nutrientAn essential dietary factor, in-
cludingcarbohydrates, proteins, certain
fats, vitamins, and minerals.
nutritionThe scientific study of food
and the processes by which it is diges-
ted and assimilated.
A good diet supplies adequate but not
excessive quantities of proteins, carbo-
hydrates, fats, vitamins, minerals, dietary
fibre, and water. The daily diet should
include foods from each of the 4 main
food groups: milk and milk products;
vegetables and fruits; breads and cere-
als; meat, eggs, and pulses.
Personal requirements of nutrients
and energyvary, depending on indi-
vidual body size, age, sex, and lifestyle.
For example, an average woman requires
about 2,000 kcal (8,400 kJ) daily, com-
pared with about 2,750 kcal (11,550 kJ)
for an average man. (See also energy
requirements.)
nutritional disordersNutritional dis-
orders may be caused by a deficiency or
excess of one or more nutrients, or by
the presence of a toxin(poisonous ele-
ment) in the diet.
A diet deficient in carbohydratesis
almost inevitably also deficient in pro-
tein, leading to the development of
protein–calorie malnutrition. Such mal-
nutrition is most often seen as a result
of severe poverty and famine (see kwash-
iorkor;marasmus).
Deficiency of specific nutrients is com-
monly associated with a disorder of the
digestive system, such as coeliac disease,
Crohn’s disease, or pernicious anaemia
(see anaemia, megaloblastic).
Inadequate intake of protein and cal-
ories may also occur in people who
excessively restrict their diet to lose
weight (see anorexia nervosa), hold mis-
taken beliefs about diet and health (see
food fad), or suffer from a loss of interest
in food associated with alcohol depen-
denceor drug dependence.
Obesityresults from taking in more
energyfrom the diet than is used up by
the body. Nutritional disorders may
also result from an excessive intake of
minerals and vitamins. An excessive
intake of saturated fat is thought to be a
contributory factor in coronary artery
diseaseand in some forms of cancer.Naturally occurring toxins can interfere
with the digestion, absorption, and/or
utilization of nutrients, or can cause
specific disorders due to their toxic
effects: for example, the ergotfungus
found on rye can cause ergotism.
nymphomaniaAn outdated term for a
condition in which a woman is domi-
nated by an insatiable appetite for
sexual activity with numerous partners.
The equivalent behaviour in men is
called satyriasis or Don Juanism. It was
said to be caused by intense narcissism
and feelings of inferiority.
nystagmusA condition in which there
is involuntary movement of the eyes.
In the most common type, jerky nys-
tagmus, the eyes repeatedly move slowly
in one direction and then rapidly in the
other. Less commonly, nystagmus is
“pendular”, with the eyes moving evenly
from side to side.
Nystagmus may be congenital, in
which case the cause is unknown. It also
occurs in albinismand as a result of any
very severe defect of vision present at
birth, such as congenitalcataract.
Persistent nystagmus appearing later
in life usually indicates a nervous sys-
tem disorder (such as multiple sclerosis,
a brain tumour, or an alcohol-related dis-
order), or a disorder of the balancing
mechanism in the inner ear. Adult-
onset nystagmus is occasionally seen
as an occupational disorder in people
who work in poor light.
Electronystagmography, a method of
recording eye movements, may be used
to identify the type of nystagmus.
nystatinAn antifungal drug used in
the treatment of candidiasis(thrush).
Nystatin may be safely used during
pregnancy. High doses taken by mouth
may cause diarrhoea, nausea, vomiting,
and abdominal pain.NUTRIENT NYSTATINN