diets prescribed by religious belief etc.), nor does it
study the relationship between diet and physical
exercise, recently investigated by Inserm.- Main results of the expertise
3.1 An overall approach to diet is required
Changes in dietary practices over the past few
decades, particularly the increase in the proportion
of fat in diet, are linked with modifications in food
supply (technological innovation, food chain) and
more generally with changes in lifestyle.
Research on the relationship between diet and
health focused primarily on the role of nutrient
intake (lipids, vitamins) or individual foodstuff intake
(fruit, vegetables, meat). This research, often exper-
imental, has confirmed certain hypotheses linking
food consumption to effects on metabolism which
can be good or bad for health. Extrapolation of
these findings, obtained in controlled trials, to real
life requires the integration of other aspects (living
conditions, income).
Certain epidemiological studies, after examining
different diets, have established a number of typolo-
gies that are more representative for studying real
dietary behaviour.
Although correlations between diet typologies and
health are clear, it is difficult to establish causalities
between changing dietary practices and certain
chronic illnesses (cancer, cardiovascular disease).
Links are more clearly established for obesity.
3 .2 The physiological mechanisms regulating food
intake are affected by environment
Physiological regulation of food intake is based on the
alternate cycle of two physiological states: hunger and
satiety. A network of internal signals, coming from the
digestive tract and from the central nervous system,
alternates food intake with satiety. This mechanism
allows self-regulation of energy intake, and is partic-
ularly effective in young children. This regulatory
system seems to have altered in obese people.
Energy compensation can take place between onemeal and the next, in the case of temporary defi-
ciency or excess. However, dietary deficiencies are
compensated far more easily than dietary excess
managed. In a society with plenty of choice, temporary
overeating is thus more likely to be poorly managed
during the following meals, leading to weight gain.
Intake is adjusted more effectively by eaters who
are attentive to the physiological signals of hunger
and fullness, and who are more careful about what
they eat. Distractions (e.g. eating in front of the TV,
in a noisy place, with stress) increase the quantity
ingested during the meal and upset the energy
compensation process from one meal to the next.
Nutritional composition and food consistency deter-
mine the satiation capacity of food. This means that
these characteristics can be used for limiting the
consumption of foods not affected by physiological
regulation (e.g. soft drinks).
Eating triggers a sensation of enjoyment by activat-
ing a physiological system in the brain called the
reward circuit. This eating enjoyment is accentuated
by palatable foods (nice taste) which are more often
than not fatty or sweet high energy-dense foods.
Enjoyment of sweet foods has been observed from
birth. In obese animals and humans, recent findings
have shown that addictive-type mechanisms can
develop for sweet foods.
Social norms and attitudes, which vary according to
age group, personal experience, and social and
cultural backgrounds, shape and set dietary behav-
iours for time schedules, family meals, and table
manners. These social conventions can affect phys-
iological regulation.3 .3 Generic nutritional information and prevention
campaigns have little short-term impact on
behaviour when used alone
Nationwide information campaigns reach first and
foremost the social groups already aware of the link
between diet and health. These messages could
thus increase behavioural disparities in the short
term. For the same reasons, nutritional labelling104