Science of Food: Linking diet and depression (column)
May 31, 2017
Over 300 million people worldwide suffer from some form of depression. Although we typically focus on how our diet affects the health of our physical bodies (weight, body mass index, heart health, bone density, etc.), the food we eat affects our mental health, as well. Herein I present some of the emerging science that supports the undeniable link between diet and depression and how you can improve your diet to improve your mood.
The enteric nervous system, our "second brain."
The enteric nervous system consists of millions of neurons that line the gastrointestinal tract from the esophagus to the anus. "Its main role is controlling digestion, from swallowing to the release of enzymes that break down food to the control of blood flow that helps with nutrient absorption to elimination … (I)t doesn't seem capable of thought as we know it, but it communicates back and forth with our big brain — with profound results," explains Jay Pasricha, M.D., director of the Johns Hopkins Center for neurogastroenterology.
The enteric nervous system, part of the gut-brain axis, links our guts with our brains and utilizes some of the same neurotransmitters that are present in the central nervous system. In fact, more than 90 percent of the neurotransmitter serotonin is present in the gastrointestinal system as it assists in bodily functions like sleeping and digestion. This is interesting because most of the typical antidepressants used today, such as Prozac and Zoloft, function by elevating serotonin levels in the brain as this neurotransmitter is also involved in regulating mood.
Since our guts are literally connected to our brains, what you feed your gut will also influence your brain. So how can you keep both your primary brain and your "second brain" healthy to reduce symptoms of depression and to promote overall well-being?
While there have been advancements in the scientific understanding of how specific nutrients influence the brain like omega-3 fats, sugars and zinc (see below), please know that it's the entire diet that matters with many nutrients that create a healthy and well functioning brain (e.g. magnesium, folate, vitamin C, vitamin B6, vitamin B12, and a balanced ratio of electrolytes to name a few…).
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Keep in mind that other chemicals like synthetic dyes, preservatives and pesticides can cause cellular harm or stress. All these dietary factors can lead to neurological dysfunction ranging from depression and anxiety, to autism and the development of children's brains, to dementia and Alzheimer's disease among the aging population.
Nourish the bacteria in your gut. The number of bacteria living in the human gut outnumbers our own cells by a ratio of nearly 10:1 and recent studies show that gut microbes directly alter neurotransmitter levels. For example, research published this year out of UCLA showed how certain metabolites from gut microbes promote serotonin production in the cells lining the colon. "If you look at the hard neuroscience that has emerged in the last year alone, all the fundamental processes that neuroscientists spend their lives working on are now all shown to be regulated by microbes," says John Cryan neuroscientist at University College Cork in Ireland.
So it is of utmost importance to create a healthy environment in your gut that will nourish the good bacteria living there and reduce the unwanted bacteria that can cause problems. Eat "probiotic foods" that contain live bacteria like low-sugar yogurt and fermented foods that will increase the good bacteria living in your gut. Eat "prebiotic foods" that contain fiber and nutrients that feed the good bacteria (such as dark leafy greens, onions, garlic, whole grains, and bananas) and that keep things moving through the GI tract to prevent the buildup of toxins. Refined sugars and certain fats found in processed foods do the opposite and will favor the growth of unwanted bacteria.
Increase omega-3 fats, reduce omega-6 fats
The modern Western diet is characterized by an excessive amount of omega-6 fats and dangerously low amounts of omega-3 fats, which is now thought to be a major cause of many chronic diseases, including depression. There are various types of omega-3 fats that are beneficial to human health that the body does not make on its own and must be consumed through foods (known as essential fats).
Researchers have narrowed in on two specific types of fats: EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) that are essential components of the phospholipid bilayer of neuronal cell membranes and are therefore crucial for the proper development and function of neurons. Omega-6 excess (found in corn, sunflower and safflower oils present in nearly every processed food; corn-fed cows, chickens and their eggs) and omega-3 deficiency leads to impaired neuronal function, and decreased activity of neurotransmitters such as serotonin and dopamine ("the happy molecules"). This imbalance of fatty acids also increases inflammation in the brain and the entire body and can lead to altered metabolism of neurotransmitters.
Add more zinc to your diet. Zinc is a micronutrient that is involved in learning, memory and mental function. In recent studies aimed at better understanding the molecular cause of depression, one hypothesis is that a specific protein in the body that assists in the growth of neurons called BDNF (brain-derived neurotropic factor) is playing a role. Therefore researchers are looking for ways to increase levels of BDNF. Zinc (found in meats, fish, whole grains, vegetables), omega-3 fatty acids (found in fish, chia, flax, walnuts), and exercise can all activate BDNF, while stress and a poor diet high in refined sugars and fats inhibit BDNF production.
Eat more tryptophan rich foods, balance sugars/carbohydrates
Ingesting more dietary tryptophan can elevate serotonin levels, as this is the biochemical precursor to serotonin. Although boosting serotonin levels in the brain can sometimes be difficult to achieve, eating tryptophan with healthy carbohydrates can increase levels of serotonin in the brain. The insulin that is released after carbohydrate intake stimulates the transportation of tryptophan across the blood-brain barrier where it can contribute toward serotonin synthesis in the brain and improve mood. However, it's important that the sugars and carbohydrates you consume come from whole grains and fruits and not processed foods, candy and drinks. These so called "empty calorie" foods and beverages that are high in sugar and that lack nutrients can turn on a cascade of hormonal reactions to bring blood sugar spikes down, which can ultimately worsen symptoms of depression.
Remember everyone is different so there is no "one diet fits all." It's important to listen to what your body is telling you and observe your body after you eat certain foods — do your "food experiments." Depression is a complex and debilitating disease, and the treatment begins by creating a diet that nourishes you, your gut and your brain.
Lisa Julian Ph.D. has a passion for organic chemistry the "molecules of life," and its application to food and health. She's the owner of Elevated Yoga & Holistic Health in Frisco and teaches Science and Nutrition at CU Denver and CMC. She can be reached at (970)401-2071 or firstname.lastname@example.org For more information about services offered at her studio, visit http://www.ElevatedYogaColorado.com.
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