Effects Of Dietary Energy Restriction Research Articles

The effects of dietary energy restriction on overloaded skeletal muscle in rats

We evaluated the effects of three levels of energy intake, 73 % (CON73), 81 % (CON81) and 100 % (CON100) of the ad libitum intake of the control diet, on skeletal muscle growth induced by functional overload in male rats. Unlike most previous studies which have employed chronic or acute food restriction where all nutrients are reduced in the diet, the present study tested the effects of energy deprivation as a single factor without inducing other nutritional deficiencies. Muscular growth of plantaris and soleus muscles was induced by removal of synergist gastrocnemius muscles in one hindlimb; muscles in the other leg were used as sham-operated intra-animal controls. After 30 d, rats on the energy-restricted CON73 and CON81 diets gained less weight and had smaller livers, kidneys, hearts and fat pads (epididymal, retroperitoneal and omental) than CON100 rats They also had smaller sham-operated plantaris muscles (CON73 --13 %, CON81 --9 %) containing less total protein (CON73 --14 %; CON81 --10 %) than CON100 rats However, the same measurements in overloaded plantaris muscles were similar among groups. Soleus muscle mass and protein contents were not significantly affected by energy restriction in our study. Percentage distributions of myosin heavy-chain isoforms (types I, IIa, IIx and IIb) were similar among rats in CON100, CON81 and CON73 groups for both plantaris and soleus muscles. We conclude that the growth reduction of plantaris muscle induced by energy restriction at 73 % and 81 % for 30 d was prevented by functional overload in male rats.

Effect of dietary energy restriction on glucose production and substrate utilization in type 2 diabetes.

A total of 8 obese subjects with type 2 diabetes were studied while on a eucaloric diet and after reduced energy intake (25 and then 75% of requirements for 10 days each). Weight loss was 2, 3, and 3 kg after 5, 10, and 20 days, respectively; all of the weight lost was body fat. Fasting blood glucose (FBG) levels fell from 11.9 +/- 1.4 at baseline to 8.9 +/- 1.6, 7.9 +/- 1.4, and 8.8 +/- 1.3 mmol/l at days 5, 10, and 20, respectively (P < 0.05, baseline vs. 5, 10, and 20 days). Endogenous glucose production (EGP) was 22 +/- 2, 18 +/- 2, 17 +/- 2, and 22 +/- 2 pmol x kg(-1) lean body mass (LBM) x min(-1) (P < 0.05, days 5 and 10 vs. baseline). Gluconeogenesis measured by mass isotopomer distribution analysis provided 31 +/- 4, 41 +/- 5, 40 +/- 4, and 33 +/- 4%, respectively, of the EGP (NS); absolute glycogenolytic contribution to the EGP was 15 +/- 2, 11 +/- 2, 11 +/- 2, and 15 +/- 2 pmol x kg(-1) LBM x min(-1), respectively (P < 0.001, baseline vs. days 5 and 10 and day 10 vs. day 20). The blood glucose clearance rate increased significantly at day 20 (P < 0.05). Neither lipolysis nor flux of plasma nonesterified fatty acids were altered compared with baseline. In conclusion, severe energy restriction per se independent of major changes in body composition reduces both FBG concentration and EGP in type 2 diabetes, the reduction in EGP results entirely from a reduction of glycogenolytic input into blood glucose, and the duration of reduced glycogenolysis is short-lived after relaxation of energy restriction even without weight gain, but effects on plasma glucose clearance persist and partially maintain the improvement in fasting glycemia.

Estrogen‐induced pituitary tumor development in the ACI rat not inhibited by dietary energy restriction

We have demonstrated that a 40% restriction of dietary energy consumption virtually abolishes the development of prolactin (PRL)-producing pituitary tumors in Fischer 344 (F344) rats treated chronically with estrogen, apparently by inhibiting the ability of estrogen to enhance survival within a rapidly proliferating lactotroph population. The purpose of the study reported here was to determine whether energy restriction exerts a similar antitumorigenic action in another rat strain, August×Copenhagen-Irish (ACI), in which PRL-producing pituitary tumors develop in response to estrogen treatment. Ovariectomized female ACI rats were either allowed to consume a control diet ad libitum or were fed a modified diet that restricted energy consumption by 40% relative to the amount of energy consumed by animals fed the control diet. We also examined the ability of 17β-estradiol (E2) administered for 20 wk via subcutaneous Silastic implants to induce development of PRL-producing pituitary tumors. Treatment with E2 increased pituitary weight as well as the pituitary weight–to–body weight ratio and induced gross hyperprolactinemia to the same extent in ACI rats fed either the control or the energy-restricted diet. Moreover, dietary energy restriction did not affect the ability of E2 to induce pituitary cell proliferation or inhibit apoptosis, as evidenced by quantification of two surrogate markers. These data provide compelling evidence that a 40% restriction of energy consumption does not inhibit the ability of E2 to induce pituitary tumor development in the ACI rat. In conjunction with our published studies of the F344 rat strain, the data presented herein indicate that the inhibitory effects of dietary energy restriction on estrogen-induced pituitary tumor development are rat-strain specific and suggest that sensitivity to specific antitumorigenic actions of energy restriction is strongly affected by genetic background. Mol. Carcinog. 26:239–253, 1999. © 1999 Wiley-Liss, Inc.

Estrogen-induced pituitary tumor development in the ACI rat not inhibited by dietary energy restriction

We have demonstrated that a 40% restriction of dietary energy consumption virtually abolishes the development of prolactin (PRL)-producing pituitary tumors in Fischer 344 (F344) rats treated chronically with estrogen, apparently by inhibiting the ability of estrogen to enhance survival within a rapidly proliferating lactotroph population. The purpose of the study reported here was to determine whether energy restriction exerts a similar antitumorigenic action in another rat strain, August x Copenhagen-Irish (ACI), in which PRL-producing pituitary tumors develop in response to estrogen treatment. Ovariectomized female ACI rats were either allowed to consume a control diet ad libitum or were fed a modified diet that restricted energy consumption by 40% relative to the amount of energy consumed by animals fed the control diet. We also examined the ability of 17beta-estradiol (E2) administered for 20 wk via subcutaneous Silastic implants to induce development of PRL-producing pituitary tumors. Treatment with E2 increased pituitary weight as well as the pituitary weight-to-body weight ratio and induced gross hyperprolactinemia to the same extent in ACI rats fed either the control or the energy-restricted diet. Moreover, dietary energy restriction did not affect the ability of E2 to induce pituitary cell proliferation or inhibit apoptosis, as evidenced by quantification of two surrogate markers. These data provide compelling evidence that a 40% restriction of energy consumption does not inhibit the ability of E2 to induce pituitary tumor development in the ACI rat. In conjunction with our published studies of the F344 rat strain, the data presented herein indicate that the inhibitory effects of dietary energy restriction on estrogen-induced pituitary tumor development are rat-strain specific and suggest that sensitivity to specific antitumorigenic actions of energy restriction is strongly affected by genetic background.

A possible role for vitamin C in age-related cataract.

While many experimental studies have shown a protective effect of vitamin C in age-related cataract, other studies have revealed contrasting roles for this nutrient. Oxidative damage in the lens can be prevented by vitamin C. However, a pro-oxidant effect of vitamin C through H2O2 generation has been suggested. Vitamin C has also been shown to play a role in protein glycation, which is observed in cataract formation. A protective effect of dietary energy restriction appears to be inversely related to plasma vitamin C levels in rodents. Moreover, conclusions from human epidemiological and intervention studies are not uniform. The available evidence suggests that maintenance of sufficient plasma vitamin C is needed to prevent oxidative damage in the lens. More research will be needed in order to confirm the relative importance of of the different roles of vitamin C in the eye lens.

Growth hormone secretagogues astherapeutic agents

Growth hormone (GH) treatment increases growth velocity in children with GH deficiency (GHD), ~ and reverses most of the abnormalities observed in adults with GHD. 2 GH treatment has also been found to reduce body fat in obese men, 3 increase muscle mass in men over 60 years of age, 4 and partially reverse the catabolic effects of dietary energy restriction. 5,6 The development of a class of GH secretagogues that includes a nonpeptidyl, oral form 7 has led to the possibility of an alternative to subcutaneous GH injections.

Effect of dietary energy restriction on follicular development and luteal function in nonlactating beef cows.

Twenty nonlactating beef cows were used to determine the effects of dietary energy restriction on ovarian follicular and corpus luteum (CL) development. Cows were fed to either gain (controls) or lose (restricted; RES) body weight. Observations continued until RES cows developed a subfunctional CL (progesterone [P4] < 1.5 ng/mL on d 10 of a cycle; n = 4) or had functional CL (P4 > or = 1.5 ng/mL on d 10 of a cycle; n = 6) followed by anestrus, at which time observations were discontinued on individual controls. Estrous cycles were then standardized for all cows. For RES cows developing subfunctional CL, cycle A was the cycle before development of the subfunctional CL, and cycle B was the 11-d period during development of a subfunctional CL. For RES cows with a functional CL, cycle A was the next to last cycle before anestrus, and cycle B was the 11-d period during formation of a functional CL. Daily P4 concentrations did not differ (P > .10) between controls or RES cows developing functional CL during cycle B but were lower (P < .05) in RES cows developing subfunctional CL. Ovulatory follicles and CL were smaller (P < .05) in RES cows during cycles A and B compared with controls. Daily IGF-l concentrations were higher on d 2 through 4 of both cycles in RES cows developing functional CL compared with RES cows developing subfunctional CL (P < .05). Feeding diets limited in energy resulted in two types of CL. These differences may have been due to IGF-I concentrations.

Effect of Dietary Energy Restriction on the Expression of Insulin-like Growth Factor-I in Liver and Corpus Luteum of Heifers

The effects of energy balance on the corpus luteum may be mediated by IGFI-I. Our objective was to determine whether negative energy balance decreases expression of IGF-I mRNA in the liver or corpus luteum of heifers. For four consecutive estrous cycles, 14 Holstein heifers were maintained in negative or positive energy balance to lose 510 g/d of BW or gain 560 g/d of BW, respectively. The liver was biopsied and the corpus luteum was collected 7 d after fourth estrus. Heifers fed below maintenance had a smaller corpus luteum than did control heifers. Compared with that of controls, negative energy balance increased growth hormone in serum but decreased IGF-I in serum and the abundance of mRNA for growth hormone receptor and IGF-I in liver. In contrast, diet did not affect the abundance of mRNA for the growth hormone receptor or IGF-I in luteal tissue. Negative energy balance increased IGF binding protein-2 in serum but did not affect IGF binding protein-3. We conclude that negative energy balance of cattle decreases IGF-I mRNA abundance in the liver but not in the 7-d corpus luteum. If decreased IGF-I mediates the adverse effect of negative energy balance on luteal growth, the mode of action is likely endocrine, not autocrine or paracrine.

Effect of dietary energy restriction on retention of protein, fat and energy in broiler chickens

1. Broiler chickens were fed 60-100% of recommended energy intakes to study the effects of energy restriction on protein and fat retention. 2. At an energy retention of 179 kJ/kg W0.75 d, only protein was retained. At higher energy intakes, each increment in retention had a rather constant composition: about 85% energy in fat and 15% in protein. At lower energy intakes body fat was mobilised whereas protein was deposited. 3. The efficiencies of energy retention in protein and fat were estimated to be 0.66 and 0.86 respectively. 4. The rather constant composition of additional retained energy after additional energy supply provides an explanation for a linear relationship between energy intake and energy retention.

Effects of energy restriction on age-associated changes of DNA methylation in mouse liver

DNA methylation is known to change with age in several mammalian species. Here we have examined the effect of dietary energy restriction on this age-associated change in liver DNA of C3H/SHN mice. The total 5-methyldeoxycytidine level in the genome decreased slightly soon after energy restriction started. The effect, however, diminished with time and no appreciable difference was detected at middle and old ages. The degree of methylation at the c-myc gene, on the other hand, was not affected by energy restriction at early periods, but the age-dependent alterations at later ages were repressed. This is a new finding to show that DNA methylation is one of the molecular indices of aging affected by energy restriction. It suggests an importance of DNA methylation in the aging process.

Serum hormone and metabolite concentrations in fasted young bulls and steers

The effect of dietary energy restriction on serum insulin, insulin-like growth factor I (IGF-I), growth hormone, (GH), cortisol, plasma urea nitrogen (PUN) and nonesterified fatty acid (NEFA) concentrations was examined. Angus bulls and steers (10 mo) were allotted to two groups of 12 animals and assigned a treatment order. In a switchback design, animals in order 1 were fed a high grain diet, then fasted, while order 2 animals were fasted, and then fed. Animals were allowed 60 hr to acclimate between treatments. Serum and plasma were obtained at 20 min intervals and 60 min, respectively, for 6 hr after feeding and for the last 6 hr of a 30 hr fast. Serum was assayed for insulin, IGF-I, GH, and cortisol (total and free). Plasma was assayed for PUN and NEFA. Mean insulin (ng/ml) differed between fed (.95 ± .08) and fasted (.26 ± .08) animals (P<01). Both mean total and free cortisol (ng/ml) were lower in fed (11.48 ± .99) (1.06 ± .12) than in fasted (17.10 ± .93) (1.62 ± .12) animals, respectively (P<.01). Animals in order 1 differed in mean IGF-I (ng/ml) between fed (199.0 ± 8.0) and fasted (116.5 ± 7.2) treatments (P<.01). Mean IGF-I for animals in order 2 was 146.7 ± 7.2 in fed and 213.9 ± 7.2 in fasted animals (P<.01). Mean GH did not differ between treatments. Mean PUN and NEFA were higher in fasted than in fed animals (P<.01). Except for % free cortisol (P<.05), the hormones did not differ between bulls and steers. The changes in serum hormones and metabolites may reflect an alteration in metabolism which favors muscle and adipose tissue growth during the fed state, and mobilization of energy substrates during the fasted state.

Effect of dietary energy restriction on metabolic and endocrine responses during the estrous cycle of the suckled beef cow.

A replicated trial was conducted with suckled Angus and Polled Hereford cows (110 d postcalving) to determine metabolic and endocrine responses to an energy-restricted diet after cows had re-established postpartum estrous cyclicity. Cows were individually fed 26.5 Mcal ME (H) or 15.2 Mcal ME (L) for a 30-d preliminary period and fitted with an indwelling jugular cannula at synchronized estrus. Average daily weight change during the estrous cycle was .60 +/- .25 and -1.37 +/- .30 kg/d for H and L, respectively (P less than .05). Blood concentrations of cortisol, progesterone and LH during the estrous cycle were not affected by diet, nor did diet affect frequency or amplitude of LH pulses (P greater than .05). No dietary differences were observed for daily concentrations of total protein, glucose, nonesterified fatty acids or acetate. Mean blood concentrations of propionate and butyrate were not different between diets; however, L cows had lower concentrations of propionate and butyrate on d 11 of the cycle (P less than .05). Cows fed L had higher concentrations of blood urea nitrogen (P less than .05), but they had lower concentrations of cholesterol (P less than .05) on d 4, 11, 18 and subsequent estrus (E). Insulin was not different on d 4 and 11; however, cows fed L had lower insulin concentrations on d 18 and d E (P less than .05). Dietary energy restriction in these cyclic cows caused no change in endocrine responses. Of metabolic responses measured, only blood urea nitrogen, cholesterol and insulin showed consistent changes.

Dietary Energy Restriction Decreases Ex Vivo Spleen Prostaglandin E2 Synthesis in Emory Mice

Dietary energy restriction prolongs life-span and enhances immune responsiveness by mechanisms yet to be elucidated. Prostaglandin E2 (PGE2) has a suppressive effect on several parameters of cell-mediated immunity. The effect of energy restriction on splenic PGE2 synthesis in Emory mice was studied. Weanling Emory mice were fed an energy-restricted (R, 71.3 kcal/wk) or control (NR, 90.8 kcal/wk) diet for 11-14 mo. The final weights of R mice were 66% of weights of NR mice (27 +/- 1 vs. 41 +/- 1 g for females and 34 +/- 1 vs. 51 +/- 1 g for males, for R and NR, respectively). NR female mice had higher spleen PGE2 levels than NR male mice (698 +/- 64 vs. 522 +/- 47 ng/mg protein, P = 0.03). In all cases, R mice had less PGE2 than NR mice, and there was no sex-related difference in R mice (418 +/- 39 vs. 698 +/- 64 ng/mg protein in R and NR females, P = 0.001 and 416 +/- 39 vs. 522 +/- 47 ng/mg protein in R and NR males, P = .009). Total spleen PGE2 was also reduced significantly by energy restriction; however, gender differences were not observed in total spleen PGE2 level of NR mice. Thus, 1) spleens from female mice synthesize more PGE2/mg protein than do those from male mice, and 2) dietary energy restriction reduces ex vivo spleen PGE2 synthesis. This phenomenon may contribute to the observed immunostimulatory effect of dietary energy restriction in mice.

Effect of exogenous thyroxine on the interval from weaning to estrus of the primiparous sow.

A total of 159 primiparous sows were fed 0 (C) or 675 mg/d of thyroprotein (TP) from d -2 until d 14 postweaning. Sows received 8 (LE) or 14 (HE) Mcal of ME/d during a 28-d lactation period. Plasma levels of 3,5,3'-triiodothyronine (T3) and 3,5,3',5'-tetraidothyronine (T4) were determined for d -4, -2, 0, 1, 2, 3, 5 and 7 postweaning. Sows consuming LE lost more weight and backfat during lactation (P less than .01) than HE sows. Litters of sows consuming LE gained less weight than litters of sows consuming HE (P less than .01). Thyroprotein increased plasma levels of both T3 and T4 (P less than .01), whereas energy intake had no effect (P greater than .10) on either of the two hormones. The response to thyroid hormone was not consistent across days postweaning (TP x day, P less than .01). Feeding TP increased T4 (P less than .01) on all days, and T3 was increased (P less than .05) on d 0, 2 and 3 postweaning. Thyroid hormones rose markedly following weaning regardless of TP level. Percentage of sows in estrus by d 7 postweaning for LE-C, LE-TP, HE-C and HE-TP were 80, 78, 92 and 90, respectively. Energy restriction during lactation resulted in fewer sows returning to estrus by d 7 (P less than .03) than those fed HE. However, feeding TP postweaning had no effect on return to estrus, suggesting that the effect of dietary energy restriction during lactation on the interval from weaning to first estrus is not mediated through postweaning thyroid hormone concentrations.

Comparative effects of dietary energy restriction in young adult and aged rats on body weight, adipose mass and lipid metabolism

The effects of dietary energy restriction on adipose mass and lipid metabolism were evaluated in young and aged F344 rats. Male rats, 8/group, 15 weeks (YA) or 16 months (AG) old were fed either control diet (C) or diets restricted to 80% or 60% (R-60, R-80) of average daily control intake for 16 weeks. Energy restriction achieved was as intended and intake of all other nutrients was similar in all groups. Body weights (BW) in the R-80 and R-60 groups decreased with increasing energy restriction. Liver and epididymal fat pad (EFP) weights declined with BW and were the lowest in the AG R-60 group; ratio of EFP to BW was also the lowest in the AG R-60 group. Liver to BW ratios were similar in all groups. A parallel loss of EFP lipid and free fatty acids was found in the R-60 group of YA & AG rats, but the greatest loss was in the AG R-60 rats. EFP lipoprotein lipase (LPL)/g tissue declined only in the AG R-60 group, whereas, LPL activity in whole EFP decreased in most restricted groups along with energy restriction. These data suggest that moderate energy restriction can alter adipose lipid metabolism to produce a significant mobilization of lipid from EFP of aged rats and to a lesser extent from young rats.

Effect of dietary energy restriction on bone mineral content of mature rats

Male adult 16 months old Fischer-344 rats (7 per group) were feda control diet ad libitum and energy modified diets restricted to 80% (R-80) and to 60% (R-60) of the control intake, while mineral and protein intakes were held constant at adequate levels. The control diet contained Ca, P, Mg & protein at 0.7, 0.4, 0.05 & 18.8%, respectively, and the two restricted diets contained higher levels of these nutrients to provide quantities equal to control diet when restricted to the respective energy level. After 16 weeks of feeding, significantly lower content in ash of the right femur (p<-0.03) accompanied by lower content in Ca, P and Mg were observed in R-60 rats as compared to the control rats (p<-0.02). Similar observations were made on tibia and fibula. Thus, the present study suggests that adequate energy intake is essential for the maintenance of normal bone mineral content, and consequently the requirement of Ca, P and Mg could increase when dietary energy consumption is restricted.

Influence of Dietary Energy Restriction on Yield and Quality of Broiler Parts

A total of 768 broilers were used in two studies to investigate the effect of dietary energy restriction on yield, fat and moisture contents, and organoleptic characteristics of broiler parts. Four dietary treatments were used with six replications of each sex. Energy intake was restricted during the last 12 days of the finishing period with full minimum daily requirements of all other nutrients maintained.Energy restriction reduced the live and ready-to-cook (RTC) weight of the whole carcass. Percentage distributions of the cut-up parts of RTC broiler carcasses were also changed due to restriction. Energy restriction changed fat composition of the RTC broiler parts. A 15% dietary restriction did not significantly affect flavor, tenderness, or juiciness of dark meat based on organoleptic tests. Higher levels of dietary restriction, however, resulted in a significant reduction (indicating an adverse effect) in juiciness scores of broiler meat.

Effects of Dietary Energy Restriction and Rehabilitation on Growth and Tissue Composition in Growing Rats

Effects of Dietary Energy Restriction and Rehabilitation on Growth and Tissue Composition in Growing Rats

Effects of food intake regulation on the energy metabolism of laying hens

1. The effects of dietary energy restriction on the energy metabolism of post‐peak‐of‐lay hens of two hybrid layer strains were studied by indirect calorimetry. 2. Starving and resting rates of heat production (SHP and RHP) were measured, over 1‐d periods, at intervals during a 25‐week period in which the experimental birds were individually restricted to 80% of their previous energy intake ad libitum. 3. In both strains mean RHP per bird was about 7% lower in the restricted birds than in controls fed ad libitum, but when RHP was expressed in terms of metabolic body size (kg0.75) the two groups did not differ. 4. Mean SHP per bird was about 18% lower in the restricted birds of both strains than in the corresponding controls; the decrease in SHP per kg0.75 was 12%. 5. Heat increment of feeding and calculated maintenance energy were higher, and net availability of metabolisable energy for maintenance and production was lower, in the restricted than in the control groups. 6. Gross efficiencies of egg production, in terms of both mass and energy, increased in the restricted birds. 7. Live‐weight and total carcass energy after 25 weeks of restriction were respectively about 15% and 30% lower in the restricted groups of both strains than in the groups fed ad libitum.

Effects of insulin on lipoprotein lipase activity in the rat heart and adipose tissue.

Effects of insulin on lipoprotein lipase activity in the rat heart and adipose tissue.