Page 10 - Nutrinsight-1

NutrInsight • About the value of controlling appetite
Food intakes
The quantity of food consumed as measured in the laboratory by means of well-controlled protocols can be considered to be an objective measure of appetite (5). Despite this, appetite and food intake can be influenced by numerous factors, for example cognitive (dieting) or environmental (availability, gustatory enjoyment of the food presented, etc.) factors. Thus, in order to focus on the internal factors, the environmental factors are kept as constant as possible and the conditions standardised (for instance, controlled eating and physical activity).
In order to measure satiation, the foods studied are presented ad libitum (in unlimited amounts) to subjects who have been told to eat until they feel «comfortably satieted».
Short-term satiety (for the hours following eating a meal) can be measured by a similar procedure: the subjects are asked to eat a fixed amount of food, which constitutes the preload. This preload may be given orally, by the intraduodenal or intravenous route, as commercial foods or ones that have been processed (modification of their energy density or palatability). After a fixed interval of time (ranging from a few minutes to a few hours), the food consumption is measured during the next meal, which is provided ad libitum.
In both cases, the quantity (in grams) of food consumed by the subject is measured (weighed before and after eating) without the subject’s being aware of this. The energy and nutrition content of the foods presented are known, and so the energy and nutrient contents of the meal can be calculated.
In order to assess the more long-term effects of the procedures performed in the laboratory on the regulation of eating, it is possible to record details of food intakes throughout the rest of the day or even over the next few days. To do this, the subjects themselves keep eating diaries in which they record everything they eat and drink.
In practice, foods have differing satieting potential (i.e. effect on satiation) and satiety potential (effect on satiety).
- The more satieting a meal, the less food will be consumed during the meal.
- The more satiety-inducing the preload, the less food will be consumed during the next meal.
Intervals between meals
The interval between meals is used to measure satiety. To do this, the time between the initial food intake (preload) and the following eating episode is not fixed. The subjects are deprived of any way of keeping track of time (daylight is controlled, watches or any other way of telling the time are removed) so that eating does not occur as a result of traditional or social parameters. After eating the preload, the subjects are told to ask for the next meal when they feel hungry enough to eat. The time between eating the preload and this spontaneous request for a meal is measured. The food consumed during
this meal can also be measured.
The greater the satiety potential of the preload, the later the next meal will be started (prolongation of the interval between meals).
Relationship between behavioural markers
Most studies combine an assessment of subjective measures and of food intake by fixing the interval between meals. A perfect match is not always found between these markers. As a result, foods can alter the subjective appetite without having any influence on the quantity eaten at the next meal. Furthermore, although the interval between meals is prolonged, this does not necessarily mean that the food intake at the next meal will change. The appeal of foods that have an effect on satiation or satiety can therefore act at various levels: either to reduce the feelings of hunger between meals, or to reduce the quantity of food eaten during the meal or the next meal.
10