Scientists at the Karlolinksa Institute, Stockholm, Sweden, have discovered why fat people find it so hard to lose weight, and this will lead to many new approaches to weight loss.
According to the study reported in the journal Nature
, the number of fat cells in a person is established during adolescence and stays the same regardless of obesity in later years.
The rising rate of obesity has focused a lot of scientific attention on the "adipocyte", the cell type that makes up the "bulk of our bellies and waistlines."
When we are getting fatter, these fat cells are actually expanding in size, but experts were not sure if the number of adipocytes could increase and decrease as well.
The Swedish researchers first tested several hundred children, adolescents and adults of different ages and found that while fat cell numbers increased through childhood, the number of fat cells stayed fixed by the time adulthood was reached.
They studied the possibility that fat cell numbers could change in extreme circumstances by taking samples of fat from patients about to undergo radical weight loss.
Fat cells were taken from those about to undergo "gastric banding"—an operation performed to help very obese patients lose weight by reducing the size of the stomach.
After the weight loss was complete, another sample of fat was taken to assess if the overall number of fat cells had decreased.
The researchers found that the level of fat cells had stayed the same even after the weight loss program thus providing an insight into why fat people find it so hard to lose weight, even after a stringent diet.
The findings, which point to a fundamental new insight into the cause of obesity, come from the international team led by Dr Kirsty Spalding, Prof Jonas Frisén and Prof Peter Arner. Their study found that the body constantly produces new fat cells to replace the break down of the already existing fat cells due to cell death.
"It explains why it's so difficult to lose weight and to keep it off - those fat cells aren't going anywhere, and they're crying out for more," said Dr Kirsty Spalding.
Dr Paul Trayhurn, from the University of Liverpool, said, "It would be nice if we could find a way to lose fat by manipulating the numbers of fat cells, but there are a lot of other options higher up the queue than that - such as diet and exercise.
"The real benefit of this is that it gives us solid evidence that we can use in future research into obesity and its causes," he added.
However, another scientist, Professor Stephen O'Rahilly, from Cambridge University, who was not convinced by the idea that fat cell numbers were set from adolescence said, "We know that, sitting in adult fat tissue, are lots of cells that don't contain fat, but are capable of doing so if the nutritional conditions are right."
"They can almost certainly do so without dividing and therefore would not be 'counted' using this technique," he added.
Prof O'Rahilly thinks it is premature to conclude that by the time we are adolescents, the 'game is up' in terms of the number of fat cells we can possess.
Lead researcher Dr Spalding said, "Until now it was not clear whether there was fat cell turnover in adults. Now we have established this does occur, we can target the process."
"Various groups are looking at compounds that might regulate the formation of fat cells but this work is at too early a stage to say when anti obesity drugs based on this understanding will be tested on patients, if at all," Dr. Spalding added.