The drug chemically triggers a gene switch called PPAR-delta which in turn activates the same fat-burning process that occurs during exercise.
According to lead researcher Dr. Ronald Evans of the Salk Institute in San Diego, the same effect could occur in humans.
The potential weight-loss drug when it was used on mice in the form of a liquid or powder, revved up their cellular metabolism in much the same way as heavy physical activity.
Evans says the drug protected the mice against weight gain on high-fat and high-caloric diets and enabled them to exercise twice as long, turning them into "marathon mice.
Evans says the drug has potential for use with people.
The pill is intended to prevent disease rather than build muscles and could hopefully be used to treat people at risk of obesity-related diseases such as diabetes and could present a medical solution for people who must lose weight.
The pill could also offer an alternative to those who for whom diets and exercise do not work or are unable to lose enough weight that way.
There have been diet pills on the market for many years but they have significant side effects and are not always effective.
Although the drug could well become an 'exercise pill', experts say it is unlikely to provide all the benefits of a real physical exercise programme.
Evans says the drug would be more effective in the context of a healthy diet and exercise and would then offer the maximum benefit.
Nutritionists have expressed caution and say though exciting, the research is very preliminary and it remains to be seen if it can translate into something useful for humans.
The Salk Institute team presented their work this week at Experimental Biology 2007 in Washington D.C.
That is why the potential of chemical metabolic engineering - possibly a one-a-day pill as opposed to permanent genetic metabolic engineering - is so exciting, says Dr. Evans. In today's society, too few people get an ideal amount of exercise, some because of medical problems or excess weight that makes exercise difficult. Having access to an "exercise pill" would improve the quality of muscles, since muscles like to be exercised, and increase the burning of energy or excess fat in the body. And that would result in less fatty tissue, lower amounts of fat circulating in the blood, lower blood glucose levels and less resistance to insulin, lowering the risks of heart disease and diabetes.
The ability to chemically engineer changes in metabolism also has given the researchers more insight into how the PPAR-d switch works, says Dr. Evans. Genetically engineering changes in metabolism in the marathon mice triggers both increased fat burning and increased endurance. Adult normal mice that receive the drug to switch on PPAR-d show increased fat burning and resistance to weight gain, but they do not show increased endurance. Dr. Evans says this suggests the delta switch can operate in different modes, and the laboratory is in the process of figuring out exactly how. He hopes his strategy will make it possible.
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