BigTex
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Stephan van Vliet, Evan L Shy, Sidney Abou Sawan, Joseph W Beals, Daniel WD West, Sarah K Skinner, Alexander V Ulanov, Zhong Li, Scott A Paluska, Carl M Parsons, Daniel R Moore, and Nicholas A Burd. Consumption of whole eggs promotes greater stimulation of postexercise muscle protein synthesis than consumption of isonitrogenous amounts of egg whites in young men. October 2017American Journal of Clinical Nutrition 106(6).
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Abstract
Background: Protein in the diet is commonly ingested from whole foods that contain various macro- and micronutrients. However, the effect of consuming protein within its natural whole-food matrix on postprandial protein metabolism remains understudied in humans.Objective: We aimed to compare the whole-body and muscle protein metabolic responses after the consumption of whole eggs with egg whites during exercise recovery in young men.Design: In crossover trials, 10 resistance-trained men [aged 21 ± 1 y; 88 ± 3 kg; body fat: 16% ± 1% (means ± SEMs)] received primed continuous l-[ring-(2)H5]phenylalanine and l-[1-(13)C]leucine infusions and performed a single bout of resistance exercise. After exercise, participants consumed intrinsically l-[5,5,5-(2)H3]leucine-labeled whole eggs (18 g protein, 17 g fat) or egg whites (18 g protein, 0 g fat). Repeated blood and muscle biopsy samples were collected to assess whole-body leucine kinetics, intramuscular signaling, and myofibrillar protein synthesis.Results: Plasma appearance rates of protein-derived leucine were more rapid after the consumption of egg whites than after whole eggs (P = 0.01). Total plasma availability of leucine over the 300-min postprandial period was similar (P= 0.75) between the ingestion of whole eggs (68% ± 1%) and egg whites (66% ± 2%), with no difference in whole-body net leucine balance (P = 0.27). Both whole-egg and egg white conditions increased the phosphorylation of mammalian target of rapamycin complex 1, ribosomal protein S6 kinase 1, and eukaryotic translation initiation factor 4E-binding protein 1 during postexercise recovery (all P < 0.05). However, whole-egg ingestion increased the postexercise myofibrillar protein synthetic response to a greater extent than did the ingestion of egg whites (P= 0.04).Conclusions: We show that the ingestion of whole eggs immediately after resistance exercise resulted in greater stimulation of myofibrillar protein synthesis than did the ingestion of egg whites, despite being matched for protein content in young men. Our data indicate that the ingestion of nutrient- and protein-dense foods differentially stimulates muscle anabolism compared with protein-dense foods.
Similar to isolated protein sources (e.g., whey and casein) (, we also showed that the consumption of protein-dense foods in the form of whole eggs and egg whites improves whole-body net protein balance. Although . insight into whole-body protein kinetics can provide valuable information on whole-body protein remodeling and net anabolism, it is not uncommon that whole-body protein kinetics may “mask” important changes within specific tissues such as skeletal muscle. In particular, the observed potentiation of postexercise myofibrillar protein synthesis rates in response to whole-egg compared with egg white ingestion was not observed on a whole-body level in which there was a similar stimulation of whole-body protein synthesis rates in both conditions.
We studied various upstream factors that are often assumed to be regulatory for postprandial muscle anabolism in an attempt to underpin how the ingestion of whole eggs supported a greater postexercise myofibrillar protein synthetic response. In particular, we showed more rapid appearance rates of protein-derived leucine into the circulation and higher peak leucinemia after egg white than after whole-egg ingestion (Figure 4). The plasma leucine profiles were similar in pattern to previous studies that used either isolated egg protein or whole eggs. However, there were no differences between the total amount of dietary protein–derived leucine that became available in circulation throughout the 5-h postprandial period between the egg white (68% ± 1%) and whole-egg (66% ± 2%) conditions. Similarly, there were no differences in the relative protein content of skeletal muscle amino acid transporters (e.g., SLC7A5/LAT1, SLC3A/CD98, and SLC38A2/SNAT2) (Figure 6) or muscle free L-[5,5,5-2H3]leucine enrichments during recovery from exercise between the egg conditions (Table 2). Collectively, these data indicate that muscle amino acid sensing, amino acid uptake, or both likely did not contribute to the differential stimulation of postexercise myofibrillar protein synthesis rates between the egg conditions.
In addition, the temporal assessment of various metabolic and molecular readouts often associated with the control of translation initiation and elongation, such as mitogen-activated protein kinase (MAPK)–related and mTORC1-related signaling pathways, did not show significant differences in phosphorylation between the egg conditions (Figure 7). The lack of differences in the phosphorylated state of mTORC1-mediated signaling between the egg conditions could imply that this anabolic pathway was maximized from the previous performance of resistance exercise and food ingestion, thereby obscuring any subtle nonprotein nutritive influences of whole-egg consumption on mTORC1 phosphorylation and its downstream targets. We also examined metabolic regulatory pathways and energy-sensing protein phosphorylation. Similar to the other assessed molecular readouts, there were no observed differences in the phosphorylated states of AMPK or Erk1/2.
The essential amino acid compositions, and leucine in particular, were nearly identical between the egg conditions. Thus, differences in the amino acid composition of the ingested egg sources likely did not have an influential role in the muscle anabolic response. In addition, the greater overall energy content, and subsequent insulinemia, within the whole-egg (256 kcal) and egg white (73 kcal) conditions likely did not influence the differential stimulation of the postprandial myofibrillar protein synthetic response. For example, it has been shown that only relatively low plasma insulin concentrations (5 μU/mL) are required to maximize the muscle anabolic potential of elevated plasma amino acid availability in humans . Moreover, the additional substrate (i.e., fat) for energy production with whole-egg ingestion did not spare the use of amino acids for oxidative “fuel” (Figure 5). Also, previous reports have shown that providing additional energy with isolated protein sources does not amplify the anabolic properties of dietary amino acids to stimulate postprandial muscle protein synthesis rates when compared with the ingestion of protein or amino acids alone.
Interestingly, research has shown that other food components, beyond dietary amino acids, may have a supporting role in modulating postprandial muscle anabolism during recovery from exercise. For example, Elliot et al. previously showed that whole-milk ingestion immediately after resistance exercise resulted in greater acid uptake across the leg than after the consumption of isonitrogenous or isoenergetic amounts of skim milk in healthy young adults. In the present study, we showed a greater early (0–120 min) postprandial dietary-derived leucine availability after the ingestion of egg whites (34% ± 2%) than after whole eggs (25% ± 3%). The greater postprandial plasma leucine availability after egg white than after whole-egg ingestion, however, did not result in a greater early stimulation of the postprandial (0–120 min) myofibrillar protein synthetic response after the ingestion of egg whites when compared with whole eggs. Hence, it seems that “extra” nutritional food constituents, and not simply a rapid aminoacidemia or leucinemia, may also have a role in modulating the postprandial muscle protein synthetic response in healthy adults. For example, as part of its whole-food matrix, the egg yolk contains various nonprotein food components that may have anabolic properties, such microRNAs, vitamins, minerals, and lipids [e.g., phosphatidic acid palmitic acid, and DHA by modifying pathways related to transcriptional or protein translational control. However, more work is required to systematically assess the role of such food components on modulating postprandial muscle protein synthesis rates in vivo in humans.
It is important to note that despite recent modifications of dietary guidelines to reflect that total dietary cholesterol intake is often misrepresented as a risk factor for cardiovascular disease, popular practice may still dictate the discarding of the yolk when multiple eggs are consumed in a meal. However, the yolk is nutrient dense and may contain a variety of important bioactive compounds such as lipids, micronutrients, antioxidant carotenoids, and microRNAs. The removal of the yolk and its associated nutrients from eggs may limit the stimulation of muscle protein synthesis rates as well as overall human health.
Overall, this work supports recommendations that nutrient- and protein-dense foods are cornerstones to meeting daily protein requirements to optimize muscle protein synthesis rates with exercise.
In conclusion, we show that postexercise myofibrillar protein synthesis rates are stimulated to a greater extent after the consumption of whole eggs than after the consumption of egg whites in healthy young men, despite being matched for protein content. We observed no differences between egg conditions in the commonly assumed regulators of postexercise muscle protein synthesis rates, such as total postprandial plasma leucine availability, whole-body leucine oxidation rates, skeletal muscle amino acid transport protein content, or molecular readouts associated with metabolic and anabolic protein signaling. Future work is required to identify the potential role of nonprotein food components to contribute to the stimulation of postprandial muscle protein synthesis rates in humans. This information is important because other nutritional components may contribute to food protein requirements and particularly when dietary protein is consumed in moderate amounts (∼15–20 g protein/meal).
.
Abstract
Background: Protein in the diet is commonly ingested from whole foods that contain various macro- and micronutrients. However, the effect of consuming protein within its natural whole-food matrix on postprandial protein metabolism remains understudied in humans.Objective: We aimed to compare the whole-body and muscle protein metabolic responses after the consumption of whole eggs with egg whites during exercise recovery in young men.Design: In crossover trials, 10 resistance-trained men [aged 21 ± 1 y; 88 ± 3 kg; body fat: 16% ± 1% (means ± SEMs)] received primed continuous l-[ring-(2)H5]phenylalanine and l-[1-(13)C]leucine infusions and performed a single bout of resistance exercise. After exercise, participants consumed intrinsically l-[5,5,5-(2)H3]leucine-labeled whole eggs (18 g protein, 17 g fat) or egg whites (18 g protein, 0 g fat). Repeated blood and muscle biopsy samples were collected to assess whole-body leucine kinetics, intramuscular signaling, and myofibrillar protein synthesis.Results: Plasma appearance rates of protein-derived leucine were more rapid after the consumption of egg whites than after whole eggs (P = 0.01). Total plasma availability of leucine over the 300-min postprandial period was similar (P= 0.75) between the ingestion of whole eggs (68% ± 1%) and egg whites (66% ± 2%), with no difference in whole-body net leucine balance (P = 0.27). Both whole-egg and egg white conditions increased the phosphorylation of mammalian target of rapamycin complex 1, ribosomal protein S6 kinase 1, and eukaryotic translation initiation factor 4E-binding protein 1 during postexercise recovery (all P < 0.05). However, whole-egg ingestion increased the postexercise myofibrillar protein synthetic response to a greater extent than did the ingestion of egg whites (P= 0.04).Conclusions: We show that the ingestion of whole eggs immediately after resistance exercise resulted in greater stimulation of myofibrillar protein synthesis than did the ingestion of egg whites, despite being matched for protein content in young men. Our data indicate that the ingestion of nutrient- and protein-dense foods differentially stimulates muscle anabolism compared with protein-dense foods.
DISCUSSION
To our knowledge, we report for the first time the potentiation of exercise-mediated stimulation of postprandial myofibrillar protein synthesis rates in response to the ingestion of whole eggs compared with isonitrogenous amounts of egg whites in healthy young men. Our work points to the concept that dietary protein may show differential anabolic properties on skeletal muscle tissue when consumed within its natural whole-food matrix.Similar to isolated protein sources (e.g., whey and casein) (, we also showed that the consumption of protein-dense foods in the form of whole eggs and egg whites improves whole-body net protein balance. Although . insight into whole-body protein kinetics can provide valuable information on whole-body protein remodeling and net anabolism, it is not uncommon that whole-body protein kinetics may “mask” important changes within specific tissues such as skeletal muscle. In particular, the observed potentiation of postexercise myofibrillar protein synthesis rates in response to whole-egg compared with egg white ingestion was not observed on a whole-body level in which there was a similar stimulation of whole-body protein synthesis rates in both conditions.
We studied various upstream factors that are often assumed to be regulatory for postprandial muscle anabolism in an attempt to underpin how the ingestion of whole eggs supported a greater postexercise myofibrillar protein synthetic response. In particular, we showed more rapid appearance rates of protein-derived leucine into the circulation and higher peak leucinemia after egg white than after whole-egg ingestion (Figure 4). The plasma leucine profiles were similar in pattern to previous studies that used either isolated egg protein or whole eggs. However, there were no differences between the total amount of dietary protein–derived leucine that became available in circulation throughout the 5-h postprandial period between the egg white (68% ± 1%) and whole-egg (66% ± 2%) conditions. Similarly, there were no differences in the relative protein content of skeletal muscle amino acid transporters (e.g., SLC7A5/LAT1, SLC3A/CD98, and SLC38A2/SNAT2) (Figure 6) or muscle free L-[5,5,5-2H3]leucine enrichments during recovery from exercise between the egg conditions (Table 2). Collectively, these data indicate that muscle amino acid sensing, amino acid uptake, or both likely did not contribute to the differential stimulation of postexercise myofibrillar protein synthesis rates between the egg conditions.
In addition, the temporal assessment of various metabolic and molecular readouts often associated with the control of translation initiation and elongation, such as mitogen-activated protein kinase (MAPK)–related and mTORC1-related signaling pathways, did not show significant differences in phosphorylation between the egg conditions (Figure 7). The lack of differences in the phosphorylated state of mTORC1-mediated signaling between the egg conditions could imply that this anabolic pathway was maximized from the previous performance of resistance exercise and food ingestion, thereby obscuring any subtle nonprotein nutritive influences of whole-egg consumption on mTORC1 phosphorylation and its downstream targets. We also examined metabolic regulatory pathways and energy-sensing protein phosphorylation. Similar to the other assessed molecular readouts, there were no observed differences in the phosphorylated states of AMPK or Erk1/2.
The essential amino acid compositions, and leucine in particular, were nearly identical between the egg conditions. Thus, differences in the amino acid composition of the ingested egg sources likely did not have an influential role in the muscle anabolic response. In addition, the greater overall energy content, and subsequent insulinemia, within the whole-egg (256 kcal) and egg white (73 kcal) conditions likely did not influence the differential stimulation of the postprandial myofibrillar protein synthetic response. For example, it has been shown that only relatively low plasma insulin concentrations (5 μU/mL) are required to maximize the muscle anabolic potential of elevated plasma amino acid availability in humans . Moreover, the additional substrate (i.e., fat) for energy production with whole-egg ingestion did not spare the use of amino acids for oxidative “fuel” (Figure 5). Also, previous reports have shown that providing additional energy with isolated protein sources does not amplify the anabolic properties of dietary amino acids to stimulate postprandial muscle protein synthesis rates when compared with the ingestion of protein or amino acids alone.
Interestingly, research has shown that other food components, beyond dietary amino acids, may have a supporting role in modulating postprandial muscle anabolism during recovery from exercise. For example, Elliot et al. previously showed that whole-milk ingestion immediately after resistance exercise resulted in greater acid uptake across the leg than after the consumption of isonitrogenous or isoenergetic amounts of skim milk in healthy young adults. In the present study, we showed a greater early (0–120 min) postprandial dietary-derived leucine availability after the ingestion of egg whites (34% ± 2%) than after whole eggs (25% ± 3%). The greater postprandial plasma leucine availability after egg white than after whole-egg ingestion, however, did not result in a greater early stimulation of the postprandial (0–120 min) myofibrillar protein synthetic response after the ingestion of egg whites when compared with whole eggs. Hence, it seems that “extra” nutritional food constituents, and not simply a rapid aminoacidemia or leucinemia, may also have a role in modulating the postprandial muscle protein synthetic response in healthy adults. For example, as part of its whole-food matrix, the egg yolk contains various nonprotein food components that may have anabolic properties, such microRNAs, vitamins, minerals, and lipids [e.g., phosphatidic acid palmitic acid, and DHA by modifying pathways related to transcriptional or protein translational control. However, more work is required to systematically assess the role of such food components on modulating postprandial muscle protein synthesis rates in vivo in humans.
It is important to note that despite recent modifications of dietary guidelines to reflect that total dietary cholesterol intake is often misrepresented as a risk factor for cardiovascular disease, popular practice may still dictate the discarding of the yolk when multiple eggs are consumed in a meal. However, the yolk is nutrient dense and may contain a variety of important bioactive compounds such as lipids, micronutrients, antioxidant carotenoids, and microRNAs. The removal of the yolk and its associated nutrients from eggs may limit the stimulation of muscle protein synthesis rates as well as overall human health.
Overall, this work supports recommendations that nutrient- and protein-dense foods are cornerstones to meeting daily protein requirements to optimize muscle protein synthesis rates with exercise.
In conclusion, we show that postexercise myofibrillar protein synthesis rates are stimulated to a greater extent after the consumption of whole eggs than after the consumption of egg whites in healthy young men, despite being matched for protein content. We observed no differences between egg conditions in the commonly assumed regulators of postexercise muscle protein synthesis rates, such as total postprandial plasma leucine availability, whole-body leucine oxidation rates, skeletal muscle amino acid transport protein content, or molecular readouts associated with metabolic and anabolic protein signaling. Future work is required to identify the potential role of nonprotein food components to contribute to the stimulation of postprandial muscle protein synthesis rates in humans. This information is important because other nutritional components may contribute to food protein requirements and particularly when dietary protein is consumed in moderate amounts (∼15–20 g protein/meal).
