A study from the Journal of Nutrition compared how the body handles protein ingested from a vegan meal compared to protein from an animal source. They compared muscle protein synthesis by the body following ingestion of a whole-food meal of100 gm of lean ground beef with a whole-food vegan meal of the same protein and calorie count. The subjects for this study were healthy older adults, a group naturally susceptible to muscle loss over time. It is known that that protein synthesis is not as robust after ingestion of protein when younger and elderly subjects are compared. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0140903 Thus, increasing our knowledge in this area is important in terms of nutritional guidance regarding what are the best dietary recommendations for preserving muscle and strength in the older population.
Protein ingestion is known to stimulate muscle protein synthesis which is a crucial factor in maintaining our skeletal muscle mass [1) After protein ingestion the circulating levels of essential amino acids is increased. These amino acids are the building blocks of the protein which will be synthesized. The amino acid composition of the protein [3] ingested is a key factor in protein synthesis. Several studies have observed that the ingestion of animal-derived proteins, such as dairy proteins, results in a greater muscle protein synthesis response when compared to the ingestion of an equal amount of plant-derived protein. One study published in the American Journal of Clinical nutrition used skim milk ingestion and compared it to ingestion of a soy protein beverage.
Am. J. Clin. Nutr. 2007; 85: 1031-1040 https://doi.org/10.1093/ajcn/85.4.1031
This study’s conclusion states that although both milk-based proteins and soy based proteins would promote muscle synthesis. “Milk-based proteins promote muscle protein accretion to a greater extent than do soy-based proteins when consumed after resistance exercise.” and they added, “chronic consumption of milk proteins after resistance exercise likely supports a more rapid lean mass accrual.”
Physical activity before or after feeding increases anabolic sensitivity and, as such, may represent an effective strategy to compensate for lower quality protein meals [56, 57, 58].
Plant-derived proteins are considered to have fewer anabolic (muscle building) properties when compared with animal-derived proteins due to plant proteins containing an incomplete amino acid profile, relatively deficient in the amino acids leucine, lysine, and methionine contents [15].
These findings seem to apply to elderly individuals but it may not be superior for younger adults. Healthy young males [16, 17, 18] in one study did not show a difference in the muscle building response following ingestion of a variety of plant-derived protein [16, 17, 18] compared with milk protein.
Addressing the need for less costly protein sources as well as the comparative environmental imoact of plant versus meat based proteins, The contribution of plant-based protein sources to the human diet likely to increase substantially over the coming years [25, 26, 27]. The matrix in which proteins are embedded in food differs substantially between plant- and animal-based protein sources [28, 29, 30]. Plant-based whole-foods typically contain many antinutritional factors (e.g., dietary fiber, trypsin inhibitors, and phytates) that lower protein digestibility and, as such, may compromise the postprandial rise in circulating amino acid concentrations and reduce the subsequent capacity to stimulate muscle protein synthesis [28, 29, 30].
Beef is protein-dense and shows rapid and complete digestibility upon ingestion [34,35]. Due to these properties, ingestion of cooked beef is followed by rapid amino acid absorption, with more than 60% of the beef-derived amino acids being released in the circulation during the early postprandial phase [35]. However, consuming cooked beef as part of a complex meal will likely lower gastric emptying rate and attenuate beef protein digestion and amino acid absorption. Despite lower protein digestibility of plant-based protein sources, domestic processing (i.e., cooking) of plant-based whole-foods can increase protein digestibility and improve the postprandial availability of plant-derived amino acids in the circulation [36,37].
With the increasing interest in more plant-based diets and/or a strict vegetarian or vegan lifestyle, it is of importance to assess potential differences between the muscle protein synthetic responses following the ingestion of complete omnivorous and vegan meals. This may be of particular relevance for older adults, as age-related muscle loss is partly attributed to the development of anabolic resistance to feeding [38, 39, 40].Despite the relatively similar EAA contents of both meals (Supplemental Table 1), we observed distinct postprandial plasma amino acid profiles. Postprandial increases in plasma EAA and leucine concentrations were substantially higher (∼127% and ∼25%, respectively) following ingestion of the MEAT compared with PLANT meal.
Clearly, the amino acid composition of protein sources and/or complete meals is not necessarily reflected in subsequent postprandial plasma amino acid profiles following ingestion. The apparent disparate postprandial plasma amino acid profile following ingestion of the isonitrogenous omnivorous compared with vegan meals can be attributed to differences in food digestibility [29], protein digestion and amino acid absorption [53], and splanchnic amino acid sequestration [54] following ingestion of plant- compared with animal-based protein sources. This seems to be in agreement with previous work presenting postprandial plasma amino acid profiles following ingestion of different protein isolates or concentrates [16,17,19]. This is the first study to compare the anabolic response following the ingestion of a complete omnivorous versus vegan meal.
Differences in the food matrix, and the presence of fibers and various antinutritional factors (e.g., trypsin inhibitors, tannins, and phytic acid), may all contribute to the attenuated protein digestion and amino acid absorption kinetics following ingestion of a vegan when compared with an omnivorous meal [29].
The present study extends on previous work of the post-prandial muscle protein synthetic response following ingestion of animal- compared with plant-derived protein isolates and concentrates [12, 13, 14,16, 17, 18, 19,59,60]. This study is the first to provide translational data on the postprandial muscle protein synthetic response to the ingestion of complete cooked whole-food omnivorous and vegan meals. We prepared a vegan meal that contained an ample amount of protein (36 g protein) provided through a variety of plant-based protein sources (Table 1).
Therefore, the vegan meal did not show any selective amino acid deficiencies (Supplemental Table 1), and the total amount of protein provided (∼0.45 g/kg body mass) was in line with the amount of protein recommended for stimulating muscle protein synthesis rates in older individuals (0.40 g/kg body mass) [61]. Despite this, we were unable to detect a significant increase in muscle protein synthesis rates following ingestion of the vegan meal. The postprandial muscle protein synthetic response following ingestion of the more traditional omnivorous meal was 47% greater when compared with the vegan meal (Figure 7). Our findings may not translate to all whole-food vegan or omnivorous meals, but these data clearly demonstrate that simply looking at the protein content of a meal does not provide proper insight into the bioavailability and functionality of the meal-derived proteins. Furthermore, the data imply that, even when part of a complete meal, animal-based whole foods provide an accessible source of meal-derived amino acids, thereby stimulating muscle protein synthesis rates.
Here we assessed postprandial muscle protein synthesis rates following ingestion of complete omnivorous and vegan meals in both older males and females. Though we support the concept of moving toward a more plant-based diet for ethical, environmental, and health considerations, there are some concerns with regards to maintaining muscle health later in life [15,62,63]. A more plant-based diet will likely provide health benefits, with many of those secondary to a low(er) energy intake due to the high fiber content and satiating effect of consuming more plant-based whole foods [64, 65, 66]. However, the anabolic properties of each main meal may be of key relevance to stimulate muscle protein synthesis rates and, as such, to support muscle maintenance.
This may be of particular importance for older adults, as the age-related loss in muscle mass is at least partly attributed to the attenuated postprandial muscle protein synthetic response to acute feeding in older compared with younger subjects [38]. A strictly vegan diet may, therefore, compromise the ability to maintain muscle mass in older adults [62]. Long-term intervention studies are warranted to assess the impact of shifting toward a more plant-based diet or adhering to a strict vegan diet on muscle mass. In this regard it will be important to assess the minimal and optimal protein intake requirements of young and older adults and to evaluate whether these requirements increase when transitioning toward a more plant-based diet.
In conclusion, ingestion of a whole-food meal containing beef results in greater postprandial muscle protein synthesis rates when compared to the ingestion of an isonitrogenous and isocaloric whole-foods plant-based meal. Omnivorous meals, consumed in a resting state, are likely to have greater anabolic properties when compared to isonitrogenous and isocaloric vegan meals in healthy, older adults.
