A disease, a disorder, or an ailment. Many of these conditions and syndromes are nutritionally-related. Heart disease is a condition that has its roots in nutrition.
Many mental illnesses have their basis in nutrition, especially niacin deficiency.
Please see the ADD section . The biggest problem with the American diet is not what we eat, although there is plenty wrong with that, but what we DON'T eat, what is lacking from our diets that we need for optimum health. While all the stories you hear, and frankly most of the medical information, focuses on what in our diets is harmful, it is the lack of sufficient supplies of nutritional substances that is of the most harm. Vitamin C is on the top of this list. As an analogy concerning the deficiencies versus the excesses, consider a construction job site.