First author

Obesity is an increasing health concern worldwide, yet little is known about the timing and regulation of fat-cell, or adipocyte, formation. Work by Kirsty Spalding, a molecular biologist at the Karolinska Institute in Stockholm, and her colleagues has determined that, in adults, new adipocytes are generated to replace those that die. The total number of these cells remains constant, with obese adults having almost twice as many as lean adults (see page 783). Spalding tells Nature that the tight regulation of this process might explain why it is so difficult for some to maintain weight loss.

How did you come to use a carbon-dating technique to monitor cell turnover?

I trained as a neuroscientist, and initially used the carbon-isotope signature from 1950s nuclear-bomb tests — the prevalence of which is decreasing over time — to detect the generation of neurons in adults. I thought the technique could also be used to establish whether cell turnover occurs in adipocytes.

So, will the current human population be able to shed more light on cell dynamics?

Yes. We all have traces of nuclear-bomb tests in our bodies. So, for example, we'll be able to study brain-cell dynamics associated with dementia as the peak population — those who grew up during the nuclear tests — reach their 70s and 80s.

How do adipocyte dynamics differ between obese and lean people?

In obese children, adipocyte number starts to increase at the age of two; this doesn't happen in lean children until they are almost six. The number of adipocytes seems to become set as people mature, so that, even in people who have lost a lot of weight, new adipocytes replace those that die. This may explain why it is difficult to keep weight off. As people lose weight, adipocyte volume decreases, possibly prompting the brain to send signals to eat more. We have not yet examined whether lean individuals are capable of making additional adipocytes if they gain a lot of weight as adults.

Does your work offer options for treatment?

Not yet, but regulation of adipocyte turnover might be a good target for therapeutic intervention if we can find a way to interrupt the interplay between cell generation and the brain signals for energy maintenance.

Do you still pursue neuroscience research?

Yes, but I definitely focus more on the obesity work. I did not appreciate how much of a struggle weight loss is for some until people began e-mailing me their life stories.