in food are used by our bodies in varying ways. Each nutrient plays
some part in normal body function (that is, body physiology).
Not all components
of food are nutrients, and not all nutrients are essential to life.
Some nutrients may have important physiological functions without
being absorbed from the gut, for example dietary fibre. Dietary fibre,
while not being essential to life, is associated with health because
of its role in the correct functioning of the bowel. Its absence may
increase the risk of bowel disease.
about nutrient intakes are made in terms of daily intakes, not all
nutrients are needed every day. Most can be stored to a lesser or
greater extent in our bodies. The macronutrients that provide energy
are stored in the liver and muscles in the form of a carbohydrate
called glycogen, and in fatty tissues (adipose tissue) and muscles
in the form of fats, known as triglycerides. The situation for micronutrients
varies. Fat-soluble vitamins, such as vitamin A, tend to be stored
in liver and fat and do not need to be replenished every day; they
can last for weeks if the stores are good. In general, water-soluble
components like vitamin C are quickly excreted in the urine. But some
water-soluble nutrients such as vitamin B-12 and folacin (folic acid)
can be stored for years and months, respectively, in the liver. Some
nutrients, for example calcium and phosphorus, are in effect stored
How often a nutrient
needs to be ingested depends on how all of the various processes shown
in Figure 4 operate for the
nutrient in question.
Although not every
nutrient is needed every day, it is safest to 'top up' regularly through
a consistent pattern of eating. Nevertheless, undue concern about
particular food preferences, for example about children who seem to
want one kind of food and not another for a few days. is probably
unnecessary. As long as a variety of foods are eaten in the longer
term, the range of essential nutrients should be provided.