How deep does the connection run? Is depression merely a manifestation of malabsoption of nutrients due to a variety of causes such as bacteria, inflammation, infection, or parasites? Could the food we eat have severe affects on mood and cause long term neurological degeneration? Researchers are noticing a relationship between functional bowel disorders and brain disorders, i.e. a high percentage of children with Autism also have improper gut motility (constipation, diarrhea) or food intolerances/allergies, but which comes first, the gut disorder or the brain disorder? Could regaining function in your bowels not only improve your mood, motivation, hope, but also eliminate pathological anxiety and depression?
In my experience, the answer is mostly yes. However, even in something as seemingly simple as nutrition, we have to be careful to avoid all or nothing thinking errors. For example, gluten, a protein found in wheat, barley, and rye that tends to cause negative gut and brain issues in many people, has gotten a very bad rap because of the disease sprue (celiac) where the immune system destroys the small intestine in attempt to kill gluten. Celiac is potentially deadly and should be taken very seriously, but the idea of "gluten intolerance or sensitivity", what is that? One thing that may cause it is if you have some kind of infection or low stomach acid, a relatively minor problem and easily treatable, yet your ability to absorb food properly may be compromised and you may have imbalanced strains of bacteria in your SI tract, causing "leaky gut." When large molecules of food penetrate this gut, and cross the blood brain barrier, it causes negative affects on the brain such as brain fog, inability to focus, fatigue, and head aches. Since gluten is one of the foods that easily penetrates this leaky gut, and its effect on the brain can be disastrous, consuming it can be problematic for many people even if they don't have celiac disease. But for some, with no dysfunction in bowel movement or absorption, gluten may pass through without causing harm to the individual. Hence the need to be careful not to assume that gluten is always the bad guy.
Functionality can be influenced both ways. For example, someone who experiences a severe trauma may develop PTSD symptoms irregardless of their diet, however the resulting anxiety, panic, depression, sleep dysregulation problems triggered by the trauma will most likely negatively affect digestion, which could perpetuate the symptoms and create a downward cycle. Researchers show that alcoholics in recovery start craving sugary foods, and those who turn to carbs and sweets are the ones mostly likely to relapse to their drug of choice and end up back in rehabilitation. However, those who change their diet to include nutrient dense, protein rich, non sweet whole foods are able to stay sober and regain functionality in mood regulation. The simple reason is they were able to regulate the gut to brain axis and thus maximize emotional regulation.
No client I have ever met likes to be told what to eat, even though the 64 oz soda they ingest every day may be negatively affecting their blood sugar regulation, bacterial and yeast balance, and a myriad of digestive and mood difficulties that result. Even soda has its positive effects, if what you are going for is a temporary mood lift and quick rise in blood sugar, then you've got the right fuel. But we know that what is good for us in the short run is not always the best in the long run. Being mindful of what you really want and need may include being aware of the connection between food and brain function.
Just as people have both strengths and weaknesses, different foods have both benefits and drawbacks. It may be wise to be wary of any experts telling you to completely ban a certain food or over promoting a certain supplement. There are benefits and risks to nearly every food, and eliminating foods can cause problems just as eating harmful foods (when your gut is compromised) can also cause problems. The important thing is not whether you eat blueberries or take fish oil every day, its about the motivation and mindfulness of eating. Are you eating because you are craving something and feeding an organism bigger than yourself like Candida overgrowth? Are you not eating because you have anxiety that this food will hurt your body or make you fat? Are you paying attention to what your mood and digestive response is to certain foods, or are you pushing through the negative symptoms and eating what you want? If you are craving it, if you have negative digestive responses eating it, the brain to gut axis is telling you something is off--be mindful of the connection gut to brain and brain to gut!
Rather than demonizing a food, balance your intake. If you chose to start avoiding simple carbs and refined foods you will have to replace it with something, and your body will have more opportunity to eat more whole foods, and foods rich in healthy fats and protein to boost your amino acid production and vitamin and mineral content, which boosts tryptophan and serotonin production in your brain. But don't completely get rid of vegetables and fruits and even carbohydrates that have many healthy benefits as well! Even a starchy potato can be good, with the skin on and cooked and chilled a potato has many resistant fiber and carbohydrate benefits that we would be remiss to eliminate from our diet. It will take some time to build healthy bacterial strains and eliminate the harmful strains creating the cravings, and some elimination of foods may be necessary for a temporary period in order to heal your gut from damage, but keep in mind that reintroducing those foods in moderate and wise amounts will be necessary so you can get the benefits from that food. Educate yourself on the benefits of food and how it affects your brain, but be wise to not believe everything you read on the internet, choose reputable sources and find the truth in what the nutritionists have discovered. Every body is different, you can find out what works for you, but be aware of the connection between the gut and the brain when you eat.