A Pharmacokinetic Evaluation of Isolated Chicken Protein as Compared to Beef Protein in Healthy Active Adults

Dietary protein sources, particularly complete sources, can have different rates of bioavailability based on many factors. These factors affect relative bioavailability includeing the fat and carbohydrate content, amino acid composition, while also noting that peptide size within the protein can slow stomach digestion, gastric motility, and subsequent absorption into circulation [1]. Additionally, food processing can also impact bioavailability. For instance, the D-amino acids and lysinoalanine (LAL, an unnatural amino acid) formed during the alkaline/heat treatment of proteins such as casein are only 40% digestible, and their presence can reduce the digestibility of protein by up to 28% [2]. Once a protein meal is ingested, approximately 50% of the amino acids are taken up by the splanchnic tissues and the remainder absorbed into the plasma circulation for use by extra-splanchnic tissues [3]. It has been shown that from 20 grams of casein protein (a slower absorbing protein than whey), only 2 grams (11%) of the amino acids were used for incorporation into Muscle Protein Synthesis (MPS), despite 55% availability in the peripheral circulation following splanchnic extraction [3]. Nevertheless, independent of these factors, the amino acid composition of dietary proteins can have differential effects on MPS, perhaps as a result of their rates on bioavailability. 

Whey protein has a high bioavailability compared to other protein sources, such as casein [4-6] and beef [1]. However, it has been shown that meat protein serves as an important protein source for augmenting muscle growth and increasing strength gains [7]. Recently, beef and chicken protein isolates have become popular in the exercise/sport nutrition arena as well within the medical nutrition therapy community based on their amino acid composition and propensity to be able to augment the rate of MPS associated with intense exercise training. In humans, comparing the bioavailability of whey, chicken, and beef protein isolates, it was shown that whey and chicken protein isolate contained a higher content of Essential Amino Acids (EAAs) with high bioavailability, being absorbed into plasma at peak concentrations at 30 minutes following ingestion. Conversely, beef protein isolate contained a greater proportion of conditionally EAAs that progressively increased over a three-hour period [1].

Within the exercise and sport nutrition industry, efforts are being made to determine alternate sources of protein isolate that may be superior to whey isolate. The purpose of this approach is for more rapid bioavailability and subsequent augmentation in MPS since protein source is an important factor in up-regulating MPS following protein consumption [5,6,8].

The purpose of this study was to determine the bioavailability (rate of appearance in blood) and Pharmacokinetic (PK) evaluation of amino acids due to ingestion of Chicken Protein Isolate (CKP) in comparison to Beef Protein Isolate (BFP) in healthy, physically-active, adult males. The specific aims were to determine the kinetic effects of CKP and BFP on Total Amino Acids (TAA), Essential Amino Acids (EAA), Sulfur-containing Amino Acids (SAA), leucine, and arginine.TAA were assessed to determine overall amino acid absorption, EAA were assessed because they are required for optimal protein synthesis, SAA were assessed because the profile amino acids in meats are different than non-meat sources, leucine was assessed because it is the amino acids responsible for stimulating protein synthesis, arginine was assessed because it is typically higher in meat protein than non-meat.

Experimental approach

Participants

Screening visit

Procedures

Supplementation protocol

Table 1: Ingredients for CKP and BFP Products.

Note: The serving size consisted of a once daily dose of 25 grams of the assigned study product as bolus. For this study, a single dose of study product (s) was taken on visit 1 (day 1) and visit 2 (day 4) at study site.

Venous blood sampling

Amino acid analysis

Pharmacokinetic parameters

Statistical analysis

Amino acid analyses

Table 7: Plasma arginine concentrations before and after administration of CKP and BFP.

Note: *Tested by the independent student t test (t) or by the non-parametric Wilcoxon rank sum test (w) if non-normally distributed. **Tested by the paired t test (t) or by the non-parametric Wilcoxon signed-ranks test (w) if non-normally distributed.

In this study we sought to determine the relative bioavailability from two different animal protein sources in physically-active healthy men. This analysis included the PK of TAA, EAA, SAA, leucine, and arginine in response to CKP and BFP ingestion in healthy, physically-active, adult males. While not to diminish the overall importance of our findings, the results that are most impactful relative to exercise/sport nutrition are those for EAA, SAA, and leucine. Unlike BFP, we observed CKP to increase EAA and leucine concentrations at all time points up to 180 minutes following ingestion (C30 min-C180 min). In addition, the increases for CKP, along with Cmax, AUC0-t, and Tmax were greater than BFP. For SAA, we observed a similar response as with EAA and leucine, which was a greater impact than the CKP. The apparent bioavailability of EAA is greater in CKP by a factor of 3.4x greater (EAA AUC0-t, h•nmol/mL 1120 (457) 329 (297)) than BFP.

Incomplete, lower-quality proteins such as soy, pea, or wheat are low or lacking in one or more EAAs; therefore, they are less effective at stimulating MPS and increases in muscle mass than complete, higher-quality sources [5,10,11]. In this context, protein quality is defined by the amount and profile of EAA, as well as the ideal digestibility (PDCAAs) [12,13]. However, independent of the protein source/quality feeding-induced hyperaminoacidemia stimulates amino acid uptake across the sarcolemma [14]. Following an increase in plasma amino acid levels, there is an approximate 30-minute delay in the stimulation of MPS before it peaks at 2 hours [15,16]. Relative to the results of our study, particularly for leucine, EAA, and SAA, this is important because the hyperaminoacidemia-induced up-regulation in MPS appears to regress to basal levels after approximately 2-3 hours, despite a continued increase in plasma amino acid levels [16]. Therefore, in regard to leucine, EAA, and SAA, the ability of CKP to result in elevated amino acid levels for 180 minutes following ingestion indicates the ability of this protein source to have a more prolonged impact on MPS when compared to BFP. 

A hyperaminoacidemia-induced increase in MPS appears to be primarily dependent on the EAA composition of protein [17]. Of these amino acids, leucine is considered to be the primary trigger for initiating MPS [18-20], and can do so in the absence of other amino acids. However, if the availability of other EAA is limited MPS will become limited, independent of leucine content [14]. Regarding the results of the present study, this is noteworthy since we observed greater increases in EAA and SAA (which involves the EAA methionine) for CKP at all time points up to 180 minutes following ingestion. This scenario implies that MPS could be more prolonged with CKP than BFP.

A previous study has shown considerably greater levels of EAA and BCAA for chicken protein isolate compared to beef protein isolate [1]. In this study they also found that the post-ingestion plasma amino acid response mirrored the amino acid composition for the protein sources. In agreement with Storcksdieck et al. [21], the amino acids found at the four highest levels (in descending order) were glutamic acid/glutamine, aspartic acid, lysine, and leucine for the chicken protein isolate, whereas for the beef protein isolate they were glycine, glutamic acid/glutamine, proline, and alanine. It was also shown that the beef protein contained only 4% leucine, which may conceivably be below the threshold needed to increase MPS [21]. Since leucine is one of the more abundant amino acids contained within chicken protein, this suggests this protein source to be more effective at inducing MPS than beef protein. This becomes an important consideration in exercise/sport nutrition since a protein source that is digested and absorbed more rapidly can improve the post-prandial availability in plasma amino acids, thereby resulting in greater increases in MPS [22,23] and perhaps overall exercise recovery.

In the present study we showed CKP to have a significantly greater Cmax and Tmax compared to BFP for leucine, EAA, and SAA. This suggests that CKP has a greater bioavailability, rate of delivery, and potential to prolong MPS than BFP. Our present results agree with those of Detzel et al. [1], who observed peak plasma amino acid levels to appear by 30 minutes following ingestion of chicken isolate protein, but not until 30-60 minutes for beef protein. A likely reason for this more favorable response of CKP is due to chicken protein isolate having over 85% of its total protein content consisting of free amino acids or peptides smaller than 5 kDa, whereas beef protein consists of larger peptides, ranging from 5-15 kDa [1]. 

Skeletal muscle is the primary target of dietary protein [24]. As a result, skeletal muscle is more responsive to variations in dietary intake than other tissues and organs [25]. The intramuscular anabolic impact of dietary protein intake is important since skeletal muscle is a primary fate of leucine and the EAA’s absorbed from dietary protein [25]. Consumption of dietary protein stimulates MPS within an hour. The present study shows the bioavailability of EAA for both CKP and BFP potentially capable of being able to stimulate MPS within this period of time; however, the duration of BFP over the course of 180 minutes was less robust than the CKP. The ability of a dietary protein such as CKP to have a rapid and sustained response in circulation is important because a significant portion of amino acids absorbed from the ingested protein will be retained in the splanchnic area, mainly in the gut [26,27]. This is also a noteworthy consideration since hyperaminoacidemia following protein intake can lead to the suppression of muscle proteolysis [28]. 

The MPS that occurs because of exercise, and extends into the post-exercise recovery period, can be augmented with sufficient intake of a dietary protein that has rapid absorption into the circulation and is able to be maintained over the course of several hours. In addition, the type of protein and the serving size ingested may impact MPS and the overall balance of muscle Protein Breakdown (PPB). While our results presented herein demonstrate both CKP and BFP to have significantly elevated levels of leucine, EAA, and SAA in circulation within an hour following ingestion, the response of CKP was significantly greater than BFP. Therefore, based on the bioavailability and observed pharmacokinetics from the present study, we conclude that CKP is potentially a more effective protein source and is more bioavailable for increasing MPS and enhancing recovery as compared to BFP. This was a small study and future studies may consider a larger study population. Future studies should may also consider applications for a variety of populations, particularly the elderly and those at risk for muscle loss who may benefit from a rapidly absorbed and easily consumable protein source. In addition comparisons to a variety of protein sources would add valuable information to the literature.

This research was funded by International Dehydrated Foods (IDF, Springfield Missouri).

Douglas Kalman-study design, data interpretation, manuscript writing. Susan Hewlings-data interpretation, manuscript writing. Robin Lee-study design, study conduct, project management. Jacob Bentley-study design, clinical conduct. Richard Foster-study design, clinical conduct. Kayce Morton, study design, principal investigator. Darryn S. Willoughby - data interpretation, manuscript writing.

Douglas Kalman, Robin Lee, Jacob Bentley, Richard Foster were employed by QPS at the time of this study, the Contract Research Organization that received funding from the sponsor to conduct the study.

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