Fat substitutes promote weight gain in rats consuming high-fat diets

The use of food products designed to mimic the sensory properties of sweet and fat while providing fewer calories has been promoted as a method for reducing food intake and body weight. However, such products may interfere with a learned relationship between the sensory properties of food and the caloric consequences of consuming those foods. In the present experiment, we examined whether use of the fat substitute, olestra, affect energy balance by comparing the effects of consuming high-fat, high-calorie potato chips to the effects of consuming potato chips that sometimes signaled high calories (using high-fat potato chips) and that sometimes signaled lower calories (using nonfat potato chips manufactured with the fat substitute olestra). Food intake, body weight gain and adiposity were greater for rats that consumed both the high-calorie chips and the low-calorie chips with olestra compared to rats that consumed consuming only the high-calorie chips, but only if animals were also consuming a chow diet that was high in fat and calories. However, rats previously exposed to both the high- and low-calorie chips exhibited increased body weight gain, food intake and adiposity when they were subsequently provided with a high fat, high calorie chow diet suggesting that experience with the chips containing olestra affected the ability to predict high calories based on the sensory properties of fat. These results extend the generality of previous findings that interfering with a predictive relationship between sensory properties of foods and calories may contribute to dysregulation of energy balance, overweight and obesity.     

Dietary self-selection vs. complete diet: body weight gain and meal pattern in rats.

Food intake and body weight gain of male adult Wistar rats were examined in two groups of animals. One group (n = 14) was allowed to select its diet from separate sources of protein (casein, 3.1 kcal/g), fat (lard and sunflower oil, 7.9 kcal/g) and carbohydrate (CHO, starch and sucrose, 3.3 kcal/g). Another group (n = 10) received a nutritionally complete diet (3.3 kcal/g). After 2 weeks of adaptation to the diets, body weights and meal patterns were recorded for at least 4 days. The total caloric intake was nearly identical for the two groups of rats. Rats given dietary choice gained less weight over 4 days than rats fed chow and showed reduced feed efficiency. During the 24-h period, self-selecting rats consumed 20.8% of calories as proteins, 21% as fats and 58.2% as CHO. Self-selecting rats ate significantly less calories during the day than did rats given chow. The chow diet consisting of 17.3% calories as protein, 7.6% as fat and 75.1% as CHO. When comparing the self-selecting group nutrient intakes to those of chow-fed group it was observed that 24-h protein calorie intakes were identical in both groups. Fat intake was significantly higher and CHO reduced as compared to chow-fed rats. During the day, CHO intake was higher in self-selecting rats, and fat intake was not significantly reduced. During the night, protein and fat intakes were significantly higher in self-selecting rats, while CHO intake was significantly decreased, particularly in the last periods of the night.(ABSTRACT TRUNCATED AT 250 WORDS)     

Selection of protein and fat by diabetic rats following separate dilution of the dietary sources

Diabetic and normal rats were allowed to select their diets from separate sources of protein, carbohydrate and fat. Following the determination of baseline intakes, diabetic and normal rats received dietary components in which either the protein (Experiment 1) or fat source (Experiment 2) was diluted by 25% or 50% by the addition of cellulose. Diabetic rats failed to maintain protein intake at both dilution levels, but made up for the loss of protein-derived calories by consuming more fat. Diabetic rats maintained fat intake at both dilution levels. Dietary dilutions had no effect on total caloric intakes or body weight gain of diabetic rats. Diabetic status, measured by fasting plasma glucose levels and urinary glucose excretion rates, also was unaffected by diet dilutions. These data suggest that diabetic rats maintain total caloric intake following dilution of either the protein or fat source of their diets, but defend intake of fat-derived calories more readily than protein-derived calories. Normal rats maintained both protein and fat intake at the 25% but not at the 50% dilution level. These findings are discussed in terms of the ability of diabetic rats to solve the metabolic problems associated with their diabetic condition.     

Changes in rats' meal patterns as a function of the caloric density of the diet

Rats in a laboratory foraging paradigm were offered each of four diets which differed in caloric density, and intakes, meal frequencies, meal sizes, and eating rates were monitored. The rats maintained a constant daily caloric intake by eating more frequent, larger meals of the lower density foods. However, caloric meal size was not regulated, and significant correlations between meal size and the length of the post-meal interval were rarely found. The 24-hour pattern of calorie intake was the same regardless of diet. Higher-calorie foods were consumed at a faster rate within meals than were lower-calorie foods. The feeding patterns observed suggest that caloric intake may be regulated over a time frame of several meals rather than on a meal-to-meal basis.     

A role for sweet taste: calorie predictive relations in energy regulation by rats

Animals may use sweet taste to predict the caloric contents of food. Eating sweet noncaloric substances may degrade this predictive relationship, leading to positive energy balance through increased food intake and/or diminished energy expenditure. These experiments were designed to test the hypothesis that experiences that reduce the validity of sweet taste as a predictor of the caloric or nutritive consequences of eating may contribute to deficits in the regulation of energy by reducing the ability of sweet-tasting foods that contain calories to evoke physiological responses that underlie tight regulation. Adult male Sprague-Dawley rats were given differential experience with a sweet taste that either predicted increased caloric content (glucose) or did not predict increased calories (saccharin). We found that reducing the correlation between sweet taste and the caloric content of foods using artificial sweeteners in rats resulted in increased caloric intake, increased body weight, and increased adiposity, as well as diminished caloric compensation and blunted thermic responses to sweet-tasting diets. These results suggest that consumption of products containing artificial sweeteners may lead to increased body weight and obesity by interfering with fundamental homeostatic, physiological processes.     

Controlling the intake of calories with the intake of food

The author presents a dietary program for weight reduction based not on the substitution of a low calorie meal for a high calorie meal, but on the pre-meal ingestion of low calorie bulk beverages that are pleasant to taste and space filling, thereby compromising the capacity of the stomach to accommodate much of the higher calorie foods of the regular meals. This method makes any form of fasting unnecessary, as the intake of calories is already limited. Because of this method, few changes need to be made in food selection for regular meals.     

A behavioral approach to increasing calorie consumption in children with cystic fibrosis

To increase calorie consumption of 5 mildly malnourished children with cystic fibrosis (CF), intervention was implemented in multiple baseline fashion across snack and three meals. Intervention involved nutritional education establishing gradually increasing calories goals, teaching parents contingency management strategies, and a reward system for achieving calorie goals. Following 6 treatment sessions, the children's calorie intake increased across meals and total calorie intake was 25 to 43% above baseline. The calorie increase was maintained at 9-month follow-up. Significant changes in weight and height were made during treatment and the year following intervention. The results suggest that the long-term oral intake of children with CF can be modified by a short-term behavioral intervention.     

Protein selection, food intake, and body composition in response to the amount of dietary protein

Though not universally observed, moderately low-protein diets have been found to increase caloric intake and body fat. It appears that animals overeat in calories in order to obtain more dietary protein. For animals to control protein intake, they must be able to distinguish between two isocaloric diets containing different percentages of protein and make the appropriate dietary selection on the basis of their previous history of protein intake. Experiment 1 examined the 24-h diet selection (5 vs. 35% casein) of Sprague-Dawley rats that had been previously fed diets containing various percentages of dietary protein (5, 10, 20, 35, or 60% casein). Animals fed 5, 10, or 20% dietary protein showed a preference for the higher protein selection diet. In contrast, no significant diet preference was found in animals pre-fed the two higher levels of dietary protein (35 or 60% casein). In this study, daily food intake and body fat of rats fed the low-protein diets (5 and 10% casein) were similar to rats fed the 20% casein diet. Experiment 2 examined the effects of the level of methionine supplementation on rats fed 10% casein. In this study, food intake and body fat were increased by approximately 20% in rats fed 10% casein diets, regardless of the level of methionine supplementation (0.3 vs. 0.15%). Together, the results suggest that the presence of low-protein-induced hyperphagia helps maintain body protein levels in the face of moderately low dietary protein and promotes an increase in the amount of body fat and energy.     

Dietary fat-induced hyperphagia in rats as a function of fat type and physical form

The influence of dietary fat on food intake and weight gain was assessed by feeding adult female rats diets that differed in the type and form of fat, as well as in the availability of other macro- and micronutrients. Compared to chow-fed controls, the various fat diets increased total food intake by 4% to 27%. Specifically, rats fed chow and a separate source of fat (fat option diet) consumed more fat and total calories, and gained more weight when the fat source was emulsified corn oil rather than pure corn oil or was vegetable shortening rather than corn oil. However, corn oil and shortening had similar effects on caloric intake and weight gain when presented as emulsified gels. Also, pure and emulsified-gel forms of shortening did not differ in their effects on caloric intake and weight gain. Supplementing the vegetable shortening with micronutrients, however, enhanced its hyperphagia-promoting effect. The results of two-choice tests revealed that the rats' preferences for the orosensory properties of the various fat sources did not account for the differential hyperphagias obtained. Rather, it appears that long-term fat selection and caloric intake are influenced primarily by postingestive factors. Fat selection and total intake were determined not only by the fat source itself, but also by the other diet options. That is, rats selected more fat and consumed more calories when chow was the alternative food than when separate sources of carbohydrate and protein were available.     

Regulation of calorie intake in rats with rostral zona incerta lesions: effects of caloric density or palatability of the diet

Following an initial period of hypophagia, the body weights of rats with zona incerta lesions approached asymptotic levels that were significantly lower than those of controls although daily food intake was not reliably depressed. In spite of persisting deficits in feeding efficiency, the ad libitum food intake of the ZI-lesioned rats (relative to body weight) recovered to preoperative levels and was regulated accurately with respect to the caloric density of the diet. However, rats with ZI lesions were finicky eaters and did not maintain stable calorie intake when given unpalatable diets. The water intake of ZI-lesioned rats remained consistently below that of neurologically intact rats but was normal relative to their own food intake and lowered body weight.     

Dietary hyperphagia in rats: role of fat, carbohydrate, and energy content

Dietary energy, fat and carbohydrate content were varied to determine the nutritional factors responsible for hyperphagia induced by feeding rats high-fat diets. In the first experiment, rats were fed isoenergetic high-fat or high-carbohydrate diets for 2 weeks. Weight gain and energy intake were lower in rats given the high-fat diet. When some of the rats were switched to a diet that was high in fat, carbohydrate and energy, gram food intake was initially unchanged, resulting in a substantial increase in energy intake and weight gain. Energy intake gradually declined over the 4 weeks following the switch to the high-energy diet. In the second experiment, rats were fed high-fat diets that were either high or low in carbohydrate content and either high or low in energy content (kcal/g). Rats fed a high-fat diet that was high in energy and carbohydrate ate the most energy and gained the most body weight and carcass fat. In the third experiment, rats were fed high-carbohydrate diets varying in fat and cellulose content. Energy intake and body weight gain varied directly as a function of caloric density regardless of the fat or cellulose content of the diets. It is concluded that hyperphagia induced by feeding high-fat diets is not due to the high dietary fat content alone. Rather, high levels of fat, carbohydrate, and energy interact to produce overeating and obesity in rats fed high-fat diets.     

Quantifying food intake in socially housed monkeys: social status effects on caloric consumption

Obesity results from a number of factors including socio-environmental influences and rodent models show that several different stressors increase the preference for calorically dense foods leading to an obese phenotype. We present here a non-human primate model using socially housed adult female macaques living in long-term stable groups given access to diets of different caloric density. Consumption of a low fat (LFD; 15% of calories from fat) and a high fat diet (HFD; 45% of calories from fat) was quantified by means of a custom-built, automated feeder that dispensed a pellet of food when activated by a radiofrequency chip implanted subcutaneously in the animal's wrist. Socially subordinate females showed indices of chronic psychological stress having reduced glucocorticoid negative feedback and higher frequencies of anxiety-like behavior. Twenty-four hour intakes of both the LFD and HFD were significantly greater in subordinates than dominates, an effect that persisted whether standard monkey chow (13% of calories from fat) was present or absent. Furthermore, although dominants restricted their food intake to daylight, subordinates continued to feed at night. Total caloric intake was significantly correlated with body weight change. Collectively, these results show that food intake can be reliably quantified in non-human primates living in complex social environments and suggest that socially subordinate females consume more calories, suggesting this ethologically relevant model may help understand how psychosocial stress changes food preferences and consumption leading to obesity.     

Aging and food restriction: effect on lipids of cerebral cortex.

In experimental animals dietary restriction reduces the body weight increase due to aging, increases longevity and delays the onset of age-related physiological deterioration, including age-related changes in serum lipids. Little is known about the influence of food restriction on brain lipids, whose concentration and composition have been shown to change with age. We studied whether some biochemical and biophysical parameters of rat brain membranes, known to be modified with age, were affected by a diet low in calories, in which 50% of lipids and 35% of carbohydrates have been replaced by fibers. The diet was started at weaning and maintained throughout the animal's entire life span. Animals fed the low calorie diet survived longer and gained less body weight than standard diet fed rats. Age-related increases in microviscosity, cholesterol/phospholipid and sphingomyelin/phosphatidylcholine ratios were reduced or restored to the levels of young animals in cortex membranes of 32 old rats fed the low calorie diet, while the age-related increase in mono- to polyunsaturated fatty acid ratios in phospholipids was further raised. In conclusion we have shown that a diet low in calories and high in fibers affects lipid composition in the rat brain, in a direction opposite to that normally believed to reduce age-related deterioration of brain functions.     

Food intake after intragastric meals of short-, medium-, or long-chain triglyceride

Food-deprived Sprague-Dawley rats were given equicaloric intragastric infusions of mixed meals consisting largely of short- (SCT), medium- (MCT), or long-chain triglyceride (LCT). When animals were allowed to feed 20 min after infusion, there was an immediate reduction of food intake that was sustained over the 2 hr feeding period. During the first hour of feeding, the SCT, which is digested and absorbed more rapidly than the MCT or the LCT, was more effective per calorie in reducing food intake than these longer-chain triglycerides. However, during the second hour, cumulative intakes after the different triglyceride infusions were not significantly different. Equicaloric infusions of the MCT and the LCT resulted in equivalent reductions of food intake at all times. The satiety effects of these two triglycerides appear to be related to their caloric properties rather than to chain length. Since the LCT reduced food intake before the absorbed fat could have entered the blood to stimulate satiety·signals, this satiety effect may be mediated by a gastroenteric signal. None of the triglyceride infusions resulted in a conditioned taste aversion suggesting that food intake was reduced through normal satiety rather than through discomfort.     

Effects of dietary caloric density on feeding behavior in Mongolian gerbils (Meriones unguiculatus)

Total daily energy intake, water intake, body weight, and meal patterns were studied in Mongolian gerbils as a function of dietary caloric density. On diets ranging in caloric density from 2.25 kcal/g to 6.09 kcal/g, gerbils consumed an average of 40 kcal per 100 g of body weight per day. In comparison to gerbils fed ground Purina Laboratory Chow (4.2 kcal/g), gerbils presented with diets diluted with nonutritive cellulose increased food intake in proportion to the percentage of cellulose added. Gerbils given diets in which the caloric density was increased by the addition of fat, decreased food intake as a direct function of the added fat. Water intake was increased on the calorically diluted diets, and decreased on the concentrated diets. Body weight did not vary as a function of dietary conditions. On a standard pelleted diet (Noyes), gerbils ate approximately 18 meals a day. Average meal size was 0.4 g. When presented with calorically diluted pellets, gerbils maintained daily energy intake by increasing both meal frequency and meal size. There were no differences in food intake, meal frequency or meal size between the light and dark portions of the 24-hr cycle.     

Testing food‐related inhibitory control to high‐ and low‐calorie food stimuli: Electrophysiological responses to high‐calorie food stimuli predict calorie and carbohydrate intake

Maintaining a healthy diet has important implications for physical and mental health. One factor that may influence diet and food consumption is inhibitory control—the ability to withhold a dominant response in order to correctly respond to environmental demands. We examined how N2 amplitude, an ERP that reflects inhibitory control processes, differed toward high‐ and low‐calorie food stimuli and related to food intake. A total of 159 participants (81 female; M age = 23.5 years; SD = 7.6) completed two food‐based go/no‐go tasks (one with high‐calorie and one with low‐calorie food pictures as no‐go stimuli) while N2 amplitude was recorded. Participants recorded food intake using the Automated Self‐Administered 24‐hour Dietary Recall system. Inhibiting responses toward high‐calorie stimuli elicited a larger (i.e., more negative) no‐go N2 amplitude; inhibiting responses toward low‐calorie stimuli elicited a smaller no‐go N2 amplitude. Participants were more accurate during the high‐calorie than low‐calorie task, but took longer to respond on go trials toward high‐calorie rather than low‐calorie stimuli. When controlling for age, gender, and BMI, larger high‐calorie N2 difference amplitude predicted lower caloric intake (β = 0.17); low‐calorie N2 difference amplitude was not related to caloric intake (β = −0.03). Exploratory analyses revealed larger high‐calorie N2 difference amplitude predicted carbohydrate intake (β = 0.22), but not protein (β = 0.08) or fat (β = 0.11) intake. Results suggest that withholding responses from high‐calorie foods requires increased recruitment of inhibitory control processes, which may be necessary to regulate food consumption, particularly for foods high in calories and carbohydrates.     

Dietary self-selection of golden hamsters in response to acute food deprivation and chronic food restriction

Adult male golden hamsters were maintained on either Purine Rat Chow (Chow diet) or a self-selection diet consisting of high-protein chow, pure fat, and pure carbohydrate (Choice diet). In Experiment 1, animals were deprived of food for single periods of up to 48 hr. Animals on the Chow diet did not increase intake at any time after deprivation; animals on the Choice diet selectively increased their consumption of fat-derived calories and increased their total caloric intake during the first 6 hr of refeeding, but not thereafter. The nature of the diet did not influence the rate at which animals regained weight following deprivation. In Experiment 2, hamsters were placed on food-restriction schedules (access to food either for 1 hr/day only or on alternate days only) until they lost 20% of starting body weight. Chow-fed animals demonstrated little or no change in food intake either during or after food restriction. Hamsters on the Choice diet consumed more calories and lost weight more slowly than did chow-fed animals during 1-hr/day feeding; intake of fat-derived calories was elevated during restriction. Choice hamsters increased total caloric intake only towards the end of the alternate-days restriction schedule. Choice hamsters were hyperphagic following both types of food-restriction schedules, but no increased preference for fat-derived calories was observed. Factors influencing food consumption of hamsters in response to deprivation and restriction are discussed.     

The unique merits of a low-fat diet for weight control

The virtual freedom from obesity enjoyed by many primitive societies may be traceable to the low fat content of their traditional diets. Recent studies indicate that humans have a very limited capacity for de novo lipogenesis from dietary carbohydrate; this implies that it should be easy to achieve negative fat balance if dietary fat intake is kept low and fat oxidation is promoted by regular exercise. Overfeeding with carbohydrate--but not with fat--provokes an insulin-mediated thermogenesis which acts to retard weight gain. Low-fat starchy foods have a relatively low caloric density, resulting in lower caloric consumption with meals. Once absorbed, carbohydrate has greater satiety value than fat. These considerations suggest that avoidance of dietary fat may be a more successful approach to weight control than "calorie counting". The efficacy of low-fat diets may be promoted by supplementary carnitine, which stimulates fat oxidation, and by chromium, which aids insulin-mediated thermogenesis. An unrefined low-fat diet, eaten to satiety and accompanied by regular exercise, may be the ideal means of maintaining a trim figure throughout life while minimizing one's risk for "Western" degenerative diseases.     

The effect of dehydroepiandrosterone on Zucker rats selected for fat food preference

When allowed to select between macronutrients in a 1-h-a-day meal paradigm, Zucker rats consume 20–80% of their total caloric intake as fat. If they receive an intraperitoneal injection of DHEA 2 h before such a test meal, they consume fewer total calories. The magnitude of this effect on each macronutrient depends upon the animal's initial preference for fat; the higher the initial fat preference, the more profound is the decrease in caloric intake and the more pronounced the effect on fat consumption. Doses as low as 25 mg DHEA/kg body weight are effective. Lean Zucker rats that prefer to consume a high-fat diet have higher epinephrine and dopamine levels in select regions of the hypothalamus known to control food intake. Administration of DHEA to such animals 2 h before decapitation reduces the content of norepinephrine and these monoamines to levels that mimic the values found in the low-fat-preferring animals. It is hypothesized that exogenous DHEA causes the acute release of norepinephrine, epinephrine, and dopamine in select regions of the hypothalamus, and this release causes a decrease in food intake, particularly fat.     

Developmental aspects of sucrose-induced obesity in rats

Daily caloric intakes and body weights were measured from weaning to 70 days of age in male Sprague-Dawley rats given access to either a standard laboratory diet and water, or the standard diet, a 32% sucrose solution and water. Lee index of obesity (3 square root body weight/naso-anal length) and fasting blood glucose levels were determined at 46, 57, and 70 days of age. Animals were sacrificed at 70 days, and body composition analyses were performed. Aniamls given access to the sucrose solution consumed significantly more calories per day than animals given only the standard diet. Sucrose animals took approximately 50 to 60% of their daily caloric intake from the sugar solution. Despite the greater caloric intakes of the sucrose animals, sucrose and control animals did not differ in body weight. While there were no differences in body weights between the two groups, the Lee Index of obesity was significantly greater in the sucrose animals than in controls as early as 46 days of age. Fasting blood glucose levels were significantly lower in sucrose animals than in controls at both 46 and 57 days of age. Direct determinations of body compositions when animals were 70 days of age revealed that animals with access to sucrose had significantly greater percentages of body fat and lower percentages of body protein than controls.