This study demonstrates that consuming different forms of fruit can significantly affect satiety and energy intake at a meal. Consuming apple segments at the start of the meal reduced lunch energy intake compared to consuming the same energy and weight of applesauce or apple juice with or without fiber. When subjects ate the apple segments at the beginning of lunch, they reduced lunch energy intake by 91 kcal [381 kJ] compared to eating applesauce, and by more than 150 kcal [628 kJ] compared to drinking either version of the apple juice. Eating apple segments also resulted in higher ratings of fullness and lower ratings of hunger compared to other forms of fruit. These results build upon previous research to show that consuming fruit before a meal can enhance satiety and reduce subsequent food intake, leading to a substantial reduction in total energy intake at the meal.
Earlier studies that investigated the effects on satiety of consuming solid and liquid forms of fruit (Bolton et al., 1981
; Haber et al., 1977
; Mattes, 2005
) found that subjects’ ratings of satiety were significantly higher following intake of fruit compared to juice. The one study that examined food intake after consumption of the preloads, however, reported no differences in energy intake as measured by 24-h food diaries (Mattes, 2005
). The present study expanded upon the findings of these previous studies by demonstrating that consumption of fruit in different forms led to differences in energy intake as measured under controlled conditions. In addition, the preloads consumed in previous studies were matched for a single parameter that could affect satiety: weight (Bolton et al., 1981
; Haber et al., 1977
) or energy content (Mattes, 2005
). The present study extended those results by matching preloads for energy content, weight, energy density, fiber content, and ingestion rate.
The present study also showed that the energy content of the apple juice both with and without fiber was compensated for by a reduction in subsequent intake; thus, drinking juice as a preload did not increase total meal energy intake. A few previous studies have found that energy intake was reduced following beverage consumption (Canty & Chan, 1991
; Holt, Sandona, & Brand-Miller, 2000
; Rolls, Kim, & Fedoroff, 1990
), while others have shown that consuming caloric beverages has little effect on food intake, resulting in increased energy intake (Almiron-Roig & Drewnowski, 2003
; DellaValle, Roe, & Rolls, 2005
; Flood et al., 2006
; Rolls, Kim, et al., 1990
). This variability in outcomes may be due to differences in beverage characteristics and experimental design. For example, it is possible that the time interval between drinking a beverage and consuming a meal may affect compensation. Beverages consumed with or between meals may be more likely to increase energy intake than beverages consumed immediately before a meal (Almiron-Roig & Drewnowski, 2003
; Almiron-Roig, Flores, & Drewnowski, 2004
; Beridot-Therond, Arts, & Fantino, 1998
; Canty & Chan, 1991
; DellaValle et al., 2005
; Holt et al., 2000
; Tsuchiya, Almiron-Roig, Lluch, Guyonnet, & Drewnowski, 2006
). More research is needed to systematically test how consuming beverages affects energy intake and satiety.
A number of reasons have been proposed to explain the greater effect on satiety of whole fruit compared with juice. It has been suggested that these different effects are due to differences in fiber content (Bolton et al., 1981
; Haber et al., 1977
), which has been shown to influence energy intake and satiety (Burton-Freeman, 2000
; Howarth et al., 2001
). In the present study, the apple, applesauce, and apple juice with fiber contained similar amounts of fiber, but had different effects on energy intake and satiety, suggesting that the form of fruit influences energy intake independently from fiber content. It has also been suggested that juice with added fiber influences satiety more than juice without any fiber (Tiwary, Ward, & Jackson, 1997
). In the present study, contrary to expectations, there were no significant differences in satiety between apple juice with and without fiber; adding fiber to the juice, however, reduced ratings of taste. Thus, adding naturally occurring levels of fiber to a beverage may not enhance satiety, and may decrease palatability.
The various forms of fruit may also produce dissimilar effects on satiety due to differential expectations of their effects on fullness. In the present study, prior to consuming each preload, subjects were asked to rate how filling they believed the preload would be; results showed that apple segments and applesauce were perceived as being more filling than juice. Also, based on previous experiences with the foods tested in this study, subjects may have expected that the plate of apples would be more filling than the glass of juice. Subjects’ ratings of thirst decreased more following consumption of both juice preloads than after eating the apple or applesauce. Therefore, it is possible that subjects perceived the beverages to be more effective at reducing thirst, while they expected the apple segments and applesauce to satisfy hunger, leading to differences in food intake and satiety (Louis-Sylvestre, Tournier, & Chabert, 1989
; McEwan & Colwill, 1996
Different forms of fruit may also have different effects on satiety due to intrinsic structural properties that affect volume and chewing. As a result of the structure provided by intact cell walls, whole apple is larger in volume than applesauce and apple juice when matched for energy content and weight. While it is likely that this difference in volume contributed to differences in satiety, it cannot provide the entire explanation because the applesauce and apple juice preloads were similar in volume, but had different effects on energy intake and satiety. In addition, consuming different forms of fruit requires different amounts of chewing. Increased chewing has been shown to initiate cephalic-phase responses involved in digestion and metabolism that could affect food intake (Lavin, French, Ruxton, & Read, 2002
; Teff & Engelman, 1996
; Teff, Levin, & Engelman, 1993
), and previous studies have suggested that different rates of consumption may affect energy intake and satiety (Zijlstra, Mars, de Wijk, Westerterp-Plantenga, & de Graff, 2008
). In the present study, ingestion rate was controlled, but chewing varied; the apple segments required substantial chewing, applesauce required minimal chewing, and the juice preloads required no chewing. As a result, the increased chewing that was required to eat the apple segments may have contributed to subsequent increases in satiety and reductions in food intake. However, more research is needed to explore how differences in cognition, volume, and chewing interact to affect food intake and satiety when different forms of fruit are consumed.
In the present study, the effect of the different forms of fruit was similar in both men and women with a range of anthropometric and psychosocial characteristics. In particular, subjects with a range of body sizes reduced energy intake after eating apple segments at the start of the meal compared to consuming no first course. It is likely, however, that for a given individual the optimal size of the first course depends on several factors, including the amount of food they usually consume at a meal (Roe, Thorwart, Pelkman, & Rolls, 1999
). Further research is needed to investigate interactions between characteristics of individuals and foods that lead to a maximal decrease in energy intake at the meal.
The results from this study suggest that eating whole fruit at the start of a meal can be an effective strategy for increasing satiety and decreasing energy intake at a meal.
Fruit consumption has been associated with diets lower in energy density (Ledikwe, Blanck, & Khan, 2006
), and research has shown that consuming a diet lower in energy density is related to reduced energy intake and body weight (Ello-Martin, Roe, Ledikwe, Beach, & Rolls, 2007
; Ledikwe, Rolls, & Smiciklas-Wright, 2007
; Rolls, Ello-Martin, et al., 2004
; Rolls, Drewnowski, & Ledikwe, 2005
). However, more research is needed to test the effects of consuming different forms of fruit on energy intake over longer periods of time before conclusions about the role of fruit in different forms in weight management can be made (Rolls, Ello-Martin, et al., 2004
). This study adds to the research suggesting that starting a meal with a low-energy-dense food, such as soup, salad, or fruit, reduces energy intake at the meal.