What's so bad about being a chocoholic? Plenty, says Adam Drewnowski, who is hunting a drug to battle cravings.

Chocolate is the food most craved by women who eat in binges, because of a brain chemical that gives them physical pleasure from the sweet indulgence, the University of Michigan nutritionist has discovered.

Now scientists are hot on the trail of drugs to block those intense cravings and battle eating disorders. "It's possible that we may be able to control the onset of binges,'' predicts Drewnowski.

At issue are not people who simply need to shed weight, but sufferers of medically defined disorders causing severe food cravings and huge eating binges, often followed by induced vomiting or laxatives to fight the resulting pounds. One such disorder, bulimia, affects one million Americans, mostly young women.

Binging women most desire foods high in fat and sugar -- chocolate is the No.

1 urge -- while men crave foods high in fat and salt, surveys show.

The brain naturally produces opiates, drug-like chemicals that cause pleasure sensations and are linked to addictions. Animal studies show these chemicals could be a trigger for sweet, fatty cravings. And consuming such foods made the brain produce even more of the chemicals, as shown in studies of rats given chocolate milk.

When the brain's normal opiate production was blocked, rats chose their normal feed over previously tempting sweets.

Drewnowski tested the theory in 41 women, bingers and normal eaters. They were offered their favourite foods, from pretzels and jelly beans to chocolate chip cookies and chocolate ice cream. Half received injections of naloxone, a drug used to treat heroin overdoses because it blocks brain opiate receptors. The rest got a placebo of salt water.

Naloxone made bingers eat notably less -- 160 fewer calories per meal, Drewnowski reported in July's American Journal of Clinical Nutrition. Their chocolate consumption dropped in favour of lower-fat foods like popcorn. And when asked to rate their favourite foods again, chocolate dropped.

Nonbingers weren't affected.

"The effect of naloxone was to reduce the pleasure response of food'' in bingers, Drewnowski concluded. "Binge eaters often know a binge is coming.

... That may be the time to take the medication.'' Naloxone is available only intravenously, an infeasible treatment for chronic bingers. Drewnowski is hunting an easier-to-take drug.

"It's a promising avenue,'' said Dr. Katherine Halmi, an eating disorder specialist at Cornell University. Drewnowski's work shows binge eating affects more than one neurotransmitter -- opiates as well as serotonin -- meaning "there is a need for a spectrum of treatments,'' she said.

But understanding of brain function is in its infancy, cautioned nutritionist Barbara Rolls of Pennsylvania State University. "These are provocative findings ... but this is one first phase,'' she said.

*** British doctors have reported that they had discovered why diets don't work -- it's all in the head.

Dieting upsets the level of chemicals in the brain, which in turn gives people an urge to overeat, E.M. Clifford and colleagues at Littlemore Hospital in Oxford found.

They cited studies on rats showing that those lacking the ability to use the neurotransmitter serotonin become overweight. Neurotransmitters are chemicals that help carry electrical signals along a nerve.

The doctors tested 12 women aged 20 to 39, and found that those on a restricted diet of 1,000 calories a day had lower levels of the essential amino acid tryptophan, which the body uses to make serotonin.

"Thus, during dieting, subjects are likely to experience urges to overeat which will compromise efforts at continued food restriction,'' they wrote in the science journal Nature.

In other words, dieting can give people the urge to binge.

"Humans have evolved powerful adaptive mechanisms for maintaining food intake. Trying to overcome these by voluntary food restriction is not only difficult but may be counterproductive in some individuals,'' they added.

But they said doctors could deliberately manipulate levels of these chemicals for those found to be clinically obese.