Strategies to Augment the Anabolic Properties of Plant-Based Proteins

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).


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).


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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