Short-term food restriction followed by controlled refeeding promotes gorging behavior, enhances fat deposition, and diminishes insulin sensitivity in mice

Replacement of dietary carbohydrate with protein increases fat mass and reduces hepatic triglyceride synthesis and content in female obese Zucker rats

Previous studies have demonstrated both energy restriction (ER) and higher protein (HP), lower carbohydrate (LC) diets downregulate hepatic de novo lipogenesis. Little is known about the independent and combined impact of ER and HP/LC diets on tissue-specific lipid kinetics in leptin receptor-deficient, obese rodents. This study investigated the effects of ER and dietary macronutrient content on body composition; hepatic, subcutaneous adipose tissue (SAT), and visceral AT (VAT) lipid metabolic flux (2 H2 O-labeling); and blood and liver measures of cardiometabolic health in six-week-old female obese Zucker rats (Leprfa+/fa+ ). Animals were randomized to a 10-week feeding intervention: ad libitum (AL)-HC/LP (76% carbohydrate/15% protein), AL-HP/LC (35% protein/56% carbohydrate), ER-HC/LP, or ER-HP/LC. ER groups consumed 60% of the feed consumed by AL. AL gained more fat mass than ER (P-energy = 0.012) and HP/LC gained more fat mass than HC/LP (P-diet = 0.025). Hepatic triglyceride (TG) concentrations (P-interaction = 0.0091) and absolute hepatic TG synthesis (P-interaction = 0.012) were lower in ER-HP/LC versus ER-HC/LP. ER had increased hepatic, SAT, and VAT de novo cholesterol fractional synthesis, absolute hepatic cholesterol synthesis, and serum cholesterol (P-energy≤0.0035). A HP/LC diet, independent of energy intake, led to greater gains in fat mass. A HP/LC diet, in the context of ER, led to reductions in absolute hepatic TG synthesis and TG content. However, ER worsened cholesterol metabolism. Increased adipose tissue TG retention with the HP/LC diet may reflect improved lipid storage capacity and be beneficial in this genetic model of obesity.

Fasting increases investment in soma upon refeeding at the cost of gamete quality in zebrafish

Fasting increases lifespan in invertebrates, improves biomarkers of health in vertebrates and is increasingly proposed as a promising route to improve human health. Nevertheless, little is known about how fasted animals use resources upon refeeding, and how such decisions affect putative trade-offs between somatic growth and repair, reproduction and gamete quality. Such fasting-induced trade-offs are based on strong theoretical foundations and have been recently discovered in invertebrates, but the data on vertebrates are lacking. Here, we report that fasted female zebrafish, Danio rerio, increase investment in soma upon refeeding, but it comes at a cost of egg quality. Specifically, an increase in fin regrowth was accompanied by a reduction in 24 h post-fertilization offspring survival. Refed males showed a reduction in sperm velocity and impaired 24 h post-fertilization offspring survival. These findings underscore the necessity of considering the impact on reproduction when assessing evolutionary and biomedical implications of lifespan-extending treatments in females and males and call for careful evaluation of the effects of intermittent fasting on fertilization.

Intermittent fasting: endocrine aspects: A review

The increasing number of overweight and obese people makes the search for new effective ways to reduce body weight extremely urgent. Recently, intermittent fasting has received a lot of attention, as a dietary protocol, presumably effective in reducing body weight. Despite the large number of studies, the effects of intermittent fasting on the human body are controversial, since studies differ in dietary options, design, and often have a small sample size. In this review of the literature, the authors cite the results of studies of the effectiveness of intermittent fasting in patients with obesity, diabetes mellitus, and high risks of developing cardiovascular diseases.

The Impact of Varying Food Availability on Gene Expression in the Liver: Testing the Match-Mismatch Hypothesis

Background

During early phases of life, such as prenatal or early postnatal development and adolescence, an organism's phenotype can be shaped by the environmental conditions it experiences. According to the Match-Mismatch hypothesis (MMH), changes to this environment during later life stages can result in a mismatch between the individual's adaptations and the prevailing environmental conditions. Thus, negative consequences in welfare and health can occur. We aimed to test the MMH in the context of food availability, assuming adolescence as a sensitive period of adaptation.

Methods

We have previously reported a study of the physiological and behavioral effects of match and mismatch conditions of high (ad libitum) and low (90% of ad libitum intake) food availability from adolescence to early adulthood in female C57BL/6J mice (n = 62). Here, we performed RNA-sequencing of the livers of a subset of these animals (n = 16) to test the effects of match and mismatch feeding conditions on the liver transcriptome.

Results

In general, we found no effect of the match-mismatch situations. Contrarily, the amount of food available during early adulthood (low vs. high) drove the differences we observed in final body weight and gene expression in the liver, regardless of the amount of food available to the animals during adolescence. Many of the differentially expressed genes and the corresponding biological processes found to be overrepresented overlapped, implicating common changes in various domains. These included metabolism, homeostasis, cellular responses to diverse stimuli, transport of bile acids and other molecules, cell differentiation, major urinary proteins, and immunity and inflammation.

Conclusions

Our previous and present observations found no support for the MMH in the context of low vs high food availability from adolescence to early adulthood in female C57BL/6J mice. However, even small differences of approximately 10% in food availability during early adulthood resulted in physiological and molecular changes with potential beneficial implications for metabolic diseases.

Increased Adiposity and Reduced Lean Body Mass in Patients with Short Bowel Syndrome

BACKGROUND

Few studies have examined the metabolic consequences of short bowel syndrome (SBS) and its effects on body composition in adults. We hypothesized that body composition of SBS patients is altered compared to a normal age-, race-, and sex-matched population, regardless of parenteral nutrition (PN) dependence.

AIM

To compare the body composition of adult patients with SBS to age-, sex-, and race-matched healthy controls.

METHODS

Twenty patients with SBS underwent body composition analysis using the GE Lunar iDXA scanner. Patients were age-, sex-, and race-matched to controls from the National Health and Nutrition Examination Survey (1999-2004). Mean differences in body mass index, fat-free mass, fat mass, percent body fat, visceral adipose tissue mass and volume, and bone mineral density were measured. Statistical analysis was performed using SAS 9.4 software.

RESULTS

Fifty-five percent of subjects had a history of PN use, and 30% were current PN users. Mean percent body fat for SBS patients was 35.1% compared to 30.9% for healthy controls (p = 0.043). Fat-free mass was reduced in SBS (p = 0.007). Patients with reduced bone mass had a trend toward significantly more years of PN exposure compared to those with normal bone mass (p = 0.094), and a trend toward older age (p = 0.075).

CONCLUSIONS

SBS is associated with increased percent body fat and reduced fat-free mass, suggesting that improved dietary and therapeutic interventions are needed to restore normal metabolic indices and avoid risk of metabolic syndrome in SBS patients.

The impact of varying food availability on health and welfare in mice: Testing the Match-Mismatch hypothesis

During early phases of life, an organism's phenotype can be shaped by the environmental conditions which it experiences. If the conditions change subsequently, the mismatch between the environment in early and later life could have negative effects on the individual's health and welfare. The aim of this study was to systematically test the predictions of this Match-Mismatch hypothesis in laboratory mice. Therefore, female C57BL/6 J mice were exposed to matching or mismatching combinations of low and high food availability in adolescence and early adulthood. A comprehensive analysis of various physiological and behavioral parameters was conducted. No indication of a mismatch effect was found, which might be attributed to the specific ecology of mice. Alternatively, food availability might cause a shaping of the phenotype only during the prenatal or early postnatal development. However, various effects of low vs high food availability were found regarding the individuals' physiology and, to a small extent, their behavior. Low food availability caused higher concentrations of fecal corticosterone metabolites, as well as higher liver and lower spleen weights, suggesting an adaptation of the metabolism to this situation.

Associations of Number of Daily Eating Occasions with Type 2 Diabetes Risk in the Women's Health Initiative Dietary Modification Trial

BACKGROUND

Over 23 million Americans have type 2 diabetes (T2D). Eating habits such as breakfast consumption, time-restricted eating, and limiting daily eating occasions have been explored as behaviors for reducing T2D risk, but prior evidence is inconclusive.

OBJECTIVES

Our objectives were to examine associations between number of daily eating occasions and T2D risk in the Women's Health Initiative Dietary Modification Trial (WHI-DM) and whether associations vary by BMI, age, or race/ethnicity.

METHODS

Participants were postmenopausal women in the WHI-DM who comprised a 4.6% subsample completing 24-h dietary recalls (24HRs) at years 3 and 6 as part of trial adherence activities (n = 2159). Numbers of eating occasions per day were obtained from the year 3 24HRs, and participants were grouped into approximate tertiles as 1-3 (n = 795), 4 (n = 713), and ≥5 (n = 651) daily eating occasions as the exposure. Incident diabetes was self-reported on semiannual questionnaires as the outcome.

RESULTS

Approximately 15% (15.4%, n = 332) of the WHI-DM 24HR cohort reported incident diabetes at follow-up. Cox proportional hazards regression tested associations of eating occasions with T2D adjusted for neighborhood socioeconomic status, BMI, waist circumference, race/ethnicity, family history of T2D, recreational physical activity, Healthy Eating Index-2005, 24HR energy intake, and WHI-DM arm. Compared with women reporting 1-3 meals/d, those consuming 4 meals/d had a T2D HR = 1.38 (95% CI: 1.03, 1.84) without further increases in risk for ≥5 meals/d. In stratified analyses, associations for 4 meals/d compared with 1-3 meals/d were stronger in women with BMI <30.0 kg/m2 (HR = 1.55; 95% CI: 1.00, 2.39) and women aged ≥60 (HR = 1.61; 95% CI: 1.11, 2.33).

CONCLUSIONS

Four meals per day compared with 1-3 meals/d was associated with increased risk of T2D in postmenopausal women, but no dose-response effect was observed for additional eating occasions. Further studies are needed to understand eating occasions in relation to T2D risk.

The suppression effects of feeding and mechanisms in CRF system of animals

CRF system is comprised of 4 homologous lineages, 2 main receptors (CRF-R1 and CRF-R2), and a binding protein CRF-BP. The homologous lineages are corticotropin-releasing factor (CRF), urotensin I (UI)/sauvagine (SVG)/urocortin 1 (UCN1), urocortin 2 (UCN2), and urocortin 3 (UCN3), and UI, SVG, UCN1 are orthologous genes. CRF system genes are widely distributed in the brain and gastrointestinal tract, which may relate to feeding regulation. According the research progress about CRF system on mammals and non-mammals, this paper summarized the discovery, structure, tissue distribution, appetite regulation and mechanism of CRF system in animals, which can provide the reference for further research and production of feeding regulation and growth in mammals and fish species.

Exposure to hot temperatures during lactation stunted offspring growth and decreased the future reproductive performance of female offspring

Among the important aspects of climate change, exposure to high temperatures (heat waves) is rapidly emerging as an important issue, in particular for female mammals during lactation. High temperatures adversely impact ability to dissipate heat, which has negative effects on reproductive output. The cumulative effects on growth of F1 offspring after weaning and future reproductive performance of offspring remain uncertain. In this study, the F1 mice that weaned from mothers lactating at 21°C and 32.5°C were housed at 21°C from day 19 till 56 of age; during which food intake and body mass were measured. The F1 adult females that had been weaned at the two temperatures were bred and then both exposed to 32.5°C during lactation. Energy intake, milk output and litter size and mass were determined. The F1 adults weaned at 32.5°C consumed less food and had lower body mass than their counterparts weaned at 21°C. Several visceral organs or reproductive tissues were significantly lower in mass in F1 weaned at 32.5°C than at 21°C. The exposure to 32.5°C significantly decreased energy intake, milk output and litter mass in F1 adult females during lactation. The F1 adult females weaned at 32.5°C produced less milk and raised lighter pups than those previously weaned at 21°C. The data suggest that transient exposure to hot temperature during lactation has long-lasting impacts on the offspring, including stunted growth and decreases in future reproductive performance when adult. This indicates that the offspring of females previously experiencing hot temperatures have a significant fitness disadvantage.

Progress in understanding the roles of Urocortin3 (UCN3) in the control of appetite from studies using animal models

Urocortin3 (UCN3), the newest member of corticotrophin releasing hormone (CRH) family polypeptides, is an anorexic factor discovered in 2001, which has a strong inhibitory effect on animal appetite regulation. UCN3 is widely distributed in various tissues of animals and has many biological functions. Based on the research progress of UCN3 on mammals and non-mammals, this paper summarized the discovery, tissue distribution, appetite regulation and mechanism of UCN3 in animals, in order to provide a reference for feeding regulation and growth in mammals and fish in further research and production.

Metabolic memory of dietary restriction ameliorates DNA damage and adipocyte size in mouse visceral adipose tissue

Dietary restriction (DR) is thought to exert its beneficial effects on healthspan at least partially by a senolytic and senostatic action, i.e. by reducing frequencies of cells with markers of DNA damage and senescence in multiple tissues. Due to its importance in metabolic and inflammation regulation, fat is a prime tissue for health span determination as well as a prime target for DR. We aimed to determine here whether the beneficial effects of DR would be retained over a subsequent period of ad libitum (AL) feeding. Male mice were kept under either 40% DR or AL feeding regimes from 3 to 12 months of age and then either switched back to the opposite feeding regimen or kept in the same state for another 3 months. Visceral adipose tissue from 4 to 5 mice per group for all conditions was analysed for markers of senescence (adipocyte size, γH2A.X, p16, p21) and inflammation (e.g. IL-6, TNFα, IL-1β) using immuno-staining or qPCR. Macrophages were detected by immunohistochemistry. We found that both 9 and 12 months DR (long term) as well as 3 month (short term, mid-life onset) DR reduced the number of cells harbouring DNA damage and adipocyte size (area and perimeter) in visceral adipocytes with similar efficiency. Importantly, beneficial health markers induced by DR such as small adipocyte size and low DNA damage were maintained for at least 3 month after termination of DR, demonstrating that the previously identified 'metabolic memory' of the DR state in male mice extends to senescence markers in visceral fat.

Restricted feeding for 9h in the active period partially abrogates the detrimental metabolic effects of a Western diet with liquid sugar consumption in mice

BACKGROUND

Obesity is a major public health concern that can result from diets high in fat and sugar, including sugar sweetened beverages. A proposed treatment for dietary-induced obesity is time-restricted feeding (TRF), which restricts consumption of food to specific times of the 24-hour cycle. Although TRF shows great promise to prevent obesity and the development of chronic disease, the effects of TRF to reverse metabolic changes and the development of NAFLD in animal models of a Western diet with sugary water consumption is not known.

OBJECTIVE

The objective of the current study was to evaluate the role of TRF in the treatment of obesity and NAFLD through examination of changes in metabolic and histopathologic parameters.

METHODS

To better understand the role of TRF in the treatment of obesity and NAFLD, we investigated the metabolic phenotype and NAFLD parameters in a mouse model of NAFLD in which obesity and liver steatosis are induced by a Western Diet (WD): a high-fat diet of lard, milkfat and Crisco with sugary drinking water. Mice were subjected to a short-term (4-weeks) and long-term (10-weeks) TRF in which food was restricted to 9h at night.

RESULTS

Prior to TRF treatment, the WD mice had increased body mass, and exhibited less activity, and higher average daytime energy expenditure (EE) than chow fed mice. Approximately 4- and 10-weeks following TFR treatment, WD-TRF had moderate but not statistically significant weight loss compared to WD-ad libitum (WD-AL) mice. There was a modest but significant reduction in the inguinal adipose tissue weight in both WD-TRF groups compared to the WD-AL groups; however, there was no difference in epididymal and retroperitoneal adipose tissue mass or adipocyte size distribution. In contrast, the diet-induced increase in normalized liver tissue weight, hepatic triglyceride, and NAFLD score was partially abrogated in the 4-week WD-TRF mice, while systemic insulin resistance was partially abrogated and glucose intolerance was completely abrogated in the 10-week WD-TRF mice. Importantly, WD-induced metabolic dysfunction (substrate utilization, energy expenditure, and activity) was partially abrogated by 4- and 10-week TRF.

CONCLUSIONS

Our results support the hypothesis that TRF aids in reducing the detrimental metabolic effects of consuming a WD with sugary drinking water but does not ameliorate obesity.

CD4+ T cells memorize obesity and promote weight regain

Body weight regain often causes failure of obesity therapies while the underlying mechanism remains largely unknown. In this study, we report that immune cells, especially CD4+ T cells, mediate the ‘memory’ of previous obese status. In a weight gain-loss-regain model, we found that C57BL/6J mice with an obesity history showed a much faster rate of body weight regain. This obesity memory could last for at least 2 months after previously obese mice were kept at the same body weight as non-obese mice. Surprisingly, such obesity memory was abrogated by dexamethasone treatment, whereas immunodeficient Rag1^−/− and H2A^−/− mice failed to establish such memory. Rag1^−/− mice repossessed the obesity memory when immune cells or CD4+ T cells isolated from previously obese mice were transferred. Furthermore, depletion of CD4+ T cells led to obesity memory ablation. Taken together, we conclude that CD4+ T cells mediate obesity memory and promote weight regain.

Potential Benefits and Harms of Intermittent Energy Restriction and Intermittent Fasting Amongst Obese, Overweight and Normal Weight Subjects-A Narrative Review of Human and Animal Evidence

Intermittent energy restriction (IER) has become popular as a means of weight control amongst people who are overweight and obese, and is also undertaken by normal weight people hoping spells of marked energy restriction will optimise their health. This review summarises randomised comparisons of intermittent and isoenergetic continuous energy restriction for weight loss to manage overweight and obesity. It also summarises the potential beneficial or adverse effects of IER on body composition, adipose stores and metabolic effects from human studies, including studies amongst normal weight subjects and relevant animal experimentation. Six small short term (<6 month) studies amongst overweight or obese individuals indicate that intermittent energy restriction is equal to continuous restriction for weight loss, with one study reporting greater reductions in body fat, and two studies reporting greater reductions in HOMA insulin resistance in response to IER, with no obvious evidence of harm. Studies amongst normal weight subjects and different animal models highlight the potential beneficial and adverse effects of intermittent compared to continuous energy restriction on ectopic and visceral fat stores, adipocyte size, insulin resistance, and metabolic flexibility. The longer term benefits or harms of IER amongst people who are overweight or obese, and particularly amongst normal weight subjects, is not known and is a priority for further investigation.

Plasticity of adipose tissue in response to fasting and refeeding in male mice

Background

Fasting is the most widely prescribed and self-imposed strategy for treating excessive weight gain and obesity, and has been shown to exert a number of beneficial effects. The aim of the present study was to determine the exact role of fasting and subsequent refeeding on fat distribution in mice.

Methods

C57/BL6 mice fasted for 24 to 72 h and were then subjected to refeeding for 72 h. At 24, 48 and 72 h of fasting, and 12, 24, 48 and 72 h of refeeding, the mice were sacrificed, and serum and various adipose tissues were collected. Serum biochemical parameters, adipose tissue masses and histomorphological analysis of different depots were detected. MRNA was isolated from various adipose tissues, and the expressions of thermogenesis, visceral signature and lipid metabolism-related genes were examined. The phenotypes of adipose tissues between juvenile and adult mice subjected to fasting and refeeding were also compared.

Results

Fasting preferentially consumed mesenteric fat mass and decreased the cell size of mesenteric depots; however, refeeding recovered the mass and morphology of inguinal adipose tissues preferentially compared with visceral depots. Thermogenesis-related gene expression in the inguinal WAT and interscapular BAT were suppressed. Mitochondrial biogenesis was affected by fasting in a depot-specific manner. Furthermore, a short period of fasting led to an increase in visceral signature genes (Wt1, Tcf21) in subcutaneous adipose tissue, while the expression of these genes decreased sharply as the fasting time increased. Additionally, lipogenesis-related markers were enhanced to a greater extent greater in subcutaneous depots compared with those in visceral adipose tissues by refeeding. Although similar phenotypic changes in adipose tissue were observed between juvenile mice and adult mice subjected to fasting and refeeding, the alterations appeared earlier and more sensitively in juvenile mice.

Conclusions

Fasting preferentially consumes lipids in visceral adipose tissues, whereas refeeding recovers lipids predominantly in subcutaneous adipose tissues, which indicated the significance of plasticity of adipose organs for fat distribution when subject to food deprivation or refeeding.

Electronic supplementary material

The online version of this article (doi:10.1186/s12986-016-0159-x) contains supplementary material, which is available to authorized users.

Weight restoration on a high carbohydrate refeeding diet promotes rapid weight regain and hepatic lipid accumulation in female anorexic rats

Background

There is currently no standard clinical refeeding diet for the treatment of anorexia nervosa (AN). To provide the most efficacious AN clinical care, it is necessary to define the metabolic effects of current refeeding diets.

Methods

An activity-based model of anorexia nervosa (AN) was used in female rats. AN was induced over 7d by timed access to low fat (LF) diet with free access to a running wheel. Plasma hormones/metabolites and body composition were assessed at baseline, AN diagnosis (day 0), and following 28d of refeeding on LF diet. Energy balance and expenditure were measured via continuous indirect calorimetry on days −3 to +3.

Results

AN induction caused stress as indicated by higher levels of corticosterone versus controls (p < 0.0001). The rate of weight gain during refeeding was higher in AN rats than controls (p = 0.0188), despite lower overall energy intake (p < 0.0001). This was possible due to lower total energy expenditure (TEE) at the time of AN diagnosis which remained significantly lower during the entire refeeding period, driven by markedly lower resting energy expenditure (REE). AN rats exhibited lower lipid accumulation in visceral adipose tissues (VAT) but much higher liver accumulation (62 % higher in AN than control; p < 0.05) while maintaining the same total body weight as controls. It is possible that liver lipid accumulation was caused by overfeeding of carbohydrate suggesting that a lower carbohydrate, higher fat diet may be beneficial during AN treatment. To test whether such a diet would be accepted clinically, we conducted a study in adolescent female AN patients which showed equivalent palatability and acceptability for LF and moderate fat diets. In addition, this diet was feasible to provide clinically during inpatient treatment in this population.

Conclusion

Refeeding a LF diet to restore body weight in female AN rats caused depressed TEE and REE which facilitated rapid regain. However, this weight gain was metabolically unhealthy as it resulted in elevated lipid accumulation in the liver. It is necessary to investigate the use of other diets, such as lower carbohydrate, moderate fat diets, in pre-clinical models to develop the optimal clinical refeeding diets for AN.

Intermittent fasting favored the resolution of Salmonella typhimurium infection in middle-aged BALB/c mice

Intermittent fasting (IF) reportedly increases resistance and intestinal IgA response to Salmonella typhimurium infection in mature mice. The aim of this study was to explore the effect of aging on the aforementioned improved immune response found with IF. Middle-aged male BALB/c mice were submitted to IF or ad libitum (AL) feeding for 40 weeks and then orally infected with S. typhimurium. Thereafter, infected animals were all fed AL (to maximize their viability) until sacrifice on day 7 or 14 post-infection. We evaluated body weight, bacterial load (in feces, Peyer's patches, spleen and liver), total and specific intestinal IgA, lamina propria IgA+ plasma cells, plasma corticosterone, and messenger RNA (mRNA) expression of α-chain, J-chain, and the polymeric immunoglobulin receptor (pIgR) in liver and intestinal mucosa. In comparison with the infected AL counterpart, the infected IF group (long-term IF followed by post-infection AL feeding) generally had lower intestinal and systemic bacterial loads as well as higher total IgA on both post-infection days. Both infected groups showed no differences in corticosterone levels, body weight, or food and caloric intake. The increase in intestinal IgA was associated with enhanced pIgR mRNA expression in the intestine (day 7) and liver. Thus, to maintain body weight and caloric intake, IF elicited metabolic signals that possibly induced the increased hepatic and intestinal pIgR mRNA expression found. The increase in IgA probably resulted from intestinal IgA transcytosis via pIgR. This IgA response along with phagocyte-induced killing of bacteria in systemic organs (not measured) may explain the resolution of the S. typhimurium infection.

17α-Estradiol Alleviates Age-related Metabolic and Inflammatory Dysfunction in Male Mice Without Inducing Feminization

Aging is associated with visceral adiposity, metabolic disorders, and chronic low-grade inflammation. 17α-estradiol (17α-E2), a naturally occurring enantiomer of 17β-estradiol (17β-E2), extends life span in male mice through unresolved mechanisms. We tested whether 17α-E2 could alleviate age-related metabolic dysfunction and inflammation. 17α-E2 reduced body mass, visceral adiposity, and ectopic lipid deposition without decreasing lean mass. These declines were associated with reductions in energy intake due to the activation of hypothalamic anorexigenic pathways and direct effects of 17α-E2 on nutrient-sensing pathways in visceral adipose tissue. 17α-E2 did not alter energy expenditure or excretion. Fasting glucose, insulin, and glycosylated hemoglobin were also reduced by 17α-E2, and hyperinsulinemic-euglycemic clamps revealed improvements in peripheral glucose disposal and hepatic glucose production. Inflammatory mediators in visceral adipose tissue and the circulation were reduced by 17α-E2. 17α-E2 increased AMPKα and reduced mTOR complex 1 activity in visceral adipose tissue but not in liver or quadriceps muscle, which is in contrast to the generalized systemic effects of caloric restriction. These beneficial phenotypic changes occurred in the absence of feminization or cardiac dysfunction, two commonly observed deleterious effects of exogenous estrogen administration. Thus, 17α-E2 holds potential as a novel therapeutic for alleviating age-related metabolic dysfunction through tissue-specific effects.