Effect of Diets Containing Sucrose vs. D‐tagatose in Hypercholesterolemic Mice

Effects of functional sweeteners on the development of the metabolic syndrome and atherosclerosis are unknown. The objective was to compare the effect of dietary carbohydrate in the form of sucrose (SUCR) to D‐tagatose (TAG; an isomer of fructose currently used as a low‐calorie sweetener) on body weight, blood cholesterol concentrations, hyperglycemia, and atherosclerosis in low‐density lipoprotein receptor deficient (LDLr^−/−) mice. LDLr^−/− male and female mice were fed either standard murine diet or a diet enriched with TAG or SUCR as carbohydrate sources for 16 weeks. TAG and SUCR diets contained equivalent amounts (g/kg) of protein, fat, and carbohydrate. We measured food intake, body weight, adipocyte diameter, serum cholesterol and lipoprotein concentrations, and aortic atherosclerosis. Macrophage immunostaining and collagen content were examined in aortic root lesions. CONTROL and TAG‐fed mice exhibited similar energy intake, body weights and blood glucose and insulin concentrations, but SUCR‐fed mice exhibited increased energy intake and became obese and hyperglycemic. Adipocyte diameter increased in female SUCR‐fed mice compared to TAG and CONTROL. Male and female SUCR‐fed mice had increased serum cholesterol and triglyceride concentrations compared to TAG and CONTROL. Atherosclerosis was increased in SUCR‐fed mice of both genders compared to TAG and CONTROL. Lesions from SUCR‐fed mice exhibited pronounced macrophage immunostaining and reductions in collagen content compared to TAG and CONTROL mice. These results demonstrate that in comparison to sucrose, equivalent substitution of TAG as dietary carbohydrate does not result in the same extent of obesity, hyperglycemia, hyperlipidemia, and atherosclerosis.     

Hepatic and adipose tissue lipogenic enzyme mRNA levels are suppressed by high fat diets in the rat

Small changes in lipogenic enzyme activity induced by dietary fats of different composition may, over the long term, have significant impact on the development of obesity. We have investigated the effect of high fat diets (45% of calories as fat) on abundance of mRNA encoding fatty acid synthetase (FAS) and glycerophosphate dehydrogenase (GPDH) in male Sprague-Dawley rats. When caloric intake was equal, the relative amount of hepatic FAS mRNA was greater in rats fed a saturated compared to a polyunsaturated fat diet. This difference could not be attributed to diet-induced changes in plasma insulin concentration. However, both fat diets suppressed hepatic FAS mRNA compared to a sucrose diet. Close correlation between FAS specific activity and the relative amount of mRNA suggested that regulation was mainly at a pre-translational level. Adipose tissue FAS mRNA was suppressed by the two fat diets equally while GPDH mRNA was unaffected by dietary composition. Retroperitoneal fat pads were significantly larger in rats fed saturated compared to those fed polyunsaturated fat for 26 weeks. We concluded that dietary saturated fats fail to suppress hepatic de novo lipogenesis as effectively as polyunsaturated fats, which may have implications for the prevention of obesity in humans.     

Cognitive Performance of G?ttingen Minipigs Is Affected by Diet in a Spatial Hole-Board Discrimination Test

Consumption of a high energy diet, containing high amounts of saturated fat and refined sugar has been associated with impairment of cognitive function in rodents and humans. We sought to contrast the effect of a high fat/cholesterol, low carbohydrate diet and a low fat, high carbohydrate/sucrose diet, relative to a standard low fat, high carbohydrate minipig diet on spatial cognition with regards to working memory and reference memory in 24 male Göttingen minipigs performing in a spatial hole-board discrimination test. We found that both working memory and reference memory were impaired by both diets relative to a standard minipig diet high in carbohydrate, low in fat and sugar. The different diets did not impact levels of brain-derived neurotrophic factor in brain tissue and neither did they affect circulatory inflammation measured by concentrations of C-reactive protein and haptoglobin in serum. However, higher levels of triglycerides were observed for minipigs fed the diets with high fat/cholesterol, low carbohydrate and low fat, high carbohydrate/sucrose compared to minipigs fed a standard minipig diet. This might explain the observed impairments in spatial cognition. These findings suggest that high dietary intake of both fat and sugar may impair spatial cognition which could be relevant for mental functioning in humans.     

Soy protein isolate in the presence of cornstarch reduces body fat gain in rats

The objective of the present study was to determine the combined effects of dietary protein and carbohydrate sources on total body energy and protein and fat gains as well as on plasma insulin and glucose and tissue lipoprotein lipase activity in male Sprague-Dawley rats fed semipurified diets for 28 days. The diets varied in both protein and carbohydrate sources, namely, casein-cornstarch, casein-sucrose, soy protein isolate (SPI)-cornstarch, SPI-sucrose, cod protein-cornstarch, and cod protein-sucrose. When SPI was combined with cornstarch, lower total body energy and fat gains were observed compared with the combination of either casein and sucrose, casein and cornstarch, or SPI and sucrose. Plasma glucose and insulin concentrations in addition to total and metabolizable energy intake and body weight gain were lower in rats fed the SPI-cornstarch diet than in those fed the casein-sucrose diet. Feeding the SPI-cornstarch diet compared with feeding either the casein-cornstarch or the SPI-sucrose diet also caused lower plasma glucose concentrations and a concomitant trend (p = 0.06) to reduced energy intake and body weight gain. Therefore, the reducing effects of the SPI-cornstarch diet compared with the casein-cornstarch, the casein-sucrose, and the SPI-sucrose diets on body energy and fat gains may result from reductions in energy intake and in plasma glucose concentrations.     

High Fat,Low Carbohydrate Diet Limit Fear and Aggression in G?ttingen Minipigs

High fat, low carbohydrate diets have become popular, as short-term studies show that such diets are effective for reducing body weight, and lowering the risk of diabetes and cardiovascular disease. There is growing evidence from both humans and other animals that diet affects behaviour and intake of fat has been linked, positively and negatively, with traits such as exploration, social interaction, anxiety and fear. Animal models with high translational value can help provide relevant and important information in elucidating potential effects of high fat, low carbohydrate diets on human behaviour. Twenty four young, male Göttingen minipigs were fed either a high fat/cholesterol, low carbohydrate diet or a low fat, high carbohydrate/sucrose diet in contrast to a standard low fat, high carbohydrate minipig diet. Spontaneous behaviour was observed through video recordings of home pens and test-related behaviours were recorded during tests involving animal-human contact and reaction towards a novel object. We showed that the minipigs fed a high fat/cholesterol, low carbohydrate diet were less aggressive, showed more non-agonistic social contact and had fewer and less severe skin lesions and were less fearful of a novel object than minipigs fed low fat, high carbohydrate diets. These results found in a porcine model could have important implications for general health and wellbeing of humans and show the potential for using dietary manipulations to reduce aggression in human society.     

Glucose tolerance, lipids, and GLP-1 secretion in JCR:LA-cp rats fed a high protein fiber diet

Background: We have shown that individually, dietary fiber and protein increase secretion of the anorexigenic and insulinotropic hormone, glucagon‐like peptide‐1 (GLP‐1). Objective: Our objective was to combine, in one diet, high levels of fiber and protein to maximize GLP‐1 secretion, improve glucose tolerance, and reduce weight gain. Methods and Procedures: Lean (+/?) and obese (cp/cp) male James C Russell corpulent (JCR:LA‐cp) rats lacking a functional leptin receptor were fed one of four experimental diets (control, high protein (HP), high fiber (HF, prebiotic fiber inulin), or combination (CB)) for 3 weeks. An oral glucose tolerance test (OGTT) was performed to evaluate plasma GLP‐1, insulin and glucose. Plasma lipids and intestinal proglucagon mRNA expression were determined. Results: Energy intake was lower with the HF diet in lean and obese rats. Weight gain did not differ between diets. Higher colonic proglucagon mRNA in lean rats fed a CB diet was associated with higher GLP‐1 secretion during OGTT. The HP diet significantly reduced plasma glucose area under the curve (AUC) during OGTT in obese rats, which reflected both an increased GLP‐1 AUC and higher fasting insulin. Diets containing inulin resulted in the lowest plasma triglyceride and total cholesterol levels. Discussion: Overall, combining HP with HF in the diet increased GLP‐1 secretion in response to oral glucose, but did not improve glucose tolerance or lipid profiles more than the HF diet alone did. We also suggest that glycemic and insulinemic response to prebiotics differ among rat models and future research work should examine their role in improving glucose tolerance in diet‐induced vs. genetic obesity with overt hyperleptinemia.     

Oligofructose Promotes Satiety in Rats Fed a High‐Fat Diet: Involvement of Glucagon‐Like Peptide‐1

Objective: To analyze the putative interest of oligofructose (OFS) in the modulation of food intake after high‐fat diet in rats and to question the relevance of the expression and secretion of intestinal peptides in that context. Research Methods and Procedures: Male Wistar rats were pretreated with standard diet or OFS‐enriched (10%) standard diet for 35 days followed by 15 days of high‐fat diet enriched or not with OFS (10%) treatment. Body weight, food intake, triglycerides, and plasma ghrelin levels were monitored during the treatment. On day 50, rats were food‐deprived 8 hours and anesthetized for blood and intestinal tissue sampling for further proglucagon mRNA, glucagon‐like peptide (GLP)‐1, and GLP‐2 quantification. Results: The addition of OFS in the diet protects against the promotion of energy intake, body weight gain, fat mass development, and serum triglyceride accumulation induced by a high‐fat diet. OFS fermentation leads to an increase in proglucagon mRNA in the cecum and the colon and in GLP‐1 and GLP‐2 contents in the proximal colon, with consequences on the portal concentration of GLP‐1 (increase). A lower ghrelin level is observed only when OFS is added to the standard diet of rats. Discussion: In rats exposed to high‐fat diet, OFS is, thus, able to modulate endogenous production of gut peptides involved in appetite and body weight regulation. Because several approaches are currently used to treat type 2 diabetes and obesity with limited effectiveness, dietary fibers such as OFS, which promote the endogenous production of gut peptides like GLP‐1, could be proposed as interesting nutrients to consider in the management of fat intake and associated metabolic disorders.     

Effect of dietary carbohydrates and copper status on blood pressure of rats

Copper deficiency was induced in rats by feeding diets containing either 62% starch, fructose or glucose deficient in copper for 6 weeks. All copper deficient rats, regardless of the dietary carbohydrate, exhibited decreased ceruloplasmin activity and decreased serum copper concentrations. Rats fed the fructose diet exhibited a more severe copper deficiency as compared to rats fed either starch or glucose. The increased severity of the deficiency was characterized by reduced body weight, serum copper concentration and hematocrit. In all rats fed the copper adequate diets, blood pressure was unaffected by the type of dietary carbohydrate. Significantly reduced systolic blood pressure was evident only in rats fed the fructose diet deficient in copper. When comparing the three carbohydrate diets, the physiological and biochemical lesions induced by copper deprivation could be magnified by feeding fructose.     

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 (TVC) existed at 4 weeks; whereas at 12 weeks, the basal IRI concentrations in the IV C 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.     

Body Fat Accumulation in Zebrafish Is Induced by a Diet Rich in Fat and Reduced by Supplementation with Green Tea Extract

Fat-rich diets not only induce obesity in humans but also make animals obese. Therefore, animals that accumulate body fat in response to a high-fat diet (especially rodents) are commonly used in obesity research. The effect of dietary fat on body fat accumulation is not fully understood in zebrafish, an excellent model of vertebrate lipid metabolism. Here, we explored the effects of dietary fat and green tea extract, which has anti-obesity properties, on body fat accumulation in zebrafish. Adult zebrafish were allocated to four diet groups and over 6 weeks were fed a high-fat diet containing basal diet plus two types of fat or a low-fat diet containing basal diet plus carbohydrate or protein. Another group of adult zebrafish was fed a high-fat diet with or without 5% green tea extract supplementation. Zebrafish fed the high-fat diets had nearly twice the body fat (visceral, subcutaneous, and total fat) volume and body fat volume ratio (body fat volume/body weight) of those fed low-fat diets. There were no differences in body fat accumulation between the two high-fat groups, nor were there any differences between the two low-fat groups. Adding green tea extract to the high-fat diet significantly suppressed body weight, body fat volume, and body fat volume ratio compared with the same diet lacking green tea extract. 3-Hydroxyacyl-coenzyme A dehydrogenase and citrate synthase activity in the liver and skeletal muscle were significantly higher in fish fed the diet supplemented with green tea extract than in those fed the unsupplemented diet. Our results suggest that a diet rich in fat, instead of protein or carbohydrate, induced body fat accumulation in zebrafish with mechanisms that might be similar to those in mammals. Consequently, zebrafish might serve as a good animal model for research into obesity induced by high-fat diets.     

Lipoprotein status in Sprague-Dawley and LA/N-corpulent rats as affected by dietary carbohydrates.

1. To compare the impact of type of carbohydrate, genotype and phenotype on the synthesis and levels of plasma lipoprotein protein. Sprague-Dawley rats and carbohydrate-sensitive LA/N-corpulent (cp) rats were fasted (2 days) and then fed diets containing 54% carbohydrate as either sucrose, fructose or cooked cornstarch for 2 days. 2. The amount of 3H-protein present in the VLDL + chylomicron fraction of Sprague-Dawley rats 2 hr after injection of 3H-leucine was affected by type of dietary carbohydrate: sucrose greater than fructose greater than starch. 3. Obese and lean LA/N-cp rats fed diets containing sucrose or fructose had lower concentrations of HDL protein and higher levels of 3H-protein in VLDL + chylomicron fraction than those fed starch. 4. Obese LA/N-cp rats had more HDL protein and higher levels of 3H-protein in VLDL + chylomicron fraction than their lean littermates.     

Fat Intake Affects Adiposity,Comorbidity Factors,and Energy Metabolism of Sprague‐Dawley Rats

Objective: Childhood obesity is an emerging health problem. This study assesses the effects of three levels of dietary fat (10%, 32%, and 45% measured by kilocalories) on weight gain, body composition, energy metabolism, and comorbidity factors in rats from weaning through maturation. Research Methods and Procedures: The role of dietary fat on the susceptibility to obesity was assessed by feeding diets containing three levels of dietary fat to rats from weaning through 7 months of age. Body composition was analyzed by DXA after 6 and 12 weeks of dietary treatment. Energy metabolism was measured by indirect calorimetry. Results: Energy intake, weight gain, fat mass, and plasma glucose, cholesterol, triglyceride, free fatty acid, leptin, and insulin levels increased dose‐dependently with increased dietary fat. No difference in absolute lean mass among the three groups was observed. Therefore, the differences in weight gain are accounted for primarily by increased fat accretion. Compared with rats that were relatively resistant to obesity when on a 45% fat diet, diet‐induced obesity‐prone rats were in positive energy balance and had an elevated respiratory quotient, indicating a switch in energy substrate use from fat to carbohydrate, which promotes body‐fat accretion. Discussion: Our data support the hypothesis that administration of increasing amount of dietary fat to very young rats enhances susceptibility to diet‐induced obesity and its comorbidities.     

Protein and carbohydrate selection respond to changes in dietary saturated fatty acids but not to changes in essential fatty acids

We previously reported differences in protein and carbohydrate selection patterns in post-weanling rats fed beef tallow or soybean oil-based diets. Two experiments were designed to determine the characteristic of the dietary fat which mediates the selection behavior. For each experiment, dietary fat was 20% (w/w) of diets and fatty acid profiles were obtained by blending fat sources. Rats were randomly assigned to diets (24% protein, 40% carbohydrate) which varied only in fatty acid composition. After 2 weeks, rats selected from 2 diets with the fat composition previously fed, but varying in their protein and carbohydrate composition (55% protein, 4% carbohydrate and 5% protein, 61% carbohydrate). Experiment 1 was designed to test the effect of relative (omega 6: omega 3 ratios of 1 and 20) and absolute (15% or 4% omega 6, 0.7% or 0.2% omega 3) differences in essential fatty acids on macronutrient selection patterns. Differences in dietary essential fatty acids had no effect on energy intake or the proportion of energy consumed as protein and carbohydrate. Experiment 2 examined the effect of differences in the level of saturated fat (3-10% diet (w/w] on protein and carbohydrate selection. Animals selecting from diets with higher levels of saturated fat consumed more energy as protein and less as carbohydrate than rats selecting from diets with lower levels of saturated fat (p less than 0.0001). Regression analysis was used to examine the relationship between percent protein or carbohydrate energy and classes of dietary fat. The strongest relationship existed between percent dietary saturated fat and percent protein or carbohydrate energy (p less than 0.0001). Polyunsaturated:saturated fat ratio was also weakly associated with percent protein and carbohydrate energy (p less than 0.05). Polyunsaturated, monounsaturated, omega 6 and omega 3 fatty acids were not significantly related to percent protein or carbohydrate energy. These results indicated that protein and carbohydrate selection patterns are altered in response to qualitatively different dietary fatty acids, and that the amount of saturated fat in the diet is the important characteristic of dietary fat mediating the behavioral alteration.     

Protein-leverage in mice: the geometry of macronutrient balancing and consequences for fat deposition

Objective: The Protein‐Leverage Hypothesis proposes that humans regulate their intake of macronutrients and that protein intake is prioritized over fat and carbohydrate intake, causing excess energy ingestion when diets contain low %protein. Here we test in a model animal, the mouse: (i) the extent to which intakes of protein and carbohydrate are regulated; (ii) if protein intake has priority over carbohydrates so that unbalanced foods low in %protein leads to increased energy intake; and (iii) how such variations in energy intake are converted into growth and storage. Methods and Procedures: We fed mice one of five isocaloric foods having different protein to carbohydrate composition, or a combination of two of these foods (N = 15). Nutrient intake and corresponding growth in lean body mass and lipid mass were measured. Data were analyzed using a geometric approach for analyzing intake of multiple nutrients. Results: (i) Mice fed different combinations of complementary foods regulated their intake of protein and carbohydrate toward a relatively well‐defined intake target. (ii) When mice were offered diets with fixed protein to carbohydrate ratio, they regulated the intake of protein more strongly than carbohydrate. This protein‐leverage resulted in higher energy consumption when diets had lower %protein and led to increased lipid storage in mice fed the diet containing the lowest %protein. Discussion: Although the protein‐leverage in mice was less than what has been proposed for humans, energy intakes were clearly higher on diets containing low %protein. This result indicates that tight protein regulation can be responsible for excess energy ingestion and higher fat deposition when the diet contains low %protein.     

Influence of dietary fat on the promotion of diethylnitrosamine-induced hepatocarcinogenesis in female rats

The effect of varying the amount and type of dietary fat on the promotion of gamma-glutamyltranspeptidase (GGT)-positive foci and hepatocarcinomas in female rats was studied. In the first study, two-thirds of the rats were first intubated with diethylnitrosamine (DEN, 10 mg/kg) 20 hr after partial hepatectomy; 1 week later, rats were fed one of three purified diets (a low-fat diet similar to the AIN-76 diet, a high saturated fat diet, or a high polyunsaturated fat diet) with or without 0.05% phenobarbital in the diet for 10 months. Increasing the fat level of the diet did not increase the number of GGT-positive foci arising spontaneously or induced by DEN alone. When phenobarbital was present in the diet, feeding the high polyunsaturated fat diet slightly increased the number of GGT-positive foci and the incidence of tumors. The low-fat diet, however, increased the incidence of fatty liver. We therefore reexamined the effect of diet on promotion by phenobarbital, using an additional low-fat diet with cornstarch rather than sucrose as the carbohydrate source. In this experiment, both high-fat diets slightly enhanced the induction of GGT-positive foci; the carbohydrate source had no effect. The incidence of tumors was not affected by diet in this experiment, but the incidence of fatty liver was again enhanced by feeding a diet high in sucrose. We conclude that increasing the fat level of the diet does not promote the development of DEN-initiated GGT-positive foci or carcinomas in female rats. Increasing the dietary fat level, however, may enhance promotion of liver foci by phenobarbital. Finally, increasing the sucrose content of the diet increases the incidence of fatty liver.     

Sucrose counteracts the anti-inflammatory effect of fish oil in adipose tissue and increases obesity development in mice

Background

Polyunsaturated n-3 fatty acids (n-3 PUFAs) are reported to protect against high fat diet-induced obesity and inflammation in adipose tissue. Here we aimed to investigate if the amount of sucrose in the background diet influences the ability of n-3 PUFAs to protect against diet-induced obesity, adipose tissue inflammation and glucose intolerance.

Methodology/Principal Findings

We fed C57BL/6J mice a protein- (casein) or sucrose-based high fat diet supplemented with fish oil or corn oil for 9 weeks. Irrespective of the fatty acid source, mice fed diets rich in sucrose became obese whereas mice fed high protein diets remained lean. Inclusion of sucrose in the diet also counteracted the well-known anti-inflammatory effect of fish oil in adipose tissue, but did not impair the ability of fish oil to prevent accumulation of fat in the liver. Calculation of HOMA-IR indicated that mice fed high levels of proteins remained insulin sensitive, whereas insulin sensitivity was reduced in the obese mice fed sucrose irrespectively of the fat source. We show that a high fat diet decreased glucose tolerance in the mice independently of both obesity and dietary levels of n-3 PUFAs and sucrose. Of note, increasing the protein∶sucrose ratio in high fat diets decreased energy efficiency irrespective of fat source. This was accompanied by increased expression of Ppargc1a (peroxisome proliferator-activated receptor, gamma, coactivator 1 alpha) and increased gluconeogenesis in the fed state.

Conclusions/Significance

The background diet influence the ability of n-3 PUFAs to protect against development of obesity, glucose intolerance and adipose tissue inflammation. High levels of dietary sucrose counteract the anti-inflammatory effect of fish oil in adipose tissue and increases obesity development in mice.     

Very low-carbohydrate versus isocaloric high-carbohydrate diet in dietary obese rats

Objective: The effects of a very low‐carbohydrate (VLC), high‐fat (HF) dietary regimen on metabolic syndrome were compared with those of an isocaloric high‐carbohydrate (HC), low‐fat (LF) regimen in dietary obese rats. Research Methods and Procedures: Male Sprague‐Dawley rats, made obese by 8 weeks ad libitum consumption of an HF diet, developed features of the metabolic syndrome vs. lean control (C) rats, including greater visceral, subcutaneous, and hepatic fat masses, elevated plasma cholesterol levels, impaired glucose tolerance, and fasting and post‐load insulin resistance. Half of the obese rats (VLC) were then fed a popular VLC‐HF diet (Weeks 9 and 10 at 5% and Weeks 11 to 14 at 15% carbohydrate), and one‐half (HC) were pair‐fed an HC‐LF diet (Weeks 9 to 14 at 60% carbohydrate). Results: Energy intakes of pair‐fed VLC and HC rats were less than C rats throughout Weeks 9 to 14. Compared with HC rats, VLC rats exhibited impaired insulin and glycemic responses to an intraperitoneal glucose load at Week 10 and lower plasma triacylglycerol levels but retarded loss of hepatic, retroperitoneal, and total body fat at Week 14. VLC, HC, and C rats no longer differed in body weight, plasma cholesterol, glucose tolerance, or fasting insulin resistance at Week 14. Progressive decreases in fasting insulin resistance in obese groups paralleled concomitant reductions in hepatic, retroperitoneal, and total body fat. Discussion: When energy intake was matched, the VLC‐HF diet provided no advantage in weight loss or in improving those components of the metabolic syndrome induced by dietary obesity and may delay loss of hepatic and visceral fat as compared with an HC‐LF diet.     

Effects of dietary carbohydrate on the development of obesity in heterozygous Zucker rats

Rats carrying one copy of the fa allele are predisposed to diet-induced metabolic disturbances which contribute to hyperinsulinemia, obesity and dyslipidemia. To investigate the role of dietary carbohydrate and fat in the development of these conditions, we fed 6-week old male heterozygous (fa/+) lean rats carbohydrate-free diets containing primarily saturated fat either ad libitum or pair-fed. These diets were compared to standard chow and to a high saturated fat mixed diet containing 10% energy from sucrose for 4 weeks. The carbohydrate-free diet resulted in significantly lower circulating glucose levels compared to all other groups (p = 0.006). Weight gain was negligible in the carbohydrate free groups compared to standard diet and 10% sucrose diet (p = 0.03). This was reflected in energy efficiency which was markedly reduced (90%) in the carbohydrate-free groups compared to the other groups (p = 0.04). Corresponding changes were noted in fat pad mass. The subscapular and epididymal fat pads were increased 42% and 44%, respectively, in animals consuming the 10% sucrose diet compared to all other groups (p < 0.01). Comparable changes in fatty acid synthase (FAS) mRNA were observed in response to the carbohydrate-free diet, which resulted in a 53% decrease in adipocyte FAS mRNA (p < 0.001). Addition of 10% sucrose to the diet completely reversed this effect resulting in a 69% increase in adipocyte FAS mRNA compared to the carbohydrate-free groups (p = 0.01). Similarly, hepatic FAS mRNA was elevated by 51% and 66% in the 10% sucrose and standard diet groups respectively, compared to the carbohydrate-free groups. Therefore, diets that contain minimal carbohydrate may minimize net lipid storage and adiposity.     

Dietary self‐selection and rules of compromise by fifth‐instar Vanessa cardui

We examined dietary self‐selection and rules of compromise for protein (P) and digestible carbohydrate (C) intake by fifth‐instar Vanessa cardui L. (Lepidoptera: Nymphalidae: Nymphalini). We presented six fat‐free diet pairs to larvae in a choice trial to determine the ‘intake target’. In addition, we fed larvae seven fat‐free single diets differing in dietary nutrient ratio in no‐choice trials to determine the rules of compromise they exhibit when constrained to a singular, sub‐optimal dietary source. In choice trials, caterpillars regulated nutrient intake to a ratio of 1 protein to 1.09 carbohydrate (1P:1.09C), exhibiting tighter regulation of protein than of carbohydrate. Furthermore, larvae from different diet pair treatments did not differ in pupal mass or stadium duration. In no‐choice experiments, larvae reduced consumption on increasingly protein‐biased diets and increased consumption on increasingly carbohydrate‐biased diets, relative to a 1P:1C ratio diet. Differences in carbohydrate consumption were much greater between no‐choice treatments than differences in protein consumption. Dietary nutrient ratio affected pupal mass when accounting for initial larval mass. Pupal mass decreased as nutrient ratio was shifted off of 1P:1C, but to a greater extent when the ratio was skewed toward carbohydrate. Stadium duration increased as nutrient ratio diverged from 1P:1C, being more pronounced when shifted toward carbohydrate than toward protein. Regulation to near 1P:1C is consistent with results found for other Lepidoptera, and the rule of compromise exhibited by V. cardui is consistent with that expected for a generalist herbivore.