Weight-loss supplements: which ones have research behind them
No supplement comes close to changing how you eat. Caffeine has a small measurable effect on energy expenditure and helps you train harder; fibre helps with fullness. Garcinia, raspberry ketone and CLA have no usable effect in human trials. The bigger risk is adulteration — products repeatedly found to contain sibutramine, a drug withdrawn worldwide.
The weight-loss supplement market is enormous because the question it claims to answer is one everybody wants answered. The thing to know before reading on is that supplements are not required to prove they work before being sold — so the fact that something is on a shelf is not evidence of anything.
Which ones have some real evidence?
- Caffeine — raises energy expenditure by a small but genuinely measurable amount, and lets you train harder, which is the larger of the two effects. The direct effect on weight is small and the body adapts.
- Fibre such as psyllium or glucomannan — helps with fullness and modestly reduces intake. Effects on weight in trials are small.
- Whey protein — works as food that fills you and protects muscle, not as a drug. That is a good enough reason on its own.
- Green tea extract (EGCG) — pooled analyses find something in the region of half a kilo to a kilo over 12 weeks, inconsistently, and high-dose extracts carry reports of liver toxicity.
Which ones does the research not support?
Garcinia cambogia — a randomised trial published in JAMA (Heymsfield 1998) with 135 people found no difference from placebo in weight or fat mass.
Raspberry ketone — the data are from cells and rodents, at doses that do not translate to anything a person could swallow. No human trial worth relying on.
CLA — effects in humans are so small as to be meaningless in practice, and some trials found worsened blood lipids and insulin resistance.
L-carnitine — in people who are not deficient, supplementing does not make the body burn more fat.
Is berberine really nature's Ozempic?
No. Berberine does have real effects on blood glucose with reasonable evidence behind them, but the mechanism is different from the GLP-1 drug class and the size of the effect on weight is not remotely comparable. The nickname is marketing, not a conclusion from any study.
What deserves more caution than hope
Regulators in several countries have repeatedly found weight-loss supplements adulterated with sibutramine — a weight-loss drug withdrawn from markets worldwide for raising cardiovascular risk. A product that works unusually fast is a warning sign, not a good sign.
If you are going to use something, check it carries a genuine registration number, buy it somewhere traceable, and tell your doctor or pharmacist everything you are taking.
Reading something you can act on beats reading something you cannot.