<p>Are fat cells forever?<br /><br /></p>.<p>Once fat cells form, can you ever get rid of them? The number of fat cells in a person’s body seems to be able to change in only one direction: up. Fat cell number increases through childhood and adolescence and generally stabilises in adulthood. But this doesn’t mean that fat cells, or adipocytes, are stagnant. The size of individual fat cells is remarkably variable, expanding and contracting with weight gain or weight loss. And as with most cell types in the body, adipocytes die eventually.<br /><br />“Usually when old ones die, they are replaced by new fat cells,” said Dr Michael Jensen, an endocrinologist and obesity researcher at the Mayo Clinic. Cell death and production appear to be tightly coupled, so although about 10% of adipocytes die each year, they’re replaced at the same rate. <br /><br />Even among bariatric surgery patients, who can lose a lot of weight, the number of fat cells tends to remain the same, although they shrink in size. Liposuction reduces the number of fat cells in a person’s body, but studies show the weight lost is typically regained within a year. It isn’t known whether this regain occurs through the production of new fat cells or expansion of existing ones.<br /><br />People who are obese tend to have more fat cells than those who are not, and several studies have found an increase in fat cell number with weight regain following weight loss. The fact that fat cell number can be increased but not decreased most likely contributes to the body’s drive to regain weight after weight loss, said Dr Kirsty L Spalding, a cell biologist at the Karolinska Institute in Sweden and the lead author of a 2008 study showing that fat cells die and are replaced. <br /><br />Beyond their role in storing fat, adipocytes secrete proteins and hormones that affect energy metabolism. “Following weight loss, adipocytes become smaller, generally smaller than those from people with a similar BMI,” Kirsty said. One <br />hypothesis is that those smaller cells might send signals to increase appetite and fat storage, which could help to explain why weight loss is so difficult to maintain, though much more research is needed.<br />Alice Callahan<br /><br />Magnetic field fears allayed by ancient pottery<br /><br />The Earth’s magnetic field — which deflects harmful space radiation — has been weakening, losing about 10% of its strength over the last two centuries. Should we be worried? Ancient pottery suggests not. In a paper published recently in PNAS, a team of scientists <br /><br />examined 67 jar handles collected from excavations of ancient Judah. <br />The ceramic jars encoded a record of Earth’s magnetic field as they were fired in kilns and then cooled. Examinations of the oldest jars, from the late-8th century BC, indicate that the field was two-and-a-half times stronger than it is today. But its intensity declined by about one-third in less than 30 years. The decline may well be part of a natural cycle, but geophysicists still are unable to explain how it works.<br />Kenneth Chang<br /><br />After mass extinction, a speedy recovery<br /><br />Fossil-hunters at Montana State University, USA have identified more than 750 ancient specimens in Idaho’s Paris Canyon, including squids, lobsters and fish. All were part of a thriving underwater ecosystem some 250 million years ago — just 1.3 million years after the Great Dying, the greatest mass extinction in Earth’s history. Most research had suggested that ecosystems needed up to 20 million years to recover. The denizens of the canyon say otherwise.<br />Nicholas St Fleur<br /><br /></p>
<p>Are fat cells forever?<br /><br /></p>.<p>Once fat cells form, can you ever get rid of them? The number of fat cells in a person’s body seems to be able to change in only one direction: up. Fat cell number increases through childhood and adolescence and generally stabilises in adulthood. But this doesn’t mean that fat cells, or adipocytes, are stagnant. The size of individual fat cells is remarkably variable, expanding and contracting with weight gain or weight loss. And as with most cell types in the body, adipocytes die eventually.<br /><br />“Usually when old ones die, they are replaced by new fat cells,” said Dr Michael Jensen, an endocrinologist and obesity researcher at the Mayo Clinic. Cell death and production appear to be tightly coupled, so although about 10% of adipocytes die each year, they’re replaced at the same rate. <br /><br />Even among bariatric surgery patients, who can lose a lot of weight, the number of fat cells tends to remain the same, although they shrink in size. Liposuction reduces the number of fat cells in a person’s body, but studies show the weight lost is typically regained within a year. It isn’t known whether this regain occurs through the production of new fat cells or expansion of existing ones.<br /><br />People who are obese tend to have more fat cells than those who are not, and several studies have found an increase in fat cell number with weight regain following weight loss. The fact that fat cell number can be increased but not decreased most likely contributes to the body’s drive to regain weight after weight loss, said Dr Kirsty L Spalding, a cell biologist at the Karolinska Institute in Sweden and the lead author of a 2008 study showing that fat cells die and are replaced. <br /><br />Beyond their role in storing fat, adipocytes secrete proteins and hormones that affect energy metabolism. “Following weight loss, adipocytes become smaller, generally smaller than those from people with a similar BMI,” Kirsty said. One <br />hypothesis is that those smaller cells might send signals to increase appetite and fat storage, which could help to explain why weight loss is so difficult to maintain, though much more research is needed.<br />Alice Callahan<br /><br />Magnetic field fears allayed by ancient pottery<br /><br />The Earth’s magnetic field — which deflects harmful space radiation — has been weakening, losing about 10% of its strength over the last two centuries. Should we be worried? Ancient pottery suggests not. In a paper published recently in PNAS, a team of scientists <br /><br />examined 67 jar handles collected from excavations of ancient Judah. <br />The ceramic jars encoded a record of Earth’s magnetic field as they were fired in kilns and then cooled. Examinations of the oldest jars, from the late-8th century BC, indicate that the field was two-and-a-half times stronger than it is today. But its intensity declined by about one-third in less than 30 years. The decline may well be part of a natural cycle, but geophysicists still are unable to explain how it works.<br />Kenneth Chang<br /><br />After mass extinction, a speedy recovery<br /><br />Fossil-hunters at Montana State University, USA have identified more than 750 ancient specimens in Idaho’s Paris Canyon, including squids, lobsters and fish. All were part of a thriving underwater ecosystem some 250 million years ago — just 1.3 million years after the Great Dying, the greatest mass extinction in Earth’s history. Most research had suggested that ecosystems needed up to 20 million years to recover. The denizens of the canyon say otherwise.<br />Nicholas St Fleur<br /><br /></p>