New Scientist - USA (2022-01-08)

8 January 2022 | New Scientist | 21

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The columnist

Annalee Newitz

bonds with a

friendly robot p22

Aperture

An electrifying image

of a Leach’s sea star as

it spawns p24

Letters

Let’s pull out all

the stops to save

the Amazon p26

Culture

In Memoria, a woman

hears noises no one

else can detect p28

Culture columnist

Jacob Aron causes

chaos in Jurassic

World Evolution 2 p30

I

N PRINCIPLE, it sounds simple:
eat less and move more. This
dietary advice for tackling
obesity has been around for
decades. Yet, despite all the calorie
counting, dieting and exercising,
worldwide obesity rates just keep
ticking up. People in the US, for
example, were heavier in 2021 than
they were in 2020, placing many
more people at risk from diabetes
and other serious chronic diseases.
So why hasn’t this approach to
weight control worked?
One possibility is that we
haven’t tried hard enough.
Perhaps we have lacked the
discipline and willpower to
maintain healthy dietary and
exercise habits – a challenge
made more difficult today for
those surrounded by inexpensive,
tasty, highly processed foods.
Or perhaps the problem is the
focus on “calorie balance” itself. In
a recent paper, my colleagues and
I question the basic assumption
of whether taking in more calories
than you burn really is the
primary cause of obesity. We argue
that the evidence actually points
the other way: we are driven to
overeat because we are getting
fatter (The American Journal of
Clinical Nutrition, doi.org/gmtn3z).
This may seem incredible, but
consider the adolescent growth
spurt. As their growth rate speeds
up, teenagers may eat hundreds of
calories more each day than they
used to. Does this “overeating”
cause the rapid growth? Or does
the rapid growth, which requires
MImore calories to build new body
CH
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NO

Comment

tissues, make teens hungrier so

they eat more? Clearly the latter,

as adults won’t grow taller, no

matter how much they eat.

The key to how this works in

obesity is hormones, especially

the fat-storage hormone insulin.

Processed, rapidly digestible

carbohydrates – foods like

sweetened breakfast cereals,

potato chips and sugary

beverages – raise our insulin level

too high. This causes our fat cells

to take in and store too many

calories, leaving fewer available

for the rest of the body. A few

hours after eating a high-carb

meal, the number of calories in

the bloodstream plummets, so we

get hungrier sooner after eating.

Consider another example:

oedema, in which excess fluid

builds up in body tissues, such as

the legs. People with oedema tend

to become thirsty, despite the

excess, because the fluid doesn’t

stay in the blood where it is needed.

From this perspective, the difficulty

resisting hunger that so many

dieters have isn’t a sign of poor

discipline, but rather a biological

problem involving how our bodies

distribute the calories we consume.

The two opposing views of cause

and effect in obesity have radically

different implications for how to

prevent and treat weight problems.

Whereas the usual approach

focuses on how much to eat,

with prescriptions for daily calorie

intake, in our view, the emphasis

should be placed on what to eat.

Replacing processed carbs

with high-fat foods – such as nuts,

full-fat dairy, olive oil, avocado and

dark chocolate – lowers insulin

levels, making more calories from

the meal available for the rest

of the body. Counter-intuitively,

higher-fat foods may help shed

body fat, a possibility supported

by clinical trials comparing

high-fat diets with low-fat ones.

This way of thinking might help

explain why calorie restriction

usually fails long before a person

with obesity approaches an ideal

body weight. A low-calorie, low-fat

diet further restricts an already

limited supply of energy to the

body, exacerbating hunger without

addressing the underlying

predisposition to store too many

calories in body fat. Consequently,

weight loss becomes a battle

between mind and metabolism

that most people will probably lose.

Although much more

research will be needed to test

this provocative idea, it is time to

question the basic assumptions

about cause and effect, calories and

weight gain that have dominated

our thinking for decades.  ❚

Rethinking obesity

Putting on weight is often blamed on overeating, but new evidence is

emerging that it is actually the other way round, says David S. Ludwig

David S. Ludwig is a

researcher at Boston

Children’s Hospital

@davidludwigmd