New Scientist - 07.09.2019

10 | New Scientist | 7 September 2019

SOME slim people seem able to

eat as much as they like without

gaining weight. It now appears

that they can do this because

their fat cells burn energy

differently. The finding could

lead to new obesity treatments.

Nele Gheldof at the Nestlé

Institute of Health Sciences in

Switzerland and her colleagues

studied 30 men and women

with body mass indexes (BMIs)

of 18.5 or under – classified as

underweight – despite eating

and exercising the same amount

as the average person.

Gheldof’s team took small

fat samples from these people’s

tummies and found that genes

involved in both breaking down

and making fat were unusually

active in their fat cells.

They also found that these

fat cells were 40 per cent

smaller than those of people

with a normal BMI and

contained greater numbers of

more active mitochondria – the

energy powerhouses of cells

(American Journal of Clinical

Nutrition, doi.org/c92q).

These findings suggest that

some slim people are resistant

to putting on weight because

their fat cells burn a lot of energy

through a “futile lipid cycle”,

says Gheldof. This means the

fat cells are stuck in a loop of

breaking down and rebuilding

fat molecules – a process that

is powered by mitochondria.

Fat cells may be smaller in

these people because the futile

lipid cycle builds up only a small

amount of fat before breaking

it down again, says Gheldof,

although further studies are

needed to confirm this.

In contrast, people with

obesity often have faulty

mitochondria in their fat

cells, meaning they can’t

burn energy via the futile lipid

cycle, says Sihem Boudina

at the University of Utah.

Several groups are

investigating ways to restore

mitochondrial activity and

start the futile lipid cycle to

drive weight loss in people with

obesity, says Boudina. The new

findings suggest that they are

on the right track, she says.

Cold exposure has been

shown to boost the futile lipid

cycle, which could explain the

trend of wearing ice vests and

having ice baths to slim down.

However, this cold shock

strategy works only for people

whose mitochondrial machinery

is already functioning. It won’t

have the same effect for people

whose mitochondria aren’t

functioning well enough for the

cycle to be initiated in the first

place, says Boudina. ❚

PLUMES of volcanic gas spotted

near a distant planet may be

the first indirect evidence we

have seen of a moon in a different

solar system – an exomoon.

Astronomers suspect that

there are huge numbers of

exomoons out there. So far,

however, we haven’t obtained

concrete evidence for any of them,

largely because they are so small.

Apurva Oza at the University

of Bern in Switzerland and his

colleagues used the La Silla

Observatory in Chile to examine

light coming from an exoplanet

orbiting a star called WASP-49B

about 550 light years from Earth.

The exoplanet has roughly half the

mass of Jupiter. The team detected

what seems to be the signature

of sodium gas around the planet.

However, the signal extends so far

into space that it probably can’t

have come from the planet’s

surface. Instead, Oza thinks the

gas may come from a volcanically

active rocky moon orbiting the

Have we seen signs of

a volcanic exomoon?

Astronomy Metabolism

Jonathan O’Callaghan Alice Klein

UNIVERSITY OF BERN, ILLUSTRATION: THIBAUT ROGER STEVE GSCHMEISSNER/SPL

News

planet (arxiv.org/abs/1908.10732).

This would make it reminiscent

of Jupiter’s moon Io, the most

volcanically active world in our

solar system.

Oza and his team say the signal

they picked up can be explained

by a flow of sodium gas from this

so-called “exo-Io” streaming

into the planet’s atmosphere.

“We’re quite confident that only

an exo-Io can fit the data for this

particular planet,” says Oza.

If they are right, Oza and his

team would have the first indirect

evidence for an exomoon. Several

candidates have emerged before,

but none have stuck. Follow-up

observations will be needed

to prove whether there really

is a moon there.

“What they are suggesting here

is certainly plausible, but it is not

a direct proof that they have found

an exomoon,” says Uri Malamud

at the Technion-Israel Institute

of Technology. Malamud says that

if the moon is confirmed, Oza’s

work could be useful for spotting

other exomoons. ❚

Exomoons are tricky to

spot, unless they happen

to spew volcanic gas

Different people

metabolise food in

different ways

Four fat-

storing cells

known as

adipocytes

SOUTH AGENCY/GETTY

550

Distance from Earth to the star

WASP-49B in light years

Fat cells are more

active in people

who stay slim