What is Depression?

Depression is a type of illness that influences how we feel. It may develop slowly over time with no external cause and, unlike a physical injury or illness, we cannot always see it just by looking at someone. This is because depression affects the parts of the brain that control how we feel. Diseases that affect our feelings, thoughts and behaviors are called mental illnesses, so depression is a type of mental illness.

We all have times when we feel happy or sad. However, for someone with depression, the feelings of sadness or low mood do not go away. Depression is more than just being sad or down, or losing interest in activities that were once enjoyed, and it can affect everyone in a different way—symptoms are often unique to each individual. A person might, for instance, feel tired all the time and not have much energy, or might find it hard to concentrate. A depressed person may have changes in sleep patterns, have feelings of guilt or low self-worth, or even have changes in appetite [1]. Symptoms can vary in severity, from rather minor depressive symptoms up to something called major depressive disorder (MDD), which is a diagnosed clinical condition where multiple symptoms may last for a long time.

Depression is an important mental illness to study, because it affects more than 300 million people from all around the world [1]. It is one of the most common mental health conditions and can affect both men and women [1]. In fact, it is predicted that depression will be the number one health concern in the world by the year 2030 [2]. These statistics show just how important it is to find ways to help prevent people from developing depression and to help people who already have depression.

There are currently a number of ways depression can be treated. One method includes taking a variety of medications. Another includes talking to specialists, such as psychologists, who are trained in treating mental health issues. Although these methods can be effective, there are many people who cannot access these treatments because of where they live, their income, the availability of specialists, or stigma and shame [1]. Even when people do have access to these treatment methods, some people who try them do not recover completely [1, 3]. For this reason, it is important to find other ways to help people with depression. For example, the food that we eat is one factor that might influence our mental health and our mood.

What is Nutrition?

There are many different components that make up the food that we eat. These include a range of nutrients and chemicals, such as macro and micronutrients. Macronutrients are nutrients we need a lot of in our diets and they include carbohydrates, proteins, and fats. Micronutrients are nutrients we need in smaller amounts and they include vitamins and minerals. Along with these nutrients, there are many other important components of food including fiber, water, and antioxidants. These components work together to contribute to the healthy functioning of the human body.

The food we eat can give us energy, help us grow, and keep us healthy—but nutrition involves much more than this. The field of nutrition considers whether people can access and afford to buy food, how foods vary across different cultures, and why we choose to eat the foods that we do. In fact, new ideas about the effects of food are being explored all the time. One idea that is of great importance is how the food we eat can affect our mood. It is possible that the components in food, such as vitamins and minerals, can influence depression. It also explores how depression can influence our food choices [4]. Figure 1 highlights the connections between what we eat and our mental and physical health.

Food and Mood

Researchers have looked at the connection between diet and depression, and there is now a great deal of evidence suggesting that what we eat every day can influence our mood [4, 5]. This research shows that a healthy dietary pattern, such as a Mediterranean-style diet, can have a positive effect on mental health [4, 5]. A typical healthy diet pattern is shown in Figure 2. This includes plenty of vegetables, fruit, nuts, seeds, and olive oil, as well as minimally processed whole grains, legumes, and moderate amounts of lean meat, fish, and dairy. A healthy diet is also low in added sugar and saturated and trans fats, and is high in fiber and antioxidants [3].

Recent studies have explored the link between this healthy dietary pattern and depression. These studies collected information from a large number of people over time. This dietary research has shown a link between unhealthy dietary patterns and symptoms of depression. An unhealthy diet contains mainly ultra-processed foods, including sugar-sweetened beverages, such as soft drinks and packaged snacks that are high in added sugar, salt, and saturated and trans fats. The discovery of this link between diet and depression is important because it suggests that following a healthy dietary pattern over time could possibly prevent depression [4, 5].

Other research has shown that a healthy dietary pattern may be able to treat depression. This research looked at the effect of a healthy dietary pattern on people who already had depression. In this Australian study, the researchers compared the results of two different groups of people with depression. Only one group was taught how to follow a healthy dietary pattern. Researchers then looked to see if the changes in their diets improved their mood compared with the group that was not taught to follow a healthy diet. The study showed that people who followed a healthy dietary pattern for 3 months reduced their symptoms of depression [5].

Why Does Food Help With Depression?

We are not yet able to explain exactly how food may positively affect our mood. However, there are a number of theories as to why this might be the case. Some theories explore the function of different components of food, such as vitamins, minerals, and antioxidants. These theories focus on the role these micronutrients play in contributing to the healthy functioning of the human body. Other theories look at the importance of the microorganisms that live in the gut, called the gut microbiome, and how the foods we eat can affect this microbiome. Lastly, other theories suggest that the changes in behavior that happen when people start to eat a healthy diet may provide the beneficial effects on mood. These behavioral changes could include cooking more at home or cooking and eating in a social setting [5]. The positive experiences associated with the cultural and social aspect of food may help with depressive symptoms. Remember, nutrition is more than just food giving us energy, keeping us healthy and helping us grow—it is also about foods from different cultures, and why we choose to eat the foods that we do. Therefore, cooking in a social setting may not only influence food choice but may also contribute to a positive food experience and a healthy social environment. Cooking more at home may also help to promote more frequent, healthier food choices.

Finally, there are some studies that look at more specific diets (such as a vegetarian diet) and mental health, but this is not something that has been explored in great detail yet. It would be interesting if more research were done on this subject in the future.

Summary: The Food We Eat Can Affect Our Mood

In conclusion, the food we eat is not only important for our physical health, but also for our mental health. Although more studies are needed to help understand how and why this may be the case, there is now plenty of research that shows what we eat can influence our mood. This suggests diet may be able to play an important role in the prevention and treatment of depression, one of the most common mental health conditions in the world.

Author Contributions

ME drafted the manuscript and approved the final version. JF contributed to the drafting of the manuscript and has approved the final version. JS contributed to the drafting of the manuscript and has approved the final version.

Glossary

Major Depressive Disorder (MDD): ↑ A type of depressive disorder, otherwise known as clinical depression, that may be mild, moderate or severe.

Mental Health: ↑ A person’s psychological and emotional well-being.

Antioxidants: ↑ Plant compounds that protect cells from damage.

Nutrition: ↑ The science that looks at the effects of food on the human body.

Trans Fat: ↑ A type of fat that has been shown by researchers to be unhealthy for your heart.

Ultra-processed Foods: ↑ Foods that have been highly manipulated and have ingredients added that are not usually used in cooking, such as artificial colors and flavors.

Gut Microbiome: ↑ The community of different bacteria and microorganisms living in the intestine.

Conflict of Interest

JF is supported by a University of Manchester Presidential Fellowship (P123958) and a UK Research and Innovation Future Leaders Fellowship (MR/T021780/1) and has received support from a NICM-Blackmores Institute Fellowship. JS has received either presentation honoraria, travel support, clinical trial grants, book royalties, or independent consultancy payments from: Integria Healthcare & MediHerb, Pfizer, Scius Health, Key Pharmaceuticals, Taki Mai, FIT-BioCeuticals, Blackmores, Soho-Flordis, Healthworld, HealthEd, HealthMasters, Kantar Consulting, Grunbiotics, Research Reviews, Elsevier, Chaminade University, International Society for Affective Disorders, Complementary Medicines Australia, SPRIM, Terry White Chemists, ANS, Society for Medicinal Plant and Natural Product Research, Sanofi-Aventis, Omega-3 Center, the National Health and Medical Research Council, CR Roper Fellowship.

The remaining author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.