A Metabolism Supplement Guide: What Is Actually on the Shelf

Caffeine, usually as anhydrous powder, and sometimes green tea or guarana standing in for it. This family is the only one that produces a sensation on the first day, which is why it appears in almost every product on the shelf whether or not the rest of the formula needs it.

The evidence is real and modest. A dose-response meta-analysis found an effect on body weight that scaled with the amount given. The reference point for healthy adults is 400 mg a day from every source, and the practical problem with this family is not efficacy but arithmetic: a product that does not print its caffeine content cannot be added into that total.

Green tea extract, standardised for catechins or specifically for EGCG. This is the family with the largest human literature in the category and the one whose findings are most often overstated in both directions.

The respiratory-chamber trial measured a 4 per cent rise in 24-hour energy expenditure from 90 mg of EGCG with 50 mg of caffeine at each of three meals, with caffeine alone doing nothing. The Cochrane review found the weight effect small and not clinically important. Both are true, and the mechanistic review explains why they are compatible.

Safety matters at extract strength rather than tea strength: the USP review covers hepatotoxicity and a systematic review proposed 338 mg of EGCG a day as a safe intake level for a solid dose.

Green coffee bean extract. Roasting destroys chlorogenic acid, so this is one of the few supplement ingredients that genuinely cannot be obtained from the food version.

A crossover study found it modified gut hormone secretion and glucose tolerance acutely, and a trial of enriched coffee measured 6.9 per cent less glucose absorbed. For body weight the 2023 meta-analysis pooled preparations delivering at least 500 mg of chlorogenic acid a day. The famous crossover that made the ingredient a household name, Vinson 2012, was retracted two years after publication.

Garcinia cambogia is the example. The proposal is inhibition of ATP-citrate lyase, which sits in the route carbohydrate takes on its way to becoming fat. As biochemistry that is coherent.

It was tested properly. The JAMA trial randomised 135 overweight adults to 1,500 mg of hydroxycitric acid a day or placebo for twelve weeks and found no separation on weight or fat mass. A safety and efficacy review surveys the wider literature and a case report describes liver injury attributed to a garcinia product.

Compounds with a plausible mechanism, cell-line data, sometimes rodent work, and no randomised human trial. They are common on this shelf because they are cheap, sound specific and cannot be contradicted by a trial that does not exist.

Raspberry ketone is the clearest case. The 2021 review is candid that the marketing runs ahead of the data, and the mouse feeding study found it reduced food intake without reducing adiposity beyond that. A reader who can identify this family on a label has learned the single most useful thing in this guide.