Nutrition is the process by which living things obtain, digest and assimilate food.  Humans need food to carry on their life functions.

The absence of proper nutrition may cause disease or death.

Nutrition is a science which studies the relationship between diet and states of health and disease.  Deficiencies, excesses and imbalances in diet can produce negative impacts on health, which may lead to disease.

Between the extremes of optimal health and absolute death, there is an array of disease states that can be caused or alleviated by changes in diet.