In recent times, the connection between nutrition and mental well-being has garnered significant attention. Epidemiological research has pointed out that adhering to healthy dietary patterns, which involve a high intake of fruits, vegetables, nuts, and legumes, moderate consumption of poultry, eggs, and dairy products, and only occasional consumption of red meat, is linked to a reduced risk of experiencing depression.

Depression and anxiety stand as the most prevalent mental health disorders on a global scale, positioning them as leading contributors to disability worldwide. Depression, characterized by symptoms like persistent low mood, diminished interest or enjoyment in life, and disruptions in sleep and appetite, affects a staggering 300 million individuals across the globe, constituting a worldwide prevalence rate of 7% among women and 4% among men. Depression exerts a substantial burden on public health and plays a significant role in global disability statistics. According to the World Health Organization, depressive and anxiety disorders result in a staggering $1 trillion annual loss in productivity for the global economy.

In recent times, the connection between nutrition and mental well-being has garnered significant attention. Epidemiological research has pointed out that adhering to healthy dietary patterns, which involve a high intake of fruits, vegetables, nuts, and legumes, moderate consumption of poultry, eggs, and dairy products, and only occasional consumption of red meat, is linked to a reduced risk of experiencing depression.

However, understanding the nature of these relationships becomes intricate due to the potential for a reverse causality effect between diet and mental health. For instance, our temporary emotional state can influence alterations in our food choices or preferences, such as turning to ‘comfort foods’ during periods of low mood or experiencing changes in appetite due to stress—common human experiences. Furthermore, the interplay between nutrition and chronic mental disorders is complicated by various barriers that hinder the maintenance of a healthy diet. These obstacles disproportionately affect individuals dealing with mental health issues and encompass factors like financial constraints, environmental determinants of health, and even the appetite-altering effects of psychiatric medications.

Fig 1: The hypothesised relationship between diet, physical health, and mental health (Firth, J et al., 2020)

Food and Stress

Every individual one comes across these days seems to be stressed about at least one thing happening in life. This phenomenon extends to adults in the workplace, individuals in office settings, young adults attending college, and even children in school, necessitating psychological interventions to assist them in managing stress. Notably, stressed individuals have been observed engaging in behaviours that pose health risks, such as unhealthy eating habits, smoking, and alcohol consumption. These risky yet often pleasurable behaviours serve as coping mechanisms for stress. Furthermore, there is a positive correlation between chronic stress and the consumption of highly appealing but nutritionally deficient foods.

The consumption of these highly palatable foods, characterized by their elevated levels of fat, sugar, or salt, can activate the endogenous opioid system, which regulates pain, reward, and addictive behaviours within the body. This activation leads to a reduction in the stress response of the hypothalamic-pituitary-adrenal (HPA) axis, ultimately alleviating stress-related symptoms. Additionally, the intake of highly palatable foods may reduce stress through mechanisms involving sensory pleasure, distraction, escapism, and various nutritional or metabolic effects.

Most research exploring the connection between perceived stress and eating behaviours has focused on college students. Among this demographic, heightened stress levels have been linked to a greater preference for ultra-processed foods. Ultra-processed foods are manufactured from food extracts or components such as fats, starches, and added sugars. They contain minimal whole-food components but are enriched with flavourings, colourants, and other additives that enhance their appeal to consumers. These foods are typically convenient, energy-dense, high in glycemic content, fatty, and salty while lacking dietary fibre, protein, essential micronutrients, and other bioactive compounds. As a result, they often replace healthier meal options like fruits, vegetables, meats, and fish. Examples of such ultra-processed foods include sweet, fatty, or salty packaged snacks, ice cream, sugary beverages, chocolates, confectioneries, French fries, burgers, poultry and fish nuggets.

Various forms of psychological stressors contribute to overeating and poor dietary choices. Prolonged occupational stress has been associated with increased consumption of calories, saturated fats, and sugars, potentially leading to weight gain, particularly among individuals who engage in restrained eating or intentional dietary restriction. Additionally, stress-induced social situations tend to promote the consumption of highly palatable foods. Both men and women with higher perceived stress levels tend to adopt higher-fat diets and engage in less frequent exercise. A study involving low-income pregnant women revealed that those with obesity, as well as those experiencing higher levels of psychosocial stress or increased depression, are more inclined to consume fast food compared to their counterparts.

Nutritional Deficiencies and Mood Disorders

Studies have investigated the influence of insufficient macronutrient intake in one’s diet on the likelihood of experiencing depressive symptoms. The composition and quantity of nutrients in one’s diet can significantly impact mental well-being. For instance, the type and amount of dietary protein (found in foods like meat, eggs, fish, dairy products, legumes, and pulses) play a crucial role in the development of depressive disorders. This is because protein serves as a vital source of amino acids, which are essential precursors for neurotransmitters in the brain. These neurotransmitters, such as serotonin, epinephrine, and norepinephrine, are pivotal for mood regulation. Notably, a study by Kofler et al. observed a noteworthy reduction in the levels of specific amino acids (tryptophan, tyrosine, phenylalanine) associated with the formation of neurotransmitters in individuals exhibiting depressive behaviour.

Furthermore, a diet rich in saturated fatty acids (found in items like butter, desi ghee, palm oil, and coconut oil) and trans fatty acids (present in fried foods prepared with reusable oils, including items like pakodas, samosas, bhaturas, pooris, namkeens, and bakery products) may elevate the risk of depression. Conversely, a diet abundant in monounsaturated fatty acids (found in almonds, hazelnuts, olive oil, canola oil, and avocados) and polyunsaturated fatty acids (found in walnuts, flax seeds, fish, sunflower oil, and soybean oil) may potentially reduce the risk of depression, although research findings are not entirely conclusive. Dehydration, which can impair nervous system function, is also worth noting, as water constitutes 75% of brain mass. According to Liska et al., dehydration at a level of ≥1% can lead to increased feelings of anger, confusion, depression, and fatigue.

Carbohydrates are a major energy source for the brain, and they also contribute to its structural and functional components. Carbohydrates are present in grains (such as wheat and rice), millets (like jowar, bajra, and ragi), corn, potatoes, fruits, and vegetables, and they can impact mood and brain function by influencing neurotransmitter levels. A diet centred around carbohydrates with a lower glycemic index (meaning they take longer to digest and lead to gradual increases in blood sugar levels compared to high glycemic index foods) can potentially lower the risk of depression. Recent findings suggest that for every 5-gram increase in total dietary fibre intake (found in whole wheat, ragi, fruit skins, dals, pulses, and legumes), there is a corresponding 5% reduction in the risk of depression. Moreover, a significant inverse relationship has been observed between the intake of fibre from vegetables and soluble fibre and the likelihood of depression, though fibre from cereal products, fruit, and insoluble fibre showed a marginal association with depression reduction.

Vitamin deficiencies can be linked to symptoms of mental disorders. B-group vitamins, which perform a range of functions in the human body, are crucial for maintaining the normal functioning of the nervous system through processes such as monoamine oxidase production, DNA synthesis, methylation, and the repair and upkeep of phospholipids. Deficiencies in B vitamins, particularly B1, B6, B9, and B12, have been associated with depression due to their essential role in neuronal function. These vitamins also provide protection against hypercysteinaemia, a condition associated with an increased risk of mood disorders. Furthermore, low levels of vitamin B9 and B12 have been linked to a less favourable response to antidepressant treatments. Ongoing research by Berkins et al. indicates that dietary intake of vitamin B6 and B12 may impact brain structure. Vegetarians, especially those experiencing depression, may benefit from supplementing their diet with vitamins B6, B9, and B12 to support optimal brain health.

Impact of Sugar on Mood

Sugar consumption is increasingly being discussed as a target for intervention to reduce the prevalence of obesity, diabetes, and other non-communicable diseases. Sugar is ingested not only as table sugar in beverages like tea and coffee, as well as in sweet treats, but also in hidden forms within preserved and packaged foods such as biscuits, baked goods, chips, chocolates, jellies, and canned foods. Numerous ecological and cross-sectional studies have indicated that higher sugar intake is associated with a higher prevalence of depression. There are several plausible biological explanations for the connection between habitual sugar consumption and the long-term risk of depression.

To begin with, reduced levels of the growth factor known as brain-derived neurotrophic factor (BDNF) have been suggested as a factor contributing to neurogenesis (the growth and development of nervous tissue) and hippocampal atrophy (a decline in cognitive function, including the ability to access old memories or form new ones) in cases of depression. Research has shown that rodents fed high-fat, high-sugar diets (as opposed to high-fat diets alone) experience a decrease in BDNF levels, potentially establishing a mechanistic link between sugar-rich diets and depression.

Additionally, carbohydrate consumption has been linked to elevated levels of inflammatory markers in circulation, which could have a mood-depressing effect. Furthermore, high-sugar diets may lead to hypoglycemia due to an excessive insulin response, which in turn can influence hormone levels and potentially affect mood states. Lastly, the addictive qualities of sugar point toward dopaminergic neurotransmission mechanisms, thus establishing a connection between frequent sugar consumption and depression.

Meal timing and Mood

The timing of food intake is an emerging area of interest in the field of nutrition due to its significant impact on metabolic health. Eating habits and nutritional choices are closely linked to mood, mental well-being, and sleep patterns. Western dietary patterns not only elevate the risk of obesity but also pose a threat to mental health. Optimal nutrition is characterized by higher consumption of fruits, vegetables, and proteins, which contain essential nutrients such as eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), alpha-tocopherol, magnesium, and folic acid, all known for their positive effects on mental health. Beyond specific food groups, one’s eating behaviour also plays a pivotal role. For instance, skipping breakfast has been associated with elevated stress levels, depression, and fatigue. Night eating syndrome (NES), an eating disorder accompanied by frequent sleep disruptions, leads to nocturnal emotional eating, increased evening depression, and diminished sleep quality. Individuals with NES experience the compulsion to eat to fall back asleep, often waking multiple times during the night and feeling ashamed or distressed.

In contrast, adhering to regular meal timings and employing strategies like time-restricted eating (TRE), where daily eating is confined to an 8–12-hour window, have shown benefits in improving circadian rhythms, combating obesity, preventing pre-type 2 diabetes, and enhancing cognitive function.

Conclusion

In conclusion, food plays a significant role in shaping an individual’s mood, either positively or negatively. Further research is needed to better comprehend the intricate pathways through which diet and nutrition can influence brain function. This knowledge could pave the way for targeted or personalized interventions aimed at improving mood, reducing anxiety, or addressing other mental health symptoms through dietary approaches. It is crucial, however, to remember that mental illnesses have diverse and multifaceted causes that often exist independently of dietary factors. Therefore, any potential links between food choices and mental well-being should not be used to make automatic assumptions or stigmatize individuals based on their dietary preferences and mental health. Such stigmatization could potentially exacerbate the risk of mental health issues. Nevertheless, ongoing research is offering promising insights for public health and clinical settings.

References

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