Protein Part 2—Research 2


Last updated March 2018

More Information on Protein

Contents

This article is a detailed discussion of the protein needs of vegans and is meant as a follow-up to our introductory article, Protein Part 1: The Basics.

Dietary Reference Intakes

We’ll start out with a brief overview of the U.S. Dietary Reference Intakes (DRI) for protein. The table below lists the DRI for protein and the amino acid lysine.

U.S. Dietary Reference Intakes for Protein and Lysine
Age Protein
(g/kg)A
Lysine
(mg/kg)A
7–12 mos 1.20 89
1–3 1.05 58
4–8 0.95 46
9–13 male 0.95 46
9–13 female 0.95 43
14-18 male 0.85 43
14-18 female 0.85 40
≥ 19 0.80 38
Pregnancy 1.1B 51
Breastfeeding 1.3 52
Aper kg of healthy body weight

The table below lists the Recommended Dietary Allowance (RDA) for protein and the essential amino acids per kg of body weight and for a 140-pound adult.

Recommended Dietary Allowance (RDA) for Protein and Amino Acids
PRO
(g)
HIS
(mg)
ISO
(mg)
LEU
(mg)
LYS
(mg)
MET+CYS
(mg)
PHE+TYR
(mg)
THR
(mg)
TRP
(mg)
VAL
(mg)
RDA–per kg of healthy body weight 0.8 14 19 42 38 19 33 20 5 24
RDA–for 140 lb. person 51 891 1,209 2,673 2,418 1,209 2,100 1,273 318 1,527
PRO-protein, HIS-histidine, ISO-isoleucine, LEU-leucine, LYS-lysine, MET+CYS-methionine plus cysteine, PHE+TYR-phenylalanine plus tyrosine, THR-threonine, TRP-tryptophan, VAL-valine

The DRI’s for protein are given in grams per kilogram of “body weight” per day. Fat mass doesn’t require much protein for maintenance, so “body weight” is generally interpreted to mean “ideal” or “healthy” body weight even though the DRI doesn’t specify that.

Protein Needs for People Over 60

One caveat to the DRI for protein is that many papers have suggested that people over 60 years old are better off with 1.0–1.3 g/kg of protein per day (1, 2, 3, and many more). Most of this research is supported by, or connected to people who have done work supported by, animal agriculture trade organizations (1, 2, and many more).

Their argument, based on some research, is that people over 60 are less efficient at maintaining muscle and bone and therefore need more protein. These arguments are convincing enough that, despite their support from animal agriculture, it’s probably a good idea for people over 60 to get more protein.

Protein and Amino Acid Content of Selected Plant Foods

See the footer in the table above, Recommended Dietary Allowance (RDA) for Protein and Amino Acids, for a key to the full names of each amino acid listed in the tables below. Most of the information in these tables are taken from the USDA Nutrient Database. See Reference 4 for specific notes on these tables.

Protein & Essential Amino Acid Content of Legumes
PRO
(g)
HIS
(mg)
ISO
(mg)
LEU
(mg)
LYS
(mg)
MET+CYS
(mg)
PHE+TYR
(mg)
THR
(mg)
TRP
(mg)
VAL
(mg)
Black Beans 0.50 cup 7.6 212 336 609 523 197 627 321 90 399
Edamame 0.50 cup 8.4 207 233 577 577 204 638 257 98 251
Garbanzos (Chick Peas) 0.50 cup 7.3 200 312 517 486 193 569 270 70 305
Kidney Beans 0.50 cup 7.7 214 339 613 527 198 631 323 91 402
Lentils–cooked 0.50 cup 8.9 251 386 647 624 193 680 320 80 444
Peanut Butter 2.00 T 8 204 284 523 290 202 746 276 78 339
Peanuts 0.33 cup 11.4 289 401 740 410 286 1,055 391 111 478
Pinto Beans–refried 0.50 cup 6.4 175 303 544 448 143 529 235 76 369
Soy Milk 1.00 cup 9.2 174 353 590 439 213 644 277 105 345
Tempeh 0.50 cup 15.4 387 730 1,187 754 305 901 661 161 764
Tofu–firm 0.50 cup 10.2 284 559 917 582 177 1,013 518 155 573
Protein & Essential Amino Acid Content of Nuts & Seeds
PRO
(g)
HIS
(mg)
ISO
(mg)
LEU
(mg)
LYS
(mg)
MET+CYS
(mg)
PHE+TYR
(mg)
THR
(mg)
TRP
(mg)
VAL
(mg)
Almonds 0.25 cup 8 199 251 532 207 122 562 214 77 292
Cashews 0.25 cup 5 137 250 440 280 191 439 203 81 356
Pecans 0.25 cup 2 65 83 148 71 83 158 76 23 102
Pistachios 0.25 cup 6 158 294 492 367 216 496 216 87 388
Pumpkin seeds–roasted 0.25 cup 9 227 373 704 360 272 823 291 168 460
Sunflower Seeds 0.25 cup 6 172 309 451 254 257 489 252 94 357
Walnuts–chopped 0.25 cup 5 114 183 342 124 130 327 174 50 220
Protein & Essential Amino Acid Content of Grains
PRO
(g)
HIS
(mg)
ISO
(mg)
LEU
(mg)
LYS
(mg)
MET+CYS
(mg)
PHE+TYR
(mg)
THR
(mg)
TRP
(mg)
VAL
(mg)
Bread–white 2.00 slice 4 89 161 290 112 159 320 121 48 180
Bread–whole wheat 2.00 slice 7 78 125 227 93 130 256 97 52 152
Corn–kernels boiled 1.00 cup 5 119 243 446 272 188 421 205 54 297
Flour Tortilla 1.00 med 4 90 141 276 98 154 322 113 49 164
Oatmeal–boiled 1.00 cup 6 126 271 505 316 335 568 225 236 374
Quinoa–cooked 1.00 cup 8 235 290 483 442 295 496 242 96 342
Rice–brown, med grain 1.00 cup 5 115 191 372 172 156 402 166 58 265
Rice–white, med grain 1.00 cup 4 104 192 366 160 195 385 158 52 270
Seitan 3.00 oz 31 671 1,293 2,247 656 1,077 2,915 839 1,498
Spaghetti–white 1.00 cup 7 136 258 456 127 292 498 176 85 284
Spaghetti–whole wheat 1.00 cup 8 175 290 510 165 275 566 200 97 323
Protein & Essential Amino Acid Content of Vegetables
PRO
(g)
HIS
(mg)
ISO
(mg)
LEU
(mg)
LYS
(mg)
MET+CYS
(mg)
PHE+TYR
(mg)
THR
(mg)
TRP
(mg)
VAL
(mg)
Baked Potato 1.00 med 4 93 175 260 263 121 351 157 67 244
Broccoli–cooked, chopped 1.00 cup 4 82 180 216 234 88 244 152 48 212
Carrot–5 12 inches long 1.00 small 1 20 38 51 51 52 51 96 6 35
Kale–cooked, shredded 1.00 cup 3 52 148 173 148 56 215 111 30 135
Romaine Lettuce–shredded 1.00 cup 1 16 58 54 58 22 60 42 6 48
Spirulina–dried 1.00 tbsp 4 76 225 346 212 126 375 208 65 246
Tomato 1.00 med 1 17 22 31 33 18 50 33 7 22
Protein & Essential Amino Acid Content of Fruit
PRO
(g)
HIS
(mg)
ISO
(mg)
LEU
(mg)
LYS
(mg)
MET+CYS
(mg)
PHE+TYR
(mg)
THR
(mg)
TRP
(mg)
VAL
(mg)
Apple 1.00 med 0 7 8 18 17 2 9 8 1 17
Banana 1.00 med 1 91 33 80 59 20 69 33 11 55
Orange 1.00 med 1 24 33 30 62 39 62 20 12 52
Strawberries–whole 1.00 cup 1 17 23 49 37 12 59 29 12 27
Protein & Essential Amino Acid Content of Protein Powders
PRO
(g)
HIS
(mg)
ISO
(mg)
LEU
(mg)
LYS
(mg)
MET+CYS
(mg)
PHE+TYR
(mg)
THR
(mg)
TRP
(mg)
VAL
(mg)
Naturade Soy Protein 0.33 cup 24 618 1,178 1,939 1,552 640 2,184 912 305 1,157
Naturade Soy-Free Protein 0.33 cup 22 533 1,182 1,785 1,455 445 1,957 918 228 1,115

Protein Balance Studies

How much total protein do vegans need?

The RDA for protein is supposed to cover the needs of 97–98% of the population. It’s currently set at .80 grams per kilogram of healthy body weight per day. In addition to the RDA, there’s also an Estimated Average Requirement (EAR) for protein, which is .66 g/kg for adults 19–50 years old (5). The EAR is supposed to be how much protein the average person requires.

The RDA for the normal population is based on nitrogen balance studies, especially a 2003 meta-analysis (6). Nitrogen balance studies are used because nitrogen is a component of protein that fat, carbohydrate, and alcohol do not have. The studies are done by measuring how much nitrogen someone eats and then subtracting how much they lose through urine, feces, hair, sweat, etc. If they lose more than they eat, then they are in negative nitrogen balance and need more protein. If they lose as much as they eat, they are considered in nitrogen balance and that is determined to be the ideal amount of protein.

With all the commotion regarding vegans and protein for the past 40 years, one would think there’d be many nitrogen balance studies performed on actual vegans. Guess how many there have been? None.

The Food and Nutrition Board, who sets the RDAs, says, “[A]vailable evidence does not support recommending a separate requirement for vegetarians who consume complementary mixtures of plant proteins[.]” But what is that available evidence?

There have been two studies looking at nitrogen balance using a vegan diet (on people who are typically not vegan).

A 1965 study had two parts (7). In the first part, eight young men were fed a vegan diet of .50 g/kg of protein per day, with the amino acid profile matching that of milk. With some small exceptions, they did not stay in nitrogen balance. No surprises there. In the second part of the study, they increased the protein to .75 g/kg using .25 g/kg of soy protein per day and the subjects were, for the most part, in nitrogen balance. This indicates that .75 g/kg might be enough protein for vegans, especially young men, but it might require .25 g/kg of that protein to be soy (or at least legumes).

A 1967 study found that protein for people eating a vegan diet (for a 3-week period) was 2.6% less digested than the protein in a non-vegetarian diet (8). The diets in this study averaged .91 g/kg of protein per day (my calculations based on weights and heights given), of which .55 g/day were legume protein. On the vegan diet, 9 out of 12 of the participants were in nitrogen balance.

A 1986 study fed young adult males a near-vegan diet (except for 41 g of dried, skim milk) for 90 days, using 1 g/kg of body weight per day (5). Some of the protein was from beans, but it’s not clear how much. Only one out of the eight subjects showed a negative nitrogen balance.

In addition to nitrogen balance, protein needs can be measured by the rate of albumin synthesis. Albumin is a protein in the blood that responds to different amounts of dietary protein.

A 2000 study of healthy men showed a 12% reduced rate of albumin synthesis when eating a diet of 63% plant protein compared to 26% plant protein (each for 10 days and equal amounts of total protein) (9). When 18 g/day of soy protein was added (increasing the plant protein percentage to 78 and total protein from 78 g/day to 96 g/day), albumin synthesis returned to normal. I have estimated the grams of protein per kg of healthy body weight per day in this study and they were eating about 1.09 g/kg without the soy and 1.34 with the soy (10). We don’t know if that much protein was required to return albumin synthesis to normal, and it’s possible that 10 days wasn’t long enough to see if someone’s albumin synthesis would become more efficient on a primarily plant-based diet.

The synthesis of two other proteins, prealbumin and transferrin, were also reduced on 63% plant protein. The fact that transferrin, an iron transport protein, decreased is interesting. Lysine supplements have been found to increase iron absorption so it’s likely these subjects were not getting enough lysine.

On the other hand, a 1999 cross-sectional study on vegans found them to have significantly higher serum albumin levels than non-vegetarians (11). The vegans were eating 1.04 grams of protein per kg of body weight (based on a BMI of 22). They were eating approximately .36 g/kg of legume protein. The authors stated, “Although serum albumin may not be a sensitive indicator of protein nutriture, the higher concentrations suggest that the diets of the vegan participants were adequate in protein.”

A study out of Boston published in 2011 but performed using data collected during the 1980s, found that vegan and non-vegan, middle-aged women had similar levels of muscle mass despite differences in protein intake of 1.0 g/kg/day for vegans and 1.3 g/kg/day for omnivores (12). However, the muscle mass wasn’t measured directly – rather it was estimated using formulas based on creatinine clearance (a byproduct of muscle metabolism). The researchers believed the formulas to be accurate, but since they have not been validated on vegans it should be viewed with some uncertainty. At 30 mg/kg/day, the vegan women did not meet the RDA for lysine which is 38 mg/kg/day. However, the study showed the vegan women to be consuming only 1,511 kcal/day vs. 1,866 kcal/day for the omnivores, yet their body mass indexes were very similar at 20.0 and 20.7 respectively. This could indicate that food intake for the vegans was underestimated, possibly due to a lack of data on vegan foods.

So where does all this research leave us? The results are compiled in the table below. It’s not obvious what they indicate for the protein needs of vegans, but an estimate is that vegans might benefit from 1.0–1.1 g/kg of protein.

Plant Protein Studies
Study Legume Protein
(g/kg)A
Protein
(mg/kg)A
Result
1965 Doyle Amino acids matched milk 0.5 Subjects not in nitrogen balance
1965 Doyle Amino acids matched milk 0.75 100% in nitrogen balance
1967 Register 0.55 0.91 75% in nitrogen balance
1986 Yanez Small amount 1.0 7 out of 8 in nitrogen balance
2000 Caso Unclear 1.09 12% lower albumin synthesis than controls
2000 Caso At least .25 1.34 Normal albumin synthesis
1999 Haddad 0.36 1.04 Normal albumin levels
2011 Andrich Lysine intake 79% RDA 1.0 Muscle mass similar to omnivores
Aper kg of healthy body weight

Nitrogen Balance Methods Critiqued

In 2010, a group of researchers from The Hospital for Sick Children in Toronto wrote a paper suggesting that the methods for determining the DRIs for protein (which includes the RDA) were underestimating protein needs (13). One of the authors, Dr. Paul B. Pencharz, was a member of the Panel on DRIs for macronutrients and a member of the Joint WHO/FAO/United Nations University (UNU) Expert Consultation on Protein and Amino Acid Requirements in Human Nutrition. They write:

The current recommendations for protein intakes in adults are primarily based on the reanalysis of existing nitrogen balance studies [1,12]. The nitrogen balance technique has inherent methodological limitations, which lead to an underestimation of the requirement estimate. Furthermore, the application of a single linear regression analysis to identify zero nitrogen balance is not appropriate because the nitrogen intake response relationship is not linear. On the basis of these concerns, we reanalyzed published nitrogen balance studies using two-phase linear regression analysis. We also applied the IAAO method to determine total protein requirements in adults. The mean and population-safe intakes based on the reanalysis were determined to be 0.91 and 1.0 g protein/kg/day and 0.93 and 1.2 g/kg/day, respectively, based on the IAAO method. These new values are approximately 40% higher than the current recommendations, and therefore, there is an urgent need to reassess recommendations for protein intake in adult humans.

They say that the inherent methodological errors in nitrogen balance studies are that nitrogen intakes are overestimated and nitrogen loss is underestimated, leading to false nitrogen balance at lower protein levels.

This group of researchers considers the average protein requirement to be .91–.93 g/kg/day and the amount to cover 97%–98% of the population (equivalent to the RDA) to be 1.0–1.2 g/kg/day.

Protein Needs of Athletes

The Institute of Medicine, which sets the RDAs, doesn’t recommend higher protein intakes for athletes. However, in a 2016 joint position paper on nutrition and athletic performance, the American College of Sports Medicine (ACSM), the Academy of Nutrition and Dietetics (AND), and Dietitians of Canada recommend higher protein intakes for athletes and also suggest that athletes should give some attention to timing of protein intake (18). They don’t differentiate between strength and endurance athletes in making the following recommendations:

  • Dietary protein intake necessary to support metabolic adaptation, repair, remodeling, and for protein turnover generally ranges from 1.2 to 2.0 g/kg/ day.
  • Daily protein needs should be met with a meal plan providing a regular spread of moderate amounts of high-quality protein across the day and following strenuous training sessions. Muscle protein synthesis is maximized by consumption of 0.3 grams protein/kg body weight every three to five hours, including consumption of this amount within two hours following exercise.

However, there are still questions about optimal intake and timing of protein for athletes. A 2017 meta-analysis of the effects of protein intakes among strength athletes found that timing of protein intake was not important for gains in muscle mass and strength (19). They suggested that a daily protein intake of 1.6 g/kg/day, separated into 0.25 g/kg doses, was sufficient for muscle protein synthesis.

While many vegan, raw foodist athletes appear to thrive on a raw, vegan diet, many vegans who are not athletes struggle with raw foods diets—it could be that the higher caloric intake of athletes allow them to meet lysine needs while eating mostly low-lysine foods.

Amino Acid Intakes and Blood Levels in Vegans

A 2015 report from EPIC-Oxford analyzed the dietary intakes and blood levels of amino acids in various diet groups in adult men (14). The study included 98 men for each diet group (vegan, lacto-ovo vegetarian, pescatarian, and meat-eater). The authors say, “[T]his is the largest study to date of amino acids in the circulation or in the diet by habitual diet group, and on average participants had followed their diet for several years.”

Amino Acid Intakes of Vegans

The study didn’t compare the intakes of the various diet groups to the US RDA for amino acids, but I have done so in the table below.

The paper didn’t include the weight of the participants, but it gave an average body mass index of 22.1 kg/m2 for vegans. If we assume an average height of 175.3 cm for a British male (15), the average weight of the vegans was 67.9 kg, and we can thus calculate an average RDA based on a weight of 67.9 kg.

EPIC-Oxford Percentage of RDA of Essential Amino Acid Intakes in Adult Vegan Men
Amino Acid Intake
(g/day)
RDA
(g/day)
Percentage of RDA
Isoleucine 2.47 1.29 191
Leucine 4.33 2.85 152
Valine 2.95 1.63 181
Histidine 1.52 0.95 160
Lysine 2.82 2.58 109
Methionine+Cysteine 1.72 1.29 133
Phenylalanine+Tyrosine 4.79 2.24 214
Theronine 2.19 1.36 161
Tryptophan 0.77 0.34 226

The table above indicates that vegan men met the RDA for all essential amino acids.

This study bolstered the idea that lysine is the limiting amino acid in vegan diets, with vegan men surpassing the RDA by the lowest amount–9%. Methionine, the amino acid of second most concern, surpassed the RDA at the next lowest level of 33%.

The 95% confidence interval for lysine was 2.69-2.95 g/day; with the lower margin coming in at 104% of the RDA. The people on the lower end might have been the people who weighed less (and thus had a lower RDA than the average vegan).

The RDA for protein and amino acids is the same for women as it is for men (based on a percentage of their body weight). Male vegans in EPIC-Oxford were found to eat 10.7% more protein than female vegans (62 vs. 56 g per day; link). If you assume female vegans eat the same percentage of high-lysine foods as men, their average lysine intakes would be only 98.7% of the RDA.

Given that women have a lower percentage of lean body mass on average, it might seem curious that they have the same RDA for protein (and amino acids). In determining the RDAs, the Institute of Medicine says (Ref 16, p. 644):

Although the data indicate that women have a lower nitrogen requirement than men per kilogram of body weight, this was only statistically significant when all studies were included, but not when the analysis was restricted to the primary data sets. This difference may be due to differences in body composition between men and women, with women and men having on average 28 and 15 percent fat mass, respectively. When controlled for lean body mass, no gender differences in the protein requirements were found. However, in view of the uncertain significance of the difference between the genders, the same protein EAR [i.e., Estimated Average Requirement, a foundation for the RDA] on a body weight basis for both men and women is chosen.

Another consideration is that the vegans in the UK may eat lower amounts of protein than those in the U.S. Adventist Health Study-2 found an average protein intake of 71 g/day for men and women combined, considerably more than in EPIC-Oxford (link). It seems safe to assume that Seventh Day Adventist woman are likely getting plenty of lysine and other amino acids.

Finally, according to the authors, “[T]he validation of the [food frequency questionnaire] showed that protein intake was particularly difficult to estimate.”

Amino Acid Blood Levels of Vegans

In comparing blood levels of amino acids between diet groups, vegans had lower levels of lysine, methionine, tryptophan, and tyrosine, and higher levels of alanine and glycine.

Interestingly, arginine, a dietary concern for vegans with the herpes virus, was actually lower in the blood of vegans, but not significantly. It was also lower in the diet (3.92 g/day for vegans vs. 4.13 g/day for meat-eaters; lacto-ovo vegetarians had the lowest intake at 3.36 g/day).

The authors didn’t seem alarmed by any of the differences found between diet groups. I decided to take things a bit further and compare the plasma levels found in this study to the reference ranges given by the U.S. National Library of Medicine (17) in the table below.

Plasma Amino Acid Levels in Adult Vegan Men
Amino Acid Plasma
µmol/l (95% CI)
Reference Range
µmol/l
Alanine 621 (595, 648) 230-510
Arginine 44 (39, 48) 13-64
Asparagine 98 (95, 102) 45-130
Aspartate 69 (66, 72) 0-6
Citrulline 40 (38, 42) 16-55
Glutamate 262 (248, 277) 18-98
Glutamine 547 (529, 566) 390-650
Glycine 452 (434, 470) 170-330
Histidine 117 (113, 120) 26-120
Isoleucine 96 (92, 100) 42-100
Leucine 191 (184, 199) 66-170
Lysine 210 (201, 219) 150-220
Methionine 27 (26, 28) 16-30
Ornithine 205 (197, 215) 27-80
Phenylalanine 97 (93, 101) 41-68
Proline 244 (233, 256) 110-360
Serine 197 (190, 205) 56-140
Theronine 165 (159, 171) 92-240
Tryptophan 65 (63, 68) n/a
Tyrosine 73 (70, 76) 45-74
Valine 217 (209, 225) 150-310
  • Alanine, glutamate, glycine, leucine, ornithine (a non-protein amino acid), phenylalanine, and serine are higher.
  • Aspartate is also higher, but the reference range is curiously low.
  • There is no reference range for tryptophan, with no explanation as to why.
  • There is a reference range for cystine (which is two cysteine molecules combined), but EPIC-Oxford didn’t list plasma levels for cystine or cysteine.

It’s not clear what any of this means and the U.S. National Library of Medicine notes that these numbers are dependent on the specific laboratory methods used.

Conclusion

The research reviewed here isn’t a great substitute for a nitrogen or protein synthesis study on vegans, but for now, it’s the best evidence we have. The takeaway message is that vegans, and particularly vegan women, should eat plenty of lysine-rich foods. Vegans might want to err on the side of getting more protein, preferably 1.0 g/kg of healthy body weight. Vegans over 60 should aim for 1.0–1.3 g/kg.

References

1. Gaffney-Stomberg E, Insogna KL, Rodriguez NR, Kerstetter JE. Increasing dietary protein requirements in elderly people for optimal muscle and bone health. J Am Geriatr Soc. 2009 Jun;57(6):1073-9.

2. Paddon-Jones D, Short KR, Campbell WW, Volpi E, Wolfe RR. Role of dietary protein in the sarcopenia of aging. Am J Clin Nutr. 2008 May;87(5):1562S-1566S.

3. Morais JA, Chevalier S, Gougeon R. Protein turnover and requirements in the healthy and frail elderly. J Nutr Health Aging. 2006 Jul-Aug;10(4):272-83.

4. Notes on the Protein and Amino Acid Content of Selected Plant Foods tables:

  • The essential amino acid methionine is paired with the non-essential cysteine, and the essential amino acid phenylalanine is paired with the non-essential tyrosine. That’s because the RDA is calculated for these pairs of amino acids together, assuming there are similar ratios in most foods. In plant foods, there are about equal amounts of methionine and cysteine, and usually more phenylalanine than tyrosine.
  • Amino acid content for pumpkin seeds was taken from the USDA database entry for Food #12016, Seeds, pumpkin and squash seed kernels, roasted, without salt. According to correspondence with Robin G. Thomas, MS, RD of the USDA Nutrient Data Laboratory, the entries for 12014, 12016 and 12516 are for pumpkin seeds only (i.e., not squash seeds also) (January 2013).
  • Seitan information is extrapolated from:

5. Yáñez E, Uauy R, Zacarías I, Barrera G. 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. J Nutr. 1986 May;116(5):865-72.

6. Rand WM, Pellett PL, Young VR. Meta-analysis of nitrogen balance studies for estimating protein requirements in healthy adults. Am J Clin Nutr. 2003 Jan;77(1):109-27.

7. Doyle MD, Morse LM, Gowan JS, Parsons MR. Observations on nitrogen and energy balance in young men consuming vegetarian diets. Am J Clin Nutr. 1965 Dec;17(6):367-76.

8. Register UD, Inano M, Thurston CE, Vyhmeister IB, Dysinger PW, Blankenship JW, Horning MC. Nitrogen-balance studies in human subjects on various diets. Am J Clin Nutr. 1967 Jul;20(7):753-9.

9. Caso G, Scalfi L, Marra M, Covino A, Muscaritoli M, McNurlan MA, Garlick PJ, Contaldo F. Albumin synthesis is diminished in men consuming a predominantly vegetarian diet. J Nutr. 2000 Mar;130(3):528-33.

10. Calculations:

Average healthy body weight of the men based on a BMI of 22 and average height of 1.74 m = 66.6 kg
78 g protein per 66.6 kg = 1.17 g/kg
96 g protein per 66.6 kg = 1.44 g/kg
Actual average body weight of the men was 77 kg
78 g protein per 77 kg = 1.01 g/kg
96 g protein per 77 kg = 1.25 g/kg
Averaging the healthy body weight with the actual body weight gives 1.09 and 1.34 g/kg

 

11. Haddad EH, Berk LS, Kettering JD, Hubbard RW, Peters WR. Dietary intake and biochemical, hematologic, and immune status of vegans compared with nonvegetarians. Am J Clin Nutr. 1999 Sep;70(3 Suppl):586S-593S.

12. Andrich DE, Filion ME, Woods M, Dwyer JT, Gorbach SL, Goldin BR, Adlercreutz H, Aubertin-Leheudre M. Relationship between essential amino acids and muscle mass, independent of habitual diets, in pre- and post-menopausal US women. Int J Food Sci Nutr. 2011 Nov;62(7):719-24. Epub 2011 May 16.

13. Elango R, Humayun MA, Ball RO, Pencharz PB. Evidence that protein requirements have been significantly underestimated. Curr Opin Clin Nutr Metab Care. 2010 Jan;13(1):52-7.

14. Schmidt JA, Rinaldi S, Scalbert A, Ferrari P, Achaintre D, Gunter MJ, Appleby PN, Key TJ, Travis RC. Plasma concentrations and intakes of amino acids in male meat-eaters, fish-eaters, vegetarians and vegans: a cross-sectional analysis in the EPIC-Oxford cohort. Eur J Clin Nutr. 2015 Sep 23.

15. Statistics reveal Britain’s ‘Mr and Mrs Average’. BBC News. 2010 Oct 13.

16. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. National Academy of Sciences. Institute of Medicine. Food and Nutrition Board. 2005.

17. Plasma amino acids. Medline Plus. U.S. National Library of Medicine. Accessed January 30, 2016.

18. Thomas DT, Erdman KA, Burke LM. Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. J Acad Nutr Diet 2016;116:501-528.

19. Morton RW, Murphy KT, McKellar SR, Schoenfeld BJ, Henselmans M, Helms E, Aragon AA, Devries MC, Banfield L, Krieger JW, Phillips SM. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. Br J Sports Med. 2018 Mar;52(6):376-384.

Also Reviewed

Evans WJ. Protein nutrition, exercise and aging. J Am Coll Nutr. 2004 Dec;23(6 Suppl):601S-609S.


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2 thoughts on “Protein Part 2—Research

  • Victor Robledo

    Hi Jack !!
    I find a mistake on RDA MET+CYS of your article (https://veganhealth.org/protein-part-2/#amino-intakes-vegans) , the table named “Recommended Dietary Allowance (RDA) for Protein and Amino Acids” was talking to me 38mg RDA MET+CYS, but RDA is 19mg/kg ,
    Then I saw a “number dancing” problem on the table; all the aminoacid numbers are one cell to the right, so all the values are wrong.

    That’s the reason why “Protein” cell (the first one) is empty.

    Cheers and congrats for your site,
    Victor Robledo.