Increasing the protein:carbohydrate ratio in a high-fat diet delays the development of adiposity and improves glucose homeostasis in mice

Dietary fat is considered an important contributing factor in the obesity epidemic, and high-fat diets are used widely to induce obesity and diabetes-related traits in susceptible rodent strains. Little attention, however, is usually paid to the interaction of fat with the other macronutrients. The aim of this study, therefore, was to investigate the effects of high-fat, isoenergetic diets with different protein:carbohydrate (CHO) ratios on obesity, energy metabolism, and glucose homeostasis in mice. Male adult C57BL/6J mice consumed ad libitum for 10 wk a control diet (41:42:17 ratio of CHO:protein:fat, 15.5 kJ/g) or 2 different high-fat diets: high carbohydrate (HC; 41:16:43, 17.7 kJ/g) or low carbohydrate (LC; 11:45:44, 17.5 kJ/g). Body weight and fat gains were rapid and were greater in HC mice than in other groups due to an initial pronounced hyperphagia and subsequent passive overconsumption. Weight and fat gains were less in LC mice but still greater than in controls. Energy expenditure was not affected by the diets, and total energy intake explained 84% of the variation in final body weight. The respiratory quotient was lower in LC mice than in other groups, indicating high fat oxidation rates due to the LC diet. Blood glucose was lower and insulin sensitivity greater in LC mice than in HC mice. We conclude that increasing the protein:CHO ratio in a high-fat diet delays but does not prevent the development of adiposity. However, glucose homeostasis was improved in LC mice, indicating that a combination of high fat and high CHO is responsible for the development of metabolic syndrome-related traits in mice.     

Energy expenditure in rats with diet-induced obesity

Effects of a diet high in fat on body weight, adiposity, and energy expenditure were investigated. Male rats were fed 8% (control) or 50% fat (by weight) for 6 mo. The high-fat group increased body weight (+26%), adipocyte size (+61%), and adipocyte number (+48%). However, food intake and resting oxygen consumption, although higher in absolute amount, were normal in that both were commensurate with the greater body mass the rats maintained. When body weight and adipocyte size were reduced by caloric restriction, the high-fat group displayed the same adaptive adjustments in resting oxygen consumption as controls. We conclude that rats fed high-fat diets for prolonged periods 1) have energy intakes and expenditures appropriate for the greater tissue mass and adipocyte number they maintain, and 2) show adaptive reductions in energy expenditure when food is restricted, which provide further evidence that the regulated level of body weight can be altered by such diets.     

Effect of energy intake on the promotion of mammary carcinogenesis by dietary fat

The effect of low-fat and high-fat diets on the induction of mammary carcinomas by 1-methyl-1-nitrosourea (MNU) was studied in female Sprague-Dawley rats. All rats were given MNU (25 mg/kg body wt) at 50 days of age. For the first 17 weeks after carcinogen administration, they were fed a purified diet containing either 5 or 20% fat incorporated into agar gel. Food intake was restricted, so that the amounts fed provided the same amount of net utilizable energy each day for both groups, regardless of the fat content of the diets. From 17 to 32 weeks, the diets were fed ad libitum. During the restricted feeding period, there was no significant difference in tumor incidence or in the number of tumors detected between the groups. During the weeks in which animals were fed ad libitum, significantly more tumors appeared in the high-fat group than in the low-fat group. The data provide support for the hypothesis that consumption of a high-fat diet can lead to an enhancement of mammary carcinogenesis. It appears, however, that diets must be consumed ad libitum for the stimulatory effect on tumor occurrence to be exhibited.     

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.     

Adipocyte gene expression is altered in formerly obese mice and as a function of diet composition

In the development of obesity, the source of excess energy may influence appetite and metabolism. To determine the effects of differences in diet composition in obesity, mice were fed either a high-carbohydrate diet (HC; 10% fat energy) or a high-fat energy-restricted diet (HFR; 60% fat energy) over 18 wk in weight-matched groups of mice. To identify obesity-associated genes with persistently altered expression following weight reduction, mice were fed either a standard low-fat diet (LF; 10% fat energy), an unrestricted high-fat diet (HF; 60% fat energy), or a HF diet followed by weight reduction (WR). Mice fed a HF diet had significantly greater gonadal fat mass and higher whole blood glucose concentrations than mice fed an HC diet. Of the mice fed a high-fat diet, total body weight and serum insulin concentrations were greater in HF than in HFR. Microarray analysis revealed that HF vs. HC feeding resulted in global differences in adipocyte gene expression patterns. Although we identified genes whose expression was altered in both moderately and severely obese mice, there were also a large number of genes with altered expression only in severe obesity. Formerly obese, WR mice did not differ significantly from lean controls in total body weight or physiological measures. However, microarray analysis revealed distinctly different patterns of adipocyte gene expression. Furthermore, there were 398 genes with altered expression in HF mice that persisted in WR mice. Genes with persistently altered expression following obesity may play a role in rebound weight gain following weight reduction.     

Low-Carbohydrate Diet Versus Caloric Restriction: Effects on Weight Loss,Hormones, and Colon Tumor Growth in Obese Mice

Our objective was to compare the effects of a low-carbohydrate diet to a high-carbohydrate/calorie-restricted diet on weight loss, hormones, and transplanted colon tumor growth. Eighty male C57BL/6 mice consumed a diet-induced obesity regimen (DIO) ad libitum for 7 weeks. From Weeks 8 to 14, the mice consumed a 1) DIO diet ad libitum (HF); 2) low-carbohydrate diet ad libitum (LC); 3) high-carbohydrate diet ad libitum (HC); or 4) HC calorie restricted diet (HC–CR). MC38 cells were injected at Week 15. At the time of injection, the HC–CR group displayed the lowest body weight (25.5 ± 0.57 g), serum insulin-like growth factor I (IGF-I; 135 ± 56.0 ng/ml), and leptin (1.0 ± 0.3 ng/ml) levels. This group also exhibited the longest time to palpable tumor (20.1 ± 0.9 days). Compared to the HF group, the HC group exhibited lower body weight (39.4 ± 1.4 vs. 32.9 ± 0.7 g, respectively), IGF-I (604 ± 44.2 vs. 243.4 ± 88.9 ng/ml, respectively), and leptin (15.6 ± 2.2 vs. 7.0 ± 0.7 ng/ml, respectively) levels but similar tumor growth. IGF-I levels were lower in the LC group (320.0 ± 39.9 ng/ml) than the HF group, but tumor growth did not differ. These data suggest LC diets do not slow colon tumor growth in obese mice.     

Occasional physical inactivity combined with a high-fat diet may be important in the development and maintenance of obesity in human subjects

BACKGROUND: A better understanding of the environmental factors that contribute to obesity is imperative if any therapeutic effect on the increasing prevalence of overweight and obesity in the United States is to be achieved. OBJECTIVE: This study examined the effect of the interaction of diet composition and physical inactivity on energy and fat balances. DESIGN: Thirty-five normal-weight and obese subjects were randomly assigned to either a 15-d isoenergetic high-carbohydrate (HC) or high-fat (HF) diet according to a crossover design. During the first 14 d, body weight and physical activity were maintained. On day 15, subjects spent 23 h in a whole-room indirect calorimeter and were fed a diet similar to that consumed during the previous 7 d while remaining physically inactive. RESULTS: Energy intakes required to maintain body weight stability during the first 14 d were similar between diets. Normal-weight and obese subjects consuming both diets had a positive energy balance on the sedentary day (day 15), suggesting that subjects were less active in the calorimeter. There was no significant effect of diet composition on total energy balance and total protein-energy balance on day 15; however, carbohydrate balance was more positive with the HC (2497.8 +/- 301.2 kJ) than with the HF (1159 +/- 301.2 kJ) diet (P = 0.0032). Most importantly, fat balance was more positive with the HF (1790.8 +/- 510.4 kJ) than with the HC (-62.8 +/- 510.4 kJ) diet (P = 0.0011). CONCLUSION: Chronic consumption of a high-carbohydrate diet could provide some protection against body fat accumulation in persons with a pattern of physical activity that includes frequent sedentary days.     

Low-carbohydrate diet versus caloric restriction: effects on weight loss, hormones, and colon tumor growth in obese mice

Our objective was to compare the effects of a low-carbohydrate diet to a high-carbohydrate/calorie-restricted diet on weight loss, hormones, and transplanted colon tumor growth. Eighty male C57BL/6 mice consumed a diet-induced obesity regimen (DIO) ad libitum for 7 weeks. From Weeks 8 to 14, the mice consumed a 1) DIO diet ad libitum (HF); 2) low-carbohydrate diet ad libitum (LC); 3) high-carbohydrate diet ad libitum (HC); or 4) HC calorie restricted diet (HC-CR). MC38 cells were injected at Week 15. At the time of injection, the HC-CR group displayed the lowest body weight (25.5 +/- 0.57 g), serum insulin-like growth factor I (IGF-I; 135 +/- 56.0 ng/ml), and leptin (1.0 +/- 0.3 ng/ml) levels. This group also exhibited the longest time to palpable tumor (20.1 +/- 0.9 days). Compared to the HF group, the HC group exhibited lower body weight (39.4 +/- 1.4 vs. 32.9 +/- 0.7 g, respectively), IGF-I (604 +/- 44.2 vs. 243.4 +/- 88.9 ng/ml, respectively), and leptin (15.6 +/- 2.2 vs. 7.0 +/- 0.7 ng/ml, respectively) levels but similar tumor growth. IGF-I levels were lower in the LC group (320.0 +/- 39.9 ng/ml) than the HF group, but tumor growth did not differ. These data suggest LC diets do not slow colon tumor growth in obese mice.     

Fish Oil Enriched n-3 Polyunsaturated Fatty Acids Improve Ketogenic Low-Carbohydrate/High-Fat Diet-Caused Dyslipidemia,Excessive Fat Accumulation,and Weight Control in Rats

Low-carbohydrate and high-fat diets have been used for body weight (BW) control, but their adverse effects on lipid profiles have raised concern. Fish oil (FO), rich in omega-3 polyunsaturated fatty acids, has profound effects on lipid metabolism. We hypothesized that FO supplementation might improve the lipid metabolic disturbance elicited by low-carbohydrate and high-fat diets. Male SD rats were randomized into normal control diet (NC), high-fat diet (HF), and low-carbohydrate/high-fat diet (LC) groups in experiment 1, and NC, LC, LC + 5% FO (5CF), and LC + 10% FO diet (10CF) groups in experiment 2. The experimental duration was 11 weeks. In the LC group, a ketotic state was induced, and food intake was decreased; however, it did not result in BW loss compared to either the HF or NC groups. In the 5CF group, rats lost significant BW. Dyslipidemia, perirenal and epididymal fat accumulation, hepatic steatosis, and increases in triglyceride and plasma leptin levels were observed in the LC group but were attenuated by FO supplementation. These findings suggest that a ketogenic low-carbohydrate/high-fat diet with no favorable effect on body weight causes visceral and liver lipid accumulation. FO supplementation not only aids in body weight control but also improves lipid metabolism in low-carbohydrate/high-fat diet-fed rats.     

Nutritional hepatic steatosis and mortality after burn injury in rats

AIMS: To investigate the effects of diet composition and starvation on hepatic steatosis and mortality after severe burn injury in rats. Methods: Experiment 1: rats received either normal chow (55 cent of energy carbohydrates, 14 cent fat, 31 cent protein), a high-fat (40 cent carbohydrates, 40 cent fat, 20 cent protein), or a high-carbohydrate diet (81 cent carbohydrates, 4 cent fat, 15 cent protein) ad libitum for 6 days. Another three groups received these diets ad libitum for 6 days after 48|h starvation. Experiment 2: mortality after 60 cent total body surface area scald burn was determined in a control group of rats and a group with nutritionally induced hepatic steatosis. Hepatic steatosis was induced by feeding the rats a high-fat diet (40 cent carbohydrates, 4 cent fat, 15 cent protein) ad libitum for 6 days. RESULTS: Without starvation, liver triglyceride content (mg/g liver) increased in response to the high-fat diet (25.6'6.9) compared to normal chow (9.4'3.8; P < 0. 05); the high-carbohydrate diet had no influence on liver triglyceride content (12.4'3.7). Refeeding after starvation resulted in elevated (P < 0.05) liver triglyceride content in the high-fat (18.8'8.3) and the high-carbohydrate group (28.7'14.4 vs control 6. 7'3.7). Liver triglyceride content correlated (R2=0.72; P < 0.05) to non-protein energy intake but not to total energy intake. Burn caused 33 cent mortality in the hepatic steatosis group and no deaths in the control group (P < 0.05). CONCLUSIONS: Diet composition and preceding starvation independently manipulate hepatic fat content in rats. Hepatic steatosis increases mortality after burn injury. Thus, nutritional interventions to reduce hepatic fat accumulation may be beneficial.     

The role of dietary fat in body fatness: evidence from a preliminary meta-analysis of ad libitum low-fat dietary intervention studies

The role of high-fat diets in weight gain and obesity has been questioned because of inconsistent reports in the literature concerning the efficacy of ad libitum low-fat diets to reduce body weight. We conducted a meta-analysis of weight loss occurring on ad libitum low-fat diets in intervention trials, and analysed the relationship between initial body weight and weight loss. We selected controlled trials lasting more than 2 months comparing ad libitum low-fat diets with a control group consuming their habitual diet or a medium-fat diet ad libitum published from 1966 to 1998. Data were included from 16 trials with a duration of 2-12 months, involving 1728 individuals. No trials on obese subjects fulfilled the inclusion criteria. The weighted difference in weight loss between intervention and control groups was 2.55 kg (95% CI, 1.5-3.5; P < 0.0001). Weight loss was positively and independently related to pre-treatment body weight (r = 0.52, P < 0.05) and to reduction in the percentage of energy as fat (0.37 kg/%, P < 0.005) in unweighted analysis. Extrapolated to a BMI of about 30 kg/m2 and assuming a 10% reduction in dietary fat, the predicted weight loss would be 4.4 kg (95% CI, 2.0 to -6.8 kg). Because weight loss was not the primary aim in 12 of the 16 studies, it is unlikely that voluntary energy restriction contributed to the weight loss. Although there is no evidence that a high intake of simple sugars contributes to passive overconsumption, carbohydrate foods with a low glycaemic index may be more satiating and exert more beneficial effects on insulin resistance and cardiovascular risk factors. Moreover, an increase in protein content up to 25% of total energy may also contribute to reducing total energy intake. In conclusion, a low-fat diet, high in protein and fibre-rich carbohydrates, mainly from different vegetables, fruits and whole grains, is highly satiating for fewer calories than fatty foods. This diet composition provides good sources of vitamins, minerals, trace elements and fibre, and may have the most beneficial effect on blood lipids and blood-pressure levels. A reduction in dietary fat without restriction of total energy intake prevents weight gain in subjects of normal weight and produces a weight loss in overweight subjects, which is highly relevant for public health.     

Variations in body composition and plasma lipids in response to a high-carbohydrate diet

OBJECTIVE: To examine the extent to which variations in body composition modulate changes in the lipid profile in response to the ad libitum consumption of a diet rich in carbohydrates (CHOs) (high-CHO diet: 58% of energy as CHOs) or high in fat and in monounsaturated fatty acids (MUFAs) (high-MUFA diet: 40% of energy as fat, 23% as MUFAs). RESEARCH METHODS AND PROCEDURES: Sixty-three men were randomly assigned to one of the two diets that they consumed for 6 to 7 weeks. Body composition and fasting plasma lipid levels were measured at the beginning and the end of the dietary intervention. RESULTS: The high-CHO and high-MUFA diets induced significant and comparable reductions in body weight and waist circumference. These changes were accompanied by significant and comparable (p < 0.01) reductions in total plasma cholesterol and low-density lipoprotein cholesterol levels. However, the high-MUFA diet had more beneficial effects on plasma triglyceride concentrations (p < 0.01) and on plasma high-density lipoprotein cholesterol levels (p = 0.02) compared with the high-CHO diet. Diet-induced changes in waist circumference were significantly associated with changes in low-density lipoprotein cholesterol levels in the high-CHO group (r = 0.39, p = 0.03) but not in the high-MUFA group (r = 0.16, p = 0.38). DISCUSSION: Improvements in plasma lipids induced by the ad libitum consumption of a high-CHO diet seem to be partly mediated by changes in body weight, whereas lipid changes induced by the high-MUFA diet seem to be independent of changes in body weight.     

Effect of hydroxycitrate on respiratory quotient, energy expenditure, and glucose tolerance in male rats after a period of restrictive feeding

OBJECTIVE: Recently we demonstrated that hydroxycitrate (HCA) suppresses food intake and body weight regain in male rats after substantial body weight loss. However, it is not known whether HCA also affects the respiration quotient (RQ), energy expenditure (EE), and glucose tolerance in this animal model. METHODS: Twenty-four male rats (initial body weight, 378 +/- 3 g) were fed restrictively (10 g/d) for 10 d and then given ad libitum access to a high-glucose diet supplemented with 3% HCA for 6 d. Controls received the same diet without the supplement. RQ and EE were measured during ad libitum days 1, 2, and 6. An oral glucose tolerance test was performed on ad libitum day 4 or 5. RESULTS: HCA decreased RQ and EE during ad libitum days 1 and 2. In all probability, these findings reflect a decrease in de novo lipogenesis. On ad libitum day 6, RQ and EE did not differ between treatment groups. HCA suppressed food intake during the first 3 d ad libitum, but overall body weight regain was not decreased in the HCA group. The oral glucose tolerance test showed that HCA significantly decreased the increase in plasma glucose from baseline (Deltaglucose) and tended to decrease the area under the curve for glucose. Deltainsulin and area under the curve for insulin did not differ between groups. CONCLUSIONS: These results indicate that, in this animal model, HCA suppresses de novo lipogenesis. Moreover, HCA may improve glucose tolerance.     

Effect of dietary carbohydrate source on the development of obesity in agouti transgenic mice

OBJECTIVES: Our objective was to evaluate the effects of a qualitative change in dietary carbohydrate source on body weight and adiposity in a rodent model of diet-induced obesity. RESEARCH METHODS AND PROCEDURES: We evaluated the effects of high-fat diets (basal) varying in carbohydrate source in aP2-agouti transgenic mice. In the ad libitum study, animals were given free access to the basal diet or one of four test diets for 6 weeks. In two of the diets, dietary carbohydrate was derived from a single source: mung bean noodles (MUNG) or rolled oats (ROLL). The remaining diets were designed to mimic commercially available instant oatmeal with added sugar (IO-S) or flavored instant oatmeal (IO-F). In the energy-restricted study, animals were given ad libitum access to the basal diet for 6 weeks. Subsequently, animals were assigned to one of six treatment groups for 6 weeks. One group was continued on the basal diet ad libitum. The remaining groups were maintained with energy restriction (70% ad libitum) on either the basal, MUNG, ROLL, IO-S, or IO-F diet. RESULTS: Subcutaneous fat pad mass was significantly higher (p<0.05) in the energy-restricted basal and IO-S groups compared with the energy-restricted ROLL diet. Similarly, visceral fat pad mass was significantly lower with ROLL and MUNG diets (p<0.05 for both) compared with basal and IO-S diets, and the insulin:glucose ratio was reduced (by 23% to 34%, p<0.05) in these two diets compared with all others. In ad libitum-fed animals, liver fatty acid synthase expression was 43% to 62% lower (p<0.05) with ROLL and MUNG diets compared with all others. DISCUSSION: These data suggest that a qualitative change in dietary carbohydrate source modulates body weight and adiposity.     

Effects of structured medium- and long-chain triacylglycerols in diets with various levels of fat on body fat accumulation in rats

The effects of structured medium- and long-chain triacylglycerols (MLCT) in diets containing 50-200 g fat/kg on body fat accumulation were compared with those of long-chain triacylglycerols (LCT) in rats. In rats fed ad libitum, weights of intra-abdominal adipose tissues and carcass fat contents were significantly smaller (P<0.05) in rats fed the 150-200 g MLCT/kg diet than in rats fed 150-200 g LCT/kg diet. Serum and liver triacylglycerol contents were significantly greater (P<0.05) in rats fed 200 g MLCT/kg diet, as were hepatic capacities of citrate synthase and cytochrome oxidase (P<0.05). The effects of MLCT on body fat were also examined in adult rats fed a limited amount of food (approximately 50 % of ad libitum intake). Reduction of body fat deposition during the food restriction was the same between in LCT and MLCT groups. These results suggest that accumulation of body fat was less efficient during long-term feeding of MLCT than LCT in rats fed high-fat diets ad libitum. The effect of MLCT on body fat might be influenced by the dietary fat content or by energy sufficiency.     

Effect of energy intake on the promotion of mammary carcinogenesis by dietary fat

The effect of low‐fat and high‐fat diets on the induction of mammary carcinomas by 1‐methyl‐1‐nitrosourea (MNU) was studied in female Sprague‐Dawley rats. All rats were given MNU (25 mg/kg body wt) at 50 days of age. For the first 17 weeks after carcinogen administration, they were fed a purified diet containing either 5 or 20% fat incorporated into agar gel. Food intake was restricted, so that the amounts fed provided the same amount of net utilizable energy each day for both groups, regardless of the fat content of the diets. From 17 to 32 weeks, the diets were fed ad libitum. During the restricted feeding period, there was no significant difference in tumor incidence or in the number Of tumors detected between the groups. During the weeks in which animals were fed ad libitum, significantly more tumors appeared in the high‐fat group than in the low‐fat group. The data provide support for the hypothesis that consumption of a high‐fat diet can lead to an enhancement of mammary carcinogenesis. It appears, however, that diets must be consumed ad libitum for the stimulatory effect on tumor occurrence to be exhibited.     

Effects of fat intake on body composition and hepatic lipogenic enzyme activities of hamsters shortly after exercise cessation

Effects of fat intake on body composition and lipogenic enzyme activities were examined in hamsters. Forty-two female hamsters were randomly divided into two groups of 21 each. One group had access to voluntary disc running; the other group was sedentary. All were fed a low-fat, high-carbohydrate diet. After 30 d, seven hamsters from each group were killed and all running activity was discontinued. Remaining hamsters were separately assigned to two groups of seven and fed either a low-fat or high-fat diet for 7 d and then killed. Voluntary running increased food intake and weight gain and reduced body fat (52%). Cessation of exercise greatly enhanced body fat gain. High-fat diet enhanced weight gain. Increased energy intake during postexercise period appeared to cause enhanced body fat gain. The high-fat diet suppressed lipogenic enzyme activities. Serum triglyceride, total cholesterol, and HDL cholesterol levels were not affected by exercise or cessation of exercise.     

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 restricted diet on protein metabolism measured by [15N]glycine in high-fat-diet-induced obese rats

The effect of restricted diets on protein metabolism was studied in obese rats (obesity had been induced by ad libitum feeding of a diet containing 30% fat and 25% casein). The obese rats were fed on one of three restricted diets, each containing 5% fat, for 2 weeks (restricted feeding groups); a high-protein diet (HPD, 50% casein), a standard-protein diet (SPD, 25% casein), or a low-protein diet (LPD, 5% casein). The food intake was restricted to 5 g per day per rat. On the eleventh day, the rats were given [15N]glycine orally, and 4 days later, they were killed. The restricted feeding groups all showed similar weight losses (about 100 g), 2 weeks after the start of the restricted diet. The 15N distribution in whole body was measured and results were compared with those of control rats given 5%- or 30%-fat diet ad libitum. The whole-body distribution of 15N in the HPD group was similar to that in the rats fed ad libitum although the diet intake was restricted. The results suggested that the amount of protein in a restricted diet is important for maintenance of protein metabolism in obese rats.     

断乳后不同饲料构成对高脂膳食大鼠肥胖发生的影响

目的研究断乳后不同饲料构成对高脂膳食大鼠肥胖发生的影响。方法雄性Wistar大鼠出生后24天断乳,按体重随机分为A、B、C三组,分别给予高碳水化合物供能的基础饲料、高蛋白质供能饲料和高不饱和脂肪供能饲料。3周后均转为基础饲料。2周后再按体重将A组分为A1、A2两组,A1组继续基础饲料,A2、B、C组则转为以猪油为主的高脂膳食,6周后结束实验。分别在不同处理期末每组随机处死8只动物,称重、留取脂肪组织,计算脂体比,采血检测血糖、血脂和激素指标。结果断乳后喂饲高不饱和脂肪饲料可以显著降低高脂膳食大鼠的体重、体脂肪含量和脂体比(P<0.05),显著降低胰岛素水平、提高胰岛素敏感性(P<0.05),显著增加胰高血糖素、甲状腺激素等促脂解激素的水平(P<0.05),增加瘦素敏感性(P<0.05),改善高脂膳食大鼠的瘦素抵抗。早期喂饲高蛋白质饲料也有一定的降低体重、体脂肪含量和促脂解作用趋势,但是该组的血糖值高于A2组。结论断乳后给予高不饱和脂肪饲料可以显著抑制高脂膳食大鼠的肥胖发生。