As fat people have an abundance of fat tissue, the natural assumption is that fat people have more fat cells, or ‘adipocytes‘. That’s only part of the story – it turns out that overweight and obese people not only have a surplus of fat cells, they have larger ones too.
The idea of these ‘fatter fat cells’ has been around since the 1970s. But their importance has been dramatically highlighted by a new study, which shows that the number of fat cells in both thin and obese people is more or less set during childhood and adolescence. During adulthood, about 8% of fat cells die every year only to be replaced by new ones. As a result, adults have a constant number of fat cells, even those who lose masses of weight. Instead, it’s changes in the volume of fat cells that causes body weight to rise and fall.
Kirsty Spalding from the Karolinska Institute in Sweden, together with a large team of international researchers, uncovered several lines of evidence to support these conclusions. Her study is a fascinating mix of cell counting, stomach surgery, radioactive Cold War fallout and a rather surprising use for carbon-dating.
