Elsevier

Appetite

Volume 58, Issue 1, February 2012, Pages 242-248
Appetite

Research report
Salad and satiety. The effect of timing of salad consumption on meal energy intake

https://doi.org/10.1016/j.appet.2011.10.003Get rights and content

Abstract

In a previous study, consuming a fixed amount of low-energy-dense salad as a first course reduced meal energy intake. We investigated whether this effect depended on serving salad before rather than with the main course, or on compulsory rather than ad libitum consumption. On five occasions, 46 women consumed ad libitum a main course of pasta, accompanied four times by low-energy-dense salad (300 g; 100 kcal [418 kJ]). At two meals the salad was served 20 min before the pasta (once compulsory; once ad libitum), and at two meals the salad was served with the pasta (once compulsory; once ad libitum). Results showed that adding a fixed amount of salad to the meal reduced energy intake by 11% (57 ± 19 kcal [238 ± 79 kJ]). Ad libitum salad consumption was less than compulsory consumption and did not significantly affect energy intake. Across all participants, the timing of serving the salad did not significantly influence energy intake, but the effect of timing depended on participant scores for flexible dietary restraint. Consuming low-energy-dense salad before rather than with the main course increased vegetable consumption by 23%. To moderate energy intake, maximizing the amount of salad eaten may be more important than the timing of consumption.

Highlights

► Consuming a low-energy-dense salad at the start of a meal can reduce energy intake. ► In a crossover design, we compared serving a salad before or with the main course. ► Compulsory salad reduced meal energy intake by 11% regardless of when it was eaten. ► The effect of timing depended on participant scores for flexible dietary restraint. ► Maximizing salad intake was an effective strategy for reducing meal energy intake.

Introduction

To address the problem of obesity, it is important to identify effective strategies for decreasing energy intake. Research has shown that reducing the energy density of foods and meals is one promising approach for moderating energy intake in both the short and long term (Rolls, 2009, Ello-Martin et al., 2007). In multiple controlled studies, consuming a preload of a low-energy-dense food such as soup, fruit, or vegetables reduced meal energy density and energy intake. It is unclear, however, whether the effect of consuming a low-energy-dense food depends upon eating it as a first course, or whether it would be as effective eaten as a side dish along with the main course. In addition, previous studies have required that participants consume a fixed amount of food (i.e., a preload), which may differ from the amount they would consume ad libitum; the consequences of this have received little attention. The objective of the present experiment was to investigate whether the effects of consuming a low-energy-dense salad depended on the timing of serving it within a meal (either before or with the main course), or on intake being fixed rather than ad libitum.

In a previous study of the influence of salad on satiety, we found that adding a preload of a large portion of a low-energy-dense salad to a meal reduced intake of the main course and decreased meal energy intake by an average of 12% (Rolls, Roe, & Meengs, 2004). In that study, the salad was served 20 min before the main course and the amount of salad was fixed. Other studies have shown similar effects on meal energy intake of adding a fixed preload of low-energy-dense soup (Rolls et al., 1999, Flood and Rolls, 2007) or fruit (Flood-Obbagy & Rolls, 2009). Because of the short interval after consuming the preload, it is likely that these results are due to engaging initial satiety mechanisms including cognitive and sensory factors (such as expectations of satiety value based on previous experience, or visual and oral cues about volume), as well as early post-ingestive cues such as stomach distension (Blundell et al., 2010). There has been little investigation, however, of variations in the timing of consuming food items served within a meal. Additionally, few studies have compared the effects of meal manipulations using fixed versus ad libitum consumption. Although using fixed amounts of food reduces variability in intake, imposed consumption differs from typical eating conditions and may have consequences due to differences in demand characteristics or motivational factors (Rolls and McDermott, 1991, Finkelstein and Fishbach, 2010).

In the present experiment, the factors involved in the influence of low-energy-dense food on satiety were investigated by varying the timing of salad consumption within a meal, as well as comparing the effects of fixed and ad libitum consumption of the salad. It was hypothesized that meal energy intake would depend on when the salad was served, because satiety mechanisms would be engaged to a greater extent by consuming the salad as a first course rather than with the main course. Also of interest was whether ad libitum intake of the salad would differ when it was served alone as a first course rather than with competing foods, because this could influence energy intake. Additionally, we wanted to confirm the finding of the previous study, that although increasing the variety of food at a meal generally leads to increased energy intake (Raynor and Epstein, 2001, Rolls et al., 1981), adding a low-energy-dense salad to a meal can lead to a reduction in meal intake. A final objective was to investigate whether individual characteristics such as dietary restraint affected the response to the experimental factors (Blundell et al., 2010). It was hypothesized that individuals with high dietary restraint, defined as the tendency to use conscious mechanisms to restrict food intake (Stunkard & Messick, 1985), would be less influenced by the timing of serving food within a meal. The findings of this experiment have implications for the understanding of factors affecting satiety as well as practical applications for structuring meals to modify food intake.

Section snippets

Experimental design

This experiment used a crossover design with repeated measures within subjects. On one day a week for five weeks, participants consumed a mid-day meal consisting of a main course of pasta accompanied by a large portion of low-energy-dense salad. Across the meals, the consumption of the salad was varied in two ways: whether it was served before the main course or together with the main course, and whether it was consumed in full (fixed intake) or consumed as desired (ad libitum intake).

Effects on energy intake

Varying the timing and method of consuming the salad had significant effects on energy intake of the salad, the pasta, and the entire meal (Fig. 1). For salad intake, there was a significant interaction between the two experimental factors [F(1,45) = 7.29; p = 0.010]. In the ad libitum conditions, salad intake was 23% greater when it was served before the main course (71 ± 3 kcal [298 ± 13 kJ]) rather than with the main course (58 ± 4 kcal [241 ± 15 kJ]; p = 0.0005). Both ad libitum intakes of salad, however,

Discussion

This experiment demonstrated that varying the timing of serving a salad, as well as whether its consumption was compulsory or ad libitum, affected both salad intake and meal energy intake. Ad libitum salad intake was increased 23% by serving the salad before rather than with the main course, and compulsory salad intake was even greater than ad libitum intake. Energy intake at the meal was reduced by 11% by adding a fixed amount of salad to the meal, similar to the findings of a previous study;

References (36)

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Acknowledgment: This research was supported by the National Institutes of Health Grants DK039177 and DK059853.

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