Effects of Food Quality, Quantity, and Variety on Intake
Barbara J. Rolls1
Not Eating Enough, 1995
Pp. 203–215. Washington, D.C.
National Academy Press
A number of highly controlled laboratory-based studies have tested whether modifications either to foods or meals can increase energy intake. One approach is to choose foods that are not very satiating, that is, calorie-for-calorie they reduce hunger less than other foods. Another approach is to alter the way the food is served so that portions are bigger or the meals are more varied. These studies will be reviewed and ways that foods might be altered to influence energy intake will be considered.
SATIETY AND FOOD INTAKE
The main reason that individuals choose particular foods is because they like the taste. While palatability of foods was found to be a major determinant
of intake in an extensive review of the literature on human food intake (Spitzer and Rodin, 1981), it is possible that other characteristics of foods such as the energy density or nutrient composition could have an impact on energy intake.
Energy Density and Food Intake
Various types of foods satisfy hunger differently (Kissileff, 1984; Rolls et al., 1990). The reasons for these differences in satiating effects are not clear. Among the causative factors that have been suggested are rate of consumption of a food, the sensory properties of the food, and beliefs about the satiety value of a food (Kissileff, 1984)/
Soup is an example of a food that is highly satiating. In a clinical survey in which intakes were analyzed from food diaries, Jordan et al. (1981) found that meals that included soup were associated both with lower caloric intakes within the meals and with lower daily caloric intakes than those meals without soup. Several studies have confirmed that soup is a highly satiating food (Kissileff et al., 1984; Rolls et al., 1990). At least part of the explanation is the low energy density of soup. Energy density, that is the calories in a given weight of food, could affect satiety by influencing the rate at which nutrients reach receptors involved in satiety (Kissileff, 1985). Foods with a low energy density require that a greater bulk of food be consumed for a given level of energy intake. The bulk of food to be consumed affects eating rate, gastric distension, and intestinal stimulation. Also, it is likely that individuals have learned the appropriate portion sizes that they should eat to experience satiety.
Energy density of foods can affect daily energy intake and body weight. In one study (Duncan et al., 1983), obese and normal-weight subjects had access to one of two different diets, for 5 days each. One diet had twice the energy density of the other; the low-energy-density diet was low in fats and sugars and high in fiber. The subjects consumed three meals a day and were allowed to eat as much of the available foods as they liked at each meal. Subjects on the high-energy-density diet. consumed nearly twice as many calories as those on the low-energy-density diet. Subjects on the low-energy-density diet were slightly hungrier at mealtimes but found the meals to be satiating. The diets in this study differed not only in energy density, but also in the fat content and in the amount of fiber, both of which could affect the amount of food consumed.
Dietary Fat and Food Intake
Foods high in fat can be readily overeaten, not only because fat increases the energy density of foods, but also because it contributes to the palatability of foods (Drewnowski, 1988). A key question is whether fat and carbohydrate,
the principal macronutrients of most diets, have similar effects on hunger and satiety since, if the proportion of fat in the diet is reduced, the proportion of carbohydrate will increase. Dietary fat may be overconsumed because it is not as satiating as other nutrients, which would relate to postabsorptive factors such as nutrient absorption, hormonal release, and oxidation of nutrients (Rolls and Shide, 1992).
Rolls et al. (1992) have conducted a number of studies that compared the effects on subsequent food intake of eating equicaloric amounts of foods that varied in fat and carbohydrate content. Results indicated that in normal-weight men who were unconcerned with their body weight, foods differing in fat and carbohydrate content were equally satiating in that they similarly affected subsequent food intake. However, in individuals who were overweight or who were concerned with their body weight, yogurt that was high in fat suppressed subsequent intake significantly less than did yogurt that was high in carbohydrate. This result suggests that in some individuals there could be a relative insensitivity to the satiety value of fat in foods. Future studies will determine whether this insensitivity plays a role in the etiology or maintenance of obesity.
Two studies conducted at Cornell University suggest that it is difficult to maintain body weight when consuming a diet composed only of low-fat foods. In the first study (Lissner et al., 1987), females of varying body weight consumed sequentially three 2-wk dietary treatments in which the energy consumed as fat was 15–20 percent, 30–35 percent, and 45–50 percent, respectively, of the diet. Relative to their energy consumption on the medium-fat diet, which resulted in significant changes in body weight. In the second study (Kendall et al., 1991), female subjects consumed a low-fat diet (20–25 percent fat) or a control diet (35–40 percent fat) for 11 weeks each, with a 7-wk washout period (when they ate their usual diets) between conditions. Results showed that subjects ate less total energy on the low-fat diet and lost twice as much weight as on the control diet. In both of these studies, subjects ate the same weight of food in the various conditions, which suggests that the weight or volume of food consumed is an important determinant of energy intake.
In another recent study, Prewitt et al. (1991) lend support to the suggestion that the fat content of the diet can have marked effects on body weight maintenance. Over a 20-wk study in lean and obese premenopausal women, a significantly greater energy intake was required to maintain subjects' body weight on a 21 percent fat diet than on the 37 percent fat maintenance diet. The authors concluded that macronutrient composition may play a role in energy requirements for weight maintenance.
When underconsumption is a problem, it is clear that the fat content or energy density of available foods can significantly affect food intake and body
weight. High-fat foods are easier to consume in quantity because they are often highly palatable, a smaller volume is required to achieve a given caloric intake, and possibly they are less satiating. To determine the optimal percentage of calories from fat in the diets of military personnel, concerns about underconsumption of energy will need to be balanced against problems that may be associated with a high-fat diet.
Dietary Fiber and Food Intake
Dietary fiber could reduce food intake for a number of reasons (Levine and Billington, 1994):
high-fiber foods take longer to eat,
some fibers such as guar gum and pectin slow gastric emptying,
fiber may reduce the digestibility of food,
increased fecal loss of energy may occur on high-fiber diets, and
fiber may affect some gastrointestinal hormones that influence food intake.
Because of the different types and doses of fiber that have been tested and the wide variety of experimental protocols, the literature on this topic is complex. Nevertheless, a number of studies have shown that high-fiber foods consumed either at breakfast (Burley et al., 1993a; Levine et al., 1989; Turconi et al., 1993) or lunch (Burley et al., 1993b; Turnbull et al., 1993) significantly reduce intake at the next meal when compared to low-fiber foods. A number of studies have also investigated the effects on weight loss of supplementing of the diet with fiber over longer periods of time (Levine and Billington, 1994; Stevens, 1988). While several of these studies show a slightly greater weight loss for subjects on a fiber-supplemented diet, the results of the studies are variable and difficult to interpret. More well-controlled studies are required that compare the effects of different types of fiber in various doses to the effects from diets of equivalent energy and protein without added fiber.
QUANTITY AND FORM OF FOOD
There is a strong tendency in many individuals to finish the food they are given, that is, to "clean the plate" (Krassner et al., 1979). Therefore it is likely that portion size will affect the amount of food eaten, although there is little published research on such effects. In one study, Shaw (1973) found that subjects consumed more of a liquid diet when it was presented in 8-oz (237-ml)
cups rather than in 2-oz (59-ml) cups. Booth and colleagues (1981) also found that when subjects were served portions 11/2 times larger than the standard portion of a variety of foods, there was an increase in the total amount consumed. However, a subsequent study (Edelman et al., 1986) found that increases in portion size resulted in enhanced consumption only when the portions were increased by about 4 times. When subjects were fed either 255 g or 426 g of lasagna, there was no difference in intake. However, when the portion size was increased to 1,000 g, intake was increased. Finally, in a recent study (D. Engell, M. Kramer, and B. Rolls, U.S. Army Natick Research, Development and Engineering Center, Natick, Mass., unpublished data, 1994), subjects were served three portions of macaroni and cheese for lunch (450, 620, and 790 g) on separate days. A significant linear relationship was found between portion size and intake. There are a number of differences among the studies, and it is not clear which of these might have influenced the results. Clearly, more studies are needed to determine situations in which portion size can affect food intake.
This author and S. Stoner (Pennsylvania State University, unpublished data, 1994) tested whether altering the way food is presented can influence food intake. Intake was compared when subjects were offered the same number of sandwiches, presented either as substantial whole units or as dainty cocktail pieces. Results showed that men ate significantly more (approximately 10 percent) of the whole sandwiches than of the sandwiches cut into parts, but women's intake showed no difference between the conditions.
Results of these studies indicate that simple changes in the way food is presented can significantly affect energy intake. Because studies thus far have only been conducted during a single meal, it is not clear whether altering food presentation can affect daily or longer-term energy intake.
Form of Food
Because hunger and thirst are regulated by different mechanisms, it is possible that offering solid and liquid forms of food could have different effects on the amount consumed. In one study, Kissileff (1985) compared consumption of a liquefied yogurt with that of a solid yogurt. He found no differences in the amount consumed, but the liquid yogurt was consumed faster. Two additional studies examining the forms of food on intake have been conducted in France (Tournier and Louis-Sylvestre, 1991). In these studies, the design is based on presenting the subjects with a fixed amount of test foods or preloads at set-time intervals and recording subsequent intake of either experimental or regular foods. In the first study, the two preloads had the same caloric content, weight, volume, composition, and temperature, but differed in physical form (a savory soup versus a pâté). Results showed that the 24-h intake was higher following liquid food than solid food consumption, but the
difference was not statistically significant. The second experiment was designed to control for cognitive and masticatory differences between solid an liquid preloads. Subjects had both a solid and a liquid in each preload, but in one condition most of the calories were in the liquid, and in the other, most were in the solid phase. Food intake during the 24 hours following the preloads was significantly higher (20 percent) for subjects who consumed most of the calories in the drink. This result could be because liquid calories are less satiating than those in solids, or it could be that the situation of taking most of the calories as a drink was unfamiliar. Perhaps over time subjects would adjust subsequent intake according to the calories in the preloads.
Through their experiences of consuming foods and through messages associated with particular foods, individuals learn to consume amounts of foods appropriate for the satisfaction of hunger (Booth, 1985; Johnson et al., 1991). Thus, the perceptions that individuals have of foods may affect the level of satiety associated with those foods, at least until experience proves these perceptions false. Rolls et al. (1992) tested the hypothesis that the perception of the fat content of foods may have an effect on consumption. Normal-weight women were given two different equicaloric yogurts, one labeled "low-fat" and the other labeled "high-fat." The subjects ate significantly more at lunch shortly after consuming the yogurt labeled "low-fat" than after consuming the yogurt labeled "high-fat.'' In another study (M. Kramer, J. Edinberg, S. Luther, and D. Engell, U.S. Army Natick Research, Development and Engineering Center, Natick, Mass., unpublished data, 1989), the palatability and consumption of pudding packaged in either commercial, military, or neutral packages were compared. The pudding in the military package was rated lower in palatability and significantly less of it was consumed than when it was served in the other packages. These studies demonstrate that perceptions of foods can affect food intake. More studies are required to determine how such perceptions affect food consumption over longer periods of time.
SENSORY-SPECIFIC SATIETY AND VARIETY
Changing Hedonic Responses to Foods During a Meal
In 1958, Siegel and Pilgrim stated that "the rejection of rations by enlisted personnel is often accompanied by the complaint that the food is monotonous. This observation suggests that repetition is a causal factor in lowered food-acceptance" (p. 756). Since that observation, studies have shown why humans desire and eat a variety of foods. The hedonic response to a food as assessed
by ratings of the pleasantness of its taste and other sensory attributes is not constant, but changes as a food is consumed.
This changing hedonic response to foods, or sensory-specific satiety, has been characterized in a series of laboratory-based studies. Rolls (1986) found that satiety, or the feeling of having had enough to eat, is specific to a particular food that has been consumed. If, for example, cheese is eaten until a subject has had all he or she wants, the rated pleasantness of the taste, smell, appearance, and texture of cheese will have declined. However, ratings of the sensory properties of other foods, particularly those very different from cheese, will not have decreased. These changes in pleasantness are related to the amounts of various foods that will be eaten during a meal. One may have eaten enough of a particular food and that food will no longer be appealing, but the appetite for other foods will remain. Thus sensory-specific satiety encourages consumption of a balanced diet because it promotes consumption of a variety of foods.
Although the greatest changes in palatability that occur after eating involve the food consumed, some uneaten foods may also decrease in palatability. This phenomenon might occur because (1) these other foods have sensory properties similar to the eaten food, (2) cognitively the foods are considered to be of the same type, or (3) perhaps the foods have the same macronutrient content (Rolls, 1986).
Thus, if foods are similar in taste to the food already consumed, they may also decrease in pleasantness. For example, after consumption of one sweet food, other sweet foods declined in pleasantness, but savory foods (i.e., salty and not sweet) were unaffected. Similarly, consumption of savory foods decreased the pleasantness of other savory foods but not sweet foods (Rolls et al., 1984). A recent study (de Graaf et al., 1993) has clearly demonstrated that consumption of sweet foods in a first course decreases the intake of sweet foods in the next course and, likewise, consumption of savory foods decreases the subsequent consumption of savory foods.
Individuals also become satiated to specific categories of foods (Rolls et al., 1986). For example, following consumption of orange gelatin, raspberry gelatin also declined in pleasantness. Similarly, following ingestion of tomato soup, consommé also decreased in pleasantness. These effects are probably due both to the way in which foods are cognitively grouped together and to similarities in the sensory properties of the foods.
Thus our perceptions of foods interact with one another so that consumption of one food may affect the pleasantness of other foods. Findings from further studies of such interactions could be used for meal planning. The goal would be to find foods that show little interaction so that palatability can be maintained at a high level throughout a meal. Meal patterns in many cultures already stress the importance of different sensory qualities of foods throughout a meal. A meal of soup or salad followed by meat with vegetables and ending
with dessert, with an emphasis on contrasts in color and texture, would reduce the possibility of specific satieties diminishing appetite during the meal.
Possibly, the specificity of satiety may be due not only to the sensory properties of foods, but also to the macronutrient content. If, as suggested by other investigators, the need for particular nutrients is an important factor in the hedonic response to foods, this type of interaction would be expected (Cabanac and Duclaux, 1970). However, Rolls et al. (1988) tested for interactions between foods of similar macronutrient composition, and the data did not support the hypothesis that hedonic changes are due to the nutrient composition of foods.
Variety and Intake During a Meal
If satiety is specific to particular properties of foods, then during a meal more should be consumed if a variety of foods is consumed than if just one food is presented (Rolls et al., 1986). In a series of experiments, it was found that variety in a meal can increase energy intake. For example, if subjects were offered a four-course meal consisting of foods that varied markedly in both sensory properties and nutrient composition, they ate 60 percent more total energy than when they had just one of the foods in the meal (Rolls et al., 1984).
These studies also tested to what degree foods could be similar in their sensory properties and still result in an enhancement of intake due to variety. Offering similar foods, such as sandwiches with four different fillings, increased intake by 33 percent (Rolls et al., 1981). Offering three different flavors of yogurt, which also differed in appearance and texture, increased intake by 20 percent compared to intake of the favorite flavor, but offering three different flavors of yogurt that did not differ in appearance or texture did not have an effect on intake (Rolls et al., 1982). Even offering in a meal the simple variation of three different pasta shapes increased intake by 15 percent compared to meal intake with only the favorite pasta shape (Rolls et al., 1982). These studies indicate that to maintain appetite throughout a meal and to encourage eating, the foods offered should be as varied as possible.
It must be emphasized that sensory-specific satiety and the effects of variety do not operate in isolation to affect food intake and selection. During normal eating, changing hedonic responses to foods will interplay with the complex environmental and physiological influences on food intake so that in some situations the palatability of foods may be the major influence on intake, while in others it may have little impact.
Monotony in the Diet
Thus far, the hedonic responses to foods during one meal have been considered. However, when assessing consumption of military rations, one must also consider changes in food acceptability and consumption that develop over longer periods. Why the acceptability of particular foods declines over time is not well understood, but one possibility is that eating a food too often affects acceptance. Studies of the effects of consuming monotonous military rations indicate that repeated presentation of some foods can lead to a persistent decrease in the pleasantness of these foods (Schutz and Pilgrim, 1958; Siegel and Pilgrim, 1958). For example, with repeated consumption, canned meats became very unpalatable and continued to be disliked for 3 to 6 months after the study. Note, however, that canned meats were not rated as very palatable at the start of the study. The effects of repeated consumption appear to be different for staple foods and foods of initial high palatability. Thus, repeated consumption did not change the palatability of desserts, sweets, canned fruits, cereal, or staples such as dairy products, bread, or coffee (Schutz and Pilgrim, 1958; Siegel and Pilgrim, 1958).
Moskowitz (1979) has described "time-preference curves" for different types of foods, which indicate that foods not consumed for about 3 months are highly desired, but those eaten the day before may not be desired at all. Foods such as meat and shellfish, foods with a heavy fat content, or foods that constitute the main component of the meal such as the entree have steep curves and are greatly desired if not eaten for a long period. Recent consumption, however, eliminates the desire for such foods. In contrast, items that are not a major component of the meal and do not have a high-fat or protein content such as bread, salad, potatoes, and some desserts have a much flatter function on the time-preference curves (hence less significant impact on preference) and could be eaten every day with no loss of preference.
Because repeat consumption of foods has been shown to lead to decreased acceptance, it is worth considering ways to avoid these monotony effects. Creating diets as varied as possible is recommended. Also, ensuring that the initial palatability of the foods offered is uniformly high should help to curtail the decline in pleasantness. One way of improving initial acceptability is to allow self-selection of items whenever possible. Kamen and Peryam (1961) found that self-selection of items to be included in a repetitive diet reduced dissatisfaction with the diet. Thus overall satisfaction with a 3-d, self-planned menu cycle was the same as with a 6-d cycle chosen by someone else.
Making people eat foods that they have not selected themselves can decrease the preference for those foods. This notion is supported by studies of young children, in which foods they were forced to eat in order to gain rewards decreased in preference (Birch et al., 1982). Much more research is needed to determine what causes the decrease in acceptability of foods.
Variety and Body Weight
Body weight maintenance may depend to some extent on the availability of a varied and palatable diet. In studies of the effects of consumption of a monotonous liquid diet, it was found that the subjects voluntarily restricted their intake and lost weight (Cabanac and Rabe, 1976; Hashim and Van Itallie, 1965). Although it is difficult to conduct controlled studies in humans, some evidence exists that if freely available diets are varied and palatable, subjects may show excessive weight gain. In studies of normal-weight and obese individuals confined to the hospital, a plentiful and varied supply of food led to overeating and weight gain over 3- to 6-d periods (Porikos et al., 1977, 1982).
The varied and palatable diets available in affluent societies probably contribute to the high incidence of obesity. When there is continual appetite stimulation created by variety both within and between meals, there will be little opportunity to compensate for overeating due to variety without conscious limitation of intake.
CONCLUSIONS AND RECOMMENDATIONS
Highly controlled laboratory-based studies have pointed to a number of ways in which the preparation and selection of foods in a meal can influence the amount consumed. Although much of this research has yet to be applied to naturalistic settings where the goal is to alter the amount consumed, the studies suggest strategies that could be used to increased consumption of military rations. These strategies include the following:
The initial palatability of foods should be high in order to delay a decreased intake due to repeat consumption. Providing opportunities for self-selection of foods also helps to avoid such monotony effects.
The diet should be as varied as possible both in terms of the number and types of food items offered and of the sensory properties of the foods. Variety of flavor, texture, and appearance of foods helps to maintain the palatability of a meal and can affect the amount consumed.
The way that foods are presented, such as the portion size, can affect the amount consumed. To satisfy the dual goals of maximizing intake and avoiding wastage, it may be necessary to allow some choice in portion size since intake varies widely between individuals.
The labels on foods and the beliefs that individuals have about the satisfaction derived from particular foods can affect food intake.
The energy delivered in drinks reportedly suppresses subsequent food intake less than the equivalent energy delivered in foods. Providing drinks of high nutrient and energy density could improve the diet and could increase food intake.
Daily energy intake is lower on low-energy density, high-fiber diets than on high-fat, energy-dense diets. In determining the optimal amounts of fat and fiber for the diets of military personnel, there must be a balance between the nutritional requirements of a healthy diet and those necessary for maintaining energy intake.
Birch, L.L., D. Birch, D.W. Martin, and L. Kramer 1982. Effects of instrumental consumption on children's food preference. Appetite 3:125–134.
Booth, D.A. 1985. Food conditioned eating preferences and aversions with interceptive elements: Conditioned appetites and satieties. Ann. N.Y. Acad. Sci. 443:22–41.
Booth, D.A., J. Fuller, and V. Lewis 1981. Human control of body weight: Cognitive or physiological? Some energy-related perceptions and misperceptions. Pp. 305–314 in The Body Weight Regulatory System: Normal and Disturbed Mechanisms, L.A. Cioffi, W.P.T. James, and T.B. Van Itallie, eds. New York: Raven Press.
Burley, V.J., A.W. Paul, and J.E. Blundell 1993a. Sustained post-ingestive action of dietary fibre: Effects of a sugar-beet-fibre-supplemented breakfast on satiety. J. Hum. Nutr. Diet. 6:253–260.
1993b. Influence of a high-fibre food (myco-protein) on appetite: Effects on satiation (within meals) and satiety (following meals). Eur. J. Clin. Nutr. 47:409–418.
Cabanac, M., and R. Duclaux 1970. Specificity of internal signals in producing satiety for taste stimuli . Nature 227:966–967.
Cabanac, M., and E.F. Rabe 1976. Influence of a monotonous diet on body weight regulation in humans. Physiol. Behav. 17:675–678.
de Graaf, C., A. Schreurs, and Y.H. Blauw 1993. Short-term effects of different amounts of sweet and nonsweet carbohydrates on satiety and energy intake. Physiol. Behav. 54:833–843.
Drewnowski, A. 1988. Fats and food acceptance: Sensory, hedonic and attitudinal aspects. Pp. 189–204 in Food Acceptance and Nutrition, J. Solms, D.A. Booth, R.M. Pangborn, and O. Raunhardt, eds. New York: Academic Press.
Duncan, K.H., J.A. Bacon, and R.L. Weinsier 1983. The effects of high and low energy density diets on satiety, energy intake, and eating time of obese and nonobese subjects. Am. J. Clin. Nutr. 37:763–767.
Edelman, B., D. Engell, P. Bronstein, and E. Hirsch 1986. Environmental effects on the intake of overweight and normal-weight men. Appetite 7:71–83.
Hashim, S.A., and T.B. Van Itallie 1965. Studies in normal and obese subjects with a monitored food dispensing device. Ann. N.Y. Acad. Sci. 131:654–661.
Johnson, S.L., L. McPhee, and L.L. Birch 1991. Conditioned preferences: Young children prefer flavors associated with high dietary fat. Physiol. Behav. 50:1245–1251.
Jordan, H.A., L.S. Levitz, K.L. Utgoff, and H.L. Lee 1981. Role of food characteristics in behavioral change and weight loss. J. Am. Diet. Assoc. 79:24–29.
Kamen, J.M., and D.R. Peryam 1961. Acceptability of repetitive diets. Food Technol. 15:173–177.
Kendall, A., D.A. Levitsky, B.J. Strupp, and L. Lissner 1991. Weight loss on a low-fat diet: Consequence of the imprecision of the control of food intake in humans. Am. J. Clin. Nutr. 53:1124–1129.
Kissileff, H.R. 1984. Satiating efficiency and a strategy for conducting food loading experiments. Neurosci. Biobehav. Rev. 8:129–135.
1985. Effects of physical state (liquid-solid) of foods on food intake: Procedural and substantive contributions. Am. J. Clin. Nutr. 42:956–965.
Kissileff, H.R., L.P. Gruss, J. Thornton, and H.A. Jordan 1984. The satiating efficiency of foods. Physiol. Behav. 32:319–332.
Krassner, H.A., K.D. Brownell, and A.J. Stunkard 1979. Cleaning the plate: Food left over by overweight and normal weight persons. Behav. Res. Ther. 17:155–156.
Levine, A.S., and C.J. Billington 1994. Dietary fiber: Does it affect food intake and body weight? Pp. 191–200 in Appetite and Body Weight Regulation: Sugar, Fat, and Macronutrient Substitutes, J. Fernstrom and G. Miller, eds. Boca Raton, Fla.: CRC Press.
Levine, A.S., J.R. Tallman, M.K. Grace, S.A. Parker, C.J. Billington, and M.D. Levitt 1989. Effect of breakfast cereals on short-term food intake. Am. J. Clin. Nutr. 50:1303–1307.
Lissner, L., D.A. Levitsky, B.J. Strupp, H.J. Kalkwarf, and D.A. Roe 1987. Dietary fat and the regulation of energy intake in human subjects. Am. J. Clin. Nutr. 46:886–892.
Moskowitz, H.R. 1979. Mind, body, and pleasure: An analysis of factors which influence sensory hedonics. Pp. 131–148 in Preference Behavior and Chemoreception, J.H.A. Kroeze, ed. London: Information Retrieval.
Porikos, K.P., G. Booth, and T.B. Van Itallie 1977. Effect of covert nutritive dilution on the spontaneous intake of obese individuals: A pilot study. Am. J. Clin. Nutr. 30:1638–1644.
Porikos, K.P., M.F. Hesser, and T.B. Van Itallie 1982. Caloric regulation in normal weight men maintained on a palatable diet of conventional foods. Physiol. Behav. 29:293–300.
Prewitt, T.E., D. Schmeisser, P.E. Bowen, P. Aye, T.A. Dolecek, P. Langenberg, T. Cole, and L. Brace 1991. Changes in body weight, body composition, and energy intake in women fed high- and low-fat diets. Am. J. Clin. Nutr. 54(2):304–310.
Rolls, B.J. 1986. Sensory-specific satiety. Nutr. Rev. 44:93–101.
Rolls, B.J., and M. Hetherington 1989. The role of variety in eating and body weight regulation. Pp. 57–84 in Handbook of Psychophysiology of Human Eating, R. Shepherd, ed. Sussex, England: John Wiley & Sons.
Rolls, B.J., and D.J. Shide 1992. The influence of dietary fat on food intake and body weight. Nutr. Rev. 50:283–290.
Rolls, B.J., E.A. Rowe, E.T. Rolls, B. Kingston, A. Megson, and R. Gunary 1981. Variety in a meal enhances food intake in man. Physiol. Behav. 26:215–221.
Rolls, B.J., E.A. Rowe, and E.T. Rolls 1982. How sensory properties of foods affect human feeding behavior. Physiol. Behav. 29:409–417.
Rolls, B.J., P.M. van Duijvenvoorde, and E.T. Rolls 1984. Pleasantness changes and food intake in a varied four-course meal. Appetite 5:337–348.
Rolls, B.J., M. Hetherington, V.J. Burley, and P.M. van Duijvenvoorde 1986. Changing hedonic responses to foods during and after a meal. Pp. 247–268 in Interaction of the Chemical Senses with Nutrition, M.R. Kare and J.G. Brand, eds. New York: Academic Press.
Rolls, B.J., M. Hetherington, and V.J. Burley 1988. The specificity of satiety: The influence of foods of different macronutrient content on the development of satiety. Physiol. Behav. 43(a):145–153.
Rolls, B.J., I.C. Fedoroff, J. Guthrie, and L.J. Laster 1990. Foods with different satiating effects in humans. Appetite 15:115–126.
Rolls, B.J., D.J. Shide, N. Hoeymans, P. Jas, and A. Nichols 1992. Information about fat content of preloads influences energy intake in women [abstract]. Appetite 19:213.
Schutz, H.G., and F.J. Pilgrim 1958. A field study of monotony. Psychol. Rep. 4:559–565.
Shaw, J. 1973. The Influence of Type of Food and Method of Presentation on Human Eating Behavior. Ph.D. Dissertation, University of Pennsylvania, Philadelphia.
Siegel, P.S., and F.J. Pilgrim 1958. The effect of monotony on the acceptance of food. Am. J. Psychol. 71:756–759.
Spitzer, L., and J. Rodin 1981. Human eating behavior: A critical review of studies in normal weight and overweight individuals. Appetite 2:293–329.
Stevens, J. 1988. Does dietary fiber affect food intake and body weight? J. Am. Diet. Assoc. 88:939–945.
Tournier, A., and J. Louis-Sylvestre 1991. Effect of the physical state of a food on subsequent intake in human subjects. Appetite 16:17–24.
Turconi, G., R. Bazzano, R. Caramella, R. Crovetti, and M. Porrini 1993. High-calorie fibre-rich breakfast: Its effect on satiety. J. Hum. Nutr. Diet. 6:245–252.
Turnbull, W.H., J. Walton, and A.R. Leeds 1993. Acute effects of mycoprotein on subsequent energy intake and appetite variables. Am. J. Clin. Nutr. 58:507–512.