Intramuscular Lipid Research Articles

Recovered insulin response by 2 weeks of leptin administration in high-fat fed rats is associated with restored AS160 activation and decreased reactive lipid accumulation

Leptin is an adipokine that increases fatty acid (FA) oxidation, decreases intramuscular lipid stores, and improves insulin response in skeletal muscle. In an attempt to elucidate the underlying mechanisms by which these metabolic changes occur, we administered leptin (Lep) or saline (Sal) by miniosmotic pumps to rats during the final 2 wk of a 6-wk low-fat (LF) or high-fat (HF) diet. Insulin-stimulated glucose transport was impaired by the HF diet (HF-Sal) but was restored with leptin administration (HF-Lep). This improvement was associated with restored phosphorylation of Akt and AS160 and decreased in reactive lipid species (ceramide, diacylglycerol), known inhibitors of the insulin-signaling cascade. Total muscle citrate synthase (CS) activity was increased by both leptin and HF diet, but was not additive. Leptin increased subsarcolemmal (SS) and intramyofibrillar (IMF) mitochondria CS activity. Total muscle, sarcolemmal, and mitochondrial (SS and IMF) FA transporter (FAT/CD36) protein content was significantly increased with the HF diet, but not altered by leptin. Therefore, the decrease in reactive lipid stores and subsequent improvement in insulin response, secondary to leptin administration in rats fed a HF diet was not due to a decrease in FA transport protein content or altered cellular distribution.

Biohydrogenation intermediates are differentially deposited between polar and neutral intramuscular lipids of lambs

AbstractThe deposition of C18 fatty acids (FA), especially in rumen biohydrogenation intermediates, was studied using 36 lambs fed four diets with graded proportions of sunflower oil (SO) and linseed oil (LO). Lambs were fed one of four diets consisting on dehydrated lucerne with either: 6% SO, 4% SO plus 2% LO, 2% SO plus 4% LO and 6% LO. The profile of C18 FA was greatly affected by replacement of SO with LO in both lipid fractions. In PL, oil replacement led to an extensive substitution of 18:2n‐6 with 18:3n‐3 and cis‐9 18:1, resulting in a fairly constant degree of unsaturation of C18 FA in membrane PL. C18 FA were differentially incorporated in NL and PL. Cis‐isomers like cis‐11; cis‐12; cis‐15 18:1 and cis‐12, cis‐15 18:2 were preferentially incorporated in PL with the exception of cis‐9, cis‐15 18:2. Trans C18 FA, including CLA isomers, were preferentially incorporated in NL with the exception of cis‐11, trans‐13 18:2. The preferential deposition of biohydrogenation derived trans C18 FA, including CLA isomers in NL, suggests that their potential to change membrane FA composition and structure is low.

Systemic Effects of White Adipose Tissue Dysregulation and Obesity‐Related Inflammation

Systemic Effects of White Adipose Tissue Dysregulation and Obesity‐Related Inflammation

Increasing skeletal muscle fatty acid transport protein 1 (FATP1) targets fatty acids to oxidation and does not predispose mice to diet-induced insulin resistance

We examined in skeletal muscle (1) whether fatty acid transport protein (FATP) 1 channels long-chain fatty acid (LCFA) to specific metabolic fates in rats; and (2) whether FATP1-mediated increases in LCFA uptake exacerbate the development of diet-induced insulin resistance in mice. We also examined whether FATP1 is altered in insulin-resistant obese Zucker rats. LCFA uptake, oxidation and triacylglycerol esterification rates were measured in control and Fatp1-transfected soleus muscles to determine FATP1-mediated lipid handling. The effects of FATP1 on insulin sensitivity and triacylglycerol accumulation were determined in high-fat diet-fed wild-type mice and in muscle-specific Fatp1 (also known as Slc27a1) overexpressing transgenic mice driven by the muscle creatine kinase (Mck [also known as Ckm]) promoter. We also examined the relationship between FATP1 and both fatty acid transport and metabolism in insulin-resistant obese Zucker rats. Transient Fatp1 overexpression in soleus muscle increased (p < 0.05) palmitate transport (24%) and oxidation (35%), without altering triacylglycerol esterification or the intrinsic rate of palmitate oxidation in isolated mitochondria. In Mck/Fatp1 animals, Fatp1 mRNA and 15-(p-iodophenyl)-3-R,S-methylpentadecanoic acid uptake in skeletal muscle were upregulated (75%). However, insulin sensitivity and intramuscular triacylglycerol content did not differ between wild-type and Mck/Fatp1 mice following a 16 week high-fat diet. In insulin-resistant obese Zucker rats, LCFA transport and triacylglycerol accumulation were increased (85% and 24%, respectively), but this was not attributable to Fatp1 expression, as neither total cellular nor sarcolemmal FATP1 content were altered. Overexpression of Fatp1 in skeletal muscle increased the rate of LCFA transport and channelled these lipids to oxidation, not to intramuscular lipid accumulation. Therefore, skeletal muscle FATP1 overabundance does not predispose animals to diet-induced insulin resistance.

Effect of trans-fatty acid intake on insulin sensitivity and intramuscular lipids—a randomized trial in overweight postmenopausal women

Intake of industrially produced trans-fatty acids (TFA) has been linked to increased risk of type 2 diabetes mellitus in observational studies. We investigated the causality of this association by examining if a high intake of TFA impairs measures of glucose homeostasis and induces intramuscular lipid deposition in abdominally obese women. In a double-blind, parallel dietary intervention study, 52 healthy but overweight postmenopausal women were randomized to receive either partially hydrogenated soybean oil (15 g/d TFA) or a control oil (mainly oleic and palmitic acid) for 16 weeks. Three markers of glucose homeostasis and 4 markers of lipolysis were derived from glucose, insulin, C-peptide, nonesterified fatty acid, and glycerol concentrations during a 3-hour frequent sampling oral glucose tolerance test. Intramuscular lipids were assessed by magnetic resonance spectroscopy. Forty-nine women completed the study. Insulin sensitivity (assessed by ISI composite), β-cell function (the disposition index), and the metabolic clearance rate of insulin were not significantly affected by the dietary intervention. Neither was the ability of insulin to suppress plasma nonesterified fatty acid and glycerol during oral glucose ingestion nor the intramuscular lipid deposition. In conclusion, high TFA intake did not affect glucose metabolism over 16 weeks in postmenopausal overweight women. A study population with a stronger predisposition to insulin resistance and/or a longer duration of exposure may be required for insulin sensitivity to be affected by intake of industrial TFA.

Changes of Phospholipids in Duck Muscle by Different Heating Methods

We studied the changes in intramuscular phospholipids on boiling and roasting duck meat. Intramuscular lipids were distilled using chloroform and methanol. The phospholipids were separated using solid phase extraction (SPE) and analyzed with high performance liquid chromatography(HPLC). The fatty acid composition of phosphatidylethanolamine (PE) and phosphatidylcholine (PC) was determined using gas chromatography-mass spectroscopy(GC-MS), and the molecular species were analyzed using HPLC-MS. The results showed that the phospholipid content decreased on cooking, and the decrease was greater with roasting. The decrement in PE was greater than that in PC, primarily because the former contains more polyunsaturated fatty acids. The relative polyunsaturated fatty acid content and the PE and PC molecular species with polyunsaturated fatty acids all decreased.

Tenderness and intramuscular lipid of most major muscles from Bos indicus cattle are less than Bos taurus cattle

Introduction In semitropical climates in the United States, Bos indicus breeds of cattle, primarily the Brahman breed, are utilized in crossbreeding programs with Bos taurus cattle to improve productivity by increasing disease and insect resistance, heat tolerance, heterosis, and additive genetic variation. About 25% of the U.S. beef population contains some Bos indicus breeding. Numerous published reports show that tenderness of ribeye and strip loin steaks and marbling are significantly reduced in Bos indicus straightbred or crossbred cattle compared to most Bos taurus breeds. One very large study reported that heritability of tenderness and marbling is around 0.4, making it a positive trait to try to improve through selection. Only one published report has compared tenderness differences between Bos indicus and Bos taurus cattle for more than the ribeye and strip loin (longissimus muscle) and that study showed that other muscles were less tender for Bos indicus cattle. The objectives of our study were: (1) to compare carcass traits between Hereford x Angus crossbred cattle with those containing at least 50% Brahman and Sahiwal inheritance, and (2) to validate Warner-Bratzler shear force of steaks and roasts and proximate composition of 10 different muscles from these cattle.

Abnormal metabolism flexibility in response to high palmitate concentrations in myotubes derived from obese type 2 diabetic patients

Insulin resistance in type 2 diabetes (T2D) is associated with intramuscular lipid (IMCL) accumulation. To determine whether impaired lipid oxidation is involved in IMCL accumulation, we measured expression of genes involved in mitochondrial oxidative metabolism or biogenesis, mitochondrial content and palmitate beta-oxidation before and after palmitate overload (600μM for 16h), in myotubes derived from healthy subjects and obese T2D patients. Mitochondrial gene expression, content and network were not different between groups. Basal palmitate beta-oxidation was not affected in T2D myotubes, whereas after 16h of palmitate pre-treatment, T2D myotubes in contrast to control myotubes, showed an inability to increase palmitate beta-oxidation (p<0.05). Interestingly, acetyl-CoA carboxylase (ACC) phosphorylation was increased with a tendency for statistical significance after palmitate pre-treatment in control myotubes (p=0.06) but not in T2D myotubes which can explain their inability to increase palmitate beta-oxidation after palmitate overload. To determine whether the activation of the AMP activated protein kinase (AMPK)-ACC pathway was able to decrease lipid content in T2D myotubes, cells were treated with AICAR and metformin. These AMPK activators had no effect on ACC and AMPK phosphorylation in T2D myotubes as well as on lipid content, whereas AICAR, but not metformin, increased AMPK phosphorylation in control myotubes. Interestingly, metformin treatment and mitochondrial inhibition by antimycin induced increased lipid content in control myotubes. We conclude that T2D myotubes display an impaired capacity to respond to metabolic stimuli.

Effect of resistance training during hemodialysis on circulating cytokines: a randomized controlled trial

The purpose of this study was to evaluate the effect of a 12-week intradialytic progressive resistance training (PRT) regimen on circulating pro- and anti-inflammatory cytokines. Forty-nine patients (62.6 ± 14.2 years) were recruited from the outpatient hemodialysis unit of the St. George Public Hospital, Sydney, Australia. Patients were randomized to: PRT + usual care (n = 24) or usual care control (n = 25). The PRT group performed two sets of 10 exercises at high intensity using free-weights, 3 times per week for 12 weeks during dialysis, while the control group did not exercise. Tumor necrosis factor-alpha, interleukin-1b, interleukin-6 (IL-6), interleukin-8 (IL-8), interleukin-10, and interleukin-12 were measured in serum before and after the intervention period. Muscle cross-sectional area (CSA), intramuscular lipid, intermuscular adipose tissue, and subcutaneous and total thigh fat, evaluated via computed tomography of the non-dominant mid-thigh, were also collected at both time points. All cytokines were significantly elevated in the total cohort at baseline compared with normative data. There were no cytokine changes over time or between groups (p > 0.05). In secondary analyses pooling the groups, changes in logIL-6 and IL-8 were inversely related to changes subcutaneous thigh fat (p < 0.05) while changes in logIL-6 were also inversely related to changes in thigh muscle CSA, and total thigh fat (p < 0.03). These data suggest that 12 weeks of intradialytic progressive resistance training does not improve circulating pro- and anti-inflammatory markers. Further research is required to elucidate the implications and mechanisms of the relationships between IL-6 and IL-8 and body composition in ESRD.

Can Increased Muscle ROS Scavenging Keep Older Animals Young and Metabolically Fit?

Insulin resistance and lipid accumulation occur with aging, perhaps due to mitochondrial dysfunction. In this issue of Cell Metabolism (Lee et al., 2010), older mice overexpressing mitochondrial targeted catalase had reduced muscle mitochondrial oxidative damage, lower intramuscular lipid, and improved insulin sensitivity, suggesting that enhanced ROS scavenging prevents age-associated mitochondrial impairments and insulin resistance.

Increased Mitochondrial Fatty Acid Oxidation Is Sufficient to Protect Skeletal Muscle Cells from Palmitate-induced Apoptosis

The mechanisms underlying the protective effect of monounsaturated fatty acids (e.g. oleate) against the lipotoxic action of saturated fatty acids (e.g. palmitate) in skeletal muscle cells remain poorly understood. This study aimed to examine the role of mitochondrial long-chain fatty acid (LCFA) oxidation in mediating oleate's protective effect against palmitate-induced lipotoxicity. CPT1 (carnitine palmitoyltransferase 1), which is the key regulatory enzyme of mitochondrial LCFA oxidation, is inhibited by malonyl-CoA, an intermediate of lipogenesis. We showed that expression of a mutant form of CPT1 (CPT1mt), which is active but insensitive to malonyl-CoA inhibition, in C2C12 myotubes led to increased LCFA oxidation flux even in the presence of high concentrations of glucose and insulin. Furthermore, similar to preincubation with oleate, CPT1mt expression protected muscle cells from palmitate-induced apoptosis and insulin resistance by decreasing the content of deleterious palmitate derivates (i.e. diacylglycerols and ceramides). Oleate preincubation exerted its protective effect by two mechanisms: (i) in contrast to CPT1mt expression, oleate preincubation increased the channeling of palmitate toward triglycerides, as a result of enhanced diacylglycerol acyltransferase 2 expression, and (ii) oleate preincubation promoted palmitate oxidation through increasing CPT1 expression and modulating the activities of acetyl-CoA carboxylase and AMP-activated protein kinase. In conclusion, we demonstrated that targeting mitochondrial LCFA oxidation via CPT1mt expression leads to the same protective effect as oleate preincubation, providing strong evidence that redirecting palmitate metabolism toward oxidation is sufficient to protect against palmitate-induced lipotoxicity.

Altered Intramuscular Lipid Metabolism Relates to Diminished Insulin Action in Men, but Not Women, in Progression to Diabetes

Whether sex differences in intramuscular triglyceride (IMTG) metabolism underlie sex differences in the progression to diabetes are unknown. Therefore, the current study examined IMTG concentration and fractional synthesis rate (FSR) in obese men and women with normal glucose tolerance (NGT) vs. those with prediabetes (PD). PD (n = 13 men and 7 women) and NGT (n = 7 men and 12 women) groups were matched for age and anthropometry. Insulin action was quantified using a hyperinsulinemic-euglycemic clamp with infusion of [6,6-(2)H(2)]-glucose. IMTG concentration was measured by gas chromatography/mass spectrometry (GC/MS) and FSR by GC/combustion isotope ratio MS (C-IRMS), from muscle biopsies taken after infusion of [U-(13)C]palmitate during 4 h of rest. In PD men, the metabolic clearance rate (MCR) of glucose was lower during the clamp (4.71 ± 0.77 vs. 8.62 ± 1.26 ml/kg fat-free mass (FFM)/min, P = 0.04; with a trend for lower glucose rate of disappearance (Rd), P = 0.07), in addition to higher IMTG concentration (41.2 ± 5.0 vs. 21.2 ± 3.4 µg/mg dry weight, P ≤ 0.01), lower FSR (0.21 ± 0.03 vs. 0.42 ± 0.06 %/h, P ≤ 0.01), and lower oxidative capacity (P = 0.03) compared to NGT men. In contrast, no difference in Rd, IMTG concentration, or FSR was seen in PD vs. NGT women. Surprisingly, glucose Rd during the clamp was not different between NGT men and women (P = 0.25) despite IMTG concentration being higher (42.6 ± 6.1 vs. 21.2 ± 3.4 µg/mg dry weight, P = 0.03) and FSR being lower (0.23 ± 0.04 vs. 0.42 ± 0.06 %/h, P = 0.02) in women. Alterations in IMTG metabolism relate to diminished insulin action in men, but not women, in the progression toward diabetes.

Study on the flavor contribution of phospholipids and triglycerides to pork

For investigating the flavor contribution of phospholipids and triglycerides to pork, the longissimus muscle of Rongchang (RC) and PIC (bred by PIC Company of England) pig were selectively removed of intramuscular triglycerides or total intramuscular lipids. After cooking, the flavor of different samples was compared by sensory evaluation, gas chromatographymass spectrometry (GC-MS), and electronic nose. The results showed that removing triglycerides had little effect on the aroma of the cooked meat, but when total intramuscular lipids were removed a remarkable difference was observed. The control samples covaried strongly with some lipid-derived products, and the petroleum ether defatted samples also positively related to these compounds, but to a lesser extent, both of them negatively covaried with chloroform-methanol extracted samples which associated with some Maillard reaction products. Moreover the flavor difference between 2 breeds would decrease when triglycerides were removed, and reduce further when phospholipids and triglycerides were removed simultaneously. These results suggested that intramuscular lipids especially phospholipids contributed significantly to pork flavor, the flavor difference between 2 breeds resulted mainly from different intramuscular lipids content and composition.

Age Related Skeletal Muscle Loss Is Associated With Increased Lipid Synthesis Genes And Intramuscular Lipid Storage

Age Related Skeletal Muscle Loss Is Associated With Increased Lipid Synthesis Genes And Intramuscular Lipid Storage

Effects of selection for decreased residual feed intake on composition and quality of fresh pork1

The objectives of this study were to determine the extent to which selection for decreased residual feed intake (RFI) affects pork composition and quality. Pigs from the fifth generation of selection for decreased RFI (select) and a randomly selected line (control) were utilized. Two experiments were conducted. In Exp. 1, barrows (22.6 ± 3.9 kg) from select and control lines were paired based on age and BW. The test was conducted in 8 replicates of pairs for the test period of 6 wk. Calpastatin activity and myosin isoforms profile were determined on samples from the LM. Control barrows were heavier (59.1 vs. 55.0 kg; P < 0.01) at the end of the test period. Calpastatin activity was greater (P < 0.01) in LM of select barrows than control barrows. In Exp. 2, composition and quality of gilts (114 kg) from control and select lines were determined. The model included fixed effects of line, slaughter date, melanocortin-4 receptor (MC4R) genotype, barn group, line × slaughter date, genotype × line interactions, a covariate of off-test BW, and sire, pen, and litter fitted as random effects. The select line (n = 80) had 0.043 kg less (P < 0.05) RFI per day than the control line (n = 89). Loin quality and composition were determined at 2 d postmortem. Desmin degradation was measured at 2 and 7 d postmortem. Purge, cook loss, sensory traits, and star probe texture were measured at 7 to 10 d postmortem on cooked chops. Residual correlations between RFI and composition and quality traits were calculated. Compared with the control line, carcasses from the select line tended to have less (P = 0.09) backfat, greater (P < 0.05) loin depth, and greater (P < 0.05) fat free lean. Loin chops from the select line had less (P < 0.01) intramuscular lipid content than loin chops from control line. Significant residual correlations between RFI and both tenderness (r = 0.24, P < 0.01) and star probe (r = -0.26, P < 0.01) were identified. Selection for decreased RFI has the potential to improve carcass composition with few effects on pH and water-holding capacity. However, decreased RFI could negatively affect tenderness and texture because of decreased lipid content and decreased postmortem protein degradation.

Relationship between proteome changes of Longissimus muscle and intramuscular fat content in finishing pigs fed conjugated linoleic acid

The present experiment was conducted to determine proteome changes in Longissimus muscle of finishing pigs fed conjugated linoleic acid (CLA), in association with alteration of intramuscular fat content. Previously, seventy-two Duroc × Landrace × Large White gilts (approximately 60 kg) had been fed maize–soyabean meal-based diets with 0, 12·5 and 25 g CLA/kg diet. The CLA contained 369·1 mg/g cis-9, trans-11 CLA, 374·6 mg/g trans-10, cis-12 CLA and 53·7 mg/g other isomers. Six pigs per treatment were slaughtered when they reached a body weight of approximately 100 kg. Data published from a previous experiment demonstrated that supplementation with 12·5 or 25 g CLA/kg diet increased intramuscular fat content (P < 0·05). The present study investigated the proteome changes in Longissimus muscle of control and pigs supplemented with 25 g CLA/kg diet. CLA significantly influenced the abundance of proteins related to energy metabolism, fatty acid oxidation and synthesis, amino acid metabolism, defence, transport and other miscellaneous processes (P < 0·05). The increase in intramuscular fat content was positively correlated with the increased abundance of carbonic anhydrase 3 and aspartate aminotransferase (P < 0·05). We suggest that the proteome changes in Longissimus muscle contributed to greater intramuscular lipid content in CLA-supplemented pigs.

Longitudinal Adaptations to Very Low–carbohydrate Weight‐reduction Diet in Obese Rats: Body Composition and Glucose Tolerance

Longitudinal effects of a very low-carbohydrate (VLC) and a calorie-matched high-carbohydrate (HC) weight reduction diet were compared in dietary obese Sprague-Dawley rats exhibiting impaired glucose tolerance and insulin resistance. Obese rats were divided into weight-matched groups: (i) VLC rats consumed an energy-restricted 5% carbohydrate, 60% fat diet for 8 weeks, (ii) HC rats consumed an isocaloric 60% carbohydrate, 15% fat diet, and (iii) HF rats consumed a high-fat diet ad libitum. HC and VLC rats showed similar reductions in body fat and hepatic lipid at the midpoint of the weight-reduction program, indicating effects due to energy deficit. At the end point, however, HC rats showed greater reductions in total and percent body fat, hepatic lipid and intramuscular lipid than did VLC rats, suggesting that diet composition induced changes in the relative efficiencies of the HC and VLC diets over time. HC rats showed marked improvement in glucose tolerance at the midpoint and end point, whereas VLC rats showed no improvement. Impaired glucose tolerance in VLC rats at the end point was due to insulin resistance and an attenuated insulin secretory response. Glucose tolerance in energy-restricted rats correlated negatively with hepatic and intramuscular lipid levels, but not visceral or total fat mass. These findings demonstrate that adaptations to diet composition eventually enabled HC rats to lose more body fat than VLC rats even though energy intakes were equal, and suggest that the elevated levels of hepatic and intramuscular lipid associated with VLC diets might predispose to insulin resistance and impaired glucose tolerance despite weight loss.

Distinct skeletal muscle fiber characteristics and gene expression in diet-sensitive versus diet-resistant obesity

Inter-individual variability in weight gain and loss under energy surfeit and deficit conditions, respectively, are well recognized but poorly understood phenomena. We documented weight loss variability in an intensively supervised clinical weight loss program and assessed skeletal muscle gene expression and phenotypic characteristics related to variable response to a 900 kcal regimen. Matched pairs of healthy, diet-compliant, obese diet-sensitive (ODS) and diet-resistant (ODR) subjects were defined as those in the highest and lowest quintiles for weight loss rate. Physical activity energy expenditure was minimal and comparable. Following program completion and weight stabilization, skeletal muscle biopsies were obtained. Gene expression analysis of rectus femoris and vastus lateralis indicated upregulation of genes and gene sets involved in oxidative phosphorylation and glucose and fatty acid metabolism in ODS compared with ODR. In vastus lateralis, there was a higher proportion of oxidative (type I) fibers in ODS compared with ODR women and lean controls, fiber hypertrophy in ODS compared with ODR women and lean controls, and lower succinate dehydrogenase in oxidative and oxidative-glycolytic fibers in all obese compared with lean subjects. Intramuscular lipid content was generally higher in obese versus lean, and specifically higher in ODS vs. lean women. Altogether, our findings demonstrate differences in muscle gene expression and fiber composition related to clinical weight loss success.

Growth performances, carcasses parameters and meat fatty acid composition of lamb fed green oak acorns (Quercus ilex) based diet.

The aim of this experiment is to compare the effects of diets containing green oak acorns (GO) and barley (BL) on the growth performances, carcasses parameters and the composition in fatty acids of lambs. Two groups of five lambs each were fed, respectively, during 105 days with diets containing 50% of oaks acorns and 50% of barley. At the end of the test, the animals of the two diets expressed comparable body weights and weight gain. A significant difference (P < 0.05) was observed for the thickness of fat cover which is 3 mm for the BL group against 1.6 mm for GO group even if no significant difference was revealed concerning the output with slaughtering. The intramuscular lipids were significantly higher (P < 0.05) in the group of animals fed with GO diet compared to the BL diet (3.88 vs 2.83 g.100-1 g of muscle). Among the saturated fatty acids (SFA), the stearic acid significantly appeared in higher proportion (P < 0.05) in GO diet (20.8 vs 18.1%) whereas the palmitic acid is prevalent in the group of animals fed with the BL diet (25 vs 30%). For the polyunsaturated fatty acid (PUFA), no significant difference was observed between the two groups. The linoleic acid is prevalent among the PUFA of two groups without significant difference. The linolenic acid is higher in the animal fed BL. The n-6: n-3 ratio is higher in the BL group (8.9 vs 7.3). At the end, the low level of incorporation of PUFA in muscle of the lamb because of biohydrogenation, suggests us supplementing the diet by green grass.

Lipid overaccumulation and drastic insulin resistance in adult catch-up growth rats induced by nutrition promotion after undernutrition

This study was designed to explore the metabolic changes resulting from catch-up growth in adult (CUGA) induced by varying degrees of nutrition promotion after undernutrition and to confirm whether these changes are transient or not. The CUGA models were developed on rats refed on intakes of normal chow or high-fat diet after a period of caloric restriction. The growth of the rats measured by body weight and length stagnated during caloric restriction and then rapidly accelerated following refeeding. Catch-up growth in adult resulted in an increase in intramuscular and intrahepatic lipid content, visceral fat deposition, and insulin resistance, which is consistent with a transient rise in food efficiency during the early stage of refeeding. In addition, ectopic lipid deposition, visceral fat accumulation, and insulin resistance were more severe in rats refed the high-fat diet than rats refed the normal chow. These findings suggest that CUGA induced by rapid nutrition promotion could result in persistent lipid overaccumulation (increased visceral fat and ectopic lipid deposition) and drastic systemic insulin resistance. The effects of CUGA on metabolic characteristics are dependent on the type of diet that is used for refeeding, especially on the amount of fat intake.