Benefits
Protein digestion via actinidin
Actinidin is an enzyme that breaks proteins into smaller pieces. In an 8-week rat study, adding KWD+ to the diet increased protein breakdown in the stomach, with effects that depended on the protein source. Rat and pig studies of green kiwifruit found faster stomach digestion of several proteins. No human trial has tested KWD+ capsules.
Plant protein use
In the KWD+ rat study, animals on a high-protein pea diet that received the extract had less fat mass relative to the protein they ate. In an earlier rat study, green kiwifruit increased stomach digestion of gluten and soy protein. No study has tested KWD+ or kiwifruit in vegetarians or vegans.
Muscle and body composition
In the same rat study, KWD+ increased muscle mass relative to protein intake on a high-protein casein diet, and on a normal-protein diet it was linked to larger muscle fibers and better fatigue resistance. These are animal results; no study has measured muscle, strength or recovery in people taking KWD+.
Protein digestion in older adults
In a randomized crossover study, 12 healthy older adults ate two green kiwifruit (which contain actinidin) or two gold kiwifruit (which do not) daily for 14 days and with a beef meal. Green kiwifruit gave a faster rise in blood essential amino acids, but the total absorbed and measures of protein metabolism did not differ. Whole fruit, not KWD+.
Bowel regularity
In a randomized crossover study, 14 healthy adults ate two whole kiwifruit twice a day for 3 days or a maltodextrin control. On MRI, kiwifruit increased water in the small bowel and ascending colon and total colon volume, and stool frequency was 1.46 a day versus 1.14 with control. This was whole fruit and has not been shown for a 300 mg extract.
Mechanism of action
Actinidin cysteine protease activity
Actinidin is a cysteine protease, the same enzyme family as bromelain (from pineapple) and papain (from papaya). It cuts the bonds that hold proteins together, producing smaller peptides. In rat and pig studies, actinidin from green kiwifruit increased protein breakdown in the stomach and sped the movement of digested protein into the small intestine.
Stated actinidin concentration
Pharmactive says its extraction process concentrates the protein-digesting enzymes to about 5 times the level in fresh kiwi fruit. This is a manufacturer figure with no published analysis behind it, and no study has compared a KWD+ dose with eating whole kiwifruit.
Aktinnamics® phenolic anti-inflammatory activity
Aktinnamics is the supplier's trade name for the phenolic (plant polyphenol) fraction of the extract. No study cited on this page examined it, so the claims that it lowers inflammatory signals such as TNF-alpha, or that it supports gut function, are unverified.
Gut motility support
In the MRI study of 14 healthy volunteers cited on this page, whole kiwifruit increased water held in the small bowel and ascending colon and enlarged total colon volume, alongside more frequent, softer stools. The study did not test which parts of the fruit were responsible, and whether a concentrated extract keeps these effects has not been tested.
Clinical trials
Eight-week study in rats fed a normal-protein casein diet, a high-protein casein diet or a high-protein pea diet, each with or without KWD+. Four of the ten authors are Pharmactive employees. (Benito-Vázquez et al. 2026, International Journal of Molecular Sciences)
Rats. No people.
KWD+ increased protein breakdown in the stomach in a way that depended on the protein source. Blood amino acid levels did not differ significantly after correction for multiple comparisons. Fat mass relative to protein intake was lower on the pea diet, muscle mass relative to protein intake was higher on the high-protein casein diet, and on the normal-protein diet muscle fibers were larger with better fatigue resistance.
Randomized, double-blind crossover study: two green or two gold kiwifruit daily for 14 days, then a metabolic study with 100 g of ground beef eaten with the fruit. (Park et al. 2021, European Journal of Nutrition)
12 healthy older adults (6 men, 6 women).
Green kiwifruit gave a faster rise in blood essential amino acids, branched-chain amino acids and leucine after the meal. The total amount of essential amino acids absorbed did not differ, and no measure of muscle or whole-body protein metabolism differed between the two fruits. This tested whole fruit, not KWD+.
Randomized two-period crossover study: two kiwifruit twice a day or a maltodextrin control for 3 days, with hourly MRI scans on day 3. (Wilkinson-Smith et al. 2019, Alimentary Pharmacology and Therapeutics)
14 healthy adult volunteers.
Kiwifruit raised the primary outcome, an MRI marker of water in the ascending colon, and increased small bowel water, total colon volume, stool frequency (1.46 vs 1.14 stools a day) and stool form score compared with control. This tested whole fruit for 3 days, not a capsule of extract.
Rats were fed diets built on one of six protein sources plus 20% freeze-dried green kiwifruit (with actinidin) or gold kiwifruit (almost no actinidin). (Montoya et al. 2014, Journal of Nutrition)
Growing rats, 8 per diet. No people.
Actinidin increased stomach digestion of beef muscle, gluten and soy protein isolate and sped stomach emptying of the beef and zein diets, but it did not do so for every protein source tested. Whole green kiwifruit in rats, not KWD+.