Variety enhances food intake in humans: Role of sensory-specific satiety

Abstract

Twenty-one subjects were studied to evaluate the effect of renewal of sensory stimulations of previously eaten foods on sensory-specific satiety and intake. The subjects ate French fries then brownie cakes ad libitum in three situations: “monotonous” — fries then brownies were consumed alone; “simultaneous” — condiments (ketchup and mayonnaise for the fries, vanilla cream and whipped cream for the brownies) were added during intakes; “successive” — after intake of fries alone, ketchup then mayonnaise were available with fries and, after intake of brownies alone, vanilla cream then whipped cream were offered with brownies. The quantities eaten in the “simultaneous” and “successive” situations were higher (p < 0.001) than those in the “monotonous” one (1485 ± 582 and 1682 ± 777 kcal vs 1195 ± 552 kcal, respectively). In the “successive” situation, hedonic ratings for fries diminished during intake but increased after the introduction of ketchup, leading to additional intake of fries. Similarly, hedonic ratings for brownies diminished during intake and increased after the introduction of vanilla cream leading to additional brownie intake (mayonnaise and whipped cream had no significant effect). Food variety, obtained by adding condiments can increase food intake in the short term. The mechanism by which food consumption is increased after the addition of condiments is introduced is at least partly related to the attenuation of sensory-satiety for a given food.

Introduction

Obesity is increasing world-wide [1], especially in western nations [2]. The reasons leading to the imbalance between energy intake and energy expenditure are multifactorial [3]. Among the different factors, food variety could play a role [4], [5], [6], [7]. Actually, several animal studies have shown that variety increases food intake and leads to body-weight gain [8], [9]. It has also been observed in normal-weight humans that food variety may stimulate food intake in the short term [10], [11], [12], [13], [14].

It is not clear how variety stimulates food-intake. From one point of view, variety may increase intake by an appetite-stimulating mechanism. This could be due to renewed palatability (i.e. the ‘liking’ or pleasantness of food) in relation to the diversity of the eaten foods [15], [16], by sustaining interest in eating [17], by another stimulating mechanism involving metabolic and hormonal responses, or environmental, psychological and social variables [6], [18]. From another point of view, food variety may increase intake by delaying satiation (i.e. meal termination). This could be related to a decrease in sensory-specific satiety [19] or by a dishabituation mechanism [5] induced by food variety.

Sensory-specific satiety (SSS) is a satiation mechanism defined as the decline in pleasantness of the flavour of a specific food that has just been eaten in contrast to other non-consumed foods [20], [21]. The decrease in pleasantness linked to SSS is observed very rapidly, 2 min after the end of ad libitum intake, before food enters the intestinal tract and before intestinal absorption [22], [23]. The implication of SSS on elevated food intake associated with varied meals has been known for a long time. Actually, as sensory-specific satiety is specific for eaten foods, when a great variety of foods is available during a meal, it may take longer for satiation to occur for all foods, which leads to greater intake [12], [24], [25].

Although the link between high consumption of varied meals and sensory-specific satiety is well established, several researchers stressed that this link needs to be strengthened. McCrory et al. [68] wrote, ‘although the mechanism by which a drive for dietary variety gets translated into increased food consumption is not known, the phenomenon of sensory-specific satiety is a probable candidate’. Similarly, Raynor and Epstein [5] wrote that ‘sensory-specific satiety may be the process through which a greater variety of food is associated with increased intake’ and, Norton et al. [31] argued that ‘a potential mechanism underlying the variety effect may be due to the increased stimulation associated with multiple foods delaying the development of sensory-specific satiety’. Furthermore, to our knowledge, neither the temporal evolution of hedonic sensations for a variety of foods offered successively and simultaneously (i.e. change in SSS) [12], nor the effect of introducing of a new flavour in a previously eaten food have been reported in fundamental experiments.

The present experiment was conducted to bring new arguments to the relationship between SSS and the high food-consumption during intake of a varied meal as well as to study how small amounts of variability may disrupt SSS. More precisely, the study set out to determine whether modification of the sensory properties of a food eaten ad libitum by adding condiments could decrease sensory satiety for that food and subsequently lead to additional intake of that food. A within-subject design was created to rate relative preference-changes of an ad libitum two-course meal in either a monotonous form or with simultaneous or successive variety via the addition of condiments. The meal was of the ‘fast-food’ type since it has been suggested that this type of meal could play a role in the prevalence of obesity [26].