As part of an investigation into weight loss/satiety claims, Carrie Ruxton, PhD, RD, performed an audit of the opinion and found only four of nine studies in the article 13 general function opinion showed positive weight loss results.
She said the evidence for konjac (Amorphophallus konjac), also known as glucomannan or voodoo lily or devil’s tongue, did not support, “EFSA’s statement that ‘most’ of the studies found a statistically significant effect.”
“The amount of weight loss achieved by adding glucomannan to the diet is also unremarkable. I would question why EFSA allowed glucomannan a weight loss claim given the balance of evidence, particularly when they have been so hard on other foods/substances. It's a strange decision.”
The opinion
In the opinion, aimed at overweight adults, EFSA’s Panel on Dietetic Products, Nutrition and Allergies (NDA) found, “…most of the intervention studies, which were of adequate sample size and duration, found a statistically significant effect of glucomannan on body weight loss in the context of a hypocaloric diet when administered as a pre-load before meals, and that the mechanism by which glucomannan could exert the claimed effect is established.”
The NDA said the claim was valid when at least 3g of glucomannan is consumed daily in three doses of at least 1g each, with 1-2 glasses of water before meals, in the context of an energy-restricted diet.
Ruxton said she was surprised by the opinion given the only two other approved weight loss claims were for calorie-restricted foods which were ‘no brainers’.
“Glucomannan is supposed to be taken in capsule form before meals as part of a calorie-controlled diet,” she said.
“To me, that looks more like a ‘herbal’ medicine than a food.”
Positive possibilities
Elise Aubin, a health claim and food safety expert at French consultancy, Nutraveris, agreed the majority of evidence in the konjac file was negative, but noted, “it seems EFSA has favoured longer studies and most of them are positive.”
She said one study (Keithley and Swanson (2005)) had demonstrated mechanism of action which had also been influential and provided added, “evidence of efficacy.”
“Moreover, konjac has been studied in a lot of Japanese trials for its effects and it is authorised as functional food for years,” she said, while adding, “It is still paradoxical because the evidence doesn’t show clearly a health benefit.”