Plant and animal
proteins differ in their anabolic properties. Animal proteins are more anabolic but there are some tricks to optimize the anabolic
response of plant-based proteins.
Among all the vegetable
proteins, soy protein is the only one studied extensively. Generally soy
protein results in lower muscle protein synthesis (MPS) rates compared with
animal protein sources such as whey (1,2), beef (3) and milk proteins (4).
The difference is most
likely due to different protein
digestion and aminoacid (AA) absorption kinetics and composition (5). The
biggest differences are seen in the content of leucine, lysine, and methionine, typically vegetable protein have a
lower content of these aminoacids (6).
(5).
Leucine
Of these 3 aminoacids leucine
is of particular importance. Leucine is
what stimulates MPS (7), and the leucine content of a protein is independently associated with the capacity
to increase MPS (7,8,9). Animal
protein has more leucine, and whey protein is considered superior for MPS
due to higher Leucine content (13.7 %) versus isolated soy (10) and hidrolized
casein (11) with 8% and 10.2 % Leucine content respectively.
On the other hand,
vegetal protein have about 6-8% of Leucine compared with animal proteins with
8.5-9% and >10% for milk proteins. This difference may be the crucial
advantage in favor of animal proteins (11).
Soy proteins appear
to support greater splanchnic (visceral) rather than peripheral (i.e., muscle)
protein synthesis and are converted to urea to a greater extent than are milk
proteins. Alternatively, observed differences might be explained by differences
in leucine content or absorption kinetics (12).
The postprandial MPS response
in healthy young individuals is dose dependent up to 20g (10 g EAAs) of
high-quality, animal-based protein (13,14,15).
For example when
comparing 0 g, 5 g, 10 g, 20
g, and 40 g of egg protein after exercise it was seen that 20g was enough to maximally stimulate MPS. This equals to about 1.7g of Leucine. However for the
40g dose (3.4g of Leucine) no significant differences in MPS occurred (13).
The difference is also
seen in long-term studies, 17.5g of
milk protein vs. soy protein (isonitrogenous amount) results in greater muscle
gains after 12 weeks of training (16). In another study, 24g of whey vs. soy
also resulted in greater lean mass gains (3.3 vs. 1.8kg) after 36 weeks of
training (17).
Strategy 1: Increasing vegetal-protein
intake per meal/total
In another comparison
between soy and whey, 33g of soy or whey similarly increased MPS after a bout
of exercise (18), which suggests that a higher quantity of plant-based protein
can minimize the long-term differences.
A greater improvement
in lean mass and increase of Type II muscle fibers was also found following an
omnivorous diet compared with a lactoovarian diet, after 12 weeks of training (19).
The difference is
attenuated when the total protein intake increases from 0.78g/kg/day to
1.15g/kg/day (20), suggesting that a greater protein intake might reduce the
differences between animal and vegetable proteins in terms of muscle mass gains
(21) and that a greater intake of
vegetable protein can in principle compensate for the lower essencial aminoacid
content.
Comparing 48g
of isolate rice protein vs. whey
(isocaloric and nitrogenous amounts), immediately after exercise, promoted
similar gains in lean mass (2.5 vs 3.2kg), after
8 weeks of training (12). At such doses, the rice protein supplement contained
approximately 3.8 g of Leucine whereas the whey protein supplement contained
5.5 g of Leucine, more than enough to optimize muscle protein accretion (12,22)
As the amount of protein consumed
increases, the importance of the relative leucine content of the protein diminishes (23,24).
The ingestion of greater amounts of
plant-based protein per meal, consequently ingesting greater amounts of EAAs (and
notably leucine), may compensate for the
lower muscle anabolic properties of plant- vs. animal-based proteins (5).
However, the consumption of greater amounts for vegetal
protein may not be practical, due to the large quantity of food, and may
not be feasible (21). For example, in elderly men Leucine oxidation rates are
elevated after 40g of soy protein compared to a similar dose of whey (21). As
other studies also suggest for plant-based proteins, part of soy aminoacids are oxidized rather than
being used for MPS compared with whey protein.
Another concern is the
fact that the elderly are more anabolic resistant and need higher doses of protein/leucine to
illicit the same MPS response (25); 20g of whey and soy protein did not
maximize the MPS response in the elderly (26).
Usually older
individuals require the ingestion of greater amounts of high-quality, animal-based
protein (>35–40 g) (27,28,29) for maximal stimulation of postprandial MPS.
Substantial amounts (>40g) of a
plant-based protein source per dose should theoretically be ingested to
maximize postprandial MPS rates in older individuals, which can be far from practical (5).
(5)
Strategy 2: Leucine fortification
A more practical strategy may be the addition of free leucine to plant-based
proteins. Soy protein supplemented with free BCAAS (leucine, isoleucine and
valine) reduced splanchnic extraction and urea synthesis, consequently shifting
dietary protein–derived AAs toward peripheral (i.e., skeletal muscle) tissue (5,29).
Free Leucine added to wheat protein, to match the leucine content present in an
isonitrogenous amount of whey protein, resulted in similar postprandial MPS
rates in an animal model (5,30).
Leucine fortification may be a more
practical and effective way to enhance the anabolic properties of plant-based
protein sources (5).
Strategy 3: Protein blends
For non-vegans, protein blends may be
another good strategy. Protein blends such as a combination of plant and dairy
proteins can be useful to maximize the anabolic potential. For example, in one
study there were no measurable differences in the MPS response during the 4-h
postexercise period with the ingestion of either 17.7 g whey protein or 19.3 g
of a protein blend (containing a mixture of 25% whey, 25% soy, and 50% casein
protein) (5,31).
Beware of blends containing >50% of
plant-based proteins, such a high amount may contain less Leucine than an isonitrogenous
amount of an animal-based protein source. This may not be critical for healthy
young populations but will likely
be of greater impact on stimulating postprandial muscle protein accretion in
older and more clinically compromised populations requirering greater amounts
of leucine (>2.5-3g) (5).
A protein blend comprised 50% caseinate, 25% whey protein, and 25% pea protein increased plasma essential amino acids,
especially branched-chain amino acids, and decreases cortisol and
3-methylhistidine in the elderly (32).
For vegans, a well-balanced combination of multiple
plant-based protein sources, to allow for ingestion of a ‘‘complete’’ EAA
profile, may suffice. Since plant-based proteins are generally only low in 1 or
2 EAAs, combining plant proteins that are lower in lysine yet higher in methionine
(e.g., wheat, rice, hemp, and maize) with plant proteins that are higher in
lysine yet lower in methionine (including black bean, oat, soy, lentil, potato,
and pea) may augment the anabolic properties of plant-based protein intake (5).
There are other
factors to take into account regarding the Aminoacid profile and Aminoacids available
for metabolic processes such as protein synthesis, such as the effect of
cooking on Lysine: cooking denatures lysine thus rendering it unavailable for
protein synthesis (33).
All cereals
protein are limited in lysine, most are limited in threonine, and maize is
limited in tryptophan; legumes are sufficient in lysine, threonine, and
tryptophan but are limited in sulphur amino acids. Hence complementation
(mixtures) of cereals and legumes can help in achieving the best possible plant
protein mixtures (33).
Take-home points:
- Animal proteins are
more anabolic due to higher Leucine content;
- High-quality
animal proteins require far less energy intake to meet essential amino acid
needs than lower quality plant proteins;
- Increase
vegetal-protein intake per meal/total (may not be practical);
- Fortify plant-based
proteins with Leucine;
- Use protein blends
(non-vegans).
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