Reducing stress and calming the mind can be helped through many different techniques: biofeedback, meditation, exercise, yoga, resting or improving the quality of sleep, improving the diet, nutrition, and avoiding stressors as much as possible. Getting outdoors regularly can be very beneficial and fun. See this study on the importance of laughter in health!
Diet
The physical problems that are improved by a better diet are legion. These improvements come from getting rid of foods that are harmful (such as possible allergic foods, too much sugar, too much salt, the wrong type of fats, etc.) as well as eating foods that support the body's functioning (such as liver-supporting vegetables, antioxidants, essential fatty acids, etc.).
One of the first things that needs to be addressed is terminology. The word "diet" has such negative connotations, it is like a prison sentence that we try to escape from -- or are waiting to get paroled from. Even small lifestyle changes in food choices have a more effective long-term effect than ANY diet.
Simple, common sense goals include eating more nutritious foods, with fewer toxins, lower addictive potential, and lower inflammatory effects. A major goal is for our foods to have a smaller glycemic effect (thereby stabilizing blood sugar levels), also to slow if not reverse progression of type 2 diabetes, as well as decreasing risk of cardiovascular and other diseases.
Nutrition
We were not born to need nutritional supplementation. Sadly, the need for nutrients in addition to our diet is a growing reality. There are many things that have caused a deterioration in the quality of the foods we eat--nutrient-depleted soil, processing, commercial formulations, and contamination of our food, water, and air. In addition, most of us experience a generally increased level of stress.
All of these creat a demand for addional nutrients. If possible, this should be accomplished by improving the quality and quantity of food; but it is very common to need some extra nutritional help. In addition, specific nutrients are often needed to deal with a variety of imbalances that manifest in unhealthy conditions. Functional analysis lab testing can often show metabolic or nutritional deficiencies that, when balanced or supported, can help the body to heal.