufacture neurotransmitters with vitamin B-6 deficiency.

Just as vitamin B-6 deficiency causes mental changes, so does excess of vitamin B-6. Vitamin B-6 supplements are used by many individuals for a variety of conditions, including carpal tunnel syndrome, premenstrual syndrome, and fibrocystic breast disease. Doses of 500 mg per day or more can cause nerve damage, dizziness, sensory loss, and numbness.

Vitamin E

Vitamin E is a fat-soluble vitamin that is plentiful in the diet, particularly in plant oils, green leafy vegetables, and fortified breakfast cereals. Vitamin E deficiency is very rare, except in disorders that impair absorption of fat-soluble vitamins into the body, such as cystic fibrosis, and liver diseases.

Vitamin E deficiency causes changes in red blood cells and nerve tissues. It progresses to dizziness, vision changes, muscle weakness, and sensory changes. If left untreated, the nerve damage from vitamin E deficiency can be irreversible. Because it is an antioxidant, vitamin E has also been studied for treatment of neurological conditions such as Parkinson's and Alzheimer's disease. Although results are inconclusive, vitamin E shows some promise in slowing the progression of Parkinson's disease.

Vitamin A

Vitamin A is a fat-soluble vitamin found in meats, fish and eggs. A form of vitamin A, beta-carotene, is found in orange and green leafy vegetables such as carrots, yellow squash, and spinach. Headache and increased pressure in the head is associated with both deficient and excess vitamin A intake. Among other effects, excess vitamin A intake can cause fatigue, irritability, and loss of appetite. Generally, doses must exceed 25,000 international units of vitamin A over several months to develop such symptoms.

Iron

Iron is a trace mineral that is essential for formation of hemoglobin, the substance that carries oxygen to cells throughout the body. Iron is found in meat, poultry, and fish. Another form of iron that is not as well absorbed as the form in animal foods is found in whole or enriched grains, green leafy vegetables, dried beans and peas, and dried fruits. Consuming a food rich in vitamin C, such as orange juice, at the same time as an iron-containing plant food will enhance iron absorption from the food.

Iron deficiency eventually leads to anemia, with insufficient oxygen reaching the brain. The anemia can cause fatigue and impair mental functioning. Iron deficiency during the first two years of life can lead to permanent brain damage.

Magnesium

The mineral magnesium is found in green leafy vegetables, whole grains, nuts, seeds, and bananas. In areas with hard water, the water may provide a significant amount of magnesium. In addition to its involvement in bone structure, magnesium aids in the transmission of nerve impulses.

Magnesium deficiency can cause restlessness, nervousness, muscular twitching, and unsteadiness. Acute magnesium deficiency can progress to apathy, delirium, convulsions, coma, and death.

Manganese

Manganese is a trace mineral found in whole grains and nuts, and to a lesser extent, fruits and vegetables. Manganese is involved in carbohydrate metabolism and brain functioning. Although very rare, manganese deficiency can cause abnormalities in brain function. Miners of manganese in South America have developed manganese toxicity called manganese madness, with neurological symptoms similar to Parkinson's disease.

Copper

The richest sources of the trace mineral copper in the diet are organ meats, seafood, nuts, seeds, whole grain breads and cereals, and chocolate. In addition to other functions, copper is involved in iron metabolism in the body and in brain function. Deficiency of copper causes anemia, with inadequate oxygen delivery to the brain and other organs. Copper deficiency also impairs brain functioning and immune system response, including changes in certain chemical receptors in the brain and lowered levels of neurotransmitters.

Zinc

The trace mineral zinc is found in red meats, liver, eggs, dairy products, vegetables, and some seafoods. Among other functions, zinc is involved in maintaining cell membranes and protecting cells from damage. Zinc deficiency can cause neurological impairment, influencing appetite, taste, smell, and vision. It has also been associated with apathy, irritability, jitteriness, and fatigue.

Selenium

Good sources of the trace mineral selenium include seafood, liver, and eggs. Grains and seeds can also be good sources of selenium depending on the selenium content of the soil they are grown in. Selenium is needed for the synthesis of some hormones and helps protect cell membranes from damage.

Although selenium deficiency is very rare, selenium toxicity has occurred in regions of the world with high selenium soil content, such as China. Selenium toxicity causes nervous system changes, fatigue, and irritability.

See also Diets; Nutrition counseling

BOOKS

Jeffery, Douglas R., M.D., Ph.D. "Nutrition and Diseases of the Nervous System." In Modern Nutrition in Health and Disease. 9th edition. Edited by Maurice E. Shils, M.D., Sc.D., James A. Olson, Ph.D., Moshe Shike, M.D., and A. Catharine Ross, Ph.D. Baltimore: Williams and Wilkins, 1999.

Katz, David L., M.D., M.P.H. Nutrition in Clinical Practice. New York: Lippincott, Williams, and Wilkins, 2001.

Shiveley, LeeAnn R., M.P.H, R.D. and Patrick J. Connolly, M.D. "Medical Nutrition Therapy for Neurologic Disorders." In Krause's Food, Nutrition, & Diet Therapy. 10th edition. Edited by L. Kathleen Mahan, M.S., R.D.,C.D.E., and Sylvia Escott-Stump, M.A., R.D., L.D.N. New York: W. B. Saunders Company, 2000.

Westermarck T., M.D., D.Sc. and E. Antila, M.D., Ph.D. "Diet in Relation to the Nervous System." In Human Nutrition and Dietetics. 10th edition. Edited by J. S. Garrow, M.D., Ph.D., W. P. T. James, M.D., S.Sc., and A. Ralph, Ph.D. New York: Churchill Livingstone, 2000.

PERIODICALS

Young, Simon N. "Clinical Nutrition: 3. The Fuzzy Boundary Between Nutrition and Psychopharmacology." Canadian Medical Association Journal 166 (2002): 205-209.

ORGANIZATIONS

American Dietetic Association. 216 West Jackson Boulevard, Chicago, Illinois, 60606-6995.<http://www.eatright.org>.

Nancy Gustafson, M.S., R.D., F.A.D.A., E.L.S.