Metabolism Supplement Guide: What The Evidence Shows

The promise on this shelf is almost always some combination of three things: a faster metabolism, less appetite, and more energy through the afternoon. Only the first of those is a measurable quantity with a standard laboratory method behind it, and it is the one worth understanding first, because every other claim on the shelf borrows its credibility.

Resting metabolic rate is the energy a body spends doing nothing: breathing, pumping blood, holding a temperature. For most adults it is somewhere between 1,300 and 1,800 kilocalories a day and it accounts for the majority of what anyone burns. Measuring a change in it means putting somebody under a ventilated hood or in a whole-room calorimeter and reading their gas exchange, which is why the trials that do it are small and short.

That method matters to a buyer for one reason. A measured rise in resting metabolic rate is a real physiological event and it is not the same event as a change on a bathroom scale. The gap between the two is where most of this category lives.

Caffeine is the only ingredient in this category with a dose-response curve that different laboratories have reproduced. A 1989 study gave lean and post-obese volunteers 100 mg and measured resting metabolic rate rising 3 to 4% over the following 150 minutes. Repeating that dose every two hours across twelve hours raised daily energy expenditure by around 150 kilocalories in the lean group.

A 1990 double-blind study went further and ran 100, 200 and 400 mg against placebo, measuring thermogenesis, metabolic markers and cardiovascular response together. The thermogenic effect was dose-dependent. So, at the top of that range, were the heart rate and blood pressure readings, which is the part of the finding that tends to fall out of the marketing.

A 2009 comparison set caffeine against green tea and tyrosine on the same protocol and found caffeine the most reliable of the three at raising energy expenditure. When a 2019 dose-response meta-analysis pooled the weight outcomes rather than the calorimetry, the effect on body weight was present and modest.

The same literature that supports caffeine sets its own limits, and both of them are practical rather than theoretical.

Tolerance is the first. The alertness effect of a daily dose fades within days in regular consumers, and a review of caffeine and human health covers how quickly habituation sets in across the effects that have been tracked. Somebody already drinking two coffees is in a different position from somebody who drinks none.

Sleep is the second, and it is the one that matters most to the outcome people are buying for. A 2013 trial gave 400 mg at zero, three and six hours before bed and found measurable disruption even at the six-hour point, when volunteers reported feeling unaffected. A 2017 review pooled the epidemiology and the trials and reached the same place.

• A daily ceiling is well established. A 2017 systematic review of caffeine safety supports roughly 400 mg a day for healthy adults, from every source combined.
• Blood pressure responds, and not equally in everybody. A 1998 workplace study recorded the rise across a working day; a 2010 study found the size of the response varies with sex, age and hormonal status.
• Capsules count towards the same ceiling as coffee. A 138 mg capsule is roughly a mug of filter coffee and belongs in place of one rather than on top of it.

Green tea extract is standardised to its catechins, and to EGCG in particular. The rationale is genuine: a 2011 meta-analysis of catechin-rich teas taken with caffeine found the pair raising energy expenditure and fat oxidation together, which is why the two so often appear on the same panel.

The trouble arrives when the outcome is weight rather than gas exchange. The Cochrane review pooled twelve and thirteen-week randomised trials and reported a mean difference outside Japan of minus 0.04 kg, with a confidence interval comfortably spanning zero. An earlier 2009 meta-analysis had found a small effect, and the two are reconciled mostly by which trials each one was willing to include.

The amounts are the other half of the story. The 2007 thermogenesis pilot used 300 mg of EGCG in a single dose; a 2010 fat-oxidation pilot ran 300 mg a day; a 2005 chamber study gave 200 mg of EGCG with 200 mg of caffeine three times daily. A capsule carrying 130 mg of a 45% EGCG extract supplies 58.5 mg.

Amounts are of EGCG, not of extract. An extract weight without a percentage beside it cannot be placed in this table at all.

Green coffee bean extract is standardised to chlorogenic acids, and its reputation was built almost entirely on one trial. That 2012 crossover study is filed by PubMed as a Retracted Publication. It is the paper behind the television segment most people half-remember, and it no longer stands.

The 2011 meta-analysis that preceded it reported a pooled result of about minus 2.5 kg while judging every included trial at high risk of bias, and its authors said plainly that the evidence was not sufficient. That combination — an attractive pooled number sitting on trials the reviewers did not trust — is the honest summary of the weight literature here.

Chlorogenic acids do have a literature, and it points somewhere else. A 2006 trial gave 140 mg of chlorogenic acid a day for twelve weeks in essential hypertension and measured blood pressure; a 2018 trial ran 400 mg a day of extract for eight weeks in metabolic syndrome; a 2024 dose-response meta-analysis and a 2021 review of cardiovascular risk factors both pooled that side of the work.

Garcinia cambogia is standardised to hydroxycitric acid, and this ingredient has something the rest of the shelf mostly lacks: a large, well-run, adequately dosed trial that reported a clear answer. The 1998 JAMA trial gave 1,500 mg of hydroxycitric acid a day for twelve weeks to 135 overweight adults and found no separation from placebo on body weight or fat mass.

A 2011 meta-analysis of the randomised trials pooled a mean difference of about minus 0.88 kg and its authors described the clinical relevance as uncertain. Nobody has since run anything larger or longer that changes the picture.

There is also a safety literature, and it is unusual for a botanical of this popularity. Published case reports describe hepatotoxicity, acute liver failure, acute hepatitis, liver failure requiring transplantation, a further hepatotoxicity report, a 2025 case involving sideroblastic anaemia, and one psychiatric case report. Case reports establish a signal rather than a rate, and the rate is unknown.

• The dosed trial exists and it is the one to read. 1,500 mg of hydroxycitric acid a day, twelve weeks, 135 people, no separation from placebo.
• Capsule amounts sit far below it. A 130 mg row at 50% hydroxycitric acid supplies 65 mg, which is roughly 4% of the trial amount.
• The liver signal is real and its size is unmeasured. The AASLD practice guidance on supplement-induced liver injury is the reference a clinician would reach for.

Raspberry ketone is the aroma compound that makes a raspberry smell of raspberry, and it reached this shelf on the strength of a 2005 rodent study in which mice were fed diets containing raspberry ketone at 0.5 to 2% of total intake for ten weeks. Scaled to a person, those proportions are nothing a capsule could approach.

A search of the human literature for an isolated randomised trial of raspberry ketone returns none. The nearest thing is a 2018 trial of a multi-ingredient supplement taken alongside exercise and a diet, in which raspberry ketone was one component among several. A combination trial measures a combination.

This is not a safety warning and it should not be read as one. It is an absence of evidence in either direction, and the only correct way to describe a row like it on a label is to say so.

This is the whole human and animal evidence base as it stands, not a selection from it.

Dietary supplements in the United States may carry structure and function claims. They may not claim to diagnose, treat, cure or prevent a disease, and obesity is a disease. That single line of law is why an entire shelf of products is described in the language of support rather than the language of results.

It also explains a disclaimer buyers scroll past. The sentence about statements not having been evaluated by the Food and Drug Administration is a legal requirement attached to the claim, not a footnote the manufacturer chose to add.

The practical consequence is worth stating plainly. A label that promises a quantity of weight lost is making a claim it is not entitled to make, and a seller willing to break that rule in public is telling you something about everything else it prints.

Every row is the literature for the INGREDIENT. No finished multi-ingredient capsule in this category has been trialled, including the one sold on this website.

Read down the right-hand column and the pattern is the point. The amounts that produced these findings are generally several times what a capsule carries, and where a capsule does reach a researched amount, it is almost always the caffeine.

That is exactly the shape of the panel this website sells. The supplement facts page prints all five rows as the bottle prints them, and the ingredients page sets each amount beside the amount its own trials used. The companion scorecard turns all of this into seven checks and then applies them here.