Your claim regarding food not having an impact your mood or mental health is a false statement. The Harvard Health Publishing makes the statement "Like an expensive car, your brain can be damaged if you ingest anything other than premium fuel" (Harvard Health Publishing). Thus, when you fuel your body with premium foods that are high in vitamins, minerals, and antioxidants, they in turn help to nourish your brain and protect it from oxidative stress, which is the waste produced by the body when it uses oxygen. This waste can even damage cells. When you consume foods of lesser sustenance, like ones that are high in refined sugars, or saturated fats, you are risking your health as if these substances make it to your brain, it has little ability to actually get rid of them. These diets not only worsen your body's regulation of insulin, but they also cause inflammation and oxidative stress, and studies found that your mood is actually worsened and can cause mood disorders such as depression (Harvard Health Publishing).
So, how does it really work? According to Harvard about 95% of serotonin is produced into your gastrointestinal tract, which is lined with hundred million nerve cells or neurons, thus your inner workings not only digest food they also guide your emotions. Your microbiome also has a huge part to play, as the bacteria play a essential role in your health, by protecting against inflammation and help you to absorb nutrients from your food which directly impact not only your gut but also your brain. It was found that diets like the Mediterranean and traditional Japanese showed risk of depression was almost 35% lower than the traditional Western diet (Harvard Health Publishing). Thus showing how much your diet really can impact your mood.
Furthermore, Better Health stresses the importance of processed foods and the effect of them especially in children and younger people. Such as hyperactivity and ADHD, as well as poor concentration and tiredness, which in the long term affect your memory and learning. They stress just how important it is to note that what you feed yourself can seriously influence stress, insomnia and depression, and by fueling your body with healthy foods you can treat depressive symptoms which has been proven through scientific studies (Better Health Clinic).
Therefore, it is important to note that what you consume play a vital role in your everyday life and mood. To say that it doesn't is dangerous and can lead to serious impacts on your health. By keeping yourself healthy and choosing better nutrient rich foods, we're not only doing our bodies an immense favor, but also our minds.
https://www.betterhealth.vic.gov.au/health/healthyliving/food-and-your-mood
https://www.health.harvard.edu/blog/nutritional-psychiatry-your-brain-on-food-201511168626