world cancer report - iarc

DIET AND NUTRITION
SUMMARY
> Up to 30% of human cancers are probably
related to diet and nutrition.
> Excess salt intake causes arterial hypertension
and an elevated risk of stomach
cancer. Due to modern methods of food
preservation, the incidence of stomach
cancer is declining worldwide.
> A Western diet (highly caloric food rich in
animal fat and protein), often combined
with a sedentary lifestyle and hence energy
imbalance, increases the risk of colon,
breast, prostate, endometrial and other
cancers.
> Physical activity, avoidance of obesity,
and frequent daily intake of fresh fruit
and vegetables reduce the risk of oral
cavity, lung, cervix uteri and other cancers.
The incidence of most cancers varies
worldwide and cancers of the breast,
colorectum, prostate, endometrium, ovary
and lung are generally much more frequent
in the developed countries. These
cancers are a major burden in countries of
Europe, North America and in Australia.
They are markedly less frequent in developing
countries of Asia and Africa. In contrast,
some cancers of the digestive system,
including those of the stomach and
liver, are more frequent in developing
countries of Central and South America,
Africa and Asia than they are in the developed
world.
These observations, which were made
more than 30 years ago with the publication
of the first reliable data on cancer
incidence from population-based cancer
registries [1,2] are still substantially valid.
They constitute one of the basic arguments
for the hypothesis that environmental
factors play an important role in
cancer etiology. A principal environmental
factor, now generally recognized as major
62 The causes of cancer
determinant of cancer incidence, is diet.
Over the past 20 years, many epidemiological
studies, particularly case-control
studies and, more recently, large cohort
studies, have investigated the role of
habitual diet in relation to the risk of
developing different types of cancer.
Vegetables and fruit
The most consistent finding on diet as a
determinant of cancer risk is the association
between consumption of vegetables
and fruit and reduced risk of several
cancers. Consumption of vegetables and
fruit is associated with reduced risk of
cancers of the pharynx, larynx, lung,
oesophagus, stomach and cervix uteri,
while only vegetables, but not fruit, seem
to protect against cancers of the colon
and rectum. During the last 30 years,
over 250 epidemiological studies (casecontrol,
cohort or ecological correlations)
have been conducted around the
world to investigate the relationship
between fruit and vegetable consumption
and cancer risk. About 80% of these
studies found a significant protective
effect of overall consumption of vegetables
and/or fruit, or at least of some
types of vegetables and fruits [3].
Preliminary results from the large
European Prospective Investigation into
Cancer and Nutrition (EPIC) study confirm
these results, suggesting, for example,
that a daily consumption of 500 g of
fruit and vegetables can decrease incidence
of cancers of the digestive tract by
as much as 25% [4].
Fruit and vegetables do not represent a
major source of protein, fat, carbohydrates
and therefore energy, but they can
be major contributors of fibre, several
vitamins, minerals and other biologically
active compounds. Current hypotheses
on mechanisms through which fruit and
vegetables may protect against cancer
invoke the interaction of micro-constituents
with the processes of carcinogen
metabolism, protection of DNA
integrity and intercellular communication.
Such mechanisms have been studied
extensively in experimental systems.
Fig. 2.52 Dietary questionnaires used to assess the quantity of different food types consumed by the participant
in a nutritional study.