GM could hold back the tears

Tom Clarke A new finding could lead to genetically modified onions that don't make us cry as we chop them. Re- searchers in Japan have identified the enzyme that re- leases a tear-duct-tickling chemical when an onion is cut. Onion's tear-jerker is a compound called propan- thial S-oxide. It is made by an enzyme known as la- chrymatory-factor synthase, Shinsuke Imai, Japan, and his colleagues have discovered. Their investigations

involved a mix of genetic sleuthing and old-fashioned biochemistry.

Previous studies had suggested that onions' flavor compounds were behind the effect. Chopping was thought to make them react with a common onion en- zyme, allinase, producing propanthial S-oxide. This suggested that in order to breed or genetically engi- neer a non-irritant onion, scientists would have to tamper with its flavor. Indeed, onions bred to be tear- free, like the Veri Sweet vegetable recently marketed in Washington State, have a characteristically different taste.

The latest study puts paid to this idea. "The chemistry is not new," says Imai. "But the way it oc- curs in the plant is not as was first thought." Now that a single, flavor-independent enzyme has been identi- fied, it would be simple to create an onion in which the enzyme was absent, or suppressed, Imai's team suggests. "Anyone skilled in the art" should be able to produce such a modified onion, says the researcher.

It's not exactly what the world has been crying out for, but S. Imai argues that it could be one of the first GM organisms acceptable to consumers. It won't require the addition of a foreign gene, simply the si- lencing of an existing one. Onion's irritant is thought to have evolved to protect the nutritious bulbs from being eaten.

For cooks the world over, this onion would have direct benefits that most existing genetically modified crops lack. "A non-lachrymatory onion would perhaps be one of the first examples where the consumer was

the main beneficiary," Imai says.

Atkins-style diets can be life-threatening, doc-

Tors warn

Owen Bowcott

Low carbohydrate diets, such as the Atkins plan, can lead to life-threatening conditions, a medical jour- nal warned yesterday. The Lancet described the case of an obese woman who had adhered strictly to the high-protein diet for a month before being admitted to hospital as an emergency.

The 40-year-old, who had taken vitamin supple- ments recommended by the Atkins plan, needed treatment in the intensive care unit of a New York hospital. She had ketoacidosis, a condition triggered by the liver's production of ketones, the acids which appear during periods of starvation or when there is a lack of insulin in the body due to diabetes.

When first admitted the patient felt nauseous and was dehydrated after vomiting for several days. She was short of breath and in "moderate distress". Four days later, after a dextrose drip, she was well enough to be discharged. The doctors said the Atkins diet was largely to blame.

Professor Klaus-Dieter Lessnau, who led the team from the New York School of Medicine, wrote: "Our patient had an underlying ketosis caused by the Atkins diet ... this problem may become more recog- nised because this diet is becoming increasingly popu- lar worldwide." The Atkins diet maintains that you

can lose weight rapidly by cutting carbohydrates en- tirely from meals.

For a month before she fell ill the woman admit- ted to the US hospital had lived on meat, cheese and salads. She had also taken vitamins recommended by the diet.

As instructed in the original Atkins diet book, she monitored her urine twice daily. During this month- long period, she lost about 9kg.

Commenting on the case elsewhere in the Lancet, Lyn Steffen, a doctor, and Jennifer Nettleton, from the University of Minnesota School of Public Health de- livered a further warning about Atkins and other carb- cutting diets. The pair wrote: "While the rapid weight loss seems to be an obvious benefit of the Atkins diet, bigger questions remain.”

First, is the diet safe? ... low carbohydrate diets for weight management are far from healthy, given their association with ketosis, constipation or diar- rhoea, halitosis, headache, and general fatigue to name a few side effects.

These diets also increase the protein load to the kidneys and alter the acid balance in the body, which can result in loss of minerals from bone stores, thus compromising bone integrity.