Utilization and requirement of dietary protein taking into account the dermal and miscellaneous nitrogen losses in Japanese women

Utilization and requirement of mixed protein in the conventional Japanese diet and the obligatory integumental and miscellaneous nitrogen losses were measured in female subjects. Twelve female students aged 18 to 24 years were given conventional low-protein diets at N intake levels of 50, 70, and 90 mg/kg/day for 10 days. Constituents of the diets corresponded to those of average intake of the Japanese in recent years (1982). N balances were estimated and regression equations between N intake (X) and N balance (Y) were calculated by the multiple level-constant variation method. The equation was Y = 0.426X - 40.0 (n = 36, r = 0.615, p less than 0.01) and the intersection of the regression line with zero nitrogen balance was 93.9 +/- 14.3 mg N/kg/day. The mean digestibility was 92.2 +/- 4.7%. In another experimental group, nitrogen losses due to hair, nails, and menstruation in ten Japanese women were 0.624 +/- 0.172, 0.020 +/- 0.005, and 1.76 +/- 0.68 mg/kg/day, respectively. In a third experimental group, mean of the integumental N losses was 2.8 mg/kg/day in both the subjects given a low-protein diet (19 women) and an ordinary-protein diet (4 women). It increased to 12.7 mg N/kg/day when subjects exercised in summer (4 subjects). The protein requirement in the conventional Japanese diet estimated as the sum of the mean requirement of dietary protein and obligatory dermal and miscellaneous nitrogen losses in Japanese women was 99.1 mg N/kg/day or 0.62 g protein/kg/day. The net protein utilization (NPU) of the proteins at the N intake level for N equilibrium was estimated as 48.     

Utilization of soy protein isolate mixed with rice protein in Japanese women

Utilization and requirement of soy protein isolate (SPI) and SPI-rice combination were examined in twenty-five female students. After 1 day on protein-free diet, each subject received a low-protein diet for 10 days. The protein sources were SPI for ten subjects and SPI-rice combination, in which the ratio of two proteins was 6:4, for fifteen subjects. The nitrogen intakes were about 45, 65 and 85 mg/kg in both the two series of experiments. Energy intake was at an approximate maintenance level of 36.1 +/- 3.0 kcal/kg. Apparent nitrogen balance improved with increase in nitrogen intake. The regression equations between nitrogen intake (X, mg/kg) and balance (Y, mg/kg) are shown in the following: SPI: Y = 0.411 X - 40.8 (n = 10, r = 0.812) SPI and rice protein: Y = 0.392 X -32.7 (n = 15, r = 0.739) From the above equations, the maintenance intakes of SPI and SPI-rice combination for an apparent nitrogen equilibrium were calculated to be 99 and 83 mg N/kg, respectively. Digestibilities were 98.2 +/- 5.0% for SPI and 93.1 +/- 6.1% for SPI-rice combination. The NPUs of SPI at intake levels of 40, 60 and 80 mg N/kg were 47 +/- 24 (n = 4), 49 (n = 2) and 44 +/- 3 (n = 4), respectively. The NPUs of SPI and rice mixed protein at intake levels of 45, 70 and 90 mg N/kg were 67 +/- 13 (n = 5), 51 +/- 7 (n = 5) and 54 +/- 12 (n = 5), respectively. It was concluded from the present study that both SPI and the SPI-rice combination had a high nutritive efficiency comparable with that of egg protein.     

Studies on the protein requirement of Brazilian rural workers ("boias frias") given a rice and bean diet

The present study was conducted to evaluate the nutritive value of a multiple level rice and bean diet fed to migrant workers. Nine healthy males, 18 to 28 years old were admitted to our metabolic unit for a three period metabolic balance study. The rice and beans based diet was fed at levels to provide 0.4, 0.6 or 0.8 g of protein/kg body weight. Mean energy intake for the three levels of intake and for all subjects was 46.9 +/- 2.9 kcal/kg Bwt/day. Each nitrogen balance period consisted of a) one day on a nitrogen free diet b) five days on an adaptation period, and c) five days on the balance period. "True digestibility', "true nitrogen balance", biologic value, and net protein utilization (NPU) were calculated. Mean protein requirements were estimated by regression analysis of pooled data of balances at different levels of intake. These results showed values of 103.8 mg N/kg Bwt/day. Mean and standard deviation for protein digestibility at each level of intake were 69.2 +/- 17.0, 75.5 +/- 5.3, and 74.9 +/- 10.6% respectively. Mean and standard deviation for NPU were 49.9 +/- 26.3, 55.6 +/- 10.6, and 57.8 +/- 14.4 respectively. The data support the conclusion that a rice and bean diet is a well balanced food combination and can serve as a fairly good source of protein for the adult human.     

Evaluation of the protein quality of an isolated soy protein in young men: relative nitrogen requirements and effect of methionine supplementation

The protein nutritional value of an isolated soy protein (Supro-620) was evaluated in a series of nitrogen balance studies in healthy young male MIT students. Experiment 1 involved giving eight subjects graded intakes of the isolated soy protein while seven additional subjects received egg protein. Mean nitrogen intake required for N balance for the isolated soy protein and the egg protein were not significantly different (p greater than 0.1). In experiment 2, nine subjects received soy and the effects on N balance at various levels of L-methionine supplementation were studied. In experiment 3 eight subjects each were studied at two nitrogen intake levels of isolated soy protein/kg/day with methionine supplementation, and an unsupplemented egg protein period included. Results from experiment 2 and 3 at an 82 mg N/kg/day test level showed that N balance for 1.6% supplementation was significantly below that of unsupplemented egg while 1.1% and unsupplemented soy were indistinguishable from egg. No beneficial effects of methionine supplementation were observed when the test nitrogen intake level was 128 mg N/kg/day. These results indicate that for healthy adults, the isolated soy protein is of high nutritional quality, comparable to that of animal protein sources, and that the methionine content is not limiting for adult protein maintenance.     

我国成年男子蛋白质需要量的研究

用短期和长期的氮平衡方法测定了我国成年男子吃动植物混合膳食时蛋白质的需要量。受试者均为成年男性职工,短期组10名,长期组6名。短期组平均年龄、体重和身高分别为37.9岁、64.3kg及173cm;长期组分别为30.2岁、67.7kg及171cm。 短期组实验分5期,每期14天,第一天吃低氮膳、第2～11天吃实验膳,最后3天吃一般膳食,不加限制。各期蛋白质水平按实验顺序分别为0.60、0.73、0.42、0.90和1.05g/kg体重/日;长期组实验期为三个月,蛋白质水平为0.93(0.91～0.94)g/kg体重/日。用凯氏定氮法测定了各代谢期中主副食及粪尿中氮的合量。短期组结果表明,在0.42、0.60和0.73g水平时,机体均处于负氮平衡状态,在0.90g时多数达到正氮平衡,而至1.05g时全部达到正氮平衡。通过直线回归方程式计算,y=-47.75±0.32x(n=46,r=0.83、P<0.01),当y=0时,x=129.4～192.5mg氮,平均为147.7±18.6mg氮,相当于每日每公斤体重摄入0.92g蛋白质才能达到氮平衡。长期组的结果表明,当蛋白质水平为0.93g/kg体重/日,在为期三个月的实验中即可维持机体正氮平衡。二组结果相一致。若加上维持氮平衡平均摄入量的二个标准差作为安全系数,则蛋白质的需要量为1.16g/kg体重/日。     

Nitrate and nitrogen balances in men

Nitrate is a nitrogen-containing compound that is not detected by the traditional Kjeldahl method of nitrogen analysis. Nitrate balance studies were done in order to determine if nitrate production in the human body contributes to the irrationally positive nitrogen balances that have been reported in healthy adults. Seven healthy young men, confined to a metabolic unit, received five diets for 9 days each: a mixed foods diet, a fiber-free egg formula diet, and egg formula with California small white beans, lima beans, and wheat bran added. Nitrate-nitrogen intake with the mixed foods diet was 75 mg/day and nonnitrate nitrogen intake was 19 g/day; crude Kjeldahl nitrogen balance (intake--(urinary + fecal)) was 0.64 +/- 1.23 g/day. Nitrate-nitrogen excretion exceeded intake by 0.10 +/- 0.05 g/day. With the four other diets, nitrate-nitrogen intake was almost nil (about 2 mg/day) and nonnitrate nitrogen intake was 95 mg/kg body weight; crude Kjeldahl nitrogen balances ranged from -0.63 +/- 0.73 to 0.02 +/- 0.45 g N/day. With these four diets, feces contained about 80 mg nitrate-nitrogen/day and urine contained about 8 mg. Saliva obtained before lunch had about 1 ppm nitrate-nitrogen with the formula diets and 5 ppm with the mixed foods diet. Net synthesis of nitrate is quite variable but appears to be of the order of 100 mg nitrate-nitrogen/day. Although the excess nitrate excretion increased total nitrogen excretion by less than 5%, it could account for as much as 10 to 20% of unexplained positive nitrogen balances previously reported in well-controlled studies.     

Comparative value of L-, and D-methionine supplementation of an oat-based diet for humans.

Total sulfur-containing amino acids have been found to be the first limiting amino acid in several foods in comparison with human amino acid requirements. Addition of methionine in appropriate amounts to these foods might be expected to improve protein value. Economically, DL-methionine would be preferable to L-methionine for this purpose. However, the comparative tuilization of L- DL-, and D-methionine is unclear. The objective of the current project was to compare the effectiveness of L-, DL-, and D-methionine supplementation of diets based on a food product known to be low in methionine value for human subjects. "Instant" oatmeal was fed to adult subjects to provide 4.0 g of nitrogen/day. In randomly arranged periods, these diets were supplemented with L-, DL-, or D-methionine at two levels (0.58 and 1.16 g of methionine/day). An unsupplemented diet was used in a control period. Diets were adequate in vitamins, minerals, and energy. Mean nitrogen balances of subjects while receiving the L-methionine supplements at the 0.58 and 1.16 g levels were minus0.10 and +0.06 g of nitrogen, respectively. At similar levels of DL-methionine supplementation, nitrogen balances were minus0.12 and minus0.15 g of nitrogen, respectively, and minus0.24 and minus0.18 g of nitrogen with D-methionine supplementation. The mean nitrogen balance when no supplement was used was minus0.22 g of nitrogen. Thus, D-methionine is seemingly poorly utilized by the human. Urinary methionine excretion data supported these results.     

Effects of low protein intake on protein metabolism of Papua New Guinea highlanders studied with [15N]glycine

The effects of low protein intake on protein metabolism, including the size of pools and the protein synthesis rates, were studied by use of [15N]glycine in Papua New Guinea highlanders. Studies were made on 9 men between October and December in 1982. In experiment 1, two subjects were given a protein-free diet (PFD) containing 49.1 kcal/kg of energy. In experiment 2, subjects were given a sweet-potato diet (SPD) containing 45.4 kcal/kg of energy and 0.507 g/kg of protein for 8 days, and then were given a low-protein sweet-potato diet (LPSPD) containing 50.0 kcal/kg of energy and 0.265 g/kg of protein. During the SPD period, the sizes of the metabolic and active protein pools (mean +/- SD) were 270 +/- 134 mgN/kg and 362 +/- 107 mgN/kg, respectively, and the rates of active and inactive protein synthesis were 463 +/- 161 mgN/kg/day and 299 +/- 38 mgN/kg/day, respectively. During the LPSPD period, the sizes of the metabolic pool and active protein pool were 131 +/- 64 mgN/kg and 378 +/- 106 mgN/kg, respectively, and the rates of active and inactive protein synthesis were 490 +/- 206 mgN/kg/day and 280 +/- 26 mgN/kg/day, respectively. The protein metabolism in the LPSPD showed no significant difference from the SPD. The results suggest that, when the energy levels were approximately the same, protein metabolism in Papua New Guinea highlanders was maintained in spite of the decrease in protein intake.     

Effect of supplemental methionine on plasma homocysteine concentrations in healthy men: a preliminary study

Hyperhomocysteinaemia is an established risk factor for vascular disease. The only source of homocysteine in humans is the amino acid methionine found in dietary protein. In an 8-week study, fasting plasma homocysteine concentrations were examined in a group of healthy male subjects (n = 6) under usual dietary conditions (weeks 1-4) and in response to weekly graded (25, 50 and 75 mg/kg/d) supplementary methionine (weeks 5, 6, 7). Nutrient intakes, including methionine, were calculated from 4 x 3 day food records. Under usual dietary conditions (mean methionine intake; 0.95 +/- 0.51 mg/d) weekly mean plasma homocysteine concentrations for the group were not significantly different (ANOVA) from each other ranging from 6.82 +/- 1.77 to 9.42 +/- 2.73 mumol/l. Doubling (supplementing with 25 mg/kg/d; + 2.04 g/d) or quadrupling (50 mg/kg/d; + 4.08 g/d) methionine intakes did not result in a significant increase in plasma homocysteine (8.56 +/- 3.68 mumol/l and 13.37 +/- 5.09 mumol/l respectively). A significant increase, however, was achieved when diets were supplemented with methionine at the highest level of 75 mg/kg/d (+6.14 g/d) resulting in a mean plasma homocysteine concentration of 18.05 +/- 11.8 mumol/l. Mean plasma homocysteine concentration returned to baseline (8.76 +/- 3.42 mumol/l), 10 days post-supplementation. The results of this study indicate that an increased dietary methionine will only cause elevated fasting homocysteine concentrations if ingested at intakes equivalent to five times usual intake. Because it is very unlikely that such levels could be achieved through dietary means alone we conclude that plasma homocysteine is unlikely to be affected by longer-term changes in food methionine intake.     

Minimum protein requirements in liver cirrhosis determined by nitrogen balance measurements at three levels of protein intake

Nitrogen balance at three levels of protein intake was measured in eight patients with cirrhosis of the liver; moreover, at each level of protein intake, the effects on nitrogen balance of branched-chain amino-acid enriched protein and natural protein were compared. From these nitrogen balance data, minimum protein requirements were calculated by linear regression analysis. The patients were in a negative nitrogen balance on a 40 g protein diet (-0.75 +/- 0.15 gN.), and in positive nitrogen balance on 60 g (+1.23 +/- 0.22 gN.) or 80 g of protein per day (+2.77 +/- 0.20 g N.). Their mean minimum protein requirement (48 +/- 5 g of protein/day or 0.75 g/kg/day) is higher than expected in healthy people; the safe level of protein intake (mean + 2 sd) is 58 g per day or 1.2 g/kg/day. Nitrogen balances and protein requirements were not different on branched-chain amino-acid enriched diets. The physical condition of the patients improved when they came into positive nitrogen balance; the higher rates of protein intake were well tolerated without onset of encephalopathy. We conclude that protein requirements are elevated in cirrhosis of the liver; diets supplying less than 60 g of protein per day should not be prescribed in long term treatment of cirrhotic patients.     

Efficiency of dietary methionine utilization by young pigs.

An assay was conducted to determine the efficiency of dietary methionine retention for protein accretion in 14-kg pigs. During an 18-d feeding period, pigs were fed a chemically defined amino acid basal diet [147.7 g protein (N x 6.25)/kg, 14.43 MJ metabolizable energy/kg, 4000 mg L-cystine/kg] containing 1150, 1725 or 2300 mg L-methionine/kg. Linear (P less than 0.01) responses in daily gain, daily food intake, daily methionine intake, gain:food ratio and empty body weight gain were obtained as dietary methionine level increased. Representative pigs were killed at the beginning of the assay for whole-body compositional analysis, and the comparative slaughter technique was used to estimate methionine retention. Absolute retention of methionine, protein, water, fat and ash increased linearly (P less than 0.05) with dietary methionine supplementation. Regressing methionine retained on methionine intake resulted in an efficiency of methionine retention above maintenance of 71.7%. The maintenance requirement for methionine was estimated to be 57 mg/d (8 mg/kg body wt 0.75) in the presence of excess dietary cystine. Concentrations of most indispensable amino acids, including methionine, in whole-body protein increased linearly, although glycine and proline concentrations decreased as dietary methionine level increased. This suggests that the ratio of whole-body collagen protein to non-collagen protein decreases as dietary methionine is incremented from deficiency to near adequacy.     

Nitrogen requirement of amino acid mixture with maintenance energy in young men

The effect of energy on nitrogen balance was examined in young men given amino acid mixture. The minimum amino acid nitrogen requirement for nitrogen equilibrium was determined together with the egg protein requirement. In experiment 1, the nitrogen sparing effect of energy was evaluated in four male students receiving diet containing an amino acid mixture and a constant nitrogen intake of 3.5 g N/day, which was equivalent to the nitrogen requirement with excess energy intake determined by Rose and Wixom (1). When the dietary energy supply was 45 kcal/kg, which is approximately the maintenance level, the mean nitrogen balance was negative, being -23.9 +/- 9.3 mg N/kg. However, with an excess energy intake of 55 kcal/kg, the nitrogen balance improved significantly, being -6.1 +/- 7.7 mg N/kg. In experiment 2, the nitrogen requirement of egg-pattern amino acid mixture for apparently zero balance was evaluated at maintenance energy intake in 28 Japanese young men and was compared with that of egg protein. After receiving standard diet, the subjects were given a semi-purified experimental diet containing egg-pattern amino acid mixture at nitrogen intake levels of 60, 75, 100, and 130 mg N/kg for two weeks. Then all groups except the 60 mg N/kg group were given isonitrogenous egg protein diet for another week. Energy intake was kept constant at approximately the maintenance level of 44.4 +/- 1.4 kcal/kg throughout the experiment. Nitrogen balance was not significantly different in groups given egg-pattern amino acid mixture and intact egg protein in each nitrogen intake level. From regression analysis, the nitrogen requirement for nitrogen equilibrium of the amino acid mixture was calculated to be 110.1 +/- 50.2 mg N/kg, which was not significantly different from the value of 88.4 +/- 40.6 mg N/kg of egg protein. It was concluded that the total amino acid requirement estimated by Rose and Wixom (1) was too low because they gave excess energy, and that there was no difference between the nitrogen requirement of egg protein and that of the corresponding amino acid mixture.     

Influence of increasing dietary intake on whole body protein kinetics in normal man

The whole body protein kinetic response to increasing dietary intake was studied in 20 normal adult male subjects receiving a defined formula diet orally. Each person received the same amount for 5 days at the rate ranging from 150 to 330 mgN/kg. day and 16 to 34 kcal/kg. day, keeping the calorie to nitrogen ratio as constant. Whole body protein flux was measured using a primed constant infusion of 15N glycine and determining isotopic enrichments in the urinary urea and ammonia. Whole body protein synthesis and breakdown rates were calculated from the flux measurement and nitrogen excretion and intake. The mean protein turnover (Q), synthesis (S) and breakdown (C) rates for all subjects were 3.72+/-0.42, 2.47+/-0.47 and 2.12+/-0.39 g protein/kg. day. These values increased with increasing dietary nitrogen intake up to 270+/-4 mgN/kg. day which is twice the daily recommended protein requirement for a normal adult man and then tended to decrease. Nitrogen intake in the range of 150 to 270 mg N/kg. day showed significant positive correlations with nitrogen balance, Q, S and S/C and the protein accretion was due to a relatively large increase in S compared to that in C. When the intake rate exceeded 270 mg N/kg. day, the nitrogen balance was still positive but now due to a larger decrease in C. These results show that the kinetic parameters of whole body protein metabolism in adult man appear to exhibit a maximum at a dietary nitrogen intake twice the daily requirement level. The mechanism of the maintenance of protein balance changes at this threshold.     

Efficiency of methionine retention in ducks

The accretion of methionine and protein as a function of methionine intake was assessed in growing ducks between 22 and 42 d post-hatching. Four graded doses of dl-methionine at 0, 0 x 5, 1 x 0 or 1 x 5 g/kg diet were added to a methionine-limiting basal diet and fed to four replicate groups of four ducks each. The growth and efficiency of food use for growth increased linearly (P<0 x 05) as a function of methionine intake. The accretion of body protein increased (P<0 x 001) from 87 x 5 to 182 x 2 g, and that of methionine from 1616 to 3125 mg, over the 21 d period as dietary methionine increased. The accretion rate of methionine in the body (y, mg/d) as a function of methionine intake (x, mg/d) of ducks fed diets containing supplemental methionine at 0, 0 x 5, 1 x 0 or 1 x 5 g/kg diet from day 22 to day 42 post-hatching gave the regression equation: y=-148 x 86 (se 32 x 558)+0 x 312 (se 0 x 0384)X, r2=0 x 8253. For protein accretion rate in the body (y, mg/d) as a function of methionine intake (x, mg/d), the regression equation was: y= -9782 (se 2204)+19 x 505 (se 2 x 5994)x, r2=0 x 8009. There was a linear relationship between methionine (y, mg/d) and protein (x, mg/d) accretion in ducks that was described by the equation y=12 x 757 (se 7 x 4019)+0 x 01 525 (se 0 x 00 107)x, r2=0 x 9355. The results of these studies suggest a constant utilisation of methionine over the range 2 x 4-3 x 9 g digestible methionine/kg diet, with an efficiency of 31 %. Furthermore, the results suggest a quantitative relationship of 15 mg methionine for every gram of protein accretion.     

Application of the indicator amino acid oxidation technique for the determination of metabolic availability of sulfur amino acids from casein versus soy protein isolate in adult men

Our objective was to determine the metabolic availability (MA) of sulfur amino acids in dietary proteins using the indicator amino acid oxidation (IAAO) technique. Five to seven men received graded levels (20, 40, 60, and 70%) of the mean total sulfur amino acid (TSAA) requirement of 13 mg x kg(-1) x d(-1) as a crystalline AA mixture, casein, and soy protein isolate (SPI) (40, 50, 60, and 70%), respectively. Five of these subjects received 40% of TSAA requirement from SPI supplemented with methionine to the level of 40% of requirement. These 5 subjects also repeated the level of 60% TSAA requirements from both casein and SPI to assess repeatability. The mean MA of TSAA from SPI (71.8 +/- 3.6%) was lower than from casein (87.4 +/- 3.8%, P < 0.05). Supplementation of SPI with methionine decreased the IAAO (11.5 +/- 0.3% administered dose) compared with unsupplemented SPI (12.8 +/- 0.5% administered dose, P < 0.05). IAAO was similar for repeated measurements of casein and SPI, respectively, at the 60% TSAA intake level (10.8 +/- 1.0 vs. 10.7 +/- 1.2% for casein; 12.7 +/- 1.3 vs. 12.9 +/- 2.6% for SPI). In conclusion, the IAAO technique can be used to determine the MA of AA for protein synthesis in test proteins for humans.     

Effects of soy protein supplemented with methionine on blood lipids and adiposity of rats

OBJECTIVE: The effects of soy protein isolate (SPI) versus casein on blood lipids and adiposity were investigated in rats fed methionine-equivalent diets. METHODS: Twenty-eight male Sprague-Dawley rats (230 to 250 g) were assigned in equal numbers to groups consuming SPI- or casein-based diets (20%) supplemented with L-methionine. After 28 d, blood was collected for triacylglycerol, total cholesterol, and high-density lipoprotein cholesterol assessment and epididymal fat pads were weighed. RESULTS: Food intake (519 +/- 90 versus 490 +/- 115 g), weight gain (144 +/- 35 versus 133 +/- 28 g), food efficiency ratio (0.29 +/- 0.09 versus 0.28 +/- 0.06), epididymal fat pad weights (5.409 +/- 2.076 versus 4.768 +/- 1.867 g), and serum concentrations of triacylglycerol (96.3 +/- 41.8 versus 93.4 +/- 37.4 mg/dL) and high-density lipoprotein cholesterol (32.6 +/- 7.4 versus 33.8 +/- 4.4 mg/dL) were similar between the casein and SPI groups, respectively. However, total cholesterol (73.8 +/- 17.8 versus 59.3 +/- 11.9 mg/dL) concentration was higher for the casein-fed rats than for the SPI-fed rats, respectively (P < 0.05). CONCLUSIONS: These results suggest that methionine supplementation may eliminate the decreased fat deposition previously ascribed to soy protein; however, methionine did not abolish the commonly observed hypocholesterolemic effects of soy.     

Effect of protein intake level on urinary energy/nitrogen ratio in Japanese

Urinary energy/nitrogen ratios were determined in 179 female and 14 male subjects given protein from various sources and at various intake levels. The ratio decreased with increasing protein intake from zero to 1 g/kg/day but was constant when protein intake was between 1 to 1.8 g/kg/day. The ratio was not affected by the variety of protein source. There was no difference between the data for semisynthetic diet and conventional diet. Mean values and standard deviations of the ratio in men and women given the diet containing 1.0 to 1.8 g protein/kg/day were 9.06 +/- 0.56 (n = 14) and 8.19 +/- 0.81 (n = 37) kcal/kg N, respectively. The difference between two figures in men and women was significant (p less than 0.05). The mean values of urinary E/N ratio actually measured did not approach those of urea (5.34 kcal/g N), the principal nitrogenous compound in urine, the proportion of which increased at higher protein intake level. Characteristically high ratios were obtained in the ma-konbu (Laminaria japonica) and enokitake (Flammulina velutipes) diet groups. The results suggest that urinary energy originates not only from nitrogen-containing compounds but also from other organic compounds containing no nitrogen. Therefore, further investigation is necessary to evaluate the urinary E/N ratio applicable to the urinary loss of incompletely oxidized nitrogenous compounds.     

A whey-supplemented, high-protein diet versus a high-carbohydrate diet: effects on endurance cycling performance

This study compared a training diet recommended for endurance athletes (H-CHO) with an isoenergetic high protein (whey supplemented), moderate carbohydrate (H-Pro) diet on endurance cycling performance. Over two separate 7-d periods subjects (n = 7) ingested either H-CHO (7.9 +/- 1.9 g x kg(-1) x d(-1) carbohydrate; 1.2 +/- 0.3 g x kg(-1) x d(-1) fat; 1.3 +/- 0.4 g x kg(-1) x d(-1) protein) or H-Pro (4.9 +/- 1.8 g x kg(-1) x d(-1); 1.3 +/- 0.3 g x kg(-1) x d(-1); 3.3 +/- 0.4 g x kg(-1) x d(-1)) diet in a randomized, balanced order. On day 8 subjects cycled (self-paced) for a body weight dependent (60 kJ/bm) amount of work. No differences occurred between energy intake (P = 0.422) or fat intake (P = 0.390) during the two dietary conditions. Performance was significantly (P = 0.010) impaired following H-Pro (153 +/- 36) compared with H-CHO (127 +/- 34 min). No differences between treatments were observed for physiological measures taken during the performance trials. These results indicate an ergolytic effect of a 7-d high protein diet on self-paced endurance cycling performance.     

Long-term validation of 1 g of protein per kilogram body weight from a predominantly vegetable mixed diet to meet the requirements of young adult males

Eight healthy young men participated in a 90-d metabolic balance study designed to assess the adequacy of 1 g of protein (N X 6.25) per kilogram body weight per day provided by a predominantly vegetable diet. The mean gross energy intake of the subjects was 49 kcal/(kg X d). The individuals received the experimental diet for eleven 8-d experimental periods. Three isoenergetic, isonitrogenous meals were served at 0800, 1200 and 1900. Anthropometric measurements and biochemical determinations in blood were made at the beginning of the study and afterwards at regular 15-d intervals. Body weight was measured daily. The mean overall weight change for the group was -0.8 kg. The mean daily urinary nitrogen output decreased from an initial value of 134.6 mg/(kg X d) to a final figure of 115.1 mg/(kg X d) (P less than 0.01), while the daily fecal N decreased from 31.5 to 26.3 mg/(kg X d) (P less than 0.05). Mean cumulative nitrogen balances were slightly positive for seven out of the eight individuals with an overall mean nitrogen balance value of +6.7 mg N/(kg X d). Biochemical and hematological values showed no significant changes throughout the study, except for a decrease in serum cholesterol. It is concluded that the "Chilean" mixed diet fed at the level of 1 g of protein per kilogram body weight per day with sufficient energy meets the long-term protein-energy needs of healthy young men, thus supporting the 1984 FAO/WHO/UNU safe recommended daily protein allowance of 0.75 g of reference protein, with a correction for the lower digestibility of vegetable sources.     

Effects of soy protein on levels of remnant-like particles cholesterol and vitamin E in healthy men.

We determined the effects of soy protein isolate (SPI) intake on remnant-like particles (RLP), lipolytic enzymes, lipid transfer protein, transaminases, sex hormones, iron, calcium, and vitamin E in healthy men. In the first randomized, crossover experiment, 14 men were given either 20 g per day of SPI or nothing (control) for each 4-week segment. After 3 weeks of SPI intake, TG and RLP cholesterol levels were significantly lower than the baseline by 13.4% (p<0.05) and 9.8% (p<0.05), respectively. However, no significant change was found in total and low-density lipoprotein (LDL) cholesterol levels or the activities of lipoprotein lipase, hepatic lipase, cholesteryl ester transfer protein, and lecithin cholesterol acyltransferase. Although the levels of transaminases. testosterone, iron, and calcium did not change, the vitamin E level was reduced from the baseline by 9.7%, a significant decrease (p<0.01). In the second study, we attempted to determine the effect of vitamin E supplement taken with SPI. For each 3-week segment, 12 men were given 20 g per day of SPI, either with or without 200 mg per day of vitamin E, in a randomized crossover design. The vitamin E level was reduced by 9.2%, a significant decrease (p<0.05), after SPI intake for 3 weeks, and vitamin E supplement increased vitamin E level significantly (p<0.05). These results demonstrate that SPI intake reduces remnant lipoproteins, TG, and the plasma level of vitamin E, although vitamin E supplementation compensates for the reduction of vitamin E. Therefore the supplementation of vitamin E may be required in subjects with long-term and abundant intake of soy protein.