Optimal health requires optimal nutrition. This means that all of the essential nutrients - carbohydrates, fats, protein, vitamins, minerals, trace minerals and water are supplied and utilised in balance that promotes optimal health. Proper nutrition is an absolute requirement for normal organ development and function, for normal reproduction, growth, and maintenance, for optimum activity level and working efficiency, for resistance to infection and disease and for the ability to repair bodily damage or injury.

A deficiency of an essential nutrient causes signs and symptoms that can be prevented or cured by an increased intake of that nutrient. Such deficiencies may be due to inadequate dietary intake, or they may be induced by either inherited or acquired inabilities to absorb, transport, store or metabolise nutrients, or by excessive loss of nutrients from the body (as seen in vomiting, blood loss, or diarrhoea).

Pregnant women, young children and infants, the elderly, alcohol and drug abusers, the chronically ill and people who restrict their diets for any reason are at the greatest risk of nutritional deficiency.

Just as a deficiency of a nutrient can cause disease, too much of a nutrient can also lead to trouble. For example, excessive intake of calories, fats and alcohol have been associated with a wide range of chronic health problems. Excessive intake of any nutrient is apt to have some short or long term side effect. For most nutrients there appears to be a safe and optimal range of intake that helps us obtain optimal health without any unwanted side effects.