Digestive enzymes reduce quality differences between plant and animal proteins: a double-blind crossover study

Background Whey protein is considered to be the optimal protein source to support muscle protein synthesis (MPS) with resistance training, based on its amino acid content (high in leucine), rapid digestibility, and high bioavailability within the muscle tissue [1]. Athletes can choose from different plant protein sources (e.g. soy, rice, pea, hemp), which differ in numerous ways, such as the presence of allergens (milk, soy), cholesterol, saturated fats, digestion rate (fast, intermediate, or slow absorption of amino acids), or the relative amount of individual amino acids. Rice protein has been shown to promote muscle hypertrophy with resistance training comparable to whey protein [2]. 48g of rice or whey protein isolate immediately post-exercise during an 8-week progressive, non-linear resistance-training protocol increased lean body mass, muscle thickness, and strength with no differences between groups. The findings are likely due to the high dose of protein used in the study, providing amounts of leucine greater than the 1.7 to 3.5g that has been proposed to be the range for optimal MPS. Rice protein, compared to whey (fast) and casein (slow), is an intermediate digesting protein and shows a 6.8% lower total amino acid appearance in the blood [3]. While dairy protein sources contain simple sugars, mainly lactose, plant proteins contain more complex carbohydrates, including fibers and glycoproteins. This study sought to investigate if co-ingestion of a plant protein specific digestive enzyme blend (Digest-All VP, a proprietary enzyme blend consisting of protease 6.0, protease 4.5, peptidase, bromelain and alpha-galactosidase, Chemi-Source, Inc., Oceanside, CA) can reduce the significant differences in amino acid appearance in the blood between plant and animal proteins.