In contrast to the much-publicised 'fat' hormone leptin that decreases body weight by reducing appetite and increasing metabolic rate, adiponectin can cause weight loss by raising metabolic rate while not affecting appetite, report scientists at the University of Pennsylvania School of Medicine.
This finding may have future implications in understanding and treating obesity and metabolic disorders like diabetes, said lead author, Rexford Ahima.
When adiponectin, which is involved in glucose and lipid metabolism, was introduced into the cerebrospinal fluid of normal mice, they showed no changes in food intake, but their metabolism rose.
"The animal burns off more calories, so over time loses weight, which was very fascinating because we knew that leptin caused weight loss by suppressing appetite and increasing metabolic rate," said Ahima. Here we have another fat hormone that can cause weight loss but without affecting intake, she added.
A common complaint from dieters is that although initially weight loss occurs, over time it becomes more difficult because the body compensates, in part, by dropping its metabolic rate.
"Adiponectin or its targets in the brain and other organs could be harnessed to sustain weight loss by maintaining a high metabolic rate," said Ahima. "This is only a possibility. We're not suggesting at this point that adiponectin will become a drug."
In severely obese mice, adiponectin rapidly decreases blood glucose and lipids, while burning fat suggesting that the hormone could be beneficial in the treatment of diabetes and heart disease associated with obesity.
The researchers found that both adiponectin and leptin require the melanocortin pathway in the brain to control body weight and glucose. However, these fat hormones also control metabolism through other distinct pathways in the brain.
"We focus on the brain because it is a major coordinator of feeding, metabolism, and hormones, including insulin," concludes Ahima.
According to a recent FAO study 36 per cent of all countries in the world already have populations consuming above the recommended maximum level of 300 milligrams per person a day of cholesterol, more than twice the rate of the early 1960s.
Likewise, 34 per cent of all countries exceed the 30 per cent threshold of fat in the diet, compared to 18 per cent 40 years ago. FAO's outlook to 2030 suggests that these indicators will continue to deteriorate as more than 40 per cent of the additional calories consumed in the future will come from fats.
Obesity is one of the main causes of non-communicable diseases. The economic and healthcare costs of NCDs are already high in many developed countries. In the US alone that cost has risen to more than $120 billion annually.
The World Health Organisation estimates that in 1995 there were 200 million obese adults worldwide and another 18 million under-five children classified as overweight. In 2000, this number lept up to over 300 million, with over 115 million people suffering from obesity-related problems in the developing countries.