A protein is a polymer composed of amino acids in a chain of α-peptide bonds which are important in many processes in the body.1 Proteins synthesized by amino acids are essential to skeletal muscle repair, the production of cell-specific metabolites, the formation of immune-supporting antibodies, replenishing enzymes, nourishing the gut microbiome, and a host of other physiological functions (Figure 1).2–4 Sufficient dietary protein can help increase skeletal muscle mass and strength, normal function of enzymes, normal hair and nail growth, and aid in wound and skin repair mechanisms, while a deficiency in protein can cause anemia, growth stunting, impaired immunity and weakness (Table 2).2 Furthermore, research has demonstrated that reduced dietary protein intake and muscle loss is associated with reduction in the functional decline of elderly individuals.5
Essential Amino Acids
Histidine*, Isoleucine*, Leucine*, Lysine*, Methionine**, Phenylalanine***, Threonine**, Tryptophan***, Valine**
Non-essential Amino Acids
Alanine, Arginine, Asparagine, Aspartate, Cysteine, Glutamate, Glutamine, Glycine, Proline, Serine, Taurine, Tyrosine
Table 2 describes each amino acid, whether they are essential or non-essential, are branched-chain, and their antioxidant effects, skin-related effects, gut-related effects, brain-related effects, other effects, and any additional comments of interest related to the amino acid.
Non-essential
No
Minimal
None
Supports glucose metabolism
Supports cognitive function by influencing glucose metabolism
Energy metabolism, muscle function
May be useful in athletes or low-carb diets
Non-essential
No
Precursor to nitric oxide, can reduce oxidative stress
May support hair growth, collagen production, and wound healing
Important for gut blood flow
Precursor to neurotransmitters like nitric oxide
Immune function, vasodilation
May cause gastrointestinal discomfort or low blood pressure in some
Non-essential
No
None
None
None
Neurotransmitter, supports brain function
Energy production in cells
Supplementation is rarely needed as it is abundant in most proteins
Non-essential
No
Antioxidant (precursor to glutathione)
Protects skin from oxidative stress
Supports gut cell health
Helps brain function via antioxidant properties
Detoxification, cell health
Can contribute to kidney stones in high doses in susceptible individuals
Non-essential
No
None
Supports collagen production
Key in gut function, promotes healing
Major neurotransmitter, excitatory in the brain
Protein synthesis, energy production
High MSG levels may cause headaches in sensitive individuals
Non-essential
No
Antioxidant (precursor to glutathione)
Supports collagen synthesis, skin elasticity
Supports gut integrity
Supports neurotransmitter functions (inhibitory)
Detoxification, collagen synthesis
High doses may cause gastrointestinal discomfort
Essential
No
None
Supports skin barrier function
Supports gut health (acid-base balance)
Precursor to histamine, which influences brain function
Myelin sheath, anemia prevention
Avoid in histamine-sensitive individuals
Essential
Yes
None
None
Supports gut barrier function
Enhances brain function by stabilizing blood glucose
Muscle repair, immune function
May cause gastrointestinal issues at high doses of BCAAs
Essential
Yes
None
Supports muscle repair, some collagen support
Supports gut barrier function
Enhances muscle recovery and cognitive performance
Stimulates muscle protein synthesis
Activates mTOR pathway for muscle protein synthesis
Essential
No
None
Supports collagen, wound healing
Supports gut health (intestinal permeability)
Supports neurotransmitter synthesis (serotonin)
Immune function, calcium absorption
Commonly used for cold sore prevention. May cause mild gastrointestinal discomfort
Essential
No
Antioxidant (precursor to cysteine and glutathione)
Supports skin health
Helps in detoxification processes
Important for brain health, mood regulation
Methylation, detoxification
Key methyl donor in detoxification and gene expression. High intake can raise homocysteine levels, increasing cardiovascular risk
Essential
No
None
Supports production of pigment
Supports gut motility
Precursor to neurotransmitters (dopamine, norepinephrine)
Mood and cognitive support
Should be avoided by individuals with PKU
Non-essential
No
None
Important for collagen production, supports skin elasticity
Supports gut integrity
Enhances brain function through collagen-related processes
Wound healing, connective tissue
Can cause digestive issues at high doses
Non-essential
No
None
Supports skin hydration and barrier function
Supports gut health (intestinal lining)
Crucial for neurotransmitter function (serotonin precursor)
Cell membrane structure, immune function
Excessive levels can disrupt neurotransmitter balance
Essential
No
None
Supports collagen, skin health
Supports gut lining integrity
Involved in brain function, especially in memory processes
Immune support, gut barrier
High doses may cause digestive upset
Essential
No
Antioxidant (precursor to serotonin, melatonin)
Supports mood regulation, sleep quality
Affects gut-brain axis
Precursor to serotonin, influencing mood and sleep
Sleep regulation, mood balance
High doses can cause serotonin syndrome when combined with serotonergic drugs
Non-essential
No
Antioxidant (precursor to dopamine)
Some indirect effects via dopamine regulation
Can affect gut-brain signaling
Important for mental performance under stress
Cognitive function, mood regulation
High doses can cause headaches or jitteriness
Essential
Yes
None
None
Supports gut barrier function
Enhances brain function via blood glucose regulation
Muscle function, energy metabolism
High doses can lead to amino acid imbalances, causing fatigue or cramps
Protein is found in foods such as meat, beans, dairy, and nuts,8 all of which contribute to the daily recommendation for intake of 0.8 g/ kg of protein.2 However, an increase of up to 1.6 g/ kg or greater for protein intake is recommended for individuals with intense physical activity.2 A protein supplement, commonly in the form of a powdered protein isolate, can be an effective addition to an individual’s diet to help them achieve their protein goals.
Protein isolate can be sourced from animal sources such as dairy (casein and whey), beef or egg-white, or from plant-based sources such as pea, soy, pumpkin seed, and rice, and hemp seeds. While various sources of protein isolates exist, they are not equivalent and contain varying compositions of non-essential amnio acids and essential amino acids, which will be denoted with a “*” throughout the manuscript (Table 1). To better understand the variability in composition, we investigated the average amino acid compositions of protein isolates from various commercial sources currently on the market.
The amino acid profiles of nine different sources of protein isolates were retrieved directly from commercial websites. At least four brands were selected for each protein isolate source and missing or incomplete data was resolved by contacting the manufacturers directly.
A diverse array of protein isolate sources were selected, including both animal-based and plant-based sources. We were specific in our search for protein isolates as opposed to protein concentrates, as the latter would likely contain additives which affect the amino acid content. The protein types chosen were whey, casein, beef, egg-white, soy, pea, rice, pumpkin seed, and hemp seed.
Commercially available protein isolates only contained 18 amino acids and none of them contained the non-essential amino acids glutamate or asparagine. Data for the amino acid content was compiled for 18 amino acids across the 9 isolates chosen. Four to five brands were chosen, from which the mean amino acid quantities in milligrams per 100 grams were calculated. These mean quantities were used to compare the amino acid profiles across the protein sources.
The amino acid profiles for each protein isolate were illustrated using a lollipop chart generated with the ggplot2 package in R (R Foundation for Statistical Computing, Vienna, Austria). This chart displayed the mean quantities of individual amino acids, enabling direct comparisons of specific amino acid contents between the protein isolates.
The total protein content for each isolate was calculated as the sum of the quantities of all 18 amino acids. Z-scores were calculated for each amino acid from every protein source by subtracting the overall mean from the corresponding amino acid quantity and dividing by the standard deviation across the nine isolates. Protein sources were then ranked by their z-scores within each amino acid. Additionally, their total z-scores, or z-score sum from all the amino acids was also considered. A heat map was generated to visualize the individual z-score results, with positive z-scores in red indicating a higher amino acid content and negative z-scores in blue indicating a lower amino acid content with respect to the mean. The mean rankings for z-scores within each amino acid were also tabulated and visualized via a bar chart. In this research, we associated quality with diversity of amino acid profile, which is determined by the z-score sum. Thus, a high-quality protein has a strong balance of amino acids.
To assess differences in amino acid content between protein isolates, a series of independent t-tests were performed. The mean quantity of each amino acid was compared to whey, chosen due to its commercial popularity. Positive t-statistics indicate the amino acid content was greater than in whey, while negative t-statistics indicated it was lower than in whey. Statistical significance was defined as p < 0.05, and percent differences between means were calculated for statistically significant comparisons.
To visualize the results, a heat map was generated with t-statistics driving the intensity of each cell. Positive t-statistics were identified in shades of red and negative t-statistics in shades of blue. Significant differences (p < 0.05 and p < 0.001) were annotated on the heat map.
Z-score sums were calculated using the equation shown below, where µ is the mean quantity across all isolates for a given amino acid
All statistical analyses and visualizations were conducted using R version 4.4.1 within the RStudio integrated development environment (Posit Software, PBC, Boston, Massachusetts, USA). Graphical representations, including the lollipop chart, heat maps, and bar chart, were created using the ggplot2 package. The datasets used for this analysis were pre-processed and analyzed in R. The Shannon diversity index was calculated using the vegan package in R.
Whey protein is derived from milk during cheese production.6 Whey protein served as the reference standard for t-test comparisons.
Arginine had a low z-score (-1.63), indicating a lower than average content compared to the other isolates. Aspartic acid, cystine, isoleucine*, leucine*, lysine*, and threonine* had high z-scores (1.13, 1.20, 1.71, 1.67, 1.65, 2.22), indicating a greater than average content compared to the other isolates.
Proline (7742.38 mg/100 g), leucine* (7398.58 mg/100 g), and lysine* (6240.98 mg/100 g) were the most represented amino acids in whey isolate.
Casein is derived from milk by precipitating the protein through acidification or enzyme (rennet) treatment.7 Amino acids which had increased relative abundance compared to those in whey protein include arginine (36.86%, p = 0.0258), histidine* (48.31%, p = 0.0243), phenylalanine* (38.83%, p = 0.0167), proline (42.91%, p = 0.0337), and tyrosine (42.08%, p = 0.0475). Amino acids which had decreased relative abundance when compared to whey protein include alanine (47.12%, p = 0.0011), aspartic acid (41.05%, p = 0.0043), cystine (82.78%, p = 0.0010), leucine* (23.69%, p = 0.0261), lysine* (28.42%, p = 0.0179), threonine* (45.65%, p = 0.0059), and tryptophan* (15.85%, p = 0.0429).
Arginine had a low z-score (-1.30), indicating a lower than average content compared to the other isolates. Glutamic acid, histidine*, methionine*, tyrosine, and valine* had high z-scores (1.08, 1.19, 1.27, 1.34, 1.13), indicating a greater than average content compared to the other isolates.
Proline (7723.38 mg/100 g), leucine* (7198.58 mg/100 g), and lysine* (6040.98 mg/100 g) were the most represented in casein isolate.
Beef protein isolate is derived from animal meat.9 Amino acids which had increased relative abundance when compared to those in whey protein include alanine (88.77%, p = 0.0000), arginine (287.72%, p = 0.0000), glycine (1205.34%, p = 0.0000), and proline (123.63%, p = 0.0001). Amino acids which had decreased relative abundance when compared to whey protein include aspartic acid (41.17%, p = 0.0060), cystine (95.42%, p = 0.0007), glutamic acid (34.15%, p = 0.0121), isoleucine* (74.15%, p = 0.0010), leucine* (66.91%, p = 0.0002), lysine* (59.45%, p = 0.0009), methionine* (60.35%, p = 0.0001), phenylalanine* (25.69%, p = 0.0151), threonine* (68.50%, p = 0.0013), tryptophan* (83.44%, p = 0.0020), tyrosine (69.72%, p = 0.0001), and valine* (48.81%, p = 0.0022).
Alanine, glycine, and proline had high z-scores (2.26, 2.58, 2.19), indicating a greater than average content compared to the other isolates. Cystine, histidine*, isoleucine*, leucine*, methionine*, phenylalanine**, tryptophan**, tyrosine, and valine** had low z-scores (-1.26, -1.28, -1.47, -1.35, -1.29, -1.36, -2.04, -1.76, -1.26), indicating a lower than average content compared to the other isolates.
Glycine (19209.52 mg/100 g), proline (12085.71 mg/100 g), and glutamic Acid (10395.24 mg/100 g) were the most represented in beef isolate.
Egg-white protein is a low-fat, and low-carb protein source that is particularly high in albumin, which is a highly bioavailable form of protein.10 The only amino acid that had increased relative abundance when compared to whey protein was arginine (162.58%, p = 0.0053). Amino acids which had decreased relative abundance include glutamic Acid (31.27%, p = 0.0156), lysine* (39.45%, p = 0.0047), and threonine* (46.76%, p = 0.0054).
Methionine*, serine, and valine* had high z-scores (1.62, 1.53, 1.20), indicating a greater than average content compared to the other isolates.
Glutamic Acid (10850.03 mg/100 g), arginine (5182.10 mg/100 g), and lysine* (5110.20 mg/100 g) were the most represented in egg-white isolate.
Soy protein is derived from soybeans.11 Amino acids which had increased relative abundance when compared to whey protein include arginine (219.07%, p = 0.0000), glycine (127.38%, p = 0.0000), histidine* (49.03%, p = 0.0088), and phenylalanine* (56.39%, p = 0.0004). Amino acids which had decreased relative abundance include alanine (23.03%, p = 0.0287), isoleucine* (35.76%, p = 0.0175), leucine* (28.37%, p = 0.0100), lysine* (38.36%, p = 0.0059), methionine* (39.80%, p = 0.0008), and threonine* (48.46%, p = 0.0062).
Cystine, glutamic acid, and histidine* had high z-scores (1.83, 1.08, 1.22), indicating a greater than average content compared to the other isolates.
Leucine* (6757.02 mg/100 g), arginine (6297.02 mg/100 g), and lysine* (5201.55 mg/100 g) were the most represented in soy isolate.
Pea protein, derived from yellow split peas, is a highly digestible plant-based protein source.12 When compared to those in whey protein, amino acids which had increased relative abundance include arginine (292.39%, p = 0.0016), glycine (147.80%, p = 0.0017), histidine* (45.73%, p = 0.0154), and phenylalanine* (79.13%, p = 0.0033). Amino acids which had decreased relative abundance include cystine (59.17%, p = 0.0034), methionine* (52.40%, p = 0.0019), threonine* (43.65%, p = 0.0080), and tryptophan* (31.86%, p = 0.0147).
Aspartic acid, histidine*, phenylalanine*, serine, and tyrosine had high z-scores (1.55, 1.22, 1.61, 1.02, 1.02), indicating a greater than average content compared to the other isolates.
Arginine (7744.03 mg/100 g), phenylalanine* (4823.52 mg/100 g), and glycine (3646.59 mg/100 g) were the most represented in Pea isolate.
Rice protein is typically derived from brown rice.13 No amino acids in rice protein had increased relative abundance in comparison to those in whey protein. Amino acids which had decreased relative abundance include aspartic acid (49.90%, p = 0.0159), cystine (52.05%, p = 0.0096), isoleucine* (58.23%, p = 0.0039), leucine* (53.07%, p = 0.0078), lysine* (80.33%, p = 0.0001), proline (57.17%, p = 0.0089), threonine* (77.70%, p = 0.0011), and tryptophan* (39.40%, p = 0.0166).
Aspartic acid, histidine*, lysine*, serine, and threonine* had low z-scores (-1.12, -1.05, -1.28, -1.14, -1.10), indicating a lower than average content compared to the other isolates.
Aspartic Acid (4761.05 mg/100 g), leucine* (4427.07 mg/100 g), and proline (2314.56 mg/100 g) were the most represented in Rice isolate.
Pumpkin seed protein is a nutrient-dense, plant-based protein that is a source of magnesium, zinc, and iron.14 When compared to the whey protein amino acid profile, arginine (304.69%, p = 0.0004) and glycine (126.28%, p = 0.0026) had increased relative abundance in pumpkin seed protein.
Arginine had a high z-score (1.10), indicating a greater than average content compared to the other isolates.
Amino acids which had decreased relative abundance include alanine (32.06%, p = 0.0057), cystine (65.78%, p = 0.0019), glutamic Acid (27.19%, p = 0.0194), isoleucine* (44.57%, p = 0.0051), leucine* (42.44%, p = 0.0019), lysine* (64.41%, p = 0.0080), proline (63.36%, p = 0.0090), threonine* (68.76%, p = 0.0009), and valine* (39.92%, p = 0.0410). Glutamic acid (11493.33 mg/100 g), arginine (7986.67 mg/100 g), and leucine* (5430.00 mg/100 g) were the most represented in pumpkin seed isolate.
Hemp seed protein is a plant-based protein derived from cleaning, hulling, and processing hemp seeds to isolate the protein.15 Amino acids which had increased relative abundance when compared to whey protein include arginine (221.05%, p = 0.0031) and glycine (50.54%, p = 0.0117). Amino acids which had decreased relative abundance when compared to whey protein include alanine (52.27%, p = 0.0005), aspartic acid (44.07%, p = 0.0030), cystine (59.62%, p = 0.0026), glutamic acid (52.54%, p = 0.0070), isoleucine* (63.29%, p = 0.0017), leucine* (63.72%, p = 0.0002), lysine* (76.20%, p = 0.0004), methionine* (33.62%, p = 0.0025), proline (60.11%, p = 0.0069), serine (34.10%, p = 0.0169), threonine* (69.40%, p = 0.0014), tryptophan* (51.83%, p = 0.0038), tyrosine (38.45%, p = 0.0141), and valine* (47.48%, p = 0.0026).
Glutamic acid, isoleucine*, leucine*, lysine*, serine, and valine* had low z-scores (-1.50, -1.01, -1.21, -1.13, -1.28, -1.20), indicating a lower than average content compared to the other isolates.
Glutamic Acid (7492.00 mg/100 g), arginine (6336.00 mg/100 g), and aspartic acid (5315.33 mg/100 g) were the most represented in hemp seed isolate.
The protein sources were ranked for each amino acid by comparison against the other protein sources and Table 5 shows a tabular histogram of how often a rank position was noted for an amino acid source. Pea and whey protein had the most instances of an amino acid ranking in the top three among the protein sources assessed. Notably, only egg-white, soy, and pea protein sources did not have an amino acid that ranked last when compared against other protein sources. An overall ranking of protein quality based on the mean z-score is depicted in Figure 6. Pea protein ranked first among all nice isolate sources followed by egg-white and soy.
4441
2348
8382
5457
3418
3802
3012
3017
2119.33
1974
2701
7652
5182
6297
7744
4245
7987
6336
9503
5602
5591
7889
9080
10394
4761
6410
5315
2338
403
107
1694
2915
954
1121
800
944
15786
16104
10395
10850
16091
15412
9489
11493
7492
1472
1456
19210
5997
3346
3647
2369
3330
2215
1515
2247
1098
1746
2258
2208
1208
1690
1317
5497
4076
1421
3959
3531
4040
2296
3047
2018
9433
7199
3122
6671
6757
7351
4427
5430
3422
8439
6041
3422
5110
5202
6628
1660
3003
2009
1915
2232
759
2433
1153
912
1477
1383
1271
2693
3738
2001
4254
4211
4824
2940
2987
2358
5404
7723
12086
5058
4015
4161
2315
1980
2156
3892
4130
3059
5144
4381
4673
2691
3273
2564
5997
3259
1889
3193
3091
3379
1337
1873
1835
1244
1047
206
1025
1224
848
754
1377
599
2610
3709
790
2690
2906
3406
2715
1483
1606
4766
5021
2439
5107
3717
4403
3391
2863
2503
Table 4 shows the z-scores for each amino acid within the nine protein isolates. Values greater than positive 1 are highlighted in red and values less than -1 are highlighted in blue. Z-scores >1 indicate a higher amino acid content relative to the mean amino acid content across all nine isolates. Z-scores < -1 indicate a lower amino acid content relative to the mean amino acid content across all nine isolates.
0.24
-0.84
2.26
0.76
-0.29
-0.09
-0.50
-0.59
-0.95
-1.63
-1.30
0.94
-0.18
0.33
0.98
-0.60
1.10
0.35
1.13
-0.72
-0.72
0.36
0.93
1.55
-1.12
-0.56
-0.85
1.20
-0.93
-1.26
0.49
1.83
-0.33
-0.14
-0.52
-0.34
0.99
1.08
-0.63
-0.49
1.08
0.87
-0.90
-0.49
-1.50
-0.59
-0.59
2.58
0.22
-0.25
-0.20
-0.43
-0.29
-0.46
-0.38
1.19
-1.28
0.12
1.22
1.22
-1.05
-0.23
-0.81
1.71
0.60
-1.47
0.51
0.18
0.66
-0.79
-0.40
-1.01
1.67
0.60
-1.35
0.35
0.39
0.74
-0.73
-0.45
-1.21
1.65
0.62
-0.52
0.21
0.25
0.98
-1.28
-0.80
-1.13
0.72
1.27
-1.29
1.62
-0.60
-0.97
-0.04
-0.31
-0.40
-0.66
0.40
-1.36
0.93
0.88
1.61
-0.41
-0.40
-1.00
0.13
0.84
2.19
0.02
-0.30
-0.26
-0.82
-0.93
-0.87
0.17
0.43
-0.74
1.53
0.70
1.02
-1.14
-0.69
-1.28
2.22
0.27
-0.71
0.22
0.15
0.39
-1.10
-0.70
-0.75
0.99
0.42
-2.04
0.35
0.94
-0.13
-0.44
0.81
-0.89
0.17
1.34
-1.76
0.26
0.49
1.02
0.29
-0.92
-0.89
0.89
1.13
-1.26
1.20
-0.08
0.65
-0.38
-0.95
-1.20
Table 5 displays the number of amino acids for which each protein isolate source was ranked first through ninth.
5
2
5
0
1
2
1
1
1
2
3
5
3
0
1
0
3
1
3
0
1
0
0
1
4
0
9
3
3
1
5
5
1
0
0
0
1
3
4
3
5
1
1
0
0
3
7
1
3
2
1
0
1
0
0
0
0
3
0
4
5
3
3
1
0
1
0
5
5
4
1
1
0
0
0
1
0
2
3
9
3
The comparison of amino acid profiles across various protein isolates reveals significant differences in both the relative and absolute quantities of essential and non-essential amino acids. The analysis underscores the impact of protein source—whether animal or plant-based—on the specific amino acid composition and highlights the importance of these differences in protein quality. The data shows marked variation in the amino acid content across different protein isolates, with each source offering unique advantages depending on its amino acid profile.
Our analysis shows that both plant-based and animal-based supplements can be a good quality source of a diverse amino acid profile. However, plant-based protein sources were the highest quality protein with pea being the high quality of protein source. Among animal derived protein, egg-white was the highest quality followed by whey. Alternatively, several of the plant and animal-based proteins were lower on quality such as beef, rice, and hemp seed sources. Our discussion is limited to the evaluation of pure protein isolates and does not include the use of blends of protein sources. Protein blends may be able to adjust for deficiencies from specific sources and is outside the scope of this manuscript.
In the context of supporting muscles and muscular growth, leucine* has emerged as a key driver, likely through the activation of the mTOR pathway.16 Assessment of the absolute leucine* content revealed that the dairy-derived protein sources (whey and casein) were the most abundant. Additionally, plant-based pea and soy also provide substantial amount of leucine*. A previous clinical study evaluating pea and whey-based protein intake showed that both sources are similar in their ability to support muscle growth, increase in muscle strength, and force production,17,18 suggesting that after a certain threshold of leucine* there may be no benefit for the presence of additional leucine* for muscle support.
On the other hand, leucine* is known to be an activator of the mTOR pathway.19 Overactivation of mTOR has been associated with increased aging,20,21 increased insulin levels with the presence of insulin resistance,22 and exacerbation of several inflammatory conditions such as acne, psoriasis, and hidradenitis suppurativa.22,23 Furthermore, whey protein has been implicated in flares of acne.24,25 When comparing whey protein to plant based protein, whey has greater activation of the mTOR pathway,26 suggesting that the leucine* content in whey may not only be beyond the threshold needed for support of muscle health but may also lead to more mTOR activation related side effects. However, more comparative studies between whey protein and other protein such as egg-white, pea, and soy are needed.
Protein and collagen supplements are frequently used in support of skin health. In particular, it appears that the ingestion of branched amino acids (isoleucine*, leucine*, and valine*) along with arginine, glutamine, and proline) may support collagen synthesis.27 Our analysis shows that pea, soy, and egg-white sources may be the most supportive as they are comparatively higher sources of arginine, glutamic acid, proline, and branched chain amino acids compared to whey. A study that comparatively evaluated the effect of soy versus casein protein supplementation for improvement of photoaging and reduction of wrinkles in post-menopausal women showed that soy was superior to casein while casein did not have a significant effect on photoaging or wrinkles.9 While more studies are needed, plant-based sources of protein appear to be superior in supporting skin health in comparison to milk derived sources.
Amino acids like arginine, which play a pivotal role in nitric oxide production, hair health, collagen production, and vascular health,27–29 were found to be more abundant in several plant-based proteins, such as pumpkin seed (7,987 mg/100 g), pea (7,744 mg/100 g), and hemp seed (6,336 mg/100 g), when compared to whey (1,974 mg/100 g). This trend, as seen in Figure 2, suggests that plant-based proteins may provide a significant source of arginine in addition to the other amino acids. Both of the milk-based sources of protein (whey and casein) had low levels of arginine in comparison to the other protein sources.
Overall, when analyzing the amino acid z-scores across the nine protein isolates, pea, egg-white, whey, and soy protein isolates are shown to rank highest. The z-scores show that, when compared to other isolates, pea protein has higher amino acid contents of phenylalanine*, histidine*, and aspartic acid. These amino acids and their functions may position pea protein to be a strong supporter of gut, skin, and brain health.30 For example, histidine* supplementation has been shown to improve atopic dermatitis31 and pea protein may be rich in histidine*. Egg-white protein, when compared to other isolates, showed notably greater quantities of serine and methionine*. These amino acids suggest a role for egg-white protein in skin and brain health, as their functions encompass skin hydration, barrier function, detoxification, and neurotransmitter function.30 Whey was notable for its higher quantities of threonine*, lysine*, leucine*, and isoleucine* when compared to those amino acids in other isolates.
Surprisingly, we found that beef derived protein was one of the lowest quality isolates, considering how beef is touted as a good source of protein. However, most consumer-focused advice in regard to beef has focused on quantity, our study highlights the importance of quality as well.
Asparagine (Asn) and glutamine (Gln) were excluded from the analyses due to their absence in the amino acid profiles provided by the manufacturers. This may be because these amino acids are considered non-essential and can be synthesized by the body.32 Some manufacturers listed these amino acids interchangeably with aspartic acid (Asp) and glutamic acid (Glu), potentially because both amino acids can be interconverted in vivo via asparaginases and glutaminases, respectively.32 While the exact reason for their exclusion remains unclear, this may reflect the manufacturers’ focus on more stable amino acids in their profiles, and further discussion of this limitation is warranted.
The Clean Label Project tested multiple protein supplements may contain heavy metal contamination which may be higher among plant-based proteins, especially among those that have a chocolate flavoring. Unfortunately, this report awaits peer-review and is not published in a peer-reviewed journal at the time of the writing of this manuscript. A peer-reviewed and published manuscript that evaluated the heavy metal contents in protein powders noted that all of the supplements (plant-based or otherwise) were not associated with an increased non-carcinogenic risk.33 The authors of this manuscript further note that heavy metal measurements should be performed in the context of the background exposure rates.33 Therefore, the current evidence supports no harm or are inconclusive at best for the potential heavy metal related health hazards from protein supplementation.
The findings from this study have significant implications for protein selection, especially for individuals with specific dietary preferences or health goals. For those focused on muscle growth, post-exercise recovery, or immune support, pea or whey protein offer similar benefits for muscle growth, although pea is likely to have a lower risk of acne exacerbation but that would require further study.
For individuals following plant-based diets or seeking alternatives due to food sensitivities or ethical considerations, blending multiple plant-based proteins—such as soy, pea, pumpkin seed, and hemp seed—may provide a more complete amino acid profile, addressing potential deficiencies in key amino acids like methionine*, cystine, and lysine*. Further research is needed to explore the synergistic effects of combining different plant-based protein isolates to optimize amino acid profiles for specific health and fitness goals.
The systematic comparison of amino acid profiles across various protein isolates emphasizes the importance of understanding the specific amino acid composition of protein sources, particularly in the context of health, fitness, and muscle recovery. Metric based ranking of quality showed that pea and egg-white were the highest quality followed by whey and soy sources. By considering the amino acid profiles of different protein isolates, individuals can better tailor their protein intake to meet their specific nutritional and performance needs. Future research should focus on developing strategies for enhancing the amino acid quality of plant-based proteins and exploring the benefits of protein blends.
Raja K Sivamani serves as a scientific advisor for LearnHealth, Arbonne, and Codex Labs and has served as a consultant or speaker for Burt’s Bees, Novozymes, Novartis, Sanofi, Bristol Myers Squibb, Pfizer, Nutrafol, Galderma, Novartis, Abbvie, Leo, UCB, Sun, and Regeneron Pharmaceuticals. All other authors declare no conflicts of interest.
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