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Dietary Carbohydrate Deprivation Increases 24-Hour Nitrogen Excretion without Affecting Postabsorptive Hepatic or Whole Body Protein Metabolism in Healthy Men
Because insulin is an important regulator of protein metabolism, we hypothesized that physiological modulation of insulin secretion, by means of extreme variations in dietary carbohydrate content, affects postabsorptive protein metabolism. Therefore, we studied the effects of three isocaloric diets with identical protein content and low-carbohydrate/high-fat (2% and 83% of total energy, respectively), intermediate-carbohydrate/intermediate-fat (44% and 41% of total energy, respectively), and high-carbohydrate/low-fat (85% and 0% of total energy, respectively) content in six healthy men. Whole body protein metabolism was assessed by 24-h urinary nitrogen excretion, postabsorptive leucine kinetics, and fibrinogen and albumin synthesis by infusion of [1-13C]leucine and [1-13C]valine.
The low-carbohydrate/high-fat diet resulted in lower absorptive and postabsorptive plasma insulin concentrations, and higher rates of nitrogen excretion compared with the other two diets: 15.3 ± 0.9 vs. 12.1 ± 1.1 (P = 0.03) and 10.8 ± 0.5 g/24 h (P = 0.005), respectively. Postabsorptive rates of appearance of leucine and of leucine oxidation were not different among the three diets. In addition, dietary carbohydrate content did not affect the synthesis rates of fibrinogen and albumin.
In conclusion, eucaloric carbohydrate deprivation increases 24-h nitrogen loss but does not affect postabsorptive protein metabolism at the hepatic and whole body level. By deduction, dietary carbohydrate is required for an optimal regulation of absorptive, rather than postabsorptive, protein metabolism.
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Stimulation of protein turnover by carbohydrate overfeeding in men
S. Welle, D. E. Matthews, R. G. Campbell and K. S. Nair
Endocrine-Metabolism Unit, Monroe Community Hospital, University of Rochester School of Medicine and Dentistry 14603.
The effect of carbohydrate overfeeding on protein metabolism was studied in 11 healthy men. Total urinary nitrogen output during 10 days of carbohydrate overfeeding (1,600 extra kcal/day) decreased 27% relative to nitrogen excretion during 10 days of weight maintenance, indicating protein accretion during over-feeding. However, postabsorptive nitrogen excretion did not change, which means that the positive nitrogen balance associated with overfeeding results from enhanced postprandial nitrogen retention. Overfeeding reduced postabsorptive glucose concentrations 4 +/- 1% and increased glucose production rate 14 +/- 2% and glucose clearance 17 +/- 4%. Overfeeding increased plasma concentrations of insulin, glucagon, and 3,5,3'-triiodothyronine approximately 20%. Alanine and branched-chain amino acid concentrations were increased after overfeeding, but serine, threonine, and asparagine concentrations were reduced. Postabsorptive leucine flux, which is an index of proteolysis, was measured using L-[1-13C]leucine as a tracer. Overfeeding increased leucine flux 13 +/- 2% compared with values after 10 days on a weight-maintenance diet. If it is assumed that overfeeding did not alter the fraction of 13CO2 not recovered in breath, there was no change in the portion of leucine flux that was oxidized. Thus the difference between flux and oxidation, which is a theoretical index of protein synthesis, increased 12 +/- 3% after overfeeding. These data suggest that excess caloric intake, without an increase in protein intake, stimulates post-absorptive proteolysis and protein synthesis.
The Strength and Power Athlete
Individuals that are involved in strength and power type sports like bodybuilding, powerlifting, football or sprinting may have even higher dietary protein needs than the endurance athlete to maintain a positive nitrogen balance. These athletes have felt for many years that increased protein consumption would promote an accelerated rate of muscle synthesis and decrease the rate of protein catabolism, resulting in greater muscle mass accumulation. There are many conflicting views over how much protein is actually needed to optimally increase muscle mass and/or strength. However, Williams (1985) feels there is sufficient data available to make some general conclusions. It is generally agreed that a pound of muscle contains about 100 g of actual protein. So in order to gain one pound of muscle mass per week we would need to consume at least 14.29 g of extra protein per day along with the additional calories (100 / 7 = 14.29). While it is not know exactly how many extra calories are necessary to synthesize a pound of muscle mass, the National Research Council notes that 5 calories are needed to support one gram of lean tissue growth (Williams, 1992). So simple math would tell us that 500 extra calories (5 x 100 = 500) may be also necessary every day to gain one pound of lean tissue per week.
Tarnopolsky et al. (1992) using both nitrogen balance and metabolic tracers methodology recommended between that 1.4 and 2.4 g/kg/d for athletes involved in strength and power exercise. Later 1.76 g/kg/d was recommended as the accepted RDA for strength and power athletes by Lemon et al (1992) and Tarnopolsky. These studies showed that whole body protein synthesis was elevated at these intakes without an increase in protein oxidation.
Fern et al. (1991) found that 2.4 g/kg/d was considered protein overload, thus providing no further increase in protein synthesis for strength and power athletes. When strength athletes increased their protein consumption to 2.4 g/kg/d amino acid oxidation increased, but there was no further protein synthesis. Researchers considered this to clearly indicate a protein overload.
It is interesting to note that Consolazio et al. (1975) Marabel et al. (1979), and Dragan et al. (1985) all reported larger increases in strength, lean body mass (LBM) and nitrogen with much higher protein intakes (3.3, 2.8, and 3.5 g/kg/d respectively). These reports tend to corroborate the more anecdotal beliefs of weight lifters that extremely high dietary protein intakes are essential for optimal muscular development.
While these results are very interesting, they still did not prove that higher intakes of more than 2.4 g/kg/d actually were responsible for improving muscle mass during resistance training. Researchers are not exactly sure what role the extra calories might have provided by consuming that much extra protein, could have had on protein synthesis. It is suspected that the more calories you take in over energy balance, the less protein you may actually need for optimal protein synthesis (Bucci 1993). In any case a higher protein intake has not been shown to impede sports that involve strength and power.
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So when amino acids are not being used to build protein or make other nitrogen-containing compounds, amino acids are “wasted” in a sense. This wasting occurs under any of four conditions:
(1) when there is not enough energy from other sources:
(2) when there is too much protein. So that not all is needed:
(3) when there is too much of any amino acid from supplements:
(4) when the diet’s protein is of to low quality, with to few essential amino acids. To prevent the wasting of dietary protein, and permit the synthesis of needed body protein, three conditions must be met. First, the dietary protein must be adequate in quality. Second, it must supply all essential amino acids in the proper amounts. Third, enough energy yielding carbohydrate and fat must be present, to permit the dietary protein to be used for body requirements and not for energy. Remember that carbohydrates are protein sparing and conserves tissue protein.
J Nutr 2002 Oct;132(10):3225S-7S
Latency, duration and dose response relationships of amino acid effects on human muscle protein synthesis.
Rennie MJ, Bohe J, Wolfe RR Division of Molecular Physiology, School of Life Sciences, University of Dundee, Scotland, United Kingdom. m.j.rennie@dundee.ac.uk
The components of the stimulatory effect of food on net deposition of protein are beginning to be identified and separated. One of the most important of these appears to be the effect of amino acids per se in stimulating muscle anabolism. Amino acids appear to have a linear stimulatory effect within the range of normal diurnal plasma concentrations from postabsorptive to postprandial. Within this range, muscle protein synthesis (measured by incorporation of stable isotope tracers of amino acids into biopsied muscle protein) appears to be stimulated approximately twofold; however, little further increase occurs when very high concentrations of amino acids (>2.5 times the normal postabsorptive plasma concentration) are made available. Amino acids provided in surfeit of the ability of the system to synthesize protein are disposed of by oxidation, ureagenesis and gluconeogenesis. The stimulatory effect of amino acids appears to be time dependent; a square wave increase in the availability of amino acids causes muscle protein synthesis to be stimulated and to fall back to basal values, despite continued amino acid availability. The relationship between muscle protein synthesis and insulin availability suggests that most of the stimulatory effects occur at low insulin concentrations, with large increases having no effect. These findings may have implications for our understanding of the body's requirements for protein. The maximal capacity for storage of amino acids as muscle protein probably sets an upper value on the extent to which amino acids can be stored after a single meal. [Note: this reveals the false belief in body builders that enormous amounts of protein produce more muscle mass.]
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J Clin Endocrinol Metab. 1989 Oct ;69 (4):745-52 2778033 [Cited: 3]
Dietary carbohydrate content determines responsiveness to growth hormone in energy-restricted humans.
D K Snyder , D R Clemmons , L E Underwood
To determine if diet composition influences responses to GH, we fed 11 obese women diets containing 12 Cal/kg ideal BW (IBW) for 2 5-week study intervals. Nonprotein calories were supplied to 6 subjects as 72% carbohydrate (high carbohydrate diet), and 5 subjects received 80% of their nonprotein calories as lipid (high lipid diet). Protein intake was constant (1.0 g/kg IBW) in both groups. During 1 study interval we gave injections of GH (0.1 mg/kg IBW) every other day for 3 weeks (weeks 2-4), and in the other interval injections of vehicle were given. Subjects ingesting the high carbohydrate diet excreted significantly less urinary nitrogen [660.2 +/- 124.1 mmol/day (mean +/- SD)] than those who received high lipid (794.2 +/- 198.5 mmol/day; P less than 0.001), and GH injections reduced nitrogen excretion in the high carbohydrate subjects (532.8 +/- 123.8 mmol/day), but not in the high lipid subjects (743.7 +/- 126.6 mmol/day). The subjects receiving the high carbohydrate diet had a significant increase in serum insulin-like growth factor-I (IGF-I; from 36.2 +/- 9.7 to 55.9 +/- 6.6 nmol/L) and urinary C-peptide excretion (from 43.9 +/- 25.6 to 60.8 +/- 29.4 nmol/day) in response to GH. The IGF-I response attenuated slowly over the 3-week treatment interval. On the other hand, the high lipid group had lesser increases in IGF-I (from 31.0 +/- 6.5 to 41.7 +/- 8.8 nmol/L) and C-peptide excretion (from 24.3 +/- 28.9 to 29.8 +/- 32.8 nmol/day), and IGF-I concentrations declined to control values after only 5 days of GH injection. We believe that this initial IGF-I response was due to an antecedent 35-Cal balanced diet. The mean increment in serum FFA 4 h after GH injection was significantly less in subjects fed the high lipid diet (0.53 +/- 0.40 meq/L) than in those fed the high carbohydrate diet (0.83 +/- 0.43 meq/L). GH injections produced more body fat loss than injections of vehicle whether expressed as percent body fat lost (GH, 3.7 +/- 1.0%; vehicle, 2.8 +/- 0.7%, P less than 0.05) or as the fraction of weight lost as fat (fat loss/weight loss; GH, 0.81 +/- 0.13; vehicle, 0.64 +/- 0.08; P less than 0.005). There was an inverse correlation between the percentage of body fat lost and mean urinary C-peptide excretion during GH injections (r = -0.70; P less than 0.05), suggesting that stimulation of insulin secretion by GH might antagonize the tendency of GH to promote fat loss.(ABSTRACT TRUNCATED AT 400 WORDS)
Dietary Carbohydrate Deprivation Increases 24-Hour Nitrogen Excretion without Affecting Postabsorptive Hepatic or Whole Body Protein Metabolism in Healthy Men
Because insulin is an important regulator of protein metabolism, we hypothesized that physiological modulation of insulin secretion, by means of extreme variations in dietary carbohydrate content, affects postabsorptive protein metabolism. Therefore, we studied the effects of three isocaloric diets with identical protein content and low-carbohydrate/high-fat (2% and 83% of total energy, respectively), intermediate-carbohydrate/intermediate-fat (44% and 41% of total energy, respectively), and high-carbohydrate/low-fat (85% and 0% of total energy, respectively) content in six healthy men. Whole body protein metabolism was assessed by 24-h urinary nitrogen excretion, postabsorptive leucine kinetics, and fibrinogen and albumin synthesis by infusion of [1-13C]leucine and [1-13C]valine.
The low-carbohydrate/high-fat diet resulted in lower absorptive and postabsorptive plasma insulin concentrations, and higher rates of nitrogen excretion compared with the other two diets: 15.3 ± 0.9 vs. 12.1 ± 1.1 (P = 0.03) and 10.8 ± 0.5 g/24 h (P = 0.005), respectively. Postabsorptive rates of appearance of leucine and of leucine oxidation were not different among the three diets. In addition, dietary carbohydrate content did not affect the synthesis rates of fibrinogen and albumin.
In conclusion, eucaloric carbohydrate deprivation increases 24-h nitrogen loss but does not affect postabsorptive protein metabolism at the hepatic and whole body level. By deduction, dietary carbohydrate is required for an optimal regulation of absorptive, rather than postabsorptive, protein metabolism.
----------------------------------------------------------------------------------------------------------
-----------------------------------------------------------------------------------------------------------
Stimulation of protein turnover by carbohydrate overfeeding in men
S. Welle, D. E. Matthews, R. G. Campbell and K. S. Nair
Endocrine-Metabolism Unit, Monroe Community Hospital, University of Rochester School of Medicine and Dentistry 14603.
The effect of carbohydrate overfeeding on protein metabolism was studied in 11 healthy men. Total urinary nitrogen output during 10 days of carbohydrate overfeeding (1,600 extra kcal/day) decreased 27% relative to nitrogen excretion during 10 days of weight maintenance, indicating protein accretion during over-feeding. However, postabsorptive nitrogen excretion did not change, which means that the positive nitrogen balance associated with overfeeding results from enhanced postprandial nitrogen retention. Overfeeding reduced postabsorptive glucose concentrations 4 +/- 1% and increased glucose production rate 14 +/- 2% and glucose clearance 17 +/- 4%. Overfeeding increased plasma concentrations of insulin, glucagon, and 3,5,3'-triiodothyronine approximately 20%. Alanine and branched-chain amino acid concentrations were increased after overfeeding, but serine, threonine, and asparagine concentrations were reduced. Postabsorptive leucine flux, which is an index of proteolysis, was measured using L-[1-13C]leucine as a tracer. Overfeeding increased leucine flux 13 +/- 2% compared with values after 10 days on a weight-maintenance diet. If it is assumed that overfeeding did not alter the fraction of 13CO2 not recovered in breath, there was no change in the portion of leucine flux that was oxidized. Thus the difference between flux and oxidation, which is a theoretical index of protein synthesis, increased 12 +/- 3% after overfeeding. These data suggest that excess caloric intake, without an increase in protein intake, stimulates post-absorptive proteolysis and protein synthesis.
The Strength and Power Athlete
Individuals that are involved in strength and power type sports like bodybuilding, powerlifting, football or sprinting may have even higher dietary protein needs than the endurance athlete to maintain a positive nitrogen balance. These athletes have felt for many years that increased protein consumption would promote an accelerated rate of muscle synthesis and decrease the rate of protein catabolism, resulting in greater muscle mass accumulation. There are many conflicting views over how much protein is actually needed to optimally increase muscle mass and/or strength. However, Williams (1985) feels there is sufficient data available to make some general conclusions. It is generally agreed that a pound of muscle contains about 100 g of actual protein. So in order to gain one pound of muscle mass per week we would need to consume at least 14.29 g of extra protein per day along with the additional calories (100 / 7 = 14.29). While it is not know exactly how many extra calories are necessary to synthesize a pound of muscle mass, the National Research Council notes that 5 calories are needed to support one gram of lean tissue growth (Williams, 1992). So simple math would tell us that 500 extra calories (5 x 100 = 500) may be also necessary every day to gain one pound of lean tissue per week.
Tarnopolsky et al. (1992) using both nitrogen balance and metabolic tracers methodology recommended between that 1.4 and 2.4 g/kg/d for athletes involved in strength and power exercise. Later 1.76 g/kg/d was recommended as the accepted RDA for strength and power athletes by Lemon et al (1992) and Tarnopolsky. These studies showed that whole body protein synthesis was elevated at these intakes without an increase in protein oxidation.
Fern et al. (1991) found that 2.4 g/kg/d was considered protein overload, thus providing no further increase in protein synthesis for strength and power athletes. When strength athletes increased their protein consumption to 2.4 g/kg/d amino acid oxidation increased, but there was no further protein synthesis. Researchers considered this to clearly indicate a protein overload.
It is interesting to note that Consolazio et al. (1975) Marabel et al. (1979), and Dragan et al. (1985) all reported larger increases in strength, lean body mass (LBM) and nitrogen with much higher protein intakes (3.3, 2.8, and 3.5 g/kg/d respectively). These reports tend to corroborate the more anecdotal beliefs of weight lifters that extremely high dietary protein intakes are essential for optimal muscular development.
While these results are very interesting, they still did not prove that higher intakes of more than 2.4 g/kg/d actually were responsible for improving muscle mass during resistance training. Researchers are not exactly sure what role the extra calories might have provided by consuming that much extra protein, could have had on protein synthesis. It is suspected that the more calories you take in over energy balance, the less protein you may actually need for optimal protein synthesis (Bucci 1993). In any case a higher protein intake has not been shown to impede sports that involve strength and power.
\
/
\
/
\
/
So when amino acids are not being used to build protein or make other nitrogen-containing compounds, amino acids are “wasted” in a sense. This wasting occurs under any of four conditions:
(1) when there is not enough energy from other sources:
(2) when there is too much protein. So that not all is needed:
(3) when there is too much of any amino acid from supplements:
(4) when the diet’s protein is of to low quality, with to few essential amino acids. To prevent the wasting of dietary protein, and permit the synthesis of needed body protein, three conditions must be met. First, the dietary protein must be adequate in quality. Second, it must supply all essential amino acids in the proper amounts. Third, enough energy yielding carbohydrate and fat must be present, to permit the dietary protein to be used for body requirements and not for energy. Remember that carbohydrates are protein sparing and conserves tissue protein.
J Nutr 2002 Oct;132(10):3225S-7S
Latency, duration and dose response relationships of amino acid effects on human muscle protein synthesis.
Rennie MJ, Bohe J, Wolfe RR Division of Molecular Physiology, School of Life Sciences, University of Dundee, Scotland, United Kingdom. m.j.rennie@dundee.ac.uk
The components of the stimulatory effect of food on net deposition of protein are beginning to be identified and separated. One of the most important of these appears to be the effect of amino acids per se in stimulating muscle anabolism. Amino acids appear to have a linear stimulatory effect within the range of normal diurnal plasma concentrations from postabsorptive to postprandial. Within this range, muscle protein synthesis (measured by incorporation of stable isotope tracers of amino acids into biopsied muscle protein) appears to be stimulated approximately twofold; however, little further increase occurs when very high concentrations of amino acids (>2.5 times the normal postabsorptive plasma concentration) are made available. Amino acids provided in surfeit of the ability of the system to synthesize protein are disposed of by oxidation, ureagenesis and gluconeogenesis. The stimulatory effect of amino acids appears to be time dependent; a square wave increase in the availability of amino acids causes muscle protein synthesis to be stimulated and to fall back to basal values, despite continued amino acid availability. The relationship between muscle protein synthesis and insulin availability suggests that most of the stimulatory effects occur at low insulin concentrations, with large increases having no effect. These findings may have implications for our understanding of the body's requirements for protein. The maximal capacity for storage of amino acids as muscle protein probably sets an upper value on the extent to which amino acids can be stored after a single meal. [Note: this reveals the false belief in body builders that enormous amounts of protein produce more muscle mass.]
---------------------------------------------------------------------------------
J Clin Endocrinol Metab. 1989 Oct ;69 (4):745-52 2778033 [Cited: 3]
Dietary carbohydrate content determines responsiveness to growth hormone in energy-restricted humans.
D K Snyder , D R Clemmons , L E Underwood
To determine if diet composition influences responses to GH, we fed 11 obese women diets containing 12 Cal/kg ideal BW (IBW) for 2 5-week study intervals. Nonprotein calories were supplied to 6 subjects as 72% carbohydrate (high carbohydrate diet), and 5 subjects received 80% of their nonprotein calories as lipid (high lipid diet). Protein intake was constant (1.0 g/kg IBW) in both groups. During 1 study interval we gave injections of GH (0.1 mg/kg IBW) every other day for 3 weeks (weeks 2-4), and in the other interval injections of vehicle were given. Subjects ingesting the high carbohydrate diet excreted significantly less urinary nitrogen [660.2 +/- 124.1 mmol/day (mean +/- SD)] than those who received high lipid (794.2 +/- 198.5 mmol/day; P less than 0.001), and GH injections reduced nitrogen excretion in the high carbohydrate subjects (532.8 +/- 123.8 mmol/day), but not in the high lipid subjects (743.7 +/- 126.6 mmol/day). The subjects receiving the high carbohydrate diet had a significant increase in serum insulin-like growth factor-I (IGF-I; from 36.2 +/- 9.7 to 55.9 +/- 6.6 nmol/L) and urinary C-peptide excretion (from 43.9 +/- 25.6 to 60.8 +/- 29.4 nmol/day) in response to GH. The IGF-I response attenuated slowly over the 3-week treatment interval. On the other hand, the high lipid group had lesser increases in IGF-I (from 31.0 +/- 6.5 to 41.7 +/- 8.8 nmol/L) and C-peptide excretion (from 24.3 +/- 28.9 to 29.8 +/- 32.8 nmol/day), and IGF-I concentrations declined to control values after only 5 days of GH injection. We believe that this initial IGF-I response was due to an antecedent 35-Cal balanced diet. The mean increment in serum FFA 4 h after GH injection was significantly less in subjects fed the high lipid diet (0.53 +/- 0.40 meq/L) than in those fed the high carbohydrate diet (0.83 +/- 0.43 meq/L). GH injections produced more body fat loss than injections of vehicle whether expressed as percent body fat lost (GH, 3.7 +/- 1.0%; vehicle, 2.8 +/- 0.7%, P less than 0.05) or as the fraction of weight lost as fat (fat loss/weight loss; GH, 0.81 +/- 0.13; vehicle, 0.64 +/- 0.08; P less than 0.005). There was an inverse correlation between the percentage of body fat lost and mean urinary C-peptide excretion during GH injections (r = -0.70; P less than 0.05), suggesting that stimulation of insulin secretion by GH might antagonize the tendency of GH to promote fat loss.(ABSTRACT TRUNCATED AT 400 WORDS)
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