The general health of the digestive system modulates immune functioning and brain activity through the microbiome-gut-brain axis. Recent research findings point to a possible link between imbalances in bowel microflora, increased inflammation of the mucosal lining of the intestines, and systemic immune dysregulation resulting in increased risk of depressed mood. Preliminary findings from animal studies and early human clinical trials suggest that probiotics have therapeutic effects in autism, depressed mood, and anxiety.
Most research findings on the relationship between nutrition and mental health are inconsistent and inconclusive. However, most mental health professionals agree that reducing or eliminating refined sugar and caffeine from the diet improves mood in many depressed patients. Foods rich in folate, pyridoxine (B6), and methyl-cobalamin (B12) are therapeutic because these vitamins are essential co-factors in the synthesis of serotonin, dopamine, and norepinephrine, 3 neurotransmitters that play central roles in mood regulation. Increased consumption of fish high in omega-3 essential fatty acids may provide a protective effect against depressed mood. Important dietary sources of omega-3s include salmon, halibut, other deep-sea fish, as well as flaxseed oil. Relatively greater intake of omega-3 fatty acids (i.e., compared to omega-6 fatty acids) is correlated with lower inflammatory markers in such as C-reactive protein and reduced risk of inflammation-mediated disorders, including depression and Alzheimer disease. In fact prevalence rates of severe depression and suicide attempts are lower in countries where fish is an important part of the average diet. In Japan, where fish consumption is very high, the annual incidence of depressed mood is only 0.12 percent, compared to 6 percent in New Zealand, where fish consumption is relatively low.
A large epidemiological study concluded that fish consumption (containing mainly omega-3 fatty acids) two to three times weekly significantly reduced the risk of cognitive decline in the elderly. High fish consumption was found to be inversely correlated with cognitive impairment. In contrast, individuals who preferred foods rich in linoleic acid (an omega-6 fatty acid) exhibited significantly higher rates of cognitive decline. Lifestyle factors—including exercise and alcohol consumption—and educational level are associated with dietary preferences, and thus a relatively lower risk of developing Alzheimer disease cannot be ascribed to fish consumption alone. Persons who consume a high-fat, high-calorie diet are at significantly greater risk of developing Alzheimer disease than persons who have moderate fat intake and restrict total calories.
Excess caloric intake and high fat intake promote the formation of damaging free radicals that cause diffuse neuropathological changes in the brain. A meta-analysis of findings from 18 community-wide studies concluded that the risk of Alzheimer disease increased linearly at a rate of 0.3 percent with every 100-calorie increase in daily intake. Average daily fat consumption was strongly correlated with increased risk of developing dementia.
Caffeine consumption increases blood levels of epinephrine, norepinephrine, and cortisol resulting in increased feelings of ‘nervousness’ and increased risk of panic attacks in individuals who are genetically predisposed to these disorders. Moderate but not heavy consumption of wine (two to four glasses per day) is associated with a reduced risk of Alzheimer disease. In a large 5-year cohort study, 19,000 women aged 70 to 80 years who drank 14 g of alcohol daily (the equivalent of one and a half glasses of wine or one 12-oz beer) were 20 percent less likely to experience significant cognitive impairment compared to nondrinkers. Chronic alcohol abuse is often associated with malnutrition due to malabsorption of essential nutrients through the mucosa of the stomach and small intestines resulting in significantly reduced blood levels of thiamin, folate, B6, and important trace minerals. Hypoglycemia can result from toxic effects of alcohol on the liver manifesting as confusion, anxiety, and impaired cognitive functioning. Alcoholics who improve their general nutrition probably have a better chance of maintaining sobriety than those who do not. Eighty-one percent of alcoholics who stayed on a caffeine-free, low–refined sugar diet high in wheat germ and fruit remained abstinent at 6 months.
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