12:43
TEDGlobal 2013

Sandra Aamodt: Why dieting doesn't usually work

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In the US, 80% of girls have been on a diet by the time they're 10 years old. In this honest, raw talk, neuroscientist Sandra Aamodt uses her personal story to frame an important lesson about how our brains manage our bodies, as she explores the science behind why dieting not only doesn't work, but is likely to do more harm than good. She suggests ideas for how to live a less diet-obsessed life, intuitively.

- Neuroscientist and science writer
Sandra Aamodt explores the neuroscience of everyday life, examining new research and its impact on our understanding of ourselves. Full bio

Three and a half years ago,
00:12
I made one of the best decisions of my life.
00:14
As my New Year's resolution,
00:17
I gave up dieting, stopped worrying about my weight,
00:19
and learned to eat mindfully.
00:23
Now I eat whenever I'm hungry,
00:26
and I've lost 10 pounds.
00:30
This was me at age 13,
00:33
when I started my first diet.
00:36
I look at that picture now, and I think,
00:38
you did not need a diet,
00:41
you needed a fashion consult.
00:43
(Laughter)
00:46
But I thought I needed to lose weight,
00:48
and when I gained it back,
00:51
of course I blamed myself.
00:53
And for the next three decades,
00:57
I was on and off various diets.
00:59
No matter what I tried,
01:02
the weight I'd lost always came back.
01:04
I'm sure many of you know the feeling.
01:07
As a neuroscientist,
01:10
I wondered, why is this so hard?
01:12
Obviously, how much you weigh depends on
01:15
how much you eat and how much energy you burn.
01:17
What most people don't realize
01:20
is that hunger and energy use
01:22
are controlled by the brain,
01:24
mostly without your awareness.
01:26
Your brain does a lot of its work behind the scenes,
01:30
and that is a good thing,
01:33
because your conscious mind --
01:35
how do we put this politely? --
01:38
it's easily distracted.
01:39
It's good that you don't have to remember to breathe
01:43
when you get caught up in a movie.
01:45
You don't forget how to walk
01:48
because you're thinking about
what to have for dinner.
01:50
Your brain also has its own sense
01:53
of what you should weigh,
01:55
no matter what you consciously believe.
01:57
This is called your set point,
02:00
but that's a misleading term,
02:02
because it's actually a range
02:04
of about 10 or 15 pounds.
02:05
You can use lifestyle choices to move your weight
02:08
up and down within that range,
02:11
but it's much, much harder to stay outside of it.
02:13
The hypothalamus, the part of the brain
02:18
that regulates body weight,
02:20
there are more than a dozen chemical signals
02:21
in the brain that tell your body to gain weight,
02:24
more than another dozen that
tell your body to lose it,
02:26
and the system works like a thermostat,
02:30
responding to signals from the body
02:33
by adjusting hunger, activity and metabolism,
02:36
to keep your weight stable as conditions change.
02:39
That's what a thermostat does, right?
02:43
It keeps the temperature in your house the same
02:45
as the weather changes outside.
02:49
Now you can try to change the temperature
02:51
in your house by opening a window in the winter,
02:54
but that's not going to change
the setting on the thermostat,
02:58
which will respond by kicking on the furnace
03:02
to warm the place back up.
03:04
Your brain works exactly the same way,
03:06
responding to weight loss by using powerful tools
03:09
to push your body back
03:13
to what it considers normal.
03:14
If you lose a lot of weight,
03:18
your brain reacts as if you were starving,
03:20
and whether you started out fat or thin,
03:24
your brain's response is exactly the same.
03:27
We would love to think that your brain could tell
03:30
whether you need to lose weight or not,
03:32
but it can't.
03:33
If you do lose a lot of weight,
03:36
you become hungry,
03:38
and your muscles burn less energy.
03:41
Dr. Rudy Leibel of Columbia University
03:44
has found that people who have lost
03:46
10 percent of their body weight
03:48
burn 250 to 400 calories less
03:50
because their metabolism is suppressed.
03:53
That's a lot of food.
03:56
This means that a successful dieter
03:58
must eat this much less forever
04:00
than someone of the same weight
04:03
who has always been thin.
04:05
From an evolutionary perspective,
04:07
your body's resistance to weight loss makes sense.
04:09
When food was scarce, our ancestors' survival
04:11
depended on conserving energy,
04:14
and regaining the weight when food was available
04:17
would have protected them
against the next shortage.
04:19
Over the course of human history,
04:22
starvation has been a much bigger problem
04:25
than overeating.
04:28
This may explain a very sad fact:
04:30
Set points can go up,
04:34
but they rarely go down.
04:37
Now, if your mother ever mentioned
04:39
that life is not fair,
04:42
this is the kind of thing she was talking about.
04:44
(Laughter)
04:47
Successful dieting doesn't lower your set point.
04:50
Even after you've kept the weight off
04:53
for as long as seven years,
04:54
your brain keeps trying to make you gain it back.
04:56
If that weight loss had been due to a long famine,
05:00
that would be a sensible response.
05:04
In our modern world of drive-thru burgers,
05:06
it's not working out so well for many of us.
05:09
That difference between our ancestral past
05:12
and our abundant present
05:16
is the reason that Dr. Yoni Freedhoff
05:18
of the University of Ottawa
05:20
would like to take some of his patients back to a time
05:23
when food was less available,
05:25
and it's also the reason
05:27
that changing the food environment
05:29
is really going to be the most effective solution
05:31
to obesity.
05:36
Sadly, a temporary weight gain
05:38
can become permanent.
05:41
If you stay at a high weight for too long,
05:43
probably a matter of years for most of us,
05:46
your brain may decide that that's the new normal.
05:48
Psychologists classify eaters into two groups,
05:53
those who rely on their hunger
05:57
and those who try to control their eating
05:58
through willpower, like most dieters.
06:01
Let's call them intuitive eaters and controlled eaters.
06:07
The interesting thing is that intuitive eaters
06:13
are less likely to be overweight,
06:16
and they spend less time thinking about food.
06:18
Controlled eaters are more vulnerable
06:22
to overeating in response to advertising,
06:26
super-sizing, and the all-you-can-eat buffet.
06:28
And a small indulgence,
06:32
like eating one scoop of ice cream,
06:34
is more likely to lead to a food binge
06:37
in controlled eaters.
06:43
Children are especially vulnerable
06:45
to this cycle of dieting and then binging.
06:47
Several long-term studies have shown
06:50
that girls who diet in their early teenage years
06:53
are three times more likely to become overweight
06:57
five years later,
07:00
even if they started at a normal weight,
07:02
and all of these studies found
07:04
that the same factors
07:07
that predicted weight gain
07:09
also predicted the development of eating disorders.
07:13
The other factor, by the way,
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those of you who are parents,
07:17
was being teased by family members
07:19
about their weight.
07:22
So don't do that.
07:23
(Laughter)
07:25
I left almost all my graphs at home,
07:27
but I couldn't resist throwing in just this one,
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because I'm a geek, and that's how I roll.
07:32
(Laughter)
07:34
This is a study that looked at the risk of death
07:37
over a 14-year period
07:39
based on four healthy habits:
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eating enough fruits and vegetables,
07:44
exercise three times a week,
07:46
not smoking,
07:48
and drinking in moderation.
07:49
Let's start by looking at the normal weight
07:51
people in the study.
07:53
The height of the bars is the risk of death,
07:55
and those zero, one, two, three, four numbers
07:57
on the horizontal axis
07:59
are the number of those healthy habits
08:00
that a given person had.
08:02
And as you'd expect, the healthier the lifestyle,
08:04
the less likely people were to die during the study.
08:07
Now let's look at what happens
08:10
in overweight people.
08:11
The ones that had no healthy habits
08:13
had a higher risk of death.
08:15
Adding just one healthy habit
08:17
pulls overweight people back into the normal range.
08:19
For obese people with no healthy habits,
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the risk is very high, seven times higher
08:25
than the healthiest groups in the study.
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But a healthy lifestyle helps obese people too.
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In fact, if you look only at the group
08:34
with all four healthy habits,
08:36
you can see that weight makes very little difference.
08:38
You can take control of your health
08:41
by taking control of your lifestyle,
08:43
even If you can't lose weight
08:45
and keep it off.
08:46
Diets don't have very much reliability.
08:48
Five years after a diet,
08:52
most people have regained the weight.
08:54
Forty percent of them have gained even more.
08:57
If you think about this,
08:59
the typical outcome of dieting
09:01
is that you're more likely to gain weight
09:03
in the long run than to lose it.
09:05
If I've convinced you that dieting
09:08
might be a problem,
09:11
the next question is, what do you do about it?
09:13
And my answer, in a word, is mindfulness.
09:15
I'm not saying you need to learn to meditate
09:20
or take up yoga.
09:22
I'm talking about mindful eating:
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learning to understand your body's signals
09:27
so that you eat when you're hungry
09:30
and stop when you're full,
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because a lot of weight gain boils down
09:35
to eating when you're not hungry.
09:37
How do you do it?
09:40
Give yourself permission to eat
09:42
as much as you want, and then work on figuring out
09:44
what makes your body feel good.
09:46
Sit down to regular meals without distractions.
09:48
Think about how your body feels
09:51
when you start to eat and when you stop,
09:53
and let your hunger decide
09:55
when you should be done.
09:58
It took about a year for me to learn this,
09:59
but it's really been worth it.
10:01
I am so much more relaxed around food
10:03
than I have ever been in my life.
10:06
I often don't think about it.
10:09
I forget we have chocolate in the house.
10:12
It's like aliens have taken over my brain.
10:15
It's just completely different.
10:17
I should say that
10:20
this approach to eating probably
won't make you lose weight
10:23
unless you often eat when you're not hungry,
10:26
but doctors don't know of any approach
10:29
that makes significant weight loss in a lot of people,
10:32
and that is why a lot of people are now focusing on
10:37
preventing weight gain
10:40
instead of promoting weight loss.
10:42
Let's face it:
10:46
If diets worked, we'd all be thin already.
10:47
(Laughter)
10:51
Why do we keep doing the same thing
10:53
and expecting different results?
10:55
Diets may seem harmless,
10:58
but they actually do a lot of collateral damage.
11:00
At worst, they ruin lives:
11:03
Weight obsession leads to eating disorders,
11:06
especially in young kids.
11:08
In the U.S., we have 80 percent of 10-year-old girls
11:11
say they've been on a diet.
11:16
Our daughters have learned to measure their worth
11:18
by the wrong scale.
11:20
Even at its best,
11:23
dieting is a waste of time and energy.
11:25
It takes willpower which you could be using
11:28
to help your kids with their homework
11:32
or to finish that important work project,
11:35
and because willpower is limited,
11:38
any strategy that relies on its consistent application
11:42
is pretty much guaranteed
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to eventually fail you
11:49
when your attention moves on to something else.
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Let me leave you with one last thought.
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What if we told all those dieting girls
11:59
that it's okay to eat when they're hungry?
12:02
What if we taught them to work with their appetite
12:05
instead of fearing it?
12:07
I think most of them would be happier and healthier,
12:09
and as adults,
12:13
many of them would probably be thinner.
12:15
I wish someone had told me that
12:18
back when I was 13.
12:21
Thanks.
12:24
(Applause)
12:26

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About the Speaker:

Sandra Aamodt - Neuroscientist and science writer
Sandra Aamodt explores the neuroscience of everyday life, examining new research and its impact on our understanding of ourselves.

Why you should listen

Sandra Aamodt is a neuroscientist and science writer, who takes the complexities of neuroscience research and whips them into fun reads that give people a better understanding of their minds and behavior. Her books Welcome to Your Brain and Welcome to Your Child's Brain (both written with Sam Wang) are designed to bring neuroscience to a general audience, and they've both been widely translated. Aamodt's science writing has also appeared in The New York Times, The Washington Post, El Mundo and the Times of London.

From 2003 to 2008, Aamodt was the editor-in-chief of Nature Neuroscience, a leading scientific journal in the field of brain research. She brings a significant scientific background to the task of explaining new research without creating neurobunk. During her career, she has read over five thousand neuroscience papers, and written many editorials on science policy.

More profile about the speaker
Sandra Aamodt | Speaker | TED.com