Background
Desert weight-loss myth
Hoodia gordonii, a plant with anorectic properties, is now used in so many weight-loss products it needs to be protected. Leiden botanists were instrumental in the development of a DNA test to trace the plant.
Thursday 5 December 2013

Life in the desert is tough: it is hot all day, cold at night and always bone dry. The few creatures and plants that live here are hardy and persistent. Anything that can survive in this wilderness has developed unique tricks to deal with the scarcity of food and water.

For instance, centuries ago, the Bushmen of the Kalahari and the Namib deserts in southern Africa learned how to use one of the indigenous plants. At first glance, Hoodia gordonii looks like a cactus but closer examination reveals it to be related to the periwinkle. The Bushmen eat it so that they feel less hungry and thirsty when hunting.

Obviously, it is an appetite suppressant, which sounds good because the world beyond the Kalahari suffers from too much rather than too little. Two thirds of Americans are overweight, about half the Dutch population is too fat and the rest of the world is well on its way to catching us up: China, India and even Bangladesh have a growing percentage of chubby people. The world could use a little help to lose weight and this tiny plant seemed promising. However, attempts to reproduce the effective substance of Hoodia were abandoned when it proved too difficult. Consequently the plant was added to all sorts of dubious weight-loss remedies, which soon acquired a bad reputation as greedy pill peddlers ignored botany and did not scruple to use all sorts of weeds – more often than not, the drugs didn’t even contain the right plant.

Meanwhile, things have made a U-turn and the problem is now that weight-loss pills do contain Hoodia gordonii.

The plants in the Kalahari were sufficient for one or two groups of Bushmen, but not for millions of fatties and as a result, the plant is an endangered species. The international CITES treaty that prohibits trade in ivory and pandas, etc. has added the plant to its long list of protected species and Customs seize any plant they discover.

The problem is that while a Customs officer is quite capable of recognising a panda, he or she has more trouble inspecting crumbled bits of plant in a grimy powder from Africa. A chemical test was designed to reveal the presence of the effective substance but it also sounded the alarm for other plants related to a greater or lesser extent to Hoodia.

An attempt to produce a test that could trace only H. gordonii’s DNA failed because the products contained too little DNA; DNA disintegrates gradually into small lumps, particularly if it is hot, which Africa tends to be.

Biologist Barbara Gravendeel is expert at working with tiny amounts of damaged DNA. Her job – at the university, Naturalis and Leiden’s University of Applied Science – entails searching for ancient plant material to find out what an extinct animal ate, for example.

Working with extremely old DNA requires dedication, clever arithmetic and quite a lot of extra hygiene to make sure researchers don’t wind up examining their own hereditary material, but she manages all that in the Naturalislab in the Van Steenis Building.

Recently, she teamed up with Customs and her student Gerard Gathier to create a DNA test that specifically reveals the presence of Hoodia gordonii. “The advantage is that is also works if the manufacturer uses young plants which don’t yet produce the effective substance. Customs can use our test in their own DNA lab”, the biologist explained.

The test is not quite perfect: “We tried samples in which the DNA had evidently degenerated so much we couldn’t be sure whether it contained any Hoodia or not. Our publication on the test in the Journal of Forensic Sciences focuses more on the method.”

She has worked with Customs before, having previously developed methods to trace calla from India and to check for traces of prohibited plants in sticks of incense. “Usually Customs are very cautious about lending goods they have seized, but they wanted to work with us, partly because we can use Naturalis’ plant collection as a reference, and in return we design these methods for them. We are setting up a project with Customs to recognise species of animals by their DNA in seized consignments of bushmeat.”

Anyway, obese people who don’t care about endangered plants are still better off avoiding anything containing Hoodia.

Just because a Bushman can hunt more efficiently for a few days longer after consuming it does not mean to say that he – let alone you - will grow thinner in the long run. And it certainly doesn’t mean that the plant is safe: a Canadian study from 2010 attempted to compare all the research on this weight-loss plant, but established that no adequate studies into the effectiveness and safety of the plant were available in public data banks.

Eventually, twelve months later, a small study published by Unilever concluded that the plant doesn’t work but does cause mild side-effects. To put it briefly, no one needs this plant so much it is wiped out.