New York: Scientists have discovered why it is harder to keep weight off than to lose it. A team at Columbia University has shown the body’s internal systems act to restore fat levels in people who have slimmed down. The body appears to interpret the loss of weight as a deficiency in the appetite hormone leptin, and acts to try to restore the usual balance. The study features in the Journal of Clinical Investigation.
   It is estimated that more than 85% of obese people who have lost weight eventually put at least some of it back on. Research suggests this is due to a number of changes in the functioning of the metabolic, hormonal and nervous systems.
   The team gave doses of leptin to lean and obese volunteers who had recently lost weight. They found that most of the metabolic and hormonal changes which mean people cannot keep the weight from creeping back on were reversed once leptin levels were restored to pre-weight loss levels.
   Leptin is produced by the body’s fat (adipose) tissue. It is known to play a role in controlling appetite, but as yet the exact way that it works is unclear.
   The researchers suggest that, after people have lost weight, the body feels the need to make more leptin and so forms new fat tissue to enable it to do that. Restoring leptin to preweight loss levels would mean it no longer feel that need. Injections of leptin have been used to help morbidly obese people with a deficiency of the hormone to lose weight, but a similar approach has no effect on obese people with normal leptin levels.
   The researchers said it might eventually be possible to develop new drugs to keep weight off that work by targeting the way the body monitors leptin levels.
   Lead researcher Dr Michael Rosenbaum told a website that historically it made sense our ancestors to defend their fat reserves, as they were often subjected to periods when food was scarce.
   “We would predict that the human genome is heavily enriched with genes that defend body fatness and relatively lacking in genes that would oppose weight gain. We essentially have lived through hundreds of thousands of years of an environment that would encourage us to eat more and move less to preserve energy. We are in an environment where those traits are maladaptive.” NYT News Service

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