It’s the time of the year again where the days grow shorter as the seasons change. As daylight fades from fall through winter, we’re more susceptible to suffer from seasonal depression, also known as Seasonal Affective Disorder, or S.A.D. According to Mental Health America, up to 5% of the population in the U.S. experiences seasonal depression. But until more recently, the link between nutrition and mental health has been significantly overlooked. Here, we will take a closer look at how our food choices and behaviors can impact our mental health and what actions we can take to use nutrition to help promote good mental health.
The gut, AKA our "second brain" is largely responsible for mood and sleep regulationThe gut is home to trillions of microbes that help regulate digestion and metabolism, synthesize vitamins from foods, protect the body from pathogens, and produce hundreds of neurochemicals for the brain to use. The gut is also referred to as the “second brain,” as it produces many of the same neurochemicals the brain uses to regulate mood and cognition. For example, 95% of serotonin is produced by our gut bacteria.[2,4] Serotonin, often referred to as the happy chemical, contributes to overall wellness and happiness, and helps to balance mood and anxiety. Serotonin also serves as a precursor to melatonin, the hormone that helps us fall asleep. So it’s not surprising that low levels of serotonin have been linked to poor mood, anxiety, and irregular sleep.
Fiber is key for promoting a healthy gut—and thus a healthy brainThe good news is that we can improve our gut bacteria a few ways. First, we can increase the quantity and diversity of the bacteria in our gut by feeding it the proper food, particularly fiber-rich ones. Whole grains like oatmeal and quinoa, legumes, and many fruits and vegetables are rich sources of fiber, making them excellent fuel for the gut microbiome. Fiber passes undigested through our gastrointestinal tract and serves as food for the good bacteria, making it a "prebiotic." These good, well-fed bacteria go on to produce byproducts that support healthy brain function among a variety of other benefits, including reduced inflammation levels, supported immune health, cholesterol metabolism regulation, and digestion support.
And while a fiber-rich diet can help support a healthy, diverse gut, the opposite can also be true—a low-fiber diet can lead to imbalances in the gut, creating a pro-inflammatory state. A recent study found that diets higher in fat and lower in fiber were associated with higher populations of bacteria species Bacteroidetes and Actinobacteria than in study subjects that had higher intakes of dietary fiber. These particular types of bacteria are pro-inflammatory, which indicates that low intake of dietary fiber may play a role in the regulation of systemic inflammation. This type of inflammation has been connected to the development of depression and anxiety in both human and animal studies.
Takeaway: A diet rich in fiber can help healthy gut bacteria grow, which in turn have positive effects in the brain and around the body. A low-fiber diet can allow pro-inflammatory gut bacteria strains to thrive, and this inflammatory state can have a ripple effect across our body and wellbeing.
Probiotics, fermented foods, and phytonutrients can also feed the gut and brainInterestingly, fiber isn't the only nutrient that can help to feed good bacteria and their fight against pro-inflammatory strains. We can also help it thrive by eating foods with live probiotics (i.e. fermented foods) or taking a probiotic supplement. In a triple-blind, placebo-controlled, randomized control trial, participants who took a probiotic food-supplement displayed less negative thoughts linked with sad mood than those who took a placebo.(3) In addition, many mouse studies show that when their gut bacteria is altered, mice display different moods.(4) Fermented foods are natural sources of these probiotics, and help to replenish the good bacteria in our intestines. Examples of fermented foods include kefir, yogurt, kimchi, and sauerkraut. For more information on probiotics, be sure to check out this blog.
Phytonutrients (the compounds that give fruits and vegetables their unique colors) also play a role in promoting gut health by reducing inflammation in the gut and promoting diversity among the good bacteria.
Takeaway: There is still much to be learned about the gut-brain connection. However, research appears to show that interventions in the gut can have promising effects in the brain, impacting mood and behavior in a positive way.
Additional vitamins and minerals associated with mental healthIn addition to promoting gut health, research shows that certain vitamins and minerals are associated with improving or maintaining good mental health.
Omega-3 fatty acids are an essential food we obtain from our diet. There are three main omega-3s: EPA, DHA, and ALA. DHA and EPA are commonly called "fish oils," because they're mostly present in seafood. They're also the forms of omega-3s that our brains can directly utilize. ALA, the third kind of omega-3s, is commonly found in chia seeds, walnuts, flaxseed and flaxseed oil, and vegetable oils like canola and soybean oil. ALA, however requires conversion to ELA or DHA before being utilized. This conversion rate is quite low—less than 15%. It's therefore important that individuals eat considerable amounts of ALA-rich foods, get EPA and DHA directly from food sources, or consider taking a supplement when appropriate. (6)
Since the brain itself is 60% fat, it's not surprising that omega-3 fatty acids have emerged as being important for both brain cell structure and function. DHA makes up a significant portion of the nerve cell wall, and anti-inflammatory EPA is responsible for communication within and among nerve cells. A number of lab, experimental and large-population studies have shown that low omega-3 levels are associated with altered mood states, anger, and depression.[7,11] In addition, higher fish and seafood consumption is associated with lower rates of depressive conditions including depression, seasonal affective disorder, bipolar depression, and postpartum depression.
Another early study demonstrated that omega-3 fatty acids may influence mood, behavior and personality. After examining a group of 106 healthy adults, those with the lowest blood levels of omega-3s reported mild depressive symptoms, a more negative outlook on life, and to be more impulsive compared to those with more normal blood levels of omega-3s.
Takeaway: Omega 3 fatty acids can play a role in maintaining or improving our mood and mental health. Aim to consistently add foods rich in these fatty acids into your diet, especially in the winter months. Even just four walnuts a day can have a significant impact on ALA levels.
Selenium is an essential ultratrace mineral meaning our body needs it in very small amounts to function. Selenium has many different functions in our body— some of which are still not completely understood. We do know, however, that selenium is a key component of selenoproteins, which function as antioxidants by removing cellular damage throughout the brain and nervous system. Due to this role in brain function, selenium has been studied in relation to mental health. One review published in Nutritional Neuroscience found that five different studies showed that low selenium levels were associated with poorer mood. Another more recent view concluded that increasing evidence indicates that an optimal range of selenium improves symptoms related to depression. Like with most cases in nutrition, more studies are needed to further investigate selenium’s influence on mental health.
So how can you ensure you're getting enough dietary selenium? Interestingly, soil concentrations of selenium vary significantly across the globe. And because plant foods absorb selenium from the soil, their levels are also extremely variable. For example, grains may contain less than 10 mcg to over 80 mcg per 100g. The recommended intake of selenium is 55 mcg/day, and approximately one in seven people around the world have low dietary selenium intake. Brazil nuts are the richest source of selenium, containing 68-91mcg of selenium for one nut—meeting an adult's daily needs (although, due to agricultural variation, some can have as low as 10 mcg/nut).
Selenium is also an essential mineral for animals, and is therefore found in dairy products (<30mcg/cup), meats (15-40mcg/3oz), and seafood (30-50ug/oz), though bioavailability from larger fish is thought to be poor. Intakes of selenium should never exceed 500mcg, as chronically-high levels can lead to toxicity.
Takeaway: If you’re struggling with mood and depression—on a normal basis or especially during the winter months—focus on meeting your selenium needs. Adding just one brazil nut a day can be more than enough to reach appropriate levels.
Folate plays a key role in the synthesis of neurotransmitters norepinephrine, serotonin and dopamine which are all important for normal brain function. According to data from the NHANES study (a large, nationally representative nutrition study from the U.S.), a diet high in folate may be associated with a lower risk of depression. Rather than grabbing a supplement, aim to include folate-rich foods such as dark leafy greens like spinach, broccoli, and fortified breakfast cereals and grains.
Research supports the fact that zinc deficiency can increase the risk of an individual developing depression. And while there are reported benefits of zinc supplementation, there are potential negative effects if implemented without medical supervision. Focus on adding in foods that are good sources of zinc including oysters, red meat, poultry, beans, nuts, whole grains, fortified cereals, and dairy products.
As reported in Psychotherapy and Psychosomatics, low vitamin B6 levels are associated with increased severity of depression and may interfere with the normal manufacture of the mood-regulating brain chemical serotonin. 
Best known for its role in bone and muscle health, low vitamin D levels can impact our mental health. Vitamin D activates genes that regulate the immune system and release neurotransmitters such as serotonin and dopamine. As mentioned earlier, these neurotransmitters play a key role in brain function and development. As we get less sunlight in the winter months, we become more susceptible to having inadequate levels of the ‘sunshine’ vitamin. You may want to consult your healthcare provider about taking a vitamin D supplement during these months.
Finally, mindfulness can play a key role in maintaining mental healthMindfulness can also be an important tool in improving or maintaining your mental health. Research has shown that implementing a mindfulness practice can positively impact both brain and immune function. Unsure of how to implement mindfulness into your life? This blog can help you begin to practice being more present and mindful.
- The foods we eat can’t prevent or cure depression or seasonal affective disorder, but it can help to improve or maintain your mental health.
- Our gut health and brain are connected—the gut is even responsible for generating key mood-regulating hormones like serotonin. Aim to keep your gut healthy with a diet rich in fiber, probiotics, and phytochemicals to maximize gut health.
- Omega-3 fatty acids, selenium, folate, zinc, vitamin B6, and vitamin D all play a role in preventing negative mental health symptoms and the onset of certain mental health disorders like depression.
- Focus on a food-first approach to get the different vitamins and minerals that can improve mental health over supplementation. When implementing a dietary supplement routine, always consult your healthcare provider.
- While no one vitamin or mineral is known to cure or be the answer to fight seasonal depression, getting adequate amounts of these nutrients from your diet can help your mental health.
- Adding a mindfulness practice into your day or around meals can help to improve not just your relationship with food but also your psychological well-being.
Stevie Lyn Smith, MS, RDN, CSSD, CDN
- Stevie Lyn is a Content Strategist and Team Nutritionist at InsideTracker. As a Registered Dietitian and Ironman triathlete, she enjoys combining her passions to help educate others on how to fuel for overall health and performance. When she’s not swimming, biking, or running with her dog, you’ll find her in the kitchen working on a new recipe to improve her biomarkers.