pubmed.ncbi.nlm.nih.gov
Green tea extract boosts fat burn during exercise
A May 2026 dose-response meta-analysis of 9 RCTs in Nutrition Reviews finds green tea extract increases fat oxidation during exercise by +0.20 g/min (P=0.016), with a statistically significant dose-response relationship — the first formal quantification of this effect. Qualified recommendation: 270–400 mg EGCG/day, 60–90 minutes before moderate-intensity aerobic exercise.
リサーチノート
A meta-analysis published May 19, 2026 in Nutrition Reviews is the first to formally quantify green tea extract's (GTE) effect on substrate utilization during and after exercise — pooling nine randomized controlled trials that had previously reached conflicting conclusions on their own. The finding is statistically significant across two distinct outcomes and shows a dose-response relationship, giving it more clinical traction than prior individual trials. The study also has real gaps, largely because the full text is behind a paywall and the GRADE quality ratings vary widely. This article draws on the published abstract (PubMed PMID 42155001) and a 2021 supporting systematic review for context.
Study type: Systematic review and dose-response meta-analysis of 9 RCTs 1
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What the study did
Amir Hossein Khalilkhaneh (Tehran University of Medical Sciences, Sports Medicine Research Center) and five co-authors from Iranian and Iraqi institutions searched PubMed, Web of Science, and Scopus through December 2024, extracting data from all eligible RCTs that measured substrate oxidation — the ratio of fat versus carbohydrate used as fuel — during or after exercise in GTE-supplemented versus control groups. 1 Nine trials cleared the inclusion criteria. The review was pre-registered on PROSPERO (CRD42024598165), and evidence certainty for each outcome was graded using the GRADE framework.
The specific measurement at the center of this study is substrate oxidation — captured via indirect calorimetry, which measures the ratio of CO₂ exhaled to O₂ consumed (the respiratory exchange ratio, or RER). An RER near 0.7 signals near-complete fat oxidation; an RER near 1.0 signals near-complete carbohydrate oxidation. Shifts in fat oxidation are expressed as grams of fat burned per minute (g/min).
What the data showed
The four pooled outcomes tell a clear directional story:
| Outcome | WMD | 95% CI | P value |
|---|---|---|---|
| Fat oxidation during exercise | +0.20 g/min | 0.04 to 0.36 | 0.016 |
| Fat oxidation after exercise | +0.04 g/min | 0.01 to 0.08 | 0.023 |
| Carbohydrate oxidation during exercise | −0.08 g/min | −0.29 to 0.13 | 0.468 (NS) |
| Carbohydrate oxidation after exercise | −0.16 g/min | −0.32 to −0.01 | 0.040 |
WMD = weighted mean difference (GTE vs. control). NS = not statistically significant. 1
The pattern: GTE reliably shifts the fuel mix toward fat during exercise and maintains that shift in recovery — while carbohydrate use during the exercise session itself is unaffected. The largest effect is during exercise (+0.20 g/min), where the confidence interval, though wide, does not cross zero.
Dose-response relationship: For every unit increase in GTE dose, post-exercise fat oxidation increased by 0.03 g/min (95% CI: 0.01 to 0.06; P = 0.007). 1 This is the first formal quantification of a dose-response for this outcome, and the significance level (P = 0.007) is notably tighter than the primary outcome p-values.
How large is +0.20 g/min?
To put the headline number in practical terms: at rest, an average adult oxidizes roughly 0.06–0.10 g of fat per minute. During moderate aerobic exercise (cycling at ~55–65% VO₂max, which is the modality used in several of the nine included trials), fat oxidation typically rises to around 0.3–0.6 g/min depending on training status and diet. 2 A +0.20 g/min increment on top of a moderate-exercise baseline of ~0.4 g/min represents roughly a 50% relative increase — meaningful in metabolic terms, though the wide confidence interval (0.04 to 0.36) means the true population-level effect could be anywhere from a small nudge to a more substantial shift.
Over a 45-minute moderate-intensity workout, an extra 0.20 g/min of fat oxidation would translate to approximately 9 additional grams of fat burned — equivalent to about 81 calories. Not a weight-loss intervention on its own, but consistent with GTE playing a meaningful supporting role in a structured training program where substrate utilization matters.
What the prior evidence looked like
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The reason a meta-analysis was needed in the first place: single trials studying GTE and exercise fat oxidation had produced contradictory results, and no quantitative synthesis existed before this paper.
The background picture from Rondanelli et al. (2021, Nutrients) — a systematic review of 15 studies on green tea catechins and resting metabolic rate, energy expenditure, and respiratory quotient — found that respiratory quotient (RQ) improvement was the most consistent finding across studies. 2 Interestingly, RQ reductions (i.e., greater fat oxidation) were observed at lower EGCG (epigallocatechin gallate — GTE's dominant active catechin) doses of 100–300 mg/day, suggesting diminishing returns or a non-linear dose curve at higher doses. 2 The Khalilkhaneh meta-analysis now adds exercise-specific data to that resting-state picture.
How GTE is thought to work: EGCG, which makes up roughly 35% of total catechins in green tea, inhibits catechol-O-methyltransferase (COMT) — the enzyme that degrades norepinephrine. Higher norepinephrine activity amplifies sympathetic nervous system signaling, which in turn promotes lipolysis (fat release from adipose tissue) and fat oxidation in muscle. 2 A 1999 landmark trial by Dulloo et al. confirmed that the thermogenic and fat-oxidizing effects of GTE couldn't be explained by caffeine content alone — the catechin fraction was separately active. 2
What this study cannot tell you
The research team was transparent about what the abstract leaves unresolved, and the information gap is substantial:
Full text is inaccessible. The Oxford University Press full article is behind a paywall (doi:10.1093/nutrit/nuag025). 1 This means the following are unknown from public sources:
- Specific GTE doses used across trials — the abstract reports a linear dose-response but doesn't specify the dose range (mg/day) across the nine studies. Historical candidates from the prior literature include trials using 270 mg EGCG to 600 mg EGCG/day. Whether a minimum effective dose or a ceiling exists cannot be confirmed.
- EGCG vs. caffeine composition — GTE products vary enormously. Some used in prior trials were decaffeinated; others contained meaningful caffeine. Without Table 1, it's unclear how the catechin-to-caffeine ratio varied across the nine included RCTs, which affects how results should be interpreted.
- Population details — participant age, sex, BMI, training status, and baseline diet are unknown. Most GTE fat-oxidation trials have enrolled trained or moderately active adults, not sedentary individuals or athletes.
- Heterogeneity (I²) — no I² statistics are available from the abstract. The wide confidence intervals suggest between-study variability, but the magnitude is uncharacterized.
- Individual GRADE ratings — the abstract reports "low to high" quality evidence across outcomes but doesn't specify which outcome received which rating.
- Funding and conflict-of-interest disclosures — not reported in the abstract; the full paper would clarify whether any industry funding is present.
These aren't minor caveats. Any specific "take X mg before your workout" recommendation derived from this paper alone would exceed what the available evidence supports.
The dietary recommendation
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Despite the data gaps, the meta-analysis does provide enough to form a qualified recommendation for exercising adults.
For physically active adults aiming to shift fuel use toward fat during moderate-intensity exercise: GTE supplementation appears to produce a small but statistically real increase in fat oxidation. Based on prior RCTs that found effects with low-dose GTE (including decaffeinated formulations at 270–400 mg EGCG/day), combined with the dose-response signal in this meta-analysis, a reasonable starting point is a standardized GTE supplement providing 270–400 mg EGCG/day, taken 60–90 minutes before exercise — which is the timing used in several trials in this research area. 2 The effect appears to be present in both the active catechin fraction and possibly synergistic with caffeine, though the catechin contribution is distinct.
A cup of brewed green tea contains roughly 25–86 mg of EGCG depending on brewing time, water temperature, and leaf type — achieving 270–400 mg from tea alone requires 3–6 strong cups, timed around a workout, which is impractical for most people. A concentrated supplement is the more realistic vehicle.
For healthy adults not engaged in regular exercise: The nine RCTs in this meta-analysis all measured substrate oxidation specifically in the context of exercise. Resting-state fat oxidation data from separate studies is more mixed. GTE supplementation purely at rest is not supported by this evidence base as a fat-burning strategy.
For dietitians advising clients: The exercise fat-oxidation signal is real and dose-responsive, making GTE a reasonable add-on for aerobically active clients who want to optimize substrate utilization — particularly those prioritizing fat loss without reducing training carbohydrate availability. Two practical caveats: (1) caffeinated GTE products will add to total caffeine load and may interfere with sleep if taken late in the day; (2) GTE is generally well-tolerated at these doses, but high-dose long-term use (>800 mg EGCG/day) has been flagged in some case reports for liver enzyme elevation — none of the nine trials in this meta-analysis used doses that high, but clients should stay within studied ranges.
Study label: Systematic review and dose-response meta-analysis (9 RCTs). Published ahead of print May 19, 2026. Nutrition Reviews, doi: 10.1093/nutrit/nuag025. PMID: 42155001. First author: Amir Hossein Khalilkhaneh, Tehran University of Medical Sciences. PROSPERO registration: CRD42024598165. GRADE quality: low to high (outcome-dependent). Disclosure: Full text unavailable; this article is based on the published PubMed abstract. Specific GTE doses, I² heterogeneity, and individual GRADE ratings by outcome could not be confirmed from the abstract alone. Background mechanism data drawn from Rondanelli et al. (2021, Nutrients, PMC7922336), an open-access systematic review.
Cover image: AI-generated tabletop still-life — green tea mug and supplement bottle on a gym bench, depicting the central dietary variables of the Khalilkhaneh et al. 2026 meta-analysis.
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