Psychological stress is known to increase the production of pro-inflammatory cytokines. The deriving inflammation is accompanied by an accumulation of highly reactive oxygen species, also known as oxidative stress, which is a contributing factor in the development of severe depression. A diet rich in antioxidants, vitamins, minerals and fiber is associated with reduced systemic inflammation. Conversely, diets that are low in essential nutrients, such as magnesium and sugar- and fat-rich western diets are associated with increased systemic inflammation.
A new study of 3040 Australian adolescents 11 to 18 years of age collected information on diet and mental health by self-report and anthropometric data by trained researchers. Improvements in diet quality were mirrored by improvements in mental health over the follow-up period, while deteriorating diet quality was associated with poorer psychological functioning. Researchers concluded that the quality of one’s nutrition is associated with adolescent mental health both cross-sectionally and prospectively. Moreover, improvements in diet quality were mirrored by improvements in mental health, while reductions in diet quality were associated with declining psychological functioning over the follow-up period.
There are many ways in which an insufficiency of healthy foods and/or an excessive intake of unhealthy and processed foods may increase the risk for mental health problems in adolescents. Fruits and vegetables, as well as other components of a healthy diet such as whole grains, fish, lean red meats and olive oils, are rich in important nutrients such as folate, magnesium, b-group vitamins, selenium, zinc, mono- and polyunsaturated fatty acids, polyphenols and fiber. Many of these nutrients have already been reported as of importance in depressive illnesses, however the critical importance of these food components as modulators of reactive oxygen species (inflammation) and immune system functioning, both pathophysiological substrates of depressive illness is increasingly appreciated.
A new meta-analysis, reporting on data collected at many time points and thus more reliable, has reported large generational increases in self-reported mental health problems among American high school and college students between the 1930s and 2007. Paralleling this increase in the rates of psychological illness among young people are data indicating a reduction in the quality of adolescents’ diets over recent decades. A report based on trends in adolescent food consumption in the US identified a reduction in the consumption of raw fruits, high-nutrient vegetables and dairy foods, which are important sources of fiber and essential nutrients, between 1965 and 1996, with an associated increase in the consumption of fast food, snacks and sweetened beverages.
Concurrently, population surveys demonstrate a substantial increase in overweight and obesity among children and adolescents over recent decades. Obesity does not necessarily indicate nutritional deficiency: paradoxically, high-energy foods typically have poor nutrient content.
Fast Food, Depression and Anxiety
Another study of 5731 men and women 46 to 49 and 70 to 74 years of age found that those with better quality diets were less likely to be depressed, whereas a higher intake of processed and unhealthy foods was associated with increased anxiety.
A third study examined the extent to which the high-prevalence mental disorders are related to habitual diet in 1,046 women 20–93 years of age. Results showed that a “traditional” dietary pattern characterized by vegetables, fruit, meat, fish, and whole grains was associated with lower odds for major depression or log-term depression (dysthymia) and anxiety disorders. A western diet of processed or fried foods, refined grains, sugary products, and beer was associated with a higher prevalence of mental disorders. These results demonstrate an association between habitual diet quality and a higher prevalence of mental disorders.
In a fourth study (1999–2010) of 12,059 Spanish university graduates discovered a detrimental relationship between a diet rich in trans unsaturated fatty acids (TFA) and depression risk, whereas weak inverse associations were found for monounsaturated fatty acids (MUFA), polyunsaturated fatty acids (PUFA) and olive oil. These findings suggest that cardiovascular disease and depression may share some common nutritional determinants related to fat intake.
Most notably, results of a 2010 randomized placebo controlled trial showed that fish oil supplements prevented conversion from a subthreshold psychotic state to full-blown schizophrenia. Another recent randomized controlled trial study suggested that omega-3 supplements may help reduce anxiety.