Benefits
Muscle and strength measures in a 12-week placebo-controlled trial
In 54 healthy Korean adults, 500 mg a day of loquat leaf extract for 12 weeks gave no difference from placebo in knee extension torque (the main outcome), grip, limb muscle mass, gait speed or chair-rise time. Both groups improved some measures over time. Only an unplanned sex-split reanalysis, not among the trial's stated outcomes, found a larger right-hand grip gain in women taking the extract.
Fasting blood markers tracked during the same trial
The same 12-week trial measured fasting glucose, the blood lipid panel, liver enzymes and kidney markers. None differed between the extract and placebo groups. No adverse effects were reported in the extract group; one placebo participant left the study because of a skin rash.
Triterpene acid content of the leaf compared with fruit and seed
Lab measurements of four triterpene acids (ursolic, corosolic, maslinic and oleanolic acid) found about 17.5 to 21.7 mg per gram in young and mature leaves, versus 7.4 mg in the fruit and 6.4 mg in the flowers, with none detected in the seeds. Content rose as leaves matured and varied with season.
Blood sugar and blood fat markers in rodent studies (animal work)
In mice, a triterpene acid fraction from the leaves at 300 mg/kg lowered blood glucose, cholesterol and triglycerides, and a water extract given with a high-fat, high-sugar diet improved glucose and lipid markers. These are animal results; the one human trial found no change in fasting glucose or lipids.
Muscle cell signaling in aged rats and cultured cells (animal and lab work)
In aged rats given a leaf extract (50 mg/kg/day) for 35 days, the decline in grip strength was smaller and muscle mass was higher than in untreated aged rats. In mouse muscle cells, the extract raised muscle-forming proteins and Akt/mTOR signaling. The human trial of a similar extract did not show these effects.
Mechanism of action
Triterpene acids concentrated in the leaf
Ursolic, corosolic, maslinic and oleanolic acid make up roughly 2% of the dry leaf by weight in lab measurements, far more than in the fruit. Most proposed actions of the leaf are attributed to these triterpenes and to its flavonoids, based on cell and animal work. How much reaches the blood after a cup of tea or a capsule has not been measured in people.
Glucose and lipid handling in rodents
In mice, leaf triterpene acids lowered blood glucose and blood fats and raised insulin and the antioxidant enzyme superoxide dismutase, and a leaf water extract improved insulin resistance and oxidative stress markers. These findings come from animal models and have not been reproduced in a human trial.
Muscle-building signals in cells and aged rats
In cultured mouse muscle cells, loquat leaf extract increased the muscle proteins MyoD, myogenin and myosin heavy chain and activated the Akt/mTOR pathway that drives protein synthesis. In aged rats it reduced loss of grip strength and muscle fiber size. A 12-week human trial found no comparable change.
Cyanogenic glycosides break down into cyanide
Amygdalin and prunasin, found in loquat seeds and unripe fruit, are broken down by plant enzymes and gut bacteria into benzaldehyde and hydrogen cyanide. Oral intake is far more toxic than intravenous use for this reason. Drying and grinding the seeds into powder makes it easy to eat a large amount of these compounds at once, which is why seed powder is the main concern.
Clinical trials
Randomized, double-blind, placebo-controlled trial at Pusan National University Yangsan Hospital, Korea: 500 mg/day loquat leaf extract (two 250 mg capsules; 102 mg/g ursolic acid, about 51 mg/day) or identical placebo for 12 weeks, taken after breakfast and dinner. Funded by a Korean government R&D program for functional food materials; the capsule maker held the randomization codes. Registered as NCT02401113. (Cho et al. 2016, Evid Based Complement Alternat Med)
54 healthy adults aged 19 to 65 recruited at a hospital in Yangsan, Korea (27 per group; 24 and 22 completed). Despite randomization, the sex ratio differed between the groups (P = 0.004).
Leg extension peak torque on a dynamometer, the primary outcome, did not differ between groups at 4 or 12 weeks, and neither did handgrip readings, DXA limb tissue, gait speed, chair-rise time or fasting blood tests. Gait speed and chair-rise time improved in both groups alike. A sex-split reanalysis, prompted by the imbalance, found one difference favoring the extract in right handgrip change within one sex subgroup at 12 weeks (2.3 vs 0.62 kg, P = 0.047; at 4 weeks P = 0.431). The methods did not plan this comparison and no correction for multiple testing was made, so it does not show an effect. No adverse effects were reported with the extract.
Animal and cell-culture study: young and aged rats fed loquat leaf extract 50 mg/kg/day for 35 days, plus C2C12 mouse muscle cells treated with the extract. Not a human study. (Sung et al. 2015, Int J Mol Med)
Young (5-month-old) and aged (18 to 19-month-old) rats; C2C12 mouse myoblasts.
In aged rats the extract reduced the age-related loss of grip strength, raised muscle mass and muscle creatine kinase activity, and preserved muscle fiber size. In cells it increased MyoD, myogenin and myosin heavy chain and activated Akt/mTOR signaling. A later 12-week human trial of a loquat leaf extract did not show a benefit over placebo.
Animal study of the total triterpene acid fraction from dried loquat leaves (Folium Eriobotryae), given by mouth at 100, 200 or 300 mg/kg/day for 7 or 14 days. Not a human study. (Lü et al. 2009, J Ethnopharmacol)
Normal mice and mice made diabetic with alloxan or streptozotocin.
300 mg/kg/day was the most effective dose: it lowered blood glucose and, in severely diabetic mice, glycated serum protein, total cholesterol and triglycerides, and raised serum insulin and superoxide dismutase activity. These are results in chemically induced diabetic mice at doses far above any human tea intake.
Repeated-dose oral toxicity study: Sprague-Dawley rats given a loquat leaf extract at 250, 500 or 1000 mg/kg/day, or water, for 13 weeks. Not a human study. (Seong et al. 2018, J Ethnopharmacol)
80 Sprague-Dawley rats (40 male, 40 female) in four groups.
No treatment-related adverse effects were found in clinical signs, body weight, urine, eye exams, blood tests, organ weights or tissue examination at any dose; the no-observed-adverse-effect level was above 1000 mg/kg/day. Rat safety data do not rule out rare reactions in people.