Persisting adiposity following chronic consumption of 10% sucrose solution: Strain differences and behavioural effects

Fighting Fire with Fire: Impact of Sugary Diets on Metabolically Deranged Mice

Background/Objectives: There is controversy about the health risks of sugary diets. A recent study reported that chronic consumption of 11% sugar solutions improved glycemic control in lean mice. Based on this finding, we hypothesized that chronic consumption of the same 11% sugar solutions would also improve glycemic control in metabolically deranged mice. Methods: We exposed mice to a high-fat/high-sugar diet for 12 weeks. Then, we switched the mice to a control (i.e., standard chow) or one of four experimental diets for 8 weeks. The experimental diets contained standard chow plus an 11% solution of glucose or high-fructose syrup. The sugar syrups were derived from corn or cellulose. We included the cellulosic syrups because they contain polyphenols, which are thought to promote glycemic control. We measured body weight, adiposity, glucose tolerance, insulinemia, insulin sensitivity, body composition, and avidity for sweeteners. Results: Mice switched to the control diet lost weight, whereas mice switched to the experimental diets remained obese and hyperinsulinemic. Thus, the experimental diets did not cause the mice to regain normal metabolic health. Nevertheless, we observed (i) improvements in glucose tolerance in mice on both the control and experimental diets; (ii) reduced insulinemia and enhanced insulin sensitivity in mice offered the cellulosic syrups; (iii) elevations in cephalic-phase insulin responses in mice on the experimental diets; and (iv) increased avidity for sweeteners in mice on the control but not the experimental diets. Conclusions: Switching metabolically deranged mice to the experimental diets, particularly those with cellulosic sugars, improved glucose tolerance and insulin sensitivity.

An Ecological Validity Model for the Prevention of Obesity: Non-Nutritive Sweetener Consumption in Rats and the Effects of Switching from Sugar-Sweetened to Diet Beverages

Reducing consumption of sugar-sweetened beverages (SSBs) has been encouraged due to its strong association with obesity. In parallel, consumption of “diet” or non-nutritive sweetened (NNS) beverages has significantly increased. This has led to burgeoning numbers of animal studies investigating metabolic consequences of NNS beverage consumption. However, most animal study designs do not reflect the way humans consume NNS drinks, thus reducing translational capacity. The present experiment aimed to find an ecologically valid model of NNS consumption and evidence of metabolic recovery following a switch from sucrose to NNS in female and male Sprague Dawley rats. The main behavioural outcome was consumption of commercially available NNS beverages during preference and acceptance testing, with changes to consumption following chronic sucrose consumption as a secondary outcome. The main metabolic outcome was retroperitoneal fat pad mass at culling, with body weight gain and fasting blood glucose levels (FBGLs) as secondary outcomes. In a two-phase experiment, behavioural tests were performed before and after 4 weeks of ad libitum access to 10% w/v sucrose. During Phase 2, the rats were given ad libitum access to assigned commercial NNS drinks for a further 4 weeks, with controls provided access to water only. FBGLs were measured at the end of Phases 1 and 2. Female and male rats accepted commercially available NNS beverages, although the volumes consumed varied considerably. Following the switch from sucrose to NNS (containing no sucrose), no group difference was observed in retroperitoneal fat mass, body weight change or FBGLs, suggesting both sexes exhibited limited metabolic recovery. These findings demonstrate that an ecologically valid model for NNS consumption can be developed for some commercially available NNS beverages to further enhance translational capacity.

Sex differences in recovery from cognitive and metabolic impairments induced by supplementary sucrose in rats

Consumption of beverages containing around 10% sucrose contributes to worldwide obesity. Studies using rats can increase understanding of the consequences of such consumption. The present experiment aimed to compare male and female rats, first, in terms of cognitive and metabolic impairments produced by excessive intakes of 10% sucrose solution (Stage 1:8 weeks) and, second, with regard to recovery once access to sucrose ceased (Stage 2:4 weeks). All animals had unrestricted access to chow and water throughout. The primary cognitive outcome was performance on a place recognition task. The primary metabolic outcome was retroperitoneal fat pad mass/kg bodyweight at cull, with body weight and glucose tolerance as secondary outcomes. In a 3 × 2 between-subject factorial design the first factor was whether rats had: (1) unlimited access to a 10% sucrose solution and water throughout both stages (Suc-Suc); (2) were switched from sucrose in the 8-week Stage 1 to water only in the 4-week Stage 2 (Suc-Water); or (3) had no access to sucrose in either stage (Water-Water). The second factor was sex. A major metabolic outcome was that of persistent adiposity in both males and females in the Suc-Water condition. As for place recognition, females in the Suc-Suc condition showed greater long-term resistance than males to the impact of excessive sucrose on spatial memory impairment. Overall, few sex differences were found in secondary metabolic outcomes.

Comparable metabolic effects of isocaloric sucrose and glucose solutions in rats

Much of the global increase in sugar intake is attributable to rising consumption of sugar-sweetened beverages (SSBs). Because people compensate poorly for liquid calories, SSB consumption increases total energy intake, raising the risk of harmful metabolic effects in addition to possible effects of sugars per se. Glucose and fructose, the constituent sugars in sucrose, can exert distinct effects on metabolism and also differ in their satiating properties, suggesting that compensation for the calories in these sugars may also vary. In light of claims that the fructose within sucrose is particularly harmful, the present study compared the effects of giving rats access to either a sucrose or an isoenergetic glucose solution. Adult male rats were fed standard chow and water supplemented with 95 ml of 10% glucose (Glucose group; n = 10), 9% sucrose solution (Sucrose group; n = 10) or water only (Control group; n = 10) daily for 7 weeks. Sugar-fed groups had higher total energy intakes than the Control group, but the extent of this incomplete compensation did not vary between Sucrose and Glucose groups. In a short-term compensation test, sugar groups were less sensitive to the effects of a sweet pre-meal, with no differences between the Glucose and Sucrose groups. Relative to water, both sugars reduced insulin sensitivity after 4 weeks on the diets and elevated fat mass at 7 weeks. Results suggest that sucrose and glucose induce comparable metabolic impairments and alter the homeostatic regulation of food intake even under conditions where daily access is capped.

Sugar consumption and behavioural inhibition in the rat

The metabolic effects of sugary drinks have been extensively studied, whereas the effects on psychological processes have received relatively limited attention. Several studies have found that high-sugar diets can produce impaired performance by rats on tests assessing spatial learning and memory. In contrast, despite claims that weakened inhibitory control underlies many sugar-induced deficits, evidence supporting this proposal has been limited. The aim of the present study was to assess the impact of high-sugar diets on response inhibition, as measured by rats' performance on a differential reinforcement of low rates schedule (DRL) in Experiments 1 and 2 and on a Pavlovian discrimination reversal task in Experiment 3. In all three experiments a 30-day diet stage, in which Sugar groups were given unrestricted access to 10% sucrose solution and Control groups had access to water only, was followed by behavioural tests. In Experiment 1 the Sugar group performed poorly on a spatial memory task, but no difference was detected between the performances of the two groups in the DRL test. In Experiment 2 longer DRL training was given and post-diet performance was assessed both before and after access to sugar was withdrawn. Null results were obtained under both conditions. In Experiment 3 rats' performance on a discrimination learned prior to the diet intervention was not affected by the high-sugar diet, but neither was performance once the discrimination was reversed. The implications of these results for understanding of sugar-induced psychological deficits are discussed.

Metabolic effects of intermittent access to caloric or non-caloric sweetened solutions in mice fed a high-caloric diet

Human consumption of obesogenic diets and soft drinks, sweetened with different molecules, is increasing worldwide, and increases the risk of metabolic diseases. We hypothesized that the chronic consumption of caloric (sucrose, high-fructose corn syrup (HFCS), maltodextrin) and non-caloric (sucralose) solutions under 2-hour intermittent access, alongside the consumption of a high-fat high-sucrose diet, would result in differential obesity-associated metabolic abnormalities in mice. Male C57BL/6 mice had ad libitum access to an HFHS diet and to water (water control group). In addition, some mice had access, 2h/day, 5days/week (randomly chosen) for 12weeks, to different solutions: i) a sucrose solution (2.1kJ/ml), ii) an HFCS solution (2.1kJ/ml), iii) a maltodextrin solution (2.1kJ/ml) and a sucralose solution (60mM) (n=15/group). Despite no changes in total caloric intake, 2h-intermittent access to the sucrose, HFCS or maltodextrin solutions led to increased body weight and accumulation of lipids in the liver when compared to the group consuming water only. The HFCS and sucrose solutions induced a higher fat mass in various fat depots, glucose intolerance, increased glucose oxidation at the expense of lipid oxidation, and a lower hypothalamic expression of NPY in the fasted state. HFCS also reduced proopiomelanocortin expression in the hypothalamus. 2h-intermittent access to sucralose did not result in significant changes in body composition, but caused a stronger expression of CART in the hypothalamus. Finally, sucrose intake showed a trend to increase the expression of various receptors in the nucleus accumbens, linked to dopamine, opioid and endocannabinoid signaling. In conclusion, 2h-intermittent access to caloric solutions (especially those sweetened with sucrose and HFCS), but not sucralose, resulted in adverse metabolic consequences in high-fat high-sucrose-fed mice.

Metabolic Effects of Access to Sucrose Drink in Female Rats and Transmission of Some Effects to Their Offspring

The aims of this study were, first, to examine the metabolic consequences for female rats of having unrestricted access to 10% sucrose solution and, second, to test for effects of this dietary intervention on their offspring. In Stage 1 females were mated following a 4-week period in which one group was given the sucrose in addition to their normal chow and a control group was given chow and water only. Sucrose was removed at parturition and the pups monitored until weaning. Despite the development of glucose intolerance in sucrose-fed mothers, no effects were detected on litter size or pup weights. In Stage 2 voluntary activity of offspring was assessed over postnatal days (PND) 51-60 and their glucose tolerance measured at PND89-94. Again no effect of maternal diet was detected. Only male offspring were used in Stage 3, which began when they were 13 weeks old. Four groups were given 10% sucrose solution for 48 days in a 2 x 2 design, in which one factor was maternal diet and the other was whether they were given 2-h access to an activity wheel on alternate days. Higher fasting glucose levels were found in offspring of sugar-fed mothers. Exercise increased insulin sensitivity in these rats but not in offspring of control mothers. Behavioural measures of memory in Stage 3 did not reveal any effects of maternal diet or exercise. Overall, this study suggested that, while providing 10% sucrose solution ad-libitum was sufficient to impair maternal metabolism, the impact of this dietary manipulation on offspring may be revealed only when the offspring's diet is similarly manipulated.

The effect of early-life stress and chronic high-sucrose diet on metabolic outcomes in female rats

Early-life stress affects metabolic outcomes and choice of diet influences the development of metabolic disease. Here we tested the hypothesis that chronic sugar intake exacerbates metabolic deficits induced by early-life stress. Early-life stress was induced in Sprague-Dawley rats using limited nesting material in early lactation (LN, postnatal days 2-9), and siblings were given chow alone or with additional sucrose post weaning (n = 9-17 per group). Female control and LN siblings had unlimited access to either chow plus water, or chow and water plus 25% sucrose solution (Sucrose), from 3-15 weeks of age. Weekly body weight and food intake were measured. Glucose and insulin tolerance were tested at 13 and 14 weeks of age, respectively. Rats were killed at 15 weeks. Hepatic triglyceride and markers of lipid synthesis - fatty acid synthase, acetyl-CoA carboxylase alpha and oxidation - and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (Pgc-1α) were examined. Mediators of hepatic glucocorticoid metabolism, specifically 11-beta hydroxysteroid dehydrogenase-1 (11βHSD-1), 5-α reductase, and glucocorticoid and mineralocorticoid receptor mRNAs were also measured. Sucrose increased caloric intake in both groups, but overall energy intake was not altered by LN exposure. LN exposure had no further impact on sucrose-induced glucose intolerance and increased plasma and liver triglycerides. Hepatic markers of fat synthesis and oxidation were concomitantly activated and 11βHSD-1 mRNA expression was increased by 53% in LN-Sucrose versus Con-Sucrose rats. Adiposity was increased by 26% in LN-Sucrose versus Con-Sucrose rats. Thus, LN exposure had minimal adverse metabolic effects despite high-sugar diet postweaning.

Cognitive and behavioural effects of sugar consumption in rodents. A review

The pronounced global rise in sugar consumption in recent years has been driven largely by increased consumption of sugar-sweetened beverages. Although high sugar intakes are recognised to increase the risk of obesity and related metabolic disturbances, less is known about how sugar might also impair cognition and learned behaviour. This review considers the effects of sugar in rodents on measures of learning and memory, reward processing, anxiety and mood. The parallels between sugar consumption and addictive behaviours are also discussed. The available evidence clearly indicates that sugar consumption can induce cognitive dysfunction. Deficits have been found most consistently on tasks measuring spatial learning and memory. Younger animals appear to be particularly sensitive to the effects of sugar on reward processing, yet results vary according to what reward-related behaviour is assessed. Sugar does not appear to produce long-term effects on anxiety or mood. Importantly, cognitive impairments have been found when intake approximates levels of sugar consumption in people and without changes to weight gain. There remain several caveats when extrapolating from animal models to putative effects of sugar on cognitive function in people. These issues are discussed in conjunction with potential underlying neural mechanisms and directions for future research.