How good is Slim Sip?

New Year’s resolutions to lose weight mean TV adverts for dietary supplements like Slim Sip (glucomannan). What is the evidence it helps?

A 10-day supply of Slim Sip costs £15 and is advertised with the claim “Glucomannan contributes to the reduction of body weight in the context of an energy-restricted diet”. Does Slim Sip work?

The claim was approved for glucomannan itself (i.e., not the Slim Sip brand in particular) by the European Food Safety Authority over half a decade ago. How effective is glucomannan?

The applicants seeking approval helpfully suggested 6 studies to consider, to which EFSA added another 3 (none of which showed a statistically significant effect).

The largest study EFSA considered (just 62 participants, in 2005) showed 23 people taking glucomannan dropped an extra 1.3kg over 5 weeks. Not bad.

But by 2008 a meta analysis of 14 relevant trials covering 531 participants found an average weight loss of 0.79kg over 5 weeks.

And the latest 2014 meta analysis of all studies to date showed an average weight loss of only 0.22kg (treatment duration not stated, assumed circa 5 weeks) and considered it to not be statistically significant.



On that basis Slim Sip costs £200 per additional kg dropped.

ps the most recent study on glucomannan weight loss I can find implies Slim Sip would help shed an extra 0.03kg over 8 weeks.

pps Slim Sip is drunk with water (otherwise it’s dangerous) before eating. However, just drinking water itself before eating however has been shown to lead to weight loss, so I do wonder how much of the praise for it is due to this appetite suppression effect.



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