The human microbiome, or gut environment, is a community of different bacteria that has co-evolved with humans to be beneficial to both a person and the bacteria. Researchers agree that a person's unique microbiome is created within the first 1,000 days of life, but there are things you can do to alter your gut environment throughout your life.
Ultra-processed foods and gut health
What we eat, especially foods that contain chemical additives and ultra-processed foods, affects our gut environment and increases our risk of diseases. Ultra-processed foods contain substances extracted from food (such as sugar and starch), added from food constituents (hydrogenated fats), or made in a laboratory (flavor enhancers, food colorings). It's important to know that ultra-processed foods such as fast foods are manufactured to be extra tasty by the use of such ingredients or additives, and are cost effective to the consumer. These foods are very common in the typical Western diet. Some examples of processed foods are canned foods, sugar-coated dried fruits and salted meat products. Some examples of ultra-processed foods are soda, sugary or savory packaged snack foods, packaged breads, buns and pastries, fish or chicken nuggets and instant noodle soups.
Researchers recommend "fixing the food first" (in other words, what we eat) before trying gut modifying-therapies (probiotics, prebiotics) to improve how we feel. They suggest eating whole foods and avoiding processed and ultra-processed foods that we know cause inflammation and disease.
But what does my gut have to do with my mood?
When we consider the connection between the brain and the gut, it's important to know that 90% of serotonin receptors are located in the gut. In the relatively new field of nutritional psychiatry we help patients understand how gut health and diet can positively or negatively affect their mood. When someone is prescribed an antidepressant such as a selective serotonin reuptake inhibitor (SSRI), the most common side effects are gut-related, and many people temporarily experience nausea, diarrhea, or gastrointestinal problems. There is anatomical and physiologic two-way communication between the gut and brain via the vagus nerve. The gut-brain axis offers us a greater understanding of the connection between diet and disease, including depression and anxiety.
When the balance between the good and bad bacteria is disrupted, diseases may occur. Examples of such diseases include: inflammatory bowel disease (IBD), asthma, obesity, metabolic syndrome, diabetes, and cognitive and mood problems. For example, IBD is caused by dysfunction in the interactions between microbes (bacteria), the gut lining and the immune system.
Diet and depression
A recent study suggests that eating a healthy, balanced diet such as the Mediterranean diet and avoiding inflammation-producing foods may be protective against depression. Another study outlines an Antidepressant Food Scale, which lists 12 antidepressant nutrients related to the prevention and treatment of depression. Some of the foods containing these nutrients are oysters, mussels, salmon, watercress, spinach, romaine lettuce, cauliflower and strawberries.
A better diet can help, but it's only one part of treatment. It's important to note that just like you cannot exercise out of a bad diet, you also cannot eat your way out of feeling depressed or anxious.
We should be careful about using food as the only treatment for mood, and when we talk about mood problems we are referring to mild and moderate forms of depression and anxiety. In other words, food is not going to impact serious forms of depression and thoughts of suicide, and it is important to seek treatment in an emergency room or contact your doctor if you are experiencing thoughts about harming yourself.
Suggestions for a healthier gut and improved mood
—Eat whole foods and avoid packaged or processed foods, which are high in unwanted food additives and preservatives that disrupt the healthy bacteria in the gut.
—Instead of vegetable or fruit juice, consider increasing your intake of fresh fruits and vegetables. Frozen fruits without added sugars/additives are a good choice too.
—Eat enough fiber and include whole grains and legumes in your diet.
—Include probiotic-rich foods such as plain yogurt without added sugars.
—To reduce sugar intake at breakfast, add cinnamon to plain yogurt with berries, or to oatmeal or chia pudding.
—Adding fermented foods such as kefir (unsweetened), sauerkraut, or kimchi can be helpful to maintain a healthy gut.
—Eat a balance of seafoods and lean poultry, and less red meat each week.
—Add a range of colorful fresh fruits and vegetables to your diet, and consider choosing certain organic produce.
(Uma Naidoo, M.D., is a contributor to Harvard Health Publications.)