Edward A. Rowe

Sensory Specific Satiety in Man

To investigate the specificity of satiety in man, subjects (n=32) rated the pleasantness of the taste of eight foods, were then given one of the foods to eat for lunch, and re-rated the pleasantness of the taste of the eight foods 2 and 20 min after the end of the meal. The pleasantness of the food eaten decreased more than that of the foods not eaten (p<0.001). In a second experiment it was shown that this relative specificity of satiety influenced subsequent food intake. Before a first course, subjects (n=24) rated their liking for the taste of eight foods, were then given one of the foods to eat for lunch, and 2 min after finishing eating re-rated their liking for the taste of the eight foods. Again liking decreased more for the food eaten than for foods not eaten. These changes in liking for the foods eaten and not eaten were highly correlated (p<0.001) with the amounts of those foods eaten in an unexpected second course. Thus in man satiety can be partly specific to foods eaten and this specificity may be an important determinant of the foods selected for consumption.

Variety in a meal enhances food intake in man

We find that in man satiety can be partly specific to foods eaten [12]. The possibility that this specificity of satiety leads to overeating if a wide variety of foods is readily available is tested here. The intakes of subjects offered a variety of foods in succession during a meal were compared to intakes when the same food was offered throughout. Subjects (n=36) ate a third more when offered sandwiches with four different fillings than when just one filling was offered (p<0.001). In another study subjects (n=24) ate significantly more when three flavors of yogurt (hazelnut, blackcurrant, orange) which were distinctive in taste, texture and color were offered than when offered just one of the flavors (p<0.01), even if the flavor was the favorite (p<0.01). However, when subjects (n=24) were offered three flavors of yogurt (strawberry, raspberry, cherry) which differed only in taste there was no enhancement of intake when the variety was offered. Having a variety of foods presented in succession during a meal enhances intake, and the more different the foods are the greater the enhancement is likely to be.

How sensory properties of foods affect human feeding behavior

The sensory properties of food which can lead to a decrease in the pleasantness of that food after it is eaten, and to enhanced food intake if that property of the food is changed by successive presentation of different foods, were investigated. After eating chocolates of one color the pleasantness of the taste of the eaten color declined more than of the non-eaten colors, although these chocolates differed only in appearance. The presentation of a variety of colors of chocolates, either simultaneously or successively, did not affect food intake compared with consumption of the subjects favorite color. Changes in the shape of food (which affects both appearance and mouth feel) were introduced by offering subjects three successive courses consisting of different shapes of pasta. Changes in shape led to a specific decrease in the pleasantness of the shape eaten and to a significant enhancement (14%) of food intake when three shapes were offered compared with intake of the subjects favorite shape. Changes in just the flavor of food (i.e., cream cheese sandwiches flavored with salt, or with the non-nutritive flavoring agents lemon and saccharin, or curry) led to a significant enhancement (15%) of food intake when all three flavors were presented successively compared with intake of the favorite. The experiments elucidate some of the properties of food which are involved in sensory specific satiety, and which determine the amount of food eaten.

Sensory-specific and motivation-specific satiety for the sight and taste of food and water in man

In normal weight humans it was shown first that the sight of food is pleasant when hungry, and that the pleasantness of the sight of a food which has been eaten to satiety decreases more than the pleasantness of the sight of foods which have not been eaten. Thus the specificity of satiety extends to the visual modality, and this may be an important factor in influencing which foods are selected for ingestion. Second, it was shown that the pleasantness of both the sight and taste of food are modulated in a motivation-specific manner, in that in hungry and thirsty humans the pleasantness of the sight and taste of food but not water is decreased by eating to satiety, and the pleasantness of the sight and taste of water but not food is decreased by drinking water to satiety. Third, it was shown that sensory-specific decreases in the pleasantness of the taste of a particular food produced by its ingestion are associated with only minor changes in the intensity of its taste, which do not account for the changes in pleasantness as shown by an analysis of covariance and by the relation between pleasantness and intensity, so that it is unlikely that sensory adaptation is an important part of the mechanism of sensory-specific satiety.

Persistent obesity in rats following a period of consumption of a mixed, high energy diet.

1. Adult male hooded rats which were offered a mixed, high energy diet for 90 days were hyperphagic and became significantly obese compared to chow‐fed control rats. Fasting plasma insulin and glucose levels were initially elevated in the experimental rats, but later in the 90 day period were similar to control levels. 2. When the high energy foods were withdrawn after 90 days and just chow was available, the obese rats maintained the elevated body weights. The obese rats were initially hypophagic, but chow intakes rapidly reached control levels. Plasma insulin and glucose levels were similar in both groups, suggesting that the persisting obesity may not be associated with altered insulin resistance. 3. Five weeks after withdrawal of the ‘fattening’ diet, half of the experimental rats were offered restricted access to chow for 27 days to reduce their weights to control levels. When the rats were again given free access to chow, they returned to the previously elevated weight. 4. Eighteen weeks after withdrawal of the ‘fattening’ diet, the experimental rats had significantly elevated body weights and fat stores. The elevated body weight was not simply due to increased growth because, although the experimental rats had slightly more lean body mass than the control rats, the increase in fat was not related to body size.

Variety in the diet enhances intake in a meal and contributes to the development of obesity in the rat

Male and female rats were given three palatable, high energy foods either simultaneously or in succession during three 40 min courses. Both simultaneous and successive variety enhanced energy intake compared to the intake of single palatable foods, which was itself enhanced compared to the intake of chow. Rats deprived of food for 24 hr showed a compensatory increase in chow intake (84%) but only a 20% increase in intake in the single palatable food conditions, and no increase in the variety conditions. Male and female rats showed a similar response to variety and deprivation. The effect of variety on body weight was also examined in rats offered either chow, or chow and one palatable food, or chow and three palatable foods in succession (changed every 12 hr) or simultaneously, for seven weeks. All rats offered the palatable foods were hyperphagic compared to chow-fed controls. Rats given the simultaneous but not the successive variety diet were more hyperphagic than the other palatable food groups and showed significantly greater body weight and fat gains. The availability of a variety of foods is an important factor in the amount eaten in the meal and in the etiology of obesity.

Lactation in lean and obese rats: Effect of cafeteria feeding and of dietary obesity on milk composition

Changes in milk composition associated with maternal dietary obesity and cafeteria feeding were investigated. Protein, lactose and fat contents, and the fat composition, were determined for lean and obese rats given a cafeteria diet at different stages of reproduction. Feeding the cafeteria diet during lactation resulted in an increase in long-chain fatty acids and a fall in the characteristic medium-chain fatty acids. This effect was modified by obesity and the diet during pregnancy. Feeding the cafeteria diet in lactation reduced the milk protein and increased the fat. The milk of obese rats contained more energy, with more fat but less protein than that of lean rats. Increases in fat and long-chain fatty acid content, and decreases in protein and medium-chain fatty acid content of the milk were correlated with increased maternal intake of energy, total fat and long-chain fatty acids. Thus, the greatest influence on milk composition is exerted by the maternal diet during lactation. However, these effects are modified by pre-existing maternal obesity and the diet during pregnancy.

Exercise and the development and persistence of dietary obesity in male and female rats

Abstract Adult male and female hooded rats were housed in sedentary conditions or were given free access to a running wheel. Exercising and sedentary rats received either a palatable, mixed, high energy diet with chow (experimental group) or only chow (control group). Exercise reduced the weight gain of the males but not of the females. All experimental groups preferentially selected the palatable foods. Both exercising and sedentary females and the sedentary males became obese compared to their controls, but the exercising males did not. The mixed diet was withdrawn after 10 weeks: thereafter the male and female sedentary experimental groups maintained the elevated body weight. The exercising experimental females showed significant weight loss. Analysis of x-ray photographs indicated that elevated body weight in the experimental rats probably reflected increased deposition of fat and not skeletal growth. The results show that the effect of exercise on the development of dietary obesity is different in males and females, and that sedentary male and female rats can both show persistent dietary obesity after withdrawal of the palatable foods.

How flavour and appearance affect human feeding

It is the purpose of this paper to consider the ways in which the different sensory aspects of food presentation such as flavour, appearance, portion size and shape influence food intake in human subjects within the range of normal body-weights. One way in which the sensory properties of food influence feeding is by contributing to a form of satiety which is partly specific for the particular food eaten.

Effects of diet and obesity on body weight regulation during pregnancy and lactation in the rat

The effects of obesity level and cafeteria feeding were studied in rats during pregnancy and lactation. The non-fetal weight gain in pregnancy was three times greater with the cafeteria diet than with chow, indicating that fat deposition is not regulated at an optimal level during pregnancy. There was a strong negative correlation between postpartum weight and weight change during lactation. Obese rats were finicky in that their weight changes in lactation were exaggerated when the diet was changed between pregnancy and lactation. Pup growth rate was proportional to maternal energy intake but in this experiment not related to maternal protein, fat or carbohydrate intake. In obese rats switched to chow, intake was inadequate for normal pup growth. Thus, the weight gains in pregnancy are not regulated at a set level, and the weight change in lactation appears to compensate for the weight gain in pregnancy.