Experts advise caution about claims of a pill that could enable people with diabetes and coeliac disease to eat foods that are normally off-limits.
The pill makes the gut less 'leaky'
People with coeliac disease need to avoid wheat and diabetics sugary foods to manage their medical conditions.
The University of Maryland, Baltimore team say a pill that makes the gut more watertight could allow these patients to eat whatever they want.
But the early studies were on rats and experts questioned the implications.
They argue the best way to manage food intolerance is by avoiding problem foods and eating a healthy, balanced diet and taking regular exercise.
The pill, called AT-1001, works by blocking the production of a protein found in the body which is called zonulin.
Zonulin regulates how porous or permeable the intestine is.
People with diseases like diabetes and coeliac disease tend to have too much zonulin, which the Baltimore scientists said means more foodstuff, toxins and other bacterial and viral particles within the gut can pass into the blood stream.
Lead investigator Dr Alessio Fasano said this, in turn, causes the body to attack itself, which can lead to problems like diabetes and coeliac disease.
He said: "With autoimmune diseases, the body mistakes its own tissue as foreign, resulting in an attack and destruction by the body's own immune system.
"These diseases are all characterised by an extremely permeable intestinal wall.
"We have been able to identify a way to prevent zonulin from causing leakage from the intestines as it does in people with these autoimmune diseases."
His team has shown that by blocking the action of zonulin with AT-1001 they can prevent diabetes in diabetes-prone rats.
These rats were able to continue on a normal diet, they reported in the Proceedings of the National Academy of Sciences.
He now plans to test the drug in people with coeliac disease and diabetes.
"I believe that it is going to be the case that restoring the intestinal barrier will mean that those prone to developing diabetes or coeliac disease can eat a normal diet," he told Chemistry & Industry magazine.
His team is working with Alba Therapeutics to develop a marketable drug.
"If everything goes to plan, we could have a product on the market by the end of 2006," he said.
Dr Angela Wilson, director of research at Diabetes UK, said: "People with diabetes should eat the same healthy, balanced diet recommended for everyone - high in fruit and vegetables and low in saturated fat and sugar.
"The development of this pill is a long way off. The focus should be on a combination of a healthy diet and regular physical activity.
"This will help to control diabetes in those who have the condition and will reduce the risk in others who may go on to develop Type 2 diabetes."
Professor Peter Howdle of St James University Hospital, Leeds, and member of Coeliac UK's medical advisory council said: "The research findings are encouraging and Coeliac UK will be following developments closely."