Effect of the detraining status on high-fat diet induced fat accumulation in the adipose tissue and liver in female rats

The purpose of the present study was to investigate the effects of a high-fat diet (HFD) in previously trained rats that have been detrained for different periods. Two groups of female rats were, first, either treadmill trained for 8 weeks or remained sedentary (Sed). Trained animals, thereafter, remained inactive for 4 weeks (Inact-4 weeks), while fed a standard diet, before being submitted to a high-fat diet (42% kcal of fat) for an additional 2 or 6 weeks. The order was reversed in a 3rd group in which rats were first kept sedentary for 4 weeks before being submitted to the same 8-week training program that ended with the initiation of the HFD (Inact-0 week). Fat accumulation in the mesenteric depot (P<0.05) and in the sum of 3 intra-abdominal (urogenital, retroperitoneal, and mesenteric; P=0.065) tissues in response to the HF feeding was higher in trained rats kept inactive for 4 weeks than in Sed and Inact-0 week animals. Liver triacylglycerol accumulation also showed a tendency to be higher (P<0.07) in Inact-4 weeks than in Inact-0 week rats. These changes were not associated with significant changes in fat cell diameter and number in the mesenteric adipose tissue. When rats in all groups were subdivided into obesity prone (OP) and obesity resistant (OR) on the basis of the change in body weight gain in response to the HFD, liver lipid infiltration was higher (P<0.01) in OP Inact-4 weeks rats than in all other groups. The present results indicate that previously trained rats that have been inactive for a while maintain higher body adiposity in response to a HFD than in freshly inactive and sedentary rats.     

Sex differences in the effects of high-fat feeding on behavior and carcass composition

Male and female Sprague-Dawley rats were fed a high-fat diet (40% by weight) for 11 weeks beginning at 70–80 days of age. At the end of the 11th week, high-fat fed rats of both sexes were significantly heavier than chow-fed controls. All rats were then food deprived and were trained to bar-press in an operant chamber for Noyes pellets. Testing on fixed ratio (FR) schedules started when their body weights reached 85% of pre-deprivation levels and they pressed bar steadily. At the end of operant testing, all rats were refed their previous diet until body weights returned to pre-deprivation levels. The animals were then sacrificed. Fat pads from retroperitoneal, inguinal and gonadal regions were dissected out and cellularity determined. Carcass composition was analyzed by chemical methods. On the operant apparatus, the high-fat fed female rats (F-HF) behaved more like VMH lesioned obese rats, i.e. decreased bar pressing responses when compared with controls. No difference in operant responding was found between males fed high-fat diet and chow. Fat cell number and size were increased in retroperitoneal and inguinal fat pad for rats fed high-fat diet. In gonadal pads, only cell size was increased. Females on the high-fat diet had higher percentages of body fat than males on the high-fat diet. The behavioral difference in F-HF rats could be attributed to their higher adiposity. The results support previously reported findings on the behavior and adipose tissue cellularity of dietary obese rats.     

Early-onset repeated dieting reduces food intake and body weight but not adiposity in dietary-obese female rats.

As dieting behavior and attempts at weight loss are becoming increasingly common in adolescent girls, we wished to determine whether early-onset repeated dieting influenced the development of obesity and its metabolic correlates. Female rats were fed a high-fat diet and subjected to six cycles of dieting and regain, beginning in the peripubertal period. Although dieted rats weighted less than nondieted high-fat fed controls at the completion of the sixth cycle, body composition analysis revealed that the two groups were equally obese. Cumulative caloric intake was less in dieted rats, suggesting that the pattern of consumption promoted by dieting helped to establish the obesity. Resting metabolic rate did not differ between the two groups. These data suggest that although early-onset repeated dieting may result in reduced body weight, the eventual level of adiposity may be unknowingly elevated, potentially leading to long-term health risks.     

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.     

Long-term effects of exogenous leptin on body weight and fat in post-obese female rats.

This study was designed to test the hypothesis that short-term leptin infusion during the post-obese refeeding phase of weight-reduced rats would reduce the rate of weight regain and, as a result, reduce the final body weight and fat content in weight-reduced rats. Ninety-six female Wistar rats were divided into four groups: (1) LFCON (low-fat control) group: Rats in this group were fed the control low-fat (LF) diet ad lib for the entire study period. (2) HFCON (high-fat control) group: Rats in this group were fed the high-fat (HF, 40% fat) diet ad lib for the study period. (3) HFRLP (high-fat fed, weight-reduced, leptin treatment) group: Obese rats in this group were weight-reduced and received leptin infusion for 2 weeks (miniosmotic pumps, 0.5 microg/kg/day) during the post-obese refeeding period. (4) HFRSM (high-fat fed, weight-reduced, sham control) group: Rats in this sham-control group were treated the same as the rats in the HFRLP group with the exception that no leptin was actually infused during the first 2 weeks of refeeding period. The results demonstrated that 2 weeks of leptin treatment during the early refeeding phase did not prevent weight regain in weight-reduced rats, but it significantly reduced body fat content in these rats as compared to ad lib fed obese control rats. One cycle of weight reduction and regain did not alter the body weight and body fat content in HFRSM rats when compared to obese control rats. Therefore, leptin treatment was effective in reducing body fat content in post-obese rats for up to 7 weeks, but the long-term effect of short-term leptin treatment needs to be further examined.     

The effects of exercise modalities on adiposity in obese rats

OBJECTIVE:

The aim of the present study was to evaluate the effect of both swimming and resistance training on tumor necrosis factor-alpha and interleukin-10 expression, adipocyte area and lipid profiles in rats fed a high-fat diet.

METHODS:

The study was conducted over an eight-week period on Wistar adult rats, who were divided into six groups as follows (n = 10 per group): sedentary chow diet, sedentary high-fat diet, swimming plus chow diet, swimming plus high-fat diet, resistance training plus chow diet, and resistance training plus high-fat diet. Rats in the resistance training groups climbed a vertical ladder with weights on their tails once every three days. The swimming groups swam for 60 minutes/day, five days/week.

RESULTS:

The high-fat diet groups had higher body weights, a greater amount of adipose tissue, and higher tumor necrosis factor-alpha expression in the visceral adipose tissue. Furthermore, the high-fat diet promoted a negative change in the lipid profile. In the resistance training high-fat group, the tumor necrosis factor-alpha expression was lower than that in the swimming high-fat and sedentary high-fat groups. Moreover, smaller visceral and retroperitoneal adipocyte areas were found in the resistance training high-fat group than in the sedentary high-fat group. In the swimming high-fat group, the tumor necrosis factor-alpha expression was lower and the epididymal and retroperitoneal adipocyte areas were smaller compared with the sedentary high-fat group.

CONCLUSION:

The results showed that both exercise modalities improved the lipid profile, adiposity and obesity-associated inflammation in rats, suggesting their use as an alternative to control the deleterious effects of a high-fat diet in humans.     

山荷减肥颗粒对饮食诱导肥胖大鼠瘦素、脂联素、抵抗素的影响

目的： 观察山荷减肥颗粒对高脂饮食诱导的肥胖模型大鼠的减肥降脂作用及对脂肪组织脂联素、抵抗素基因表达的影响。方法： 肥胖模型大鼠随机分为山荷减肥颗粒高、中、低剂量3个实验组及高脂对照组、正常组。对给药8周的动物称体重,测体长,计算Lees指数,测定大鼠血清胆固醇（TC）、甘油三酯（TG）、低密度脂蛋白（LDL）及高密度脂蛋白（HDL）的水平,用ELISA法测瘦素水平,用RT-PCR 检测附睾周围脂肪组织脂联素、抵抗素mRNA 表达。结果：山荷减肥颗粒组大鼠体重、Lees指数、脂肪重量、血清TC、TG、LDL水平明显低于高脂组大鼠（P<0.05）,瘦素明显低于高脂模型组（P>0.05）,脂肪组织脂联素、抵抗素mRNA的表达水平明显高于高脂组大鼠（P<0.05）。结论：山荷减肥颗粒对肥胖大鼠具有减肥降脂作用,调整肥胖大鼠脂肪组织瘦素、脂联素、抵抗素mRNA的表达水平,可能是其治疗肥胖的作用机制之一。     

The effects of high-fat diet on the renal structure and morphometric parametric of kidneys in rats

To characterize the kidney in a high-fat-induced obesity model, we examined the renal structure of adult Sprague-Dawley rats fed a control diet or a high-fat diet for 3 months. Ten adult female Sprague-Dawley rats were fed a diet consisting highly of fat (30%) for a period of 3 months. Ten control rats were maintained with standard rat chow. All animals were weighed every 10 days for 3 months. At the end of the experiment, the naso-anal length of the anaesthetized rats was measured to calculate body mass index, and subsequently whole kidneys of intracardially formalin-perfused animals were removed. Quantitative features of the kidney were analysed with the Cavalieri and physical dissector methods applied to serial paraffin sections. Kidney samples were also examined histologically. The body mass indices of the control and treatment groups were 4.528 +/- 0.242 and 5.876 +/- 0.318 kg m(-2), respectively. The difference between the body mass indices of the two groups was statistically significant (P < 0.01, Mann-Whitney U-test), suggesting that the animals fed with a high-fat diet may be overweight. Stereological examination of the kidneys revealed differences in kidney weight, total kidney volume, volume of cortex, medulla, glomeruli, proximal and distal tubules, and numerical density of glomeruli and glomerular height in the treatment group compared with the control group. Light microscopic investigation showed a dilatation in blood vessels and Bowman's space, mononuclear cell infiltration, degeneration in nephrons, including glomerulosclerosis and tubular defects, and an increase in the connective tissue in the kidneys in the treatment group. We concluded that a fatty diet is responsible for the rats' obesity and may lead to renal deformities as a result of histopathological changes such as dilatation, tubular defects, inflammation and connective tissue enlargement of the kidney.     

Chronic stress, energy balance and adiposity in female rats

Stress preferentially increases the consumption of high fat foods in women, suggesting the interaction of these two factors may disproportionately predispose women toward excess weight gain. In the present study, female rats were exposed to a chronic high fat or chow diet and were exposed to 4 weeks of chronic variable stress (CVS) or served as home cage controls. Control females exposed to a high fat diet displayed many symptoms of the metabolic syndrome including increased body weight gain, total and visceral adiposity and insulin and leptin concentrations relative to all groups. However, CVS-high fat, CVS chow and control chow groups had similar body weight gain and caloric efficiency. This finding suggests that CVS increases energy expenditure much more in females exposed to a high fat diet relative to those fed a standard chow diet. The CVS-high fat group had increased adiposity and increased circulating leptin and insulin concentrations, despite the fact that their body weight did not differ from the controls. These results underscore the importance of assessing the degree of adiposity, rather than body weight alone, as an index of overall metabolic health. Overall, the data indicate that in female rats, chronic stress prevents high fat diet related increases in body weight, but does not prevent high fat diet induced increases in adiposity when compared to chow-fed females.     

Hypothalamic knife-cut hyperphagia and obesity in weanling rats

In previous reports weanling female rats fed a high-fat diet had a delayed response to hypothalamic knife cuts. In the present report similar cuts in similar rats fed a standard low fat diet became overweight without delay, suggesting that dietary fat is a critical variable in juvenile onset obesity. Adult rats given knife-cuts comparable to those in the weanlings gained weight far more rapidly and achieved higher weights than did those cut as weanlings, suggesting that appetite modulating axons can develop after weaning. Finally, group vs single housing did not influence the age of onset or the magnitude of knife-cut obesity.     

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

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

Whole-Body Vibration Training Effect on Physical Performance and Obesity in Mice

The purpose of this study was to verify the beneficial effects of whole-body vibration (WBV) training on exercise performance, physical fatigue and obesity in mice with obesity induced by a high-fat diet (HFD). Male C57BL/6 mice were randomly divided into two groups: normal group (n=6), fed standard diet (control), and experimental group (n=18), fed a HFD. After 4-week induction, followed by 6-week WBV of 5 days per week, the 18 obese mice were divided into 3 groups (n=6 per group): HFD with sedentary control (HFD), HFD with WBV at relatively low-intensity (5.6 Hz, 0.13 g) (HFD+VL) or high-intensity (13 Hz, 0.68 g) (HFD+VH). A trend analysis revealed that WBV increased the grip strength in mice. WBV also dose-dependently decreased serum lactate, ammonia and CK levels and increased glucose level after the swimming test. WBV slightly decreased final body weight and dose-dependently decreased weights of epididymal, retroperitoneal and perirenal fat pads and fasting serum levels of alanine aminotransferase, CK, glucose, total cholesterol and triacylglycerol. Therefore, WBV could improve exercise performance and fatigue and prevent fat accumulation and obesity-associated biochemical alterations in obese mice. It may be an effective intervention for health promotion and prevention of HFD-induced obesity.     

Beneficial effects of Ginkgo biloba extract on insulin signaling cascade,dyslipidemia, and body adiposity of diet-induced obese rats

Ginkgo biloba extract (GbE) has been indicated as an efficient medicine for the treatment of diabetes mellitus type 2. It remains unclear if its effects are due to an improvement of the insulin signaling cascade, especially in obese subjects. The aim of the present study was to evaluate the effect of GbE on insulin tolerance, food intake, body adiposity, lipid profile, fasting insulin, and muscle levels of insulin receptor substrate 1 (IRS-1), protein tyrosine phosphatase 1B (PTP-1B), and protein kinase B (Akt), as well as Akt phosphorylation, in diet-induced obese rats. Rats were fed with a high-fat diet (HFD) or a normal fat diet (NFD) for 8 weeks. After that, the HFD group was divided into two groups: rats gavaged with a saline vehicle (HFD+V), and rats gavaged with 500 mg/kg of GbE diluted in the saline vehicle (HFD+Gb). NFD rats were gavaged with the saline vehicle only. At the end of the treatment, the rats were anesthetized, insulin was injected into the portal vein, and after 90s, the gastrocnemius muscle was removed. The quantification of IRS-1, Akt, and Akt phosphorylation was performed using Western blotting. Serum levels of fasting insulin and glucose, triacylglycerols and total cholesterol, and LDL and HDL fractions were measured. An insulin tolerance test was also performed. Ingestion of a hyperlipidic diet promoted loss of insulin sensitivity and also resulted in a significant increase in body adiposity, plasma triacylglycerol, and glucose levels. In addition, GbE treatment significantly reduced food intake and body adiposity while it protected against hyperglycemia and dyslipidemia in diet-induced obesity rats. It also enhanced insulin sensitivity in comparison to HFD+V rats, while it restored insulin-induced Akt phosphorylation, increased IRS-1, and reduced PTP-1B levels in gastrocnemius muscle. The present findings suggest that G. biloba might be efficient in preventing and treating obesity-induced insulin signaling impairment.     

Ascorbic acid oral treatment modifies lipolytic response and behavioural activity but not glucocorticoid metabolism in cafeteria diet‐fed rats

Aim: To analyse the effects of vitamin C (VC), a potent dietary antioxidant, oral supplementation on body weight gain, behavioural activity, lipolytic response and glucocorticoid metabolism in the early stages of diet‐induced overweight in rats. Methods: Food intake, locomotive activity and faecal corticosterone were assessed during the 14 day trial period. After 2 weeks, the animals were sacrificed and the body composition, biochemical markers and lipolytic response from isolated adipocytes from retroperitoneal white adipose tissue were examined. Results: The intake of a high‐fat diet by rats induced a significant increase in body weight, adiposity and insulin resistance markers as well as a decrease in faecal corticosterone levels compared with standard diet‐fed rats. Interestingly, the animals fed on the cafeteria diet showed a significant increase in the isoproterenol‐induced lipolytic response in isolated adipocytes. Furthermore, this cafeteria‐fed group showed a reduced locomotive behaviour than the control rats. On the other hand, oral VC supplementation in animals receiving the high‐fat diet restored the cafeteria diet effect in some of the analysed variables such as final body weight and plasma insulin to control group levels. Remarkably, increases in locomotive behaviour and a significant decrease in the lipolytic response induced by isoproterenol on isolated adipocytes from animals treated with VC were observed. Conclusion: This work demonstrates that an oral ascorbic acid supplementation has direct effects on behavioural activity and on adipocyte lipolysis in early obesity stages in rats, which could indicate a protective short‐term role of this vitamin against adiposity induced by chronic high‐fat diet consumption.     

Abdominal adiposity, insulin and bone quality in young male rats fed a high-fat diet containing soybean or canola oil

OBJECTIVES:

A low ratio of omega-6/omega-3 polyunsaturated fatty acids is associated with healthy bone properties. However, fatty diets can induce obesity. Our objective was to evaluate intra-abdominal adiposity, insulin, and bone growth in rats fed a high-fat diet containing low ratios of omega-6/omega-3 provided in canola oil.

METHODS:

After weaning, rats were grouped and fed either a control diet (7S), a high-fat diet containing soybean oil (19S) or a high-fat diet of canola oil (19C) until they were 60 days old. Differences were considered to be significant if p<0.05.

RESULTS:

After 60 days, the 19S and 19C groups showed more energy intake, body density growth and intra-abdominal fat mass. However, the 19S group had a higher area (200%) and a lower number (44%) of adipocytes, while the 7S and 19C groups did not differ. The serum concentrations of glucose and insulin and the insulin resistance index were significantly increased in the 19C group (15%, 56%, and 78%, respectively) compared to the 7S group. Bone measurements of the 19S and 19C groups showed a higher femur mass (25%) and a higher lumbar vertebrae mass (11%) and length (5%). Computed tomography analysis revealed more radiodensity in the proximal femoral epiphysis and lumbar vertebrae of 19C group compared to the 7S and 19S groups.

CONCLUSIONS:

Our results suggest that the amount and source of fat used in the diet after weaning increase body growth and fat depots and affect insulin resistance and, consequently, bone health.     

Acute exposure to a high-fat diet alters meal patterns and body composition

Weight gain and adiposity are often attributed to the overconsumption of unbalanced, high-fat diets however, the pattern of consumption can also contribute to associated body weight and compositional changes. The present study explored the rapid alterations in meal patterns of normal-weight rats given continuous access to high-fat diet and examined body weight and composition changes compared to chow fed controls. Ten Long-Evans rats were implanted with subcutaneous microchips for meal pattern analysis. Animals were body weight matched and separated into two groups: high-fat or chow fed. Each group was maintained on their assigned diet for nine days and monitored for 22 h each day for meal pattern behavior. Body weight was evaluated every other day, and body composition measures were taken prior and following diet exposure. High-fat fed animals gained more weight and adipose tissue than chow fed controls and displayed a reduced meal frequency and increased meal size. Furthermore, meal size was significantly correlated with the gain of adipose tissue. Together, these results suggest that consumption of a high-fat diet can rapidly alter meal patterns, which in turn contribute to the development of adiposity.     

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.     

游泳对高脂膳食诱导肥胖和肥胖抵抗模型大鼠的作用

BACKGROUND:The animal model of high fat diet-induced obesity is the first choice for the study of human obesity. Leptin and its receptor expression play an important role in the high fat diet-induced obesity and obesity resistant, but the exact mechanism and the role of swimming are not clear. OBJECTIVE:To explore the effect of 7-week swimming on serum leptin and leptin receptor expression in hypothalamus in rats with high fat diets.  METHODS:A total of 60 Sprague-Dawley rats were fed with high fat diets for 8 weeks. The diet-induced obese and obese resistant rats were selected based on the body weight. 14 obese rats were equally divided into two groups: obese group and obese-exercise group; and 14 obese resistant rats were equally divided into two groups: obese resistant group and obese resistant-exercise group. All the rats were continually given high fat diets. Exercise groups accepted free swimming training for 7 weeks at the same time. RESULTS AND CONCLUSION:Compared with the obese group, obese-exercise group had obviously decreased in body weight, fat pad weight, fat pad weight/body weight and serum leptin concentration. And obese-exercise group had obviously increased receptor mRNA expression in hypothalamus. There was no significant change in above indexes between the obese resistant group and obese resistant-exercise group. The results showed that swimming exercise can increase energy consumption and improve metabolism, which decreased the concentration of leptin and effectively improved leptin receptor expression in the hypothalamus to ease leptin resistance and improve the body’s metabolism.     

Consumption of a high-fat diet alters the homeostatic regulation of energy balance

Humans in many countries are currently experiencing what has been called an epidemic of obesity. That is, the average body weight (and amount of fat stored in the body) is increasing over years, carrying with it a multitude of associated medical, psychological, and economic problems. While there is no shortage of possible causes of this epidemic, increased availability and consumption of high-fat (HF), calorically dense and generally quite palatable food is often touted as a likely culprit. In order to better assess the impact of consuming a diet with those qualities, we have developed a well-controlled animal model in which the effects of chronic consumption of a high-fat diet can be dissociated from those of becoming obese per se. Long-Evans rats are fed one of two semipurified pelleted diets, a HF diet that contains 20% fat by weight and a low-fat (LF) diet that contains 4% fat by weight. Pair-fed animals consume the HF diet but are limited to the daily caloric intake of LF rats. Another group receives pelleted chow. Relative to animals consuming diets low in fat, HF animals weigh more, have more carcass fat, are hyperinsulinemic and hyperleptinemic, and are insulin resistant. HF-fed animals, independent of whether they become obese or not, also have central insulin and MTII insensitivity. Finally, HF rats have a down-regulated hypothalamic apo A-IV system that could contribute to their hyperphagia.     

Photoperiod, but not a high-fat diet, alters body fat in Shaw's jird

Many animal species living in temperate zones show annual body fat cycles. In an apparent regulation of total body fat, species showing naturally occurring decreases in adiposity in the fall (e.g., meadow voles and Siberian hamsters) are resistant to high-fat diet (HFD)-induced obesity in short, "winter-like" days (SDs), and in long, "summer-like" days (LDs) at their peak adiposity. SD-exposed Shaw's jirds (Meriones shawi) show SD-induced decreases in body fat; therefore, we predicted they also would be resistant to HFD-induced obesity. Male jirds were fed a standard chow diet or a HFD, and half of each group was exposed to LDs or SDs. SD-exposed jirds significantly decreased their carcass lipid content and testes mass compared with LD controls, but not body or WAT pad masses. HFD feeding in either photoperiod did not affect any of these measures, nor did it trigger overeating. Thus, it appears disadvantageous for this, and other species, that exhibit body fat peaks in the LDs of summer and nadirs in the SDs of winter, to fatten further or dampen their body fat losses, respectively, whereas species that exhibit body fat nadirs in the LDs of summer and peaks in the SDs of winter do become fat in LDs, and even fatter in SDs, when fed a HFD (e.g., Syrian hamsters). This dichotomous separation of HFD-induced body fat responses to HFD feeding among species showing opposite seasonal lipid mass peaks and nadirs may prove useful in understanding resistance or susceptibility to HFD-induced obesity, especially because they are naturally occurring.