It is important to remember, the food we eat impacts every cell in your body and allows processes to occur... of course, this can only take place if we have eaten the necessary nutrients. Did you ever think about the fact that we can be overfed and yet undernourished? Sounds crazy right? But it comes down to what we are eating, not how much. Processed foods have been stripped of their nutritional value and have chemicals, stabilizers and added flavorings to help give them more shelf life and make them more palatable. These types of food may be quick and easy to eat, but they are not giving your body what it needs to function optimally. When focusing on good nutrition you will be giving your body the raw materials it needs to properly function and remain strong and balanced. The nutrients you bring in will affect how your immune system, nervous system, hormones, brain function, etc. stay in balance.
For instance, in order for your body to make melatonin you need to eat tryptophan (the amino acid found in turkey, chicken, eggs, fish and cheese) which converts into serotonin, which also needs other cofactors, like Iron, Vitamin C, Vitamin D, and B-vitamins, to make this conversion possible. From serotonin the body will then convert, again, with specific enzymes present, into the final product melatonin. So, if you have a sleep issue...having low melatonin may be a reason, but your diet is what allows you to make it in the first place.
This is just one example of how the food we eat impacts how we function and feel day to day. What we eat impacts how we feel, how we look, how we perform and ultimately our health. It is truly amazing when you think about how the nutrients we eat impacts every aspect of how our bodies work.