When does sucrose increase appetite and adiposity?

Genetic controls of Tas1r3-independent sucrose consumption in mice

We have previously used crosses between C57BL/6ByJ (B6) and 129P3/J (129) inbred strains to map a quantitative trait locus (QTL) on mouse chromosome (Chr) 4 that affects behavioral and neural responses to sucrose. We have named it the sucrose consumption QTL 2 (Scon2), and shown that it corresponds to the Tas1r3 gene, which encodes a sweet taste receptor subunit TAS1R3. To discover other sucrose consumption QTLs, we have intercrossed B6 inbred and 129.B6-Tas1r3 congenic mice to produce F₂ hybrids, in which Scon2 (Tas1r3) does not segregate, and hence does not contribute to phenotypical variation. Chromosome mapping using this F₂ intercross identified two main-effect QTLs, Scon3 (Chr9) and Scon10 (Chr14), and an epistatically interacting QTL pair Scon3 (Chr9)-Scon4 (Chr1). Using serial backcrosses, congenic and consomic strains, we conducted high-resolution mapping of Scon3 and Scon4 and analyzed their epistatic interactions. We used mice with different Scon3 or Scon4 genotypes to understand whether these two QTLs influence sucrose intake via gustatory or postoral mechanisms. These studies found no evidence for involvement of the taste mechanisms, but suggested involvement of energy metabolism. Mice with the B6 Scon4 genotype drank less sucrose in two-bottle tests, and also had a higher respiratory exchange ratio and lower energy expenditure under basal conditions (when they had only chow and water available). Our results provide evidence that Scon3 and Scon4 influence mouse-to-mouse variation in sucrose intake and that both likely act through a common postoral mechanism.

Diverse physiological consequences of long-term sucrose consumption in female rats

Although a considerable amount of work has addressed the short-term consequences of sucrose ingestion on a variety of morphological, physiological and hematological measures, relatively few studies have investigated these parameters following long-term sucrose intake. Results of the present experiments indicated that female rats given ad libitum access to a 10% sucrose solution for 9 months were conspicuously larger and had significantly heavier thyroid and spleen weights compared to rats offered either a restricted (20 min) daily sucrose option or control rats given only water. Rats given free access to sucrose also displayed abnormal serum levels of creatinine, sodium, phosphorus, alkaline phosphatase, alanine aminotransferase, uric acid and cholesterol which could indicate dysfunction in many organs including the kidney and liver. In the brain, however, chronic sucrose access was not associated with any discernable changes in neuronal or glial cell density within selected brain regions, but brain weight was found to be highly negatively correlated (r = - 0.97) with total sucrose intake. Finally, we report that high doses of estradiol can significantly attenuate the intake of sucrose in female rats. Together these findings demonstrate that free access to a sucrose solution for long periods can induce profound effects on rat physiology and may have important implications for the management of diet in humans.

Obesity by choice revisited: effects of food availability, flavor variety and nutrient composition on energy intake

Recent work suggested that the energy intake and weight gain of rats maintained on chow and 32% sucrose solution could be increased by simply offering more sources of sucrose [Tordoff M.G. Obesity by choice: the powerful influence of nutrient availability on nutrient intake. Am J Physiol 2002;282:R1536-R1539.]. In Experiment 1 this procedure was replicated but the effect was not: rats given one bottle of sucrose and five bottles of water consumed as much sucrose as those given five bottles of sucrose and one of water. Adding different flavors to the sucrose did not increase intakes further in Experiment 2. The relative potency of sucrose and other optional foods was studied in Experiment 3. Sucrose solution stimulated more overeating and weight gain than fat (vegetable shortening), and offering both sucrose and shortening did not generate further increases in energy intake. Finally, foods commonly used to produce overeating and weight gain were compared. Sucrose was less effective than a high-fat milk diet, and offering cookies in addition to the milk did not increase energy intake further. The nature of optional foods (nutrient composition and physical form) was markedly more important than the number of food sources available to the animals, and is a better contender as the reason for "obesity by choice".

Fruit juice intake predicts increased adiposity gain in children from low-income families: weight status-by-environment interaction

OBJECTIVE

Our goal was to test the hypothesis that increased fruit juice intake and parental restriction of children's eating are associated with increased adiposity gain and whether exposure to nutritional counseling predicted reduced adiposity gain among children.

PATIENTS AND METHODS

A sample of parents or guardians of children aged 1 to 4 years who attended 1 of 49 Special Supplemental Nutrition Program for Women, Infants, and Children agencies in New York State were surveyed in 1999 or 2000 (N = 2801). The survey addressed children's dietary intake, parental feeding practices, and parental exposure to nutritional counseling messages to increase fruit, vegetable, and low-fat milk intakes. Each child's height and weight were measured approximately every 6 months for up to 48 months. A prospective cohort design was used in which survey variables were the predictors and the outcome was change in children's adiposity, defined as change in age- and gender-standardized BMI per month (ie, BMI z-score slope).

RESULTS

Controlling for gender and ethnicity, the relationship between juice intake and adiposity gain depended on children's initial overweight status. Among children who were initially either at risk for overweight or overweight, increased fruit juice intake was associated with excess adiposity gain, whereas parental offerings of whole fruits were associated with reduced adiposity gain. Each additional daily serving of fruit juice was associated with an excess adiposity gain of 0.009 SD per month. Feeding restriction was greater among parents whose children were initially at risk for overweight or overweight compared with those at a healthy weight. Parental exposure to nutritional messages was not associated with reduced child adiposity gain.

CONCLUSION

This study supports the Institute of Medicine recommendations to reduce fruit juice intake as a strategy for overweight prevention in high-risk children.

Feeding response of rats to no-fat and high-fat cakes

The nutritional effects of high-fat diets have been extensively studied in laboratory animals, but as yet few experiments have examined the feeding response of animals to newly developed fat substitutes. The present study used commercially available no-fat (0% fat, 92% carbohydrate) and high-fat (41% fat, 54% carbohydrate) cake to determine the effects of fat substitutes on food preference and caloric intake in rats. The first experiment showed that nondeprived rats found the high-fat and no-fat cakes equally palatable and highly preferred to lab chow. Food deprived rats, however, preferred the high-fat cake to the no-fat cake, which may be related to its higher caloric density. In the second experiment, rats fed high-fat cake, in addition to chow, for 30 days consumed more calories and gained more weight than did rats fed no-fat cake and chow. The no-fat cake group, however, overate and gained more weight than chow-only controls. The hyperphagic response to the no-fat cake can be attributed to its carbohydrate content, moisture, and high palatability. Thus, removing fat from the cake reduced, but did not eliminate, its obesity-promoting effect. Obviously, low-fat foods must be consumed in moderation if used for weight control.

Effect of high sucrose feeding on fat accumulation in the male Wistar rat

High sucrose intake is generally thought to be a risk factor for obesity and insulin resistance. We examined the effects of feeding sucrose on fat accumulation and insulin release in male rats. Six-week-old male Wistar rats were maintained on a high sucrose diet for 4 or 12 weeks. Control rats were fed a diet based on starch. No significant difference in daily caloric intake or weight gain existed between the two dietary groups. There was no difference between the two dietary groups in the gain of abdominal subcutaneous fat (SC) at 4-week. In contrast, rats fed the high sucrose diet had significantly more mesenteric fat (MES) than controls (p < 0.01). At 12 weeks, rats fed the high sucrose diet had significantly more SC and MES than controls (SC: p < 0.05, MES: p < 0.01). Basal immunoreactive insulin (IRI) concentrations in the portal vein (PV) of rats fed the high sucrose diet was significantly higher compared to those of controls (4 wk: p < 0.05, 12 wk: p < 0.05). No difference between the two dietary groups in basal IRI concentrations in the inferior vena cava (IVC) existed at 4 weeks; whereas at 12 weeks, the basal IRI concentrations in the IVC in rats fed the high sucrose diet were significantly higher than in controls (p < 0.05). The mesenteric and subcutaneous fat accumulations were closely related to hyperinsulinemia in the portal vein and inferior vena cava, respectively. Twelve weeks of high sucrose feeding caused accumulation of abdominal adipose tissue with marked hyperinsulinemia and hyperlipidemia. Our study is the first to demonstrate that abdominal fat induced by high sucrose intake in male rats is accompanied by an abnormal metabolic state similar to an insulin-resistant state.

Primary school teachers' beliefs and advice to parents concerning sugar consumption and activity in children

The available body of scientific evidence does not support the notion that sugar consumption has significant adverse effects on children's behaviours; however, responses to a mailed questionnaire indicated that more than 80% of 389 Canadian primary school teachers believed that sugar consumption contributes to increasing activity of normal children and to the behavioural problems of hyperactive children. Moreover, in the previous three years, 55% of all respondents had counselled the parents of children whom they believed to be hyperactive to consider reducing their child's sugar consumption to control the child's activity, and parents frequently did so. These results indicate that teachers need to be provided with accurate and up-to-date information about the effects of sugar on children's behaviour and about effective treatments for hyperactivity. Possible origins of beliefs about the reputed adverse behavioural effects of sugar and about factors that may serve to perpetuate these beliefs are discussed.

Dietary sucrose supplementation fails to modify fat deposition in lean or obese rats

The effects of sucrose supplementation on body composition and heat production were studied in lean, dietary (cafeteria diet) and genetically (Zucker fa/fa) obese adult (60 days) rats. Sucrose supplement (29 kJ) for 10 days did not result in significant changes in the pattern of energy (fat) deposition or carcass composition. There were no alterations, either, in heat production measured by direct calorimetry. Under the conditions studied, sucrose intake did not affect lipid deposition or thermogenesis.

High-fat diets stimulate transient hyperphagia whereas wet diets stimulate prolonged hyperphagia in Fischer rats

The effectiveness of several different kinds of diets in stimulating hyperphagia in Fischer strain rats was compared. Of three different high-fat diets examined, only one stimulated significant hyperphagia and stimulated weight gain; this diet was high in both fat and carbohydrate. However, this hyperphagia and increased weight gain was transient, lasting less than four weeks. A high-sucrose diet stimulated energy intake for only one week. In contrast, adding water to a high-starch diet or adding saccharin to a wet diet stimulated energy intake and weight gain for at least ten weeks. Once water or saccharin were removed from these diets, hyperphagia subsided or even turned into hypophagia, until body weights approached control levels. The degree of hyperphagia during the first week did not correlate with subsequent hyperphagia or weight gain. These results suggest that wet diets act by different mechanisms than do dry high-fat and high-sucrose diets.

Effect of the physical state of a food on subsequent intake in human subjects

The effect of the physical state of food on further intake was studied. Human subjects were served two experimental foods at lunchtime 1 week apart. In a first experiment, the two-food meals had the same caloric content, weight, volume, composition and temperature but differed only in their physical form (solid or liquid). As compared to the solid meal, the 24-h total caloric intake following the liquid food was higher. This difference could be attributed to cognitive cues from the form of food or to the lack of masticatory movements while ingesting the liquid meal. The last hypothesis was tested in a second experiment. "In which the test-meals appeared absolutely identical to the senses and were composed of a liquid and a solid item; however, the major part of calories was either in the liquid or in the solid part. When most of the calories had to be drunk, the total subsequent caloric intake was higher than when the most of the calories had to be eaten. It seems that calories ingested in a liquid form are not well taken in account and could induce a subsequent overconsumption, at least until satiety was conditioned to the fluid.

Does dietary hyperphagia contradict the lipostatic theory?

It has frequently been suggested that body weight or fat somehow exerts an inhibitory influence on food intake in a way that acts to maintain a stable body weight or fat. The principal evidence supporting this idea is that animals that have been induced to overeat and become overweight by various means, eat less than control rats when they are permitted to eat freely. If the degree of suppression of appetite by overweight is as large as several experiments suggest, then dietary hyperphagia should be self-limiting. Any overeating induced by dietary treatments should disappear after animals become moderately overweight. Animals fed some kinds of hyperhagia-promoting diets do show this pattern. However, animals fed other kinds of diets do not show this pattern, and with most diets, dietary hyperphagia continues for extended periods. This implies that either 1) overweight does not suppress appetite as much as suggested by various authorities, 2) dietary manipulations can override normal regulatory mechanisms, or 3) certain diets induce irreversible changes in body fat that are not evident from changes in body weight.

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.

Drinking saccharin increases food intake and preference--II. Hydrational factors

Rats that drink saccharin solution increase their short-term food intake and develop a preference for flavored food eaten when saccharin is ingested. In this paper, we examined whether these changes in feeding behavior were due to overhydration resulting from drinking hyposmotic saccharin solution. Consistent with this possibility, the short-term food intake of rats was increased by drinking hyposmotic 0.2% saccharin dissolved in water, unaffected by drinking isosmotic 0.9% NaCl, and decreased by drinking 0.2% saccharin dissolved in 0.9% NaCl. In addition, rats showed a sustained increase in saccharin-induced food intake after antidiuretic hormone treatment, which was designed to exacerbate their positive water balance. Less consistent with a hydrational explanation of saccharin-induced feeding was the finding that rats drinking only 2ml 0.2% saccharin solution increased food intake. Also, gastric intubation of similar volumes of water produced a small, transient increase in feeding behavior, which was apparent after the first intubation only and could not be preserved by adding water-contingent flavors to the food. Taken together, these results suggest that the hydrational effects of drinking hyposmotic saccharin solution contribute to, but cannot account for, the increase in food intake. Hydration had no observable influence on the acquisition of flavored food preference.

Dietary hyperphagia and obesity: what causes them?

Diets that cause animals to overeat and become obese have been used in many investigations of obesity. Most of this research, however, has concentrated on the consequences rather than the causes of overeating. Furthermore, in most studies, several nutritional variables were manipulated simultaneously, making cause and effect relationship impossible to disentangle. Consequently, progress has been slow. Diets could alter energy intake by virtue of their effects on oral-sensory, gastrointestinal or postabsorptive effects. Palatability is the most popular oralsensory hypothesis but the empirical basis for this hypothesis is particularly weak. A substantial body of evidence is consistent with the possibility that the osmotic effects of diets in the gastrointestinal tract and metabolic postabsorptive factors may play a major role in dietary hyperphagia and obesity. Suggestions for future research directions are offered.

Sucrose-induced hyperphagia and obesity in rats fed a macronutrient self-selection diet

Adult female rats were allowed to self-select their diet from separate sources of fat, protein, and carbohydrate (starch). Other rats were fed a composite diet that matched the nutrient composition chosen by the self-selecting rats (50% fat, 28% protein, 22% carbohydrate) or a low-fat, high-carbohydrate chow diet. Half of the rats in each diet condition were given access to a 32% sucrose solution for 30 days. Sucrose availability increased total caloric intake (approximately 20%) and body weight gain in all three groups compared to control groups not fed the sucrose solution. The selection animals compensated for their sucrose intake by reducing their fat intake, and to a lesser degree, their starch intake; protein intake was the least affected by sucrose availability. The selection rats consumed less sucrose than the chow-fed rats and displayed a smaller increase in weight, relative to controls, than the chow-fed rats. These differences were attributed to the high-fat intake of the selection animals since similar results were obtained with the rats fed the composite diet. In particular, both the selection and composite diets produced mild obesity in the absence of sucrose. The results demonstrate that sucrose-induced overeating and overweight is not an artifact of restraining the diet choices of rats to a pure sugar and a nutritionally complete diet.

Starch-induced overeating and overweight in rats: influence of starch type and form

In Experiment 1, adult female rats were fed, in addition to chow and water, a carbohydrate source that consisted of pure amylopectin corn starch or hydrolyzed corn starch (Polycose) in either a dry powder form or a hydrated gel form. Over the 30-day test periods, carbohydrate intake, total food intake, and body weight gain were greater with the Polycose than with the amylopectin, and greater with the gel form than with the powder form of the carbohydrates. The amylopectin gel produced overeating and overweight relative to a chow-fed control group, although the effects were less than that obtained with the Polycose gel. In a second experiment, test meals of the carbohydrate gels produced larger postmeal increases in plasma glucose than did the carbohydrate powders. There was no effect of carbohydrate type (amylopectin vs. Polycose) on the plasma glucose response. In Experiment 3, the addition of amylopectin to a Polycose gel reduced carbohydrate and total caloric intake. Both orosensory and postingestive factors may contribute to the differential food intake and body weight gains produced by the different types (Polycose vs. amylopectin) and forms (gel vs. powder) of carbohydrates.

Overeating, overweight and obesity induced by an unpreferred diet

Rats fed diets containing 50-71% added water (liquid diets) eat more energy and gain more weight than rats fed the same diets without added water (solid diets). The present experiments examined the effects of making a liquid diet less palatable. The first experiment examined the effects of sucrose octaacetate on diet preference. Rats, given a choice of a liquid diet containing 0.5% sucrose octaacetate and a plain solid diet, preferred the plain solid diet for three weeks. When the concentration of sucrose octaacetate was reduced to 0.05%, the rats did not show a reliable preference for either the sucrose octaacetate liquid or plain dry diet. In subsequent experiments, each rat was given only one diet at a time. In the second experiment, rats were fed 0.5% sucrose octaacetate liquid diet for three weeks followed by 0.05% sucrose octaacetate liquid diet for another four weeks. The rats fed the sucrose octaacetate liquid diet overate and became obese compared to the rats fed plain solid diet throughout. In the third experiment, rats fed 0.5% sucrose octaacetate liquid diet for six weeks became obese compared to rats fed plain solid diet throughout. Thus, the overeating and obesity induced by liquid diets cannot be attributed solely to their high palatability.

Practical liquid diets for rats: effects on growth

Liquid diets based on the AIN-76 formula are described. The diets employ xanthan gum as a stabilizer. Information is provided on how these diets may be modified to meet the requirements of a particular experiment (e.g., variations in water content, type of protein or carbohydrate or fat, etc.). These diets are superior to widely used diets with regard to nutritional adequacy, cost, ease of preparation, versatility, stability, osmolality, and use of natural ingredients. An experiment is described which compares the effects of feeding rats a solid diet or a liquid diet prepared three different ways. The results confirm that a properly prepared liquid diet can produce overweight and obesity.

Diet texture, moisture and starch type in dietary obesity

A series of experiments demonstrated that the texture of a diet has less effect on growth than does the water content. Rats fed diets containing 50-71% water become obese. On the other hand, diets containing as little as 30% or as much as 75% water failed to increase growth. Varying the concentration of the suspending agent (xanthan gum) from 0.5% to 2% greatly altered the viscosity of liquid diets but had no reliable effect on growth. Diets containing gelatinized starch became semi-solid when water was added but the rats still grew faster when fed the moist rather than the dry gelatinized starch diets. However, feeding a diet containing a very high level of gelatinized starch reduced growth independently of the moisture content. Rats fed a dry powdered diet gained weight at about the same rate as rats fed a pelleted diet. These results indicate that the moisture content of a diet has a major influence on its ability to induce obesity. The type of starch fed to the rats also seems to be an important determinant of growth rate.