Editors' ChoiceObesity

Tracking human fat turnover with carbon dating

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Science Translational Medicine  25 Sep 2019:
Vol. 11, Issue 511, eaaz4961
DOI: 10.1126/scitranslmed.aaz4961

Abstract

Lipid turnover in adipose tissue is important in long-term body weight gain and weight loss maintenance after bariatric surgery in humans.

Obesity is associated with the expansion of adipose tissue depots as well as metabolic adaptations in adipose tissues. Previous studies only assessed short-term changes in adipose lipid metabolism in humans, whereas long-term effects of lipid metabolism in adipose tissues on body weight have been relatively unexplored due to methodological limitations.

Arner and colleagues used carbon dating to track changes in lipid turnover, the rate at which lipids are removed or stored in adipose tissues (biopsies taken from beneath the skin in human subjects) for up to 16 years. The rationale of this method is that retrospectively measuring how much fat tissues accumulate radioactive carbon-14, which is rapidly declining in the atmosphere since the 1960s following the cessation of overground nuclear bomb tests, enables determination of long-term changes in lipid turnover.

The first part of their study investigated the effects of aging on adipose lipid turnover in 54 healthy subjects (including 11 men) over a period of 13 to16 years. They observed that a majority of subjects had reduced lipid removal rates that did not coincide with changes in body weight, but instead correlated with lipid storage rate in adipose tissues as determined by food intake. This finding suggests that the failure to balance increased lipid storage with increased lipid removal with age contributes to long-term weight gain.

The investigators next measured adipose lipid turnover in 41 morbidly obese women before and 4 to 7 years after bariatric surgery. Lipid removal rates did not change after surgery, but decreased lipid storage rate was associated with drastic post-surgical weight loss, suggesting that weight loss after surgery was predominantly determined by reduced food intake. Conversely, higher baseline lipid removal rate of the subjects measured before surgery correlated with greater post-surgical weight loss. The authors also observed that lipid removal rate was higher in patients with persistent weight loss and lower in those with rebound weight gain after surgery. These results suggest that changes in lipid turnover are important in maintaining post-surgical weight loss.

This study highlights the role of adipose tissue lipid turnover in determining body weight changes associated with aging and after weight-loss surgery. Future studies should study other factors such as sex and ethnicity differences, as well as examining other adipose depots in adipose lipid turnover. Carbon dating opens new opportunities to monitor long-term changes in lipid metabolism in human adipose tissues during healthy and diseased states.

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