Benefits
Improved protein digestion
Added to a protein meal, the protease blend is intended to increase the breakdown of protein into absorbable amino acids. The human evidence behind this is a single open label, manufacturer funded study that measured amino acids appearing in the blood after one large whey shake. Faster amino acid appearance is the effect that was actually tested; getting more out of your protein is an inference drawn from it rather than something that was measured. The enzyme's effect on the body's actual use of that protein has not been tested.
Higher circulating amino acids
One open label study in 42 healthy men found that taking 2.5 g or 5 g of the enzyme with a 50 gram whey shake raised blood levels of amino acids, including branched-chain amino acids, compared with the same shake alone. That study had no placebo group and no randomized comparison, it was funded by the company that made and sold the ingredient, and it has never been independently repeated, so the finding is suggestive rather than settled. Note also that the amounts used were far above what a typical product provides.
Less post-protein bloating
By aiding digestion of large protein loads, the enzyme is marketed to reduce the gas and bloating some people experience after protein shakes or high protein meals. To be plain about the evidence, neither human study of this ingredient measured bloating or gas as an outcome. The four hour absorption study collected no digestive symptom data at all, and the 30 day study recorded only symptoms volunteered to its dietitian, with mild upset stomach and nausea reported in both the enzyme group and the plain whey group. So this is a reasonable idea based on how the enzyme works rather than a measured result.
Mechanism of action
Proteolytic hydrolysis
Fungal proteases cleave the peptide bonds in dietary protein, producing smaller peptides and free amino acids that are easier for the gut to absorb.
Acid and heat stability
Aspergillus derived proteases are selected to stay active across a range of stomach and intestinal acidity, allowing them to work alongside the body's own digestive enzymes. This is a laboratory and manufacturing property of the enzymes, not something the two human studies of this product tested.
Clinical trials
Open label study measuring blood amino acid levels over four hours after a single 50 gram whey protein dose taken with versus without 2.5 g or 5 g of the Aminogen protease blend. There was no placebo group and no randomized allocation, and only the laboratory analysis was blinded. Funded by Triarco Industries, the company that made and sold Aminogen, through a contract research organization, and one of the three authors was employed by that company. (Oben et al. 2008, Journal of the International Society of Sports Nutrition)
Forty two healthy lean men aged 19 to 35, with 41 completing. No women were studied. Each man took the whey shake alone first and the enzyme shake nine days later, so the comparison was against himself on an earlier day rather than against a randomized placebo group.
Taking the protease with protein increased circulating amino acids, including branched-chain amino acids, and 24 hour nitrogen retention compared with protein alone, and C-reactive protein fell. These are blood and urine measurements taken in the hours after one large shake. The study measured no muscle outcome of any kind: no strength, no lean mass, no soreness, no recovery. It also recorded no digestive symptoms such as bloating or gas. Faster amino acid appearance in the blood is not the same thing as more muscle.
Randomized, double-blind, 30 day study of safety and tolerability, not of protein digestion. Forty resistance-trained men took two 40 gram whey protein servings a day, one group with the protease blend added and one group without, and were assessed with standard blood panels. The study was funded by Triarco Industries, which made and sold Aminogen, and its sole author worked in that company's research department. (Anderson 2013, Food Digestion)
Forty healthy resistance-trained men, average age 27, with 36 completing. No women were studied.
This study did not measure protein digestion, amino acid levels or nitrogen balance at all. It measured blood pressure, body weight, blood lipids, glucose, electrolytes, liver enzymes and kidney markers, and found no safety signal in either group over 30 days. The only significant changes were rises in total cholesterol, LDL cholesterol and serum calcium in the whey-only group, which the manufacturer author read as a lipid advantage for the enzyme group, though the study was not designed to test that. Mild upset stomach, nausea and headache were volunteered in both groups, with no serious events and no dropouts for that reason. It is evidence that the enzyme was tolerated for a month. It is not evidence that the enzyme improves digestion, and it should not be counted as a second study supporting the absorption claim.