Beer : Health and Nutrition

The Basics of Human Nutrition 87
ing family.) One joule is de ned as the amount of energy exerted when a force of one
newton is applied over a displacement of one metre. It is the equivalent to one watt of
power radiated or dissipated for one second. However, calorie is so widely known and
used as a term that I employ it here: the term calorie is proving impossible to shake from
popular parlance. The reader should be warned that often calorie (without the capital
C) is employed in the literature rather than kilocalorie.
The number of calories in a foodstuff can be determined in the laboratory by combustion.
However the ‘true’ calori c content of a food as it pertains to the diet depends
on the extent to which those calories are available to the body.
This applies to all components of the diet. Just because something is present in high
quantity in a foodstuff it does not necessarily follow that it will get into the body to
exert any effect. Many factors may impact, including the form in which the nutrient is
present in a food. A metal such as iron may not be assimilated if it is attached to some
other component of the diet that passes straight through the gut. Much of the modern
work on antioxidants is awed in this way. For example, only if the speci c antioxidants
get into the body will they get to the key site where they are able to act.
Returning to carbohydrates, those such as starch and sugar are almost completely
digested and oxidised by the body and they are ascribed a calori c value of 3.75 kcal/g.
Fats, which are digested up to 95%, afford a higher energy level (9 kcal/g) because they
are less oxidised than the carbohydrates. The calori c value of protein is generally held
to be similar to that of carbohydrate, at 4 kcal/g. Ethanol is ascribed a calori c value
of 7 kcal/g, indicating that, molecule for molecule, it is an extremely rich source of
energy, second only to fat.
If calories in excess of those needed to maintain the body in equilibrium are taken
in, then the surplus will be built up in the form of fat, for the simple reason that, pound
for pound, fat is a richer energy store than is starch or protein. The converse applies:
enhanced energy demand through exercise will ‘burn up’ fat provided that the extra
calorie requirement is not met from fresh food intake.
We will address the calorie composition (and other key analytical measures) of a range
of foodstuffs, including beer, in the next chapter. In North America groups including
the National Academy of Sciences and the Institute of Medicine collaborated on the
establishment of dietary reference intakes (DRIs). The precise requirement that a human
will have for the various components of the diet will differ, depending on issues such
as age, sex, climate, activity and weight. Individuals, too, will differ to varying degrees
in their metabolic activity. Pregnant and breast-feeding women will need more of each
type of nutrient. The DRIs re ect some of these differences. As this is a book dealing
with beer, I will restrict consideration to adults over the age of 18 (see Table 4.1). (The
reader must bear in mind that the legal drinking age in some countries, including the
US, is higher than 18, at 21.)