Benefits
Fasting blood sugar and insulin markers
In a crossover trial, 35 adults with prediabetes took a yuzu peel ethanol extract (4,250 mg a day) or placebo for 8 weeks each. Fasting glucose, fasting insulin and HOMA-IR, an insulin-resistance score, were lower after the extract than after placebo but not versus baseline, and post-meal glucose was not significantly improved. The journal is not indexed in PubMed.
Liver fat and blood cholesterol in mice
In mice on a high-cholesterol diet, 1% or 5% yuzu peel extract in the feed lowered body weight, liver fat, and total and LDL cholesterol, and in high-fat-fed mice 5% extract lowered serum triglycerides and cholesterol. These are animal findings. A 12-week placebo-controlled cholesterol trial in Korean adults was completed in 2017, but no results have been posted or published.
Body weight and body fat in high-fat-fed mice
In high-fat-fed mice, an extract of green (unripe) yuzu peel at 100 mg/kg a day reduced weight gain, body fat percentage and visceral fat, and 5% peel extract in the feed reduced weight gain in another mouse study. No published human trial has measured body weight or body fat with yuzu.
Platelet aggregation in lab and animal tests
A yuzu extract, hesperidin and naringin reduced clumping of human platelets in test tubes and of rat platelets in vitro and ex vivo, and oral yuzu extract prolonged bleeding time in mice. No human trial has tested this. The same effect is a reason for caution with blood thinners rather than a proven benefit.
Flavanone and vitamin C content of the fruit
Fresh yuzu averaged about 90 mg of vitamin C, 64 mg of naringin and 66 mg of hesperidin per 100 g, with more in the peel than the flesh, and hesperidin and naringin in the peel rose as the fruit ripened. Among three Korean citrus fruits, yuzu had the highest antioxidant activity and total phenolics in lab assays.
Mechanism of action
Glucose uptake through AMPK and PPAR-gamma
In C2C12 muscle cells, an ethanol extract of yuzu peel, but not of the pulp, raised glucose uptake and increased AMPK and PPAR-gamma activity; blocking AMPK reduced the effect. Muscle AMPK activation was also seen in high-fat-fed mice. These are cell and mouse findings.
Liver fat-burning and cholesterol-making genes
In HepG2 liver cells and in mice on a high-cholesterol diet, yuzu peel extract raised PPAR-alpha and CPT1, which drive fat burning, and lowered HMGCR, the rate-limiting enzyme in cholesterol production. These are cell and mouse findings.
Fat-cell formation signals
In 3T3-L1 cells, a green yuzu peel extract curbed the formation of fat cells by lowering PI3K-Akt signaling and the fat-making regulators PPAR-gamma, C/EBP-alpha and DGAT2. This is a cell finding.
Seed limonoids and inflammatory signals in cells
Limonoids isolated from yuzu seeds lowered inflammatory messengers such as IL-6, IL-8 and TNF-alpha in stimulated mouse immune cells and human colon cells. Whether supplements supply these compounds in useful amounts is unknown.
Clinical trials
Randomized, double-blind, placebo-controlled crossover trial of an ethanol extract of yuzu (yuja) peel, published in a journal not indexed in PubMed; participant numbers and dose are as tabulated in a 2021 review. (Hwang et al. 2015, J Funct Foods)
35 adults with prediabetes (impaired fasting glucose; the review classes them as combined impaired fasting glucose and impaired glucose tolerance); 4,250 mg a day of extract or placebo for 8 weeks per period.
The abstract reports significantly lower fasting glucose, fasting insulin and HOMA-IR after the extract than after placebo, with post-meal glucose and C-peptide only slightly reduced and no difference in safety measures. As reported by a 2021 review, the p values were 0.049, 0.038 and 0.019, none of the three changed significantly from baseline, C-peptide was marginally lower (p = 0.057), and no adverse events occurred. Funding is not stated in the abstract.
Randomized, double-blind, placebo-controlled, parallel trial registered as NCT03332641 by Hanyang University, Seoul. (Hanyang University 2017, ClinicalTrials.gov)
Adults aged 19 to 75 with total cholesterol of 200 to 239 mg/dL, not on lipid-lowering drugs; the record lists 70 enrolled, though its description mentions twenty subjects. No dose is given.
The study is marked completed in September 2017, but no results have been posted and no publication is linked, so the effect on cholesterol is unknown.
Single-arm, open-label, uncontrolled study registered as UMIN000051566 by Kochi University. (Kochi University 2023, UMIN Clinical Trials Registry)
9 healthy female students aged 20 to 24 who reported feeling cold; 10 g a day of a processed yuzu peel food for 7 days.
Primary outcomes were skin surface temperature, blood pressure, pulse and body temperature. The study is marked completed in 2023 with no results posted or published, and with no control group it could not separate any change from day-to-day variation.
Cell-culture and mouse feeding study comparing peel and pulp extracts of yuzu. (Kim et al. 2013, Evid Based Complement Alternat Med)
C2C12 mouse muscle cells and mice fed a high-fat diet with or without 5% yuzu peel ethanol extract.
Only the peel ethanol extract raised muscle-cell glucose uptake, through AMPK and PPAR-gamma. In mice it reduced weight gain, liver fat, serum triglycerides, total cholesterol and insulin resistance. These are animal and cell results, not evidence of effects in people.