From Mary Shomon Your Thyroid Guide
Weight Loss Breakthroughs -- Four New Studies Expand Knowledge Of Hormones, Appetite Control And Body Weight
August 15, 2002-- Four studies published this month in the Journal of Clinical Endocrinology & Metabolism (JCEM) and Endocrinology, highlight the relationship between hormones, food intake, genes and weight regulation. All four studiestwo basic research and two clinical researchwill help scientists and physicians move closer to understanding the causes and possible treatments for obesity, which affects nearly 20 percent of adults in the United States.
Researchers recently discovered that a hormone called ghrelin can stimulate hunger. New research, published this month in JCEM, shows that insulin levels directly impact ghrelin levels and, therefore, play a role in appetite regulation. Dr. Mohammed Saad and researchers at the University of California, Los Angeles School of Medicine, found that changes in insulin levels were associated with changes in plasma ghrelin levels. The researchers infused insulin for two hours in eight patients between 42 and 50 years old. Regular blood samples measured the plasma insulin and ghrelin concentrations. The results indicated that insulin is a physiological regulator of ghrelin. Additionally, the relative level of insulin was shown to mediate the effects of nutritional status on ghrelin.
"In all of our subjects, changes in insulin levels were directly associated with swift and reciprocal changes in ghrelin levels," explained Dr. Saad. "Our research demonstrates that insulin plays a pivotal role in the regulation of feeding behavior and body weight through its opposite affect on ghrelin, a hormone that stimulates food intake and leptin, a hormone that inhibits food intake and supports weight loss. Larger and longer studies are now needed to confirm this finding."
In a second study on ghrelin, which is also published in the August issue of JCEM, researchers studied the contribution of the ghrelin gene to height, body mass and glucose tolerance in 70 obese, tall children and discovered that variations in the ghrelin gene contribute to obesity in children. The researchers found that a common polymorphism (SNP247) of the ghrelin gene is associated with an increase in body mass index and lower insulin secretion.
"SNP247 was found to be associated with an earlier onset of obesity in children in our study," explained Dr. Marta Korbonits, the lead investigator on the study and a researcher at St. Bartholomew's Hospital in London.
One of the biggest challenges for dieters is keeping the weight off. Previous research has shown that the hormone leptin decreases food consumption while increasing fat metabolism and energy expenditure. In a study published in the August issue of Endocrinology, researchers at the Malcom Randall VA Medical Center and the University of Florida College of Medicine delivered leptin into the brains of obese rats to determine whether an increase in energy expenditure alone would maintain, over an extended period of time, weight loss achieved through an initial food reduction. The researchers measured food consumption, body weight and energy expenditure for nearly five months.
"We concluded that a reduction in food intake mediated the initial loss of body weight, however, only an increase in energy expenditure was necessary to maintain the reduced weight, even after food consumption returned to normal," explained Dr. Philip Scarpace, the lead investigator on the study. "Our findings suggest that a continuation of reduced food consumption is not critical to maintain a reduced body weight as long as there is a sustained increase in energy expenditure."
In another study also published in this month's issue of Endocrinology, researchers at the University of Cincinnati Medical Center determined that two neuropeptides (small hormones produced in the brain) influence the desire for high fat and low fat foods. High fat and low fat diets were fed to separate groups of rats who were injected with one of two neuropeptidesorexin-A or melanin-concentrating hormone (MCH). The study determined that orexin-A stimulates the consumption of high fat foods. The researchers also discovered that MCH stimulates the consumption of high fat and low fat foods equally.
Another aspect of the study involved opioidsa hormone that is involved with the rewarding and motivational aspects of food intake. The researchers, lead by Dr. Deborah Clegg, assessed whether food intake elicited by orexin-A and MCH is sensitive to drugs that inhibit opioid receptors. The findings suggest that only orexin-A enhances the rewarding aspects of food.
Taken together, these four new studies help advance our understanding of the hormonal control of food intake and energy expenditure, findings which may be used to design more effective approaches to the treatment of obesity.
Source: The Endocrine Society press release