We have previously shown that acute changes in MPS induced
by protein consumption after resistance exercise (Wilkinson and
others 2007) can predict long-term changes in body composition
in response to protein feeding during resistance training
(Hartman and others 2007). Specifically, we have shown that the
MPS response following an acute bout of resistance exercise is
greater with milk (18 g protein) as compared with soy (18 g
protein) (Wilkinson and others 2007). These results translated to
greater gains in lean mass, type I and II muscle fiber cross-sectional
area, and greater losses of fat mass with postexercise milk (35 g
protein) as compared with soy (35 g protein) consumption during
12 wk of resistance training in untrained young men, with no
difference in strength gains (Hartman and others 2007). Similarly,
Volek and others (2013) found greater gains in lean body mass
with whey protein (about 22 g/d) consumption during a 9-mo
supplementation and resistance training intervention as compared
with soy (about 22 g/d). In addition, whey protein increased
fasting plasma leucine concentration to a greater extent than soy
supplementation, and fasting leucine concentrations were positively
correlated with changes in lean body mass (Volek and others
2013), again highlighting the importance of leucine in stimulating
MPS and inducing muscle hypertrophy. Likewise, Cribb
and others (2006) found that whey induced a greater increase
in lean body mass and a greater decrease in fat mass, as compared
with casein, during a 10-wk resistance training protocol in
resistance-trained men. Furthermore, whey induced greater increases
in strength as compared with casein consumption during
resistance training, even when expressed relative to body weight
(BW) (Cribb and others 2006). However, not all trials have found
whey to be superior to soy (Candowand others 2006; DeNysschen
and others 2009) or rice protein (Joy and others 2013) in promoting
muscle hypertrophy with resistance training. In a study by Joy
and others (2013) subjects were randomized to consume either
48 g of rice or whey protein isolate immediately postexercise during
an 8-wk progressive, nonlinear resistance-training protocol.
While lean body mass, muscle thickness, and strength increased,
there were no differences between groups. The authors acknowledged
that this finding was likely due to the high dose of protein
(48 g) used in the study, which provided 5.5 and 3.8 g of leucine
in the whey and rice drinks, respectively, which are both greater
than the 2.0 to 3.5 g of leucine that has been proposed to be
the range of leucine intake where MPS is maximally stimulated
(Moore and others 2009). In addition, all subjects were put on a
diet consisting of 25% protein throughout the intervention and
thus habitual daily protein intake might have already saturated the
MPS response. In the 2 studies that did not find a difference in
lean mass or strength gains between whey- and soy-supplemented
groups following resistance training the habitual diet of the subjects
contained 1.2 g and 1.6 to 1.9 g/kg/day protein without
the inclusion of the supplement and thus might have been providing
enough protein throughout the day and immediately postexercise
to maximally stimulate MPS and induce equal increases
in strength and muscle hypertrophy (Candow and others 2006;
DeNysschen and others 2009). On balance, we view the available
evidence as being strongly suggestive that whey protein is superior
to other protein types in stimulating MPS following a bout of resistance
exercise and inducing muscle hypertrophy with resistance
training.