Impact of high-protein diets with either moderate or low carbohydrate on weight loss, body composition, blood pressure and glucose tolerance in rats

One approach to achieve weight loss and decrease both obesity and associated morbidities involves high-protein, low-carbohydrate (HPLC) diets. This study compares the impact on metabolic health of HPLC and high-protein, medium-carbohydrate (HPMC) diets offered to diet-induced obese (DIO) rats. Weanling male rats were fed either a 37 % fat diet (n 48) or stock pellets (n 12) for 22 weeks. Rats fed the 37 % fat diet accumulated more body fat (26.6 versus 14.8 % body weight, P < 0.001) compared with those on stock diet. The DIO rats had higher systolic blood pressure (+6.6 mmHg, P = 0.002), fasting insulin (+63 % P = 0.006) and areas under the glucose (+21 %, P < 0.001) and insulin (+81 %, P < 0.001) curves following an oral glucose tolerance test. DIO rats were then separated into four groups and offered for 8 weeks either: (1) the 37 % fat diet; (2) an HPLC or (3) HPMC diet; or (4) fed the 37 % fat diet to the intake of the HPMC group. Rats offered the 37 % fat or HPLC diets gained while those on HPMC lost body fat. Blood pressure was not altered by the dietary switch. Both HPLC and HPMC rats had lowered fasting insulin (P = 0.027) and improved homeostatic assessment (HOMA; P = 0.011) that was not different from those of stock animals. These improvements occurred despite differences in fat gain, and indicate that both weight loss and macronutrient intake can impact favourably on obesity-associated morbidities.     

Postprandial glycogen and lipid synthesis in prednisolone-treated rats maintained on high-protein diets with varied carbohydrate levels

OBJECTIVE: The present experiment was designed to study the effect of a high-protein, high-carbohydrate diet versus a high-protein, low-carbohydrate diet on in vivo postprandial glycogen and lipid synthesis of rats treated with prednisolone. METHODS: Thirty-two 6-wk-old male Sprague-Dawley rats were randomly assigned to one of four equal groups: high-protein, high-carbohydrate; high-protein, high-carbohydrate with prednisolone; high-protein, low-carbohydrate; and high-protein, low-carbohydrate with prednisolone. Rats were sham operated or subcutaneously implanted with prednisolone pellets while being maintained on their respective diets (39% of energy from protein) for 6 wk. Food intake and body weight were monitored throughout the experiment. At the end of the feeding period, overnight-fasted rats were fed a test meal and injected with 3H2O to measure in vivo rates of glycogen and lipid synthesis. Final plasma glucose, insulin, and triacylglycerol concentrations and hepatic glycogen content were also measured. RESULTS: Results showed that hepatic glycogen content (milligrams per gram of liver) was similar across all four experimental groups. Total hepatic glycogen synthesis and its percentage synthesis via pyruvate (indirect pathway) were higher in rats maintained on the high-protein, high-carbohydrate diet compared with those on the high-protein, low-carbohydrate diet and this was not substantially affected by prednisolone administration. Hepatic and epididymal fat pad lipid syntheses were not altered by diet or prednisolone treatments. CONCLUSION: Under long-term high-protein conditions, prednisolone administration does not seem to affect hepatic glycogen synthesis, which was increased with the increased carbohydrate content of the diet.     

High-protein diets containing different milk protein fractions differently influence energy intake and adiposity in the rat

This study was designed to determine whether (1) protein type and (2) the dietary carbohydrate to lipid content affected daily energy intake, body weight and adiposity in rats receiving high-protein diets ad libitum over a 25 d period. Each of the ten groups (n 8) consumed ad libitum one of the diets described below. A normal protein diet (P14C56L30, containing whole milk protein) and nine high-protein diets were used. The composition of the high-protein diets varied in terms of two parameters: macronutrient composition and protein type. Three macronutrient compositions (P55C35L10, P55C15L30 and P55L45) combined with three protein types (Milk, Whey and betaLac) allowed us to test nine diets. The results show that both protein type (betaLac > Whey > Milk) and the carbohydrate to lipid ratio (P55L45>P55C35L10 or P55C15L30) modulated reductions in energy intake, body weight and adiposity in rats receiving high-protein diets ad libitum, when compared with rats fed a normal diet under the same conditions. By contrast, blood lipid profiles were mainly influenced by the carbohydrate to lipid ratio (P55C15L30>P55L45 or P55C35L10). Moreover, betaLac protein was also the most efficient in tending to preserve lean body mass at the expense of fat mass, and improve blood metabolism hormones (insulin, leptin). Taken together, the present results show that whey-derived protein sources, and particularly beta-lactoglobulin-enriched fraction, are of considerable value because of their ability to reduce both body weight gain and the adiposity index.     

Effects of a high-protein ketogenic diet on hunger, appetite, and weight loss in obese men feeding ad libitum

BACKGROUND: Altering the macronutrient composition of the diet influences hunger and satiety. Studies have compared high- and low-protein diets, but there are few data on carbohydrate content and ketosis on motivation to eat and ad libitum intake. OBJECTIVE: We aimed to compare the hunger, appetite, and weight-loss responses to a high-protein, low-carbohydrate [(LC) ketogenic] and those to a high-protein, medium-carbohydrate [(MC) nonketogenic] diet in obese men feeding ad libitum. DESIGN: Seventeen obese men were studied in a residential trial; food was provided daily. Subjects were offered 2 high-protein (30% of energy) ad libitum diets, each for a 4-wk period-an LC (4% carbohydrate) ketogenic diet and an MC (35% carbohydrate) diet-randomized in a crossover design. Body weight was measured daily, and ketosis was monitored by analysis of plasma and urine samples. Hunger was assessed by using a computerized visual analogue system. RESULTS: Ad libitum energy intakes were lower with the LC diet than with the MC diet [P=0.02; SE of the difference (SED): 0.27] at 7.25 and 7.95 MJ/d, respectively. Over the 4-wk period, hunger was significantly lower (P=0.014; SED: 1.76) and weight loss was significantly greater (P=0.006; SED: 0.62) with the LC diet (6.34 kg) than with the MC diet (4.35 kg). The LC diet induced ketosis with mean 3-hydroxybutyrate concentrations of 1.52 mmol/L in plasma (P=0.036 from baseline; SED: 0.62) and 2.99 mmol/L in urine (P<0.001 from baseline; SED: 0.36). CONCLUSION: In the short term, high-protein, low-carbohydrate ketogenic diets reduce hunger and lower food intake significantly more than do high-protein, medium-carbohydrate nonketogenic diets.     

Ghrelin and glucagon-like peptide 1 concentrations, 24-h satiety, and energy and substrate metabolism during a high-protein diet and measured in a respiration chamber

BACKGROUND: The mechanism of protein-induced satiety remains unclear. OBJECTIVE: The objective was to investigate 24-h satiety and related hormones and energy and substrate metabolism during a high-protein (HP) diet in a respiration chamber. DESIGN: Twelve healthy women aged 18-40 y were fed in energy balance an adequate-protein (AP: 10%, 60%, and 30% of energy from protein, carbohydrate, and fat, respectively) or an HP (30%, 40%, and 30% of energy from protein, carbohydrate, and fat, respectively) diet in a randomized crossover design. Substrate oxidation, 24-h energy expenditure (EE), appetite profile, and ghrelin and glucagon-like peptide 1 (GLP-1) concentrations were measured. RESULTS: Sleeping metabolic rate (6.40 +/- 0.47 compared with 6.12 +/- 0.40 MJ/d; P < 0.05), diet-induced thermogenesis (0.91 +/- 0.25 compared with 0.69 +/- 0.24 MJ/d; P < 0.05), and satiety were significantly higher, and activity-induced EE (1.68 +/- 0.32 compared with 1.86 +/- 0.41; P < 0.05), respiratory quotient (0.84 +/- 0.02 compared with 0.88 +/- 0.03; P < 0.0005), and hunger were significantly lower during the HP diet. There was a tendency for a greater 24-h EE during the HP diet (P = 0.05). Although energy intake was not significantly different between the diet groups, the subjects were in energy balance during the HP diet and in positive energy balance during the AP diet. Satiety was related to 24-h protein intake (r2 = 0.49, P < 0.05) only during the HP diet. Ghrelin concentrations were not significantly different between diets. GLP-1 concentrations after dinner were higher during the HP than during the AP diet (P < 0.05). CONCLUSION: An HP diet, compared with an AP diet, fed at energy balance for 4 d increased 24-h satiety, thermogenesis, sleeping metabolic rate, protein balance, and fat oxidation. Satiety was related to protein intake, and incidentally to ghrelin and GLP-1 concentrations, only during the HP diet.     

高蛋白、低碳水化合物饮食对营养性肥胖大鼠体重和胃肠激素表达的影响

目的 观察长期高蛋白、低碳水化合物饮食对营养性肥胖大鼠体重和胃肠激素表达的影响. 方法 利用高脂饲料建立营养性肥胖大鼠模型24只,用随机数字表法按体重分层随机分为高蛋白饲养组(HP组,36.7%蛋白质)、普通饲养组(NC组,22.4%蛋白质),每组12只.正常等热量饲养24周后,测定体重、内脏脂肪及空腹血浆胃促生长素、胰高血糖素样肽1(GLP-1),免疫组织化学检测胃底胃促生长素、回肠GLP-1蛋白表达水平. 结果 24周后,NC、HP组体重分别为(490.92±39.47)、(545.55±31.08)g(t=-3.664,P＜0.01);内脏脂肪分别为(22.42±7.04)、(32.33±9.27)g(t=-2.503,P＜0.05);空腹血浆胃促生长素分别为(2.36±0.82)、(1.95±0.64)ng/ml(t=1.337,P＞0.05),并与体重(r=-0.370,t=-1.899,P＜0.05)、内脏脂肪量(r=-0.454,t=-2.52,P＜0.01)呈负相关;空腹血浆GLP-1分别为(0.52±0.13)、(0.71±0.19)μg/L(t=-2.758,P＜0.05);胃底胃促生长素表达分别为25 473±8701、10 526±6194(t=2.501,P＜0.05);回肠GLP-1蛋白表达分别为27 431±5813、36 601±5083(t=-1.833,P=0.081). 结论 长期高蛋白、低碳水化合物饮食可引起营养性肥胖大鼠体重、体脂下降,胃促生长素表达升高,GLP-1下降.

Abstract：

Objective To investigate the effects of long-term high-protein,low-carbohydrate diet on body weight and the expression of gastrointestinal hormones in diet-induced obesity rats. Methods Twentyfour diet-induced obesity rat models were established by feeding fat-enriched diet,then were randomly divided into two groups by stratified sampling method by weight:the high-protein diet group (HP,36.7% of energy from protein),and the normal chow group (NC,22.4% of energy from protein),12 rats in each group.The total calorie intake of each rat per day was similar and was maintained for 24 weeks,then body weight,visceral fat mass,fasting plasma ghrelin and glucagon-like peptide-1 (GLP-1) were determined,as well as protein expression of ghrelin in stomach,GLP-1 in ileum were detected by immunohistochemistry. Results After 24 weeks,body weight of HP,NC groups were (490.92±39.47)g and (545.55±31.08)g,respectively (t=-3.664,P＜0.01);visceral fat mass were (22.42±7.04)g and (32.33±9.27) g,respectively(t=-2.503,P＜0.05);plasma ghrelin level were (2.36±0.82) and (1.95±0.64) ng/ml,respectively(t=1.337,P＞0.05),and plasma ghrelin level was negatively correlated to body weight (r=-0.370,t=-1.899,P＜0.05),visceral fat mass(r=-0.454,t=-2.52,P＜0.01);plasma GLP-1 concentration were (0.52±0.13)and(0.71±0.19)ng/ml,respectively(t=-2.758,P＜0.05);ghrelin protein expression in stomach were 25 473±8701 and 10 526 ± 6194,respectively (t=2.501,P＜0.05);GLP-1 prot ein expression in ileum were 27 431±5813 and 36 601±5083,respectively (t=-1.833,P=0.081). Conclusion Long-term isocaloric high-protein,low-carbohydrate diet can reduce body weight and visceral fat,increase the expression of ghrelin,and decline GLP-1 expression in diet-induced obesity rats.     

Effect of a high-protein,energy-restricted diet on body composition,glycemic control,and lipid concentrations in overweight and obese hyperinsulinemic men and women

BACKGROUND: It is not clear whether varying the protein-to-carbohydrate ratio of weight-loss diets benefits body composition or metabolism. OBJECTIVE: The objective was to compare the effects of 2 weight-loss diets differing in protein-to-carbohydrate ratio on body composition, glucose and lipid metabolism, and markers of bone turnover. DESIGN: A parallel design included either a high-protein diet of meat, poultry, and dairy foods (HP diet: 27% of energy as protein, 44% as carbohydrate, and 29% as fat) or a standard-protein diet low in those foods (SP diet: 16% of energy as protein, 57% as carbohydrate, and 27% as fat) during 12 wk of energy restriction (6-6.3 MJ/d) and 4 wk of energy balance ( approximately 8.2 MJ/d). Fifty-seven overweight volunteers with fasting insulin concentrations > 12 mU/L completed the study. RESULTS: Weight loss (7.9 +/- 0.5 kg) and total fat loss (6.9 +/- 0.4 kg) did not differ between diet groups. In women, total lean mass was significantly (P = 0.02) better preserved with the HP diet (-0.1 +/- 0.3 kg) than with the SP diet (-1.5 +/- 0.3 kg). Those fed the HP diet had significantly (P < 0.03) less glycemic response at weeks 0 and 16 than did those fed the SP diet. After weight loss, the glycemic response decreased significantly (P < 0.05) more in the HP diet group. The reduction in serum triacylglycerol concentrations was significantly (P < 0.05) greater in the HP diet group (23%) than in the SP diet group (10%). Markers of bone turnover, calcium excretion, and systolic blood pressure were unchanged. CONCLUSION: Replacing carbohydrate with protein from meat, poultry, and dairy foods has beneficial metabolic effects and no adverse effects on markers of bone turnover or calcium excretion.     

Soy protein isolate and its hydrolysate reduce body fat of dietary obese rats and genetically obese mice (yellow KK)

This study examined in dietary obese and genetically obese rodents the effects of soy protein isolate (SPI) and its hydrolysate (SPI-H) on the rate of body-fat disappearance. Male Sprague-Dawley rats (4-16 wk old) and yellow KK mice (6-10 wk old) were made obese by feeding high-fat diets containing 30% fat. They were then fed energy-restricted, low-fat (5.0%), and high-protein (35% casein, SPI, or SPI-H) diets for 4 wk at 60% of the level of the energy intake of rodents on laboratory chow. The body-fat contents of rats and mice fed a high-fat diet were 27.3 and 33.6 g/100 g body weight, respectively, at the end of the obese period. For rats, the apparent absorbability of dietary energy and fat was significantly lower in the SPI and SPI-H groups than in the casein group, but vice-versa for nitrogen balance. Body-fat content in mice fed SPI and SPI-H diets was significantly lower than in those fed the casein diet. In rats, plasma total cholesterol level was lower with the SPI-H diet, and plasma glucose level was lower with the SPI and SPI-H diets than with the casein diet. These results indicate that SPI and SPI-H are suitable protein sources in energy-restricted diets for the treatment of obesity.     

Monosodium glutamate in standard and high-fiber diets: metabolic syndrome and oxidative stress in rats

OBJECTIVE: This study determined the effects of adding monosodium glutamate (MSG) to a standard diet and a fiber-enriched diet on glucose metabolism, lipid profile, and oxidative stress in rats. METHODS: Male Wistar rats (65 +/- 5 g, n = 8) were fed a standard diet (control), a standard diet supplemented with 100 g of MSG per kilogram of rat body weight, a diet rich in fiber, or a diet rich in fiber supplemented with 100 g of MSG per kilogram of body weight. After 45 d of treatment, sera were analyzed for concentrations of insulin, leptin, glucose, triacylglycerol, lipid hydroperoxide, and total antioxidant substances. A homeostasis model assessment index was estimated to characterize insulin resistance. RESULTS: Voluntary food intake was higher and feed efficiency was lower in animals fed the standard diet supplemented with MSG than in those fed the control, fiber-enriched, or fiber- and MSG-enriched diet. The MSG group had metabolic dysfunction characterized by increased levels of glucose, triacylglycerol, insulin, leptin, and homeostasis model assessment index. The adverse effects of MSG were related to an imbalance between the oxidant and antioxidant systems. The MSG group had increased levels of lipid hydroperoxide and decreased levels of total antioxidant substances. Levels of triacylglycerol and lipid hydroperoxide were decreased in rats fed the fiber-enriched and fiber- and MSG-enriched diets, whereas levels of total antioxidant substances were increased in these animals. CONCLUSIONS: MSG added to a standard diet increased food intake. Overfeeding induced metabolic disorders associated with oxidative stress in the absence of obesity. The fiber-enriched diet prevented changes in glucose, insulin, leptin, and triacylglycerol levels that were seen in the MSG group. Because the deleterious effects of MSG, i.e., induced overfeeding, were not seen in the animals fed the fiber-enriched diets, it can be concluded that fiber supplementation is beneficial by discouraging overfeeding and improving oxidative stress that is induced by an MSG diet.     

Very low-carbohydrate and low-fat diets affect fasting lipids and postprandial lipemia differently in overweight men

Hypoenergetic very low-carbohydrate and low-fat diets are both commonly used for short-term weight loss; however, few studies have directly compared their effect on blood lipids, with no studies to our knowledge comparing postprandial lipemia, an important independently identified cardiovascular risk factor. The primary purpose of this study was to compare the effects of a very low-carbohydrate and a low-fat diet on fasting blood lipids and postprandial lipemia in overweight men. In a balanced, randomized, crossover design, overweight men (n = 15; body fat >25%; BMI, 34 kg/m(2)) consumed 2 experimental diets for 2 consecutive 6-wk periods. One was a very low-carbohydrate (<10% energy as carbohydrate) diet and the other a low-fat (<30% energy as fat) diet. Blood was drawn from fasting subjects on separate days and an oral fat tolerance test was performed at baseline, after the very low-carbohydrate diet period, and after the low-fat diet period. Both diets had the same effect on serum total cholesterol, serum insulin, and homeostasis model analysis-insulin resistance (HOMA-IR). Neither diet affected serum HDL cholesterol (HDL-C) or oxidized LDL (oxLDL) concentrations. Serum LDL cholesterol (LDL-C) was reduced (P < 0.05) only by the low-fat diet (-18%). Fasting serum triacylglycerol (TAG), the TAG/HDL-C ratio, and glucose were significantly reduced only by the very low-carbohydrate diet (-44, -42, and -6%, respectively). Postprandial lipemia was significantly reduced when the men consumed both diets compared with baseline, but the reduction was significantly greater after intake of the very low-carbohydrate diet. Mean and peak LDL particle size increased only after the very low-carbohydrate diet. The short-term hypoenergetic low-fat diet was more effective at lowering serum LDL-C, but the very low-carbohydrate diet was more effective at improving characteristics of the metabolic syndrome as shown by a decrease in fasting serum TAG, the TAG/HDL-C ratio, postprandial lipemia, serum glucose, an increase in LDL particle size, and also greater weight loss (P < 0.05).     

A high-protein diet induces sustained reductions in appetite, ad libitum caloric intake, and body weight despite compensatory changes in diurnal plasma leptin and ghrelin concentrations

BACKGROUND: Ad libitum, low-carbohydrate diets decrease caloric intake and cause weight loss. It is unclear whether these effects are due to the reduced carbohydrate content of such diets or to their associated increase in protein intake. OBJECTIVE: We tested the hypothesis that increasing the protein content while maintaining the carbohydrate content of the diet lowers body weight by decreasing appetite and spontaneous caloric intake. DESIGN: Appetite, caloric intake, body weight, and fat mass were measured in 19 subjects placed sequentially on the following diets: a weight-maintaining diet (15% protein, 35% fat, and 50% carbohydrate) for 2 wk, an isocaloric diet (30% protein, 20% fat, and 50% carbohydrate) for 2 wk, and an ad libitum diet (30% protein, 20% fat, and 50% carbohydrate) for 12 wk. Blood was sampled frequently at the end of each diet phase to measure the area under the plasma concentration versus time curve (AUC) for insulin, leptin, and ghrelin. RESULTS: Satiety was markedly increased with the isocaloric high-protein diet despite an unchanged leptin AUC. Mean (+/-SE) spontaneous energy intake decreased by 441 +/- 63 kcal/d, body weight decreased by 4.9 +/- 0.5 kg, and fat mass decreased by 3.7 +/- 0.4 kg with the ad libitum, high-protein diet, despite a significantly decreased leptin AUC and increased ghrelin AUC. CONCLUSIONS: An increase in dietary protein from 15% to 30% of energy at a constant carbohydrate intake produces a sustained decrease in ad libitum caloric intake that may be mediated by increased central nervous system leptin sensitivity and results in significant weight loss. This anorexic effect of protein may contribute to the weight loss produced by low-carbohydrate diets.     

Low-carbohydrate diets cause obesity, low-carbohydrate diets reverse obesity: a metabolic mechanism resolving the paradox

High-fat diets produce obesity in part because, per calorie, glucose produces greater post-prandial thermogenesis than lipids, an effect probably mediated by glucose-sensing neurons. A very low-carbohydrate/high-fat/high-protein Atkins-type diet produces obesity but is marginally ketogenic in mice. In contrast, high-sucrose/low-fat diets, and very low-carbohydrate/high-fat/low-protein (anti-epileptic) ketogenic diets reverse diet-induced obesity independent of caloric intake. We propose that a non-ketogenic high-fat diet reduces glucose metabolism and signaling in glucose-sensing neurons, thereby reducing post-prandial thermogenesis, and that a ketogenic high-fat diet does not reduce glucose signaling, thereby preventing and/or reversing obesity.     

Effects of high-whey-protein intake and resistance training on renal, bone and metabolic parameters in rats

Consumption of high-protein (HP) diets is postulated to exert a negative influence on bone and renal health. However, no conclusive evidence has been presented related to this issue or to the potential protective action of resistance training on HP-induced systemic effects. We examined the effects of HP diet consumption on food intake, body-weight gain, body composition, and renal, bone and metabolic parameters of rats performing resistance training. A total of ninety-six adult male Wistar rats were randomly distributed in twelve experimental groups (n 8): normal-protein (10%) or HP (45%) diets, with or without resistance training, killed for experimental periods of 1, 2 or 3 months. Diets were based on a commercial whey protein hydrolysate. Consumption of HP diets and resistance training significantly affected food intake, body weight and body composition, as well as the plasma levels of total cholesterol, HDL-cholesterol and TAG. The buffering action of resistance training on such diet-induced alterations was especially evident in the levels of plasma TAG. Consumption of HP diets led to a considerable increase in kidney weight, urinary volume and acidity, as well as in the urinary excretion of Ca, with a parallel reduction in the urinary excretion of citrate (P < 0·05). No apparent deleterious effect on bone mineral content was found. In conclusion, consumption of HP diets caused alterations in renal health status and some metabolic parameters, but did not seem to affect bone status. Resistance training had a protective action against alterations of renal health status and some metabolic parameters such as plasma TAG.     

Maternal consumption of high-prebiotic fibre or -protein diets during pregnancy and lactation differentially influences satiety hormones and expression of genes involved in glucose and lipid metabolism in offspring in rats

Risk of developing the metabolic syndrome may be influenced by nutritional environment early in life. We examined the effects of high-fibre (HF) and high-protein (HP) diets consumed during pregnancy and lactation on satiety hormones and expression of genes involved in glucose and lipid metabolism in offspring. Wistar dams were fed a control (C), HF or HP diets during pregnancy and lactation. At parturition, litters were culled to ten pups. At 21 d, all pups were weaned onto C diet. At 7, 14, 21, 28 and 35 d after birth, blood was analysed for satiety hormones and tissues for mRNA expression in offspring. No differences were observed in litter size or birth weight. At 21 d, offspring of HF dams had greater adjusted intestinal mass and lower liver weight than those of C but not of HP dams. Plasma glucose at 28 d and amylin at 7, 14 and 28 d were lower in HF v. C and HP offspring. Glucagon-like peptide-1 was higher in HP offspring than in HF offspring at 7 d but was higher in HF v. C offspring at 21 d. Offspring of HF dams had higher glucose transporter (GLUT2 and Na+-dependent glucose/galactose transporter) mRNA expression at 21 d v. C and HP offspring. In brown adipose tissue, HF and HP up-regulated uncoupling protein-1 and PPAR-γ coactivator. HP was associated with increased resistin and IL-6 mRNA expression. The present study demonstrates that maternal diet composition differentially regulates circulating satiety hormones and genes involved in glucose transport and energy metabolism in offspring. These early changes could have long-term consequences for obesity risk.     

Increasing the protein content in a carbohydrate-free diet enhances fat loss during 35% but not 75% energy restriction in rats

The purpose of the present study was to test the influence of the amount of protein in a carbohydrate-free diet during a weight reducing program using severe (75%) or more moderate (35%) energy restriction in rats. In Expt. 1, 3 groups (n = 6) consumed ad libitum a high-carbohydrate, low-fat diet [P21C69L10 containing 21% of energy as protein (P21), 69% carbohydrate (C69) and 10% lipids (L10)], a high-carbohydrate, high-fat diet (P21C34L45), or a carbohydrate-free, high-fat, high-protein diet (P55L45). In Expt. 2, 7 groups (n = 7) were studied. For 20 d, groups 1-4 consumed ad libitum diets containing macronutrients at the proportions indicated in their designations [P14C56L30 (control diet), P30L70, P50L50, and P90L10]. Groups 5-7 were pair-fed the same diets at the level of the spontaneous intake of the P90L10 group on the previous day (35% energy restriction). In Expt. 3, 5 groups (n = 7) were fed 1 of the following diets for 20 d. Group 1 consumed the control diet (P14C56L30) ad libitum. Groups 2-5 were energy restricted to 25% of the daily energy intake of group 1 with diets varying in their protein and lipid concentrations (P14C56L30, P50L50, P70L30, and P90L10). A high-fat content in the diet devoid of carbohydrate did not increase energy intake and body adiposity and neither body weight nor body composition was significantly affected by the protein to lipid ratio when energy restriction was 75%; however, a protein content > 50% preserved lean body mass at the expense of fat mass when energy restriction was 35%. Our results show that the absence of carbohydrates from the diet induces a low energy intake and the preferential deposition of protein.     

Long-term high protein intake does not increase oxidative stress in rats

The maximum dietary protein intake that does not cause adverse effects in a healthy population is uncertain. We tested whether a high protein intake enhances oxidative stress. Adult rats were adapted to different casein-based diets containing either an adequate (13.8%; AP), medium (25.7%; MP), or high (51.3%; HP) level of crude protein; a fourth group received a HP diet but no RRR-alpha-tocopherol acetate (HP-toc). After 15 wk of feeding, plasma protein carbonyl concentration, liver lipid peroxide levels [thiobarbituric acid-reacting substances (TBARS)], reduced glutathione (GSH) status and leucine kinetics ([1-(13)C]leucine) were measured. Higher concentrations of protein carbonyls and TBARS were found in rats fed the AP and the HP-toc diets compared with those fed the MP and HP diets (P: < 0.05). GSH concentrations in plasma did not differ but total blood GSH concentrations were significantly (P: < 0.05) lower in rats fed the HP-toc diet compared with those fed the AP, MP and HP diets. Liver GSH concentrations were significantly (P: < 0.01) lower in rats fed the AP diet compared with the other groups. Rates of postabsorptive leucine oxidation (LeuOX) and flux (Q(Leu)) were positively correlated with the dietary protein level (for AP, MP, and HP, respectively: LeuOX, 74.9 +/- 28.5, 109 +/- 35.2, 142.3 +/- 38.4 micromol/(kg. h); Q(Leu), 425 +/- 102, 483 +/- 82, 505 +/- 80 micromol/(kg. h). Only HP-toc resulted in a significantly greater protein breakdown (PB(Leu)) and Q(Leu). No difference was seen in nonoxidative leucine disposal. Long-term intake of high protein diets did not increase variables of oxidative stress, in contrast to our initial hypothesis. An unexpected finding was that adequate protein feeding (AP) may in fact induce oxidative stress.     

A high-protein, high-fat, carbohydrate-free diet reduces energy intake, hepatic lipogenesis, and adiposity in rats

The aim of this work was to determine the effects in rats of ingesting 1 of 3 diets with normal or high protein concentrations and various carbohydrate:lipid ratios on weight gain, body composition, and the development and metabolism of white adipose tissue (WAT). For this purpose, male Wistar rats were fed for 20 or 42 d a high-carbohydrate, low-fat, normal-protein diet (76, 10, and 14% of energy as carbohydrate, lipid, and protein, respectively, carbohydrate:lipid ratio (C/L) = 7.6), a normal-carbohydrate, low-fat, high-protein diet (35, 10, and 55% of energy as carbohydrate, lipid, and protein respectively, C:L = 3.5), or a carbohydrate-free, high-fat, high-protein diet (45 and 55% of energy as fat and protein, respectively, C:L = 0). Growth, food intake, body composition, WAT cellularity, and several markers of lipogenesis including fatty acid synthase and lipoprotein lipase activities were measured in adipose tissue and liver. Lowering the C:L ratio reduced the development of WAT, weight gain, body fat mass, and adipocyte size, and in rats fed the carbohydrate-free diet (C:L = 0), the total number of adipocytes in subcutaneous WAT. These reductions in adipose tissue development with decreases in the C:L ratio of the diet seemed to be due primarily to reduced hepatic lipogenesis.     

High-protein, low-fat diets are effective for weight loss and favorably alter biomarkers in healthy adults

Although popular and effective for weight loss, low-carbohydrate, high-protein, high-fat (Atkins) diets have been associated with adverse changes in blood and renal biomarkers. High-protein diets low in fat may represent an equally appealing diet plan but promote a more healthful weight loss. Healthy adults (n = 20) were randomly assigned to 1 of 2 low-fat (<30% energy), energy-restricted groups: high-protein (30% energy) or high-carbohydrate (60% energy); 24-h intakes were strictly controlled during the 6-wk trial. One subject from each group did not complete the trial due to out-of-state travel; two subjects in the high-carbohydrate group withdrew from the trial due to extreme hunger. Body composition and metabolic indices were assessed pre- and post-trial. Both diets were equally effective at reducing body weight (-6%, P < 0.05) and fat mass (-9 to -11%, P < 0.05); however, subjects consuming the high-protein diet reported more satisfaction and less hunger in mo 1 of the trial. Both diets significantly lowered total cholesterol (-10 to -12%), insulin (-25%), and uric acid (-22 to -30%) concentrations in blood from fasting subjects. Urinary calcium excretion increased 42% in subjects consuming the high-protein diet, mirroring the 50% increase in dietary calcium with consumption of this diet; thus, apparent calcium balance was not adversely affected. Creatinine clearance was not altered by diet treatments, and nitrogen balance was more positive in subjects consuming the high-protein diet vs. the high-carbohydrate diet (3.9 +/- 1.4 and 0.7 +/- 1.7 g N/d, respectively, P < 0.05). Thus, low-fat, energy-restricted diets of varying protein content (15 or 30% energy) promoted healthful weight loss, but diet satisfaction was greater in those consuming the high-protein diet.     

Prenatal high protein exposure decreases energy expenditure and increases adiposity in young rats

Epidemiologic results suggest that protein intake in infancy and later adiposity might be related. We examined whether high dietary protein exposure in utero and/or during postnatal life affects body fatness. Two groups of female rats were mated and pair-fed isocaloric high (40% protein; HP) or adequate protein (20% protein; AP) diets throughout pregnancy. The male offspring were suckled (3 wk) by foster mothers pair-fed HP or AP diets, resulting in 4 pre-/postnatal groups (AP-AP, AP-HP, HP-AP, HP-HP). Subsequently, they were pair-fed the same diets their nurses received during lactation until wk 9. Offspring of HP dams had a lower body weight on d 2 of life than their AP counterparts (7.6 +/- 0.7 vs. 8.3 +/- 0.8 g; P < 0.001). HP-AP rats had a higher body weight than AP-AP controls at wk 3, 5, and 6 (P < 0.05), in contrast to HP-HP which did not differ from controls. Prenatal HP exposure resulted in a greater total and relative fat mass and decreased total energy expenditure at wk 9 (P < 0.05). Postnatal HP alone had no significant effect on body composition or metabolic rate. These results indicate that in utero exposure to a high protein level reprograms body weight and energy homeostasis.