The bad news - vegans may have a problem... - but as long as one pays attention to the real muscle mass and blood work you may be able to be vegan...

The article mentioned using vegan protein that are fortified (enhanced) with some missing amino acids -   but at this point it is only a speculation that this approach would help. 

The Skeletal Muscle Anabolic Response to Plant- versus Animal-Based Protein Consumption1

1. Stephan van Vliet2,3, 
2. Nicholas A Burd2,3, and 
3. Luc JC van Loon3,*

+Author Affiliations

1. 2Department of Kinesiology and Community Health, University of Illinois at Urbana-Champaign, Urbana, IL; and
2. 3Department of Human Movement Sciences, Faculty of Health, Medicine, and Life Sciences, School for Nutrition and Translational Research in Metabolism (NUTRIM), Maastricht University, Maastricht, Netherlands

1. ↵*To whom correspondence should be addressed. E-mail:[email protected].

Abstract

Clinical and consumer market interest is increasingly directed toward the use of plant-based proteins as dietary components aimed at preserving or increasing skeletal muscle mass. However, recent evidence suggests that the ingestion of the plant-based proteins in soy and wheat results in a lower muscle protein synthetic response when compared with several animal-based proteins. The possible lower anabolic properties of plant-based protein sources may be attributed to the lower digestibility of plant-based sources, in addition to greater splanchnic extraction and subsequent urea synthesis of plant protein–derived amino acids compared with animal-based proteins. The latter may be related to the relative lack of specific essential amino acids in plant- as opposed to animal-based proteins. Furthermore, most plant proteins have a relatively low leucine content, which may further reduce their anabolic properties when compared with animal proteins. However, few studies have actually assessed the postprandial muscle protein synthetic response to the ingestion of plant proteins, with soy and wheat protein being the primary sources studied. Despite the proposed lower anabolic properties of plant vs. animal proteins, various strategies may be applied to augment the anabolic properties of plant proteins. These may include the following: 1) fortification of plant-based protein sources with the amino acids methionine, lysine, and/or leucine; 2) selective breeding of plant sources to improve amino acid profiles; 3) consumption of greater amounts of plant-based protein sources; or 4) ingesting multiple protein sources to provide a more balanced amino acid profile. However, the efficacy of such dietary strategies on postprandial muscle protein synthesis remains to be studied. Future research comparing the anabolic properties of a variety of plant-based proteins should define the preferred protein sources to be used in nutritional interventions to support skeletal muscle mass gain or maintenance in both healthy and clinical populations.

This is interesting thanks for sharing it Hala.  I translate the conclusions to mean that if youre trying to gain muscle mass through exercise you will build it faster according to the study using complete animal protein sources than the same protein amount from plant based protein sources some of which are not 100% complete proteins when eaten alone. (or are low in leucine) 

I for  one though am not really trying to gain muscle weight at this point from my ( mostly cardio)  exercise - keeping my fat cells empty i more my purpose .  I also  as mesomorph which many of us here are have a fairly easy time gaining and keeping muscle ANYWAY . 

Its interesting to note that the connection between skeletal mass preservation (  bone density) and plant based sources of protein has been noticed by clinical researchers though.  I personally can TELL whose a long term vegetarian among those I meet by their 1) young healthy look 2) perfect  full set of teeth 3) great posture and height.  Plant based calcium ROCKS 

Not only building new muscles - but muscles repair - our muscles gets damaged by suing so there is a constant repair - new muscles synthesis... 

as we get older - it is more difficult to maintain current muscles (we don't want to get flabby)  - it can be so easy. 

Vegan proteins do not provide a complete - proper ratios so any tissue repair (including our skin, organs, heart muscles) may be compromised... 

they did not say it is impossible - just that the muscle repair - new muscle formation is not as good with plan based protein as it is with animal based proteins.. 

But vegetarian - that consume dairy and eggs, most likely can ingest enough of complete proteins that will not affect their muscle turnover. 

The vegan - need to make sure they either get a lot of the proteins (more grams) and use variety of vegan proteins, or use some protein supplements that have been fortified with the missing amino acids. 

Due to allergy to dairy proteins (whey, casein,etc.) I no longer can eat cheese or yogurt. When I don't feel like eating - I need to remember to pick vegan protein source that offers the best amino acid profile... and make sure that it is not my only protein source for the day or a week...