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By Jack Challoner
In the battle to lose weight, hunger is the dieter's worst enemy. But research
has revealed a simple aid to taming the appetite: soup. It's dieting's best
kept secret says one science writer.
Imagine a typical lunchtime meal - say, chicken and vegetables with a glass of
water.
If you eat the food and drink the water, you will feel full for a couple of
hours before hunger kicks in. But if you blend the food with the water - to
make soup - you will stay hunger-free for much longer, and less likely to snack
through the afternoon.
How can blending the food into soup make such a difference? The answer lies in
the stomach. Scientists have used ultrasound and MRI scans of people's stomachs
to investigate what happens after eating solid-food-plus-water meals compared
with the same food made into soup.
After you eat a meal, the pyloric sphincter valve at the bottom of your stomach
holds food back so that the digestive juices can get to work.
Water, however, passes straight through the sphincter to your intestines, so
drinking water does not contribute to "filling you up".
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Wednesday, 27 May at 2000 BST
When you eat the same meal as a soup, the whole mixture remains in the stomach,
because the water and food are blended together. The scientists' scans confirm
that the stomach stays fuller for longer, staving off those hunger pangs.
The key to this low-tech weapon against hunger is a hormone called ghrelin. It
is one of the major players in the body's appetite system.
Discovered as recently as 1999, ghrelin is released by specialised cells in the
stomach wall.
'Cupcake circuit'
These cells produce a constant stream of ghrelin whenever the stomach is empty.
The ghrelin travels via the blood stream to the brain's appetite centre, an
organ called the hypothalamus. As a result, the hypothalamus screams "You are
hungry - find food."
But whenever the stomach wall is stretched - when the stomach is full - the
cells stop producing ghrelin, and the hypothalamus responds accordingly,
turning off the appetite signal. The longer the stomach remains full, the
longer you feel satisfied and the less you are likely to eat.
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The stomach gradually empties, more slowly for the soup than the solid meal
plus water. The BBC staged an experiment for the programme 10 Things You Need
to Know About Losing Weight to test this theory. In this experiment, and in
previous experiments, participants reported feeling full for up to an
hour-and-a-half longer than their solid meal counterparts.
Although some researchers refer to appetite as "the cupcake circuit", the
mechanism behind human appetite evolved long before cupcakes were invented - at
a time when food was scarce.
As a result, we are hardwired to eat high-calorie foods, which are
unfortunately so abundant in the modern world.
Finding ways to control the appetite signal is crucial if we are to stave off
the meteoric rise in obesity. Food scientists and pharmaceutical companies
alike are on a major quest to find ways to do just that.
Appetite is one of the most researched areas of weight-loss science.
Unfortunately, the appetite system is complex, and still poorly understood.
There are probably dozens of hormones that play a role in regulating appetite.
Of those that have already been discovered, there is one that is released after
eating protein-rich meals (called PYY), one that is released by fat cells
(leptin) and several that respond to the presence of any kind of food.
But of all the hormones that make up the appetite system, it is ghrelin that
has caused the most interest. In addition to its role in sending the "stomach
empty" signal to the brain, ghrelin also promotes fat storage.
Even worse, it inhibits the breakdown of stored fat during times of weight
loss. Inject ghrelin into the bloodstream of a rat and the animal eats
insatiably - and quickly becomes obese.
In 2006, scientists at the Scripps Research Centre in the US developed a
vaccine to counteract the influence of ghrelin, in an attempt to control
appetite.
It is still undergoing clinical trials - so for now, the best and simplest way
to keep hunger at bay is to reduce your stomach's release of ghrelin: blend
your food into a healthy, voluminous soup. The best sort? Vegetable soup, as it
produces a more consistent blend and is generally lower calorie than chicken or
fish soup.
Jack Challoner is a science writer and author of the website
explaining-science.co.uk.
Below is a selection of your comments.
It has been interesting to read a scientific article on what I held to be true,
simply by feeding my family. We often have freshly made soup at home and it
seems to satisfy well for hours. Liza Moon, London
Is the same true of cereal with milk, or does milk act like water and head
straight for the old pyloric sphincter? I love cereal, not so keen on soup
though. What about porridge, I quite like that? Ben, Norwich
While the science behind the fact has probably not been quite so clearly laid
out before, the knowledge that soup makes one feel full for longer (than an
equivalent solid meal consumed with water) is not new.. It is, however, always
interesting to learn of such scientific studies as the weight-conscious amongst
us continue to wade through the ever changing (and often contradictory) expert
advice on the matter. Tom, Hong Kong
I have been routinely having soup for lunch as part of a campaign to lose
weight triggered by concerned comments from my wife and doctor. I have found it
a very effective way of eating less without feeling hungry and it has helped me
to lose around 10 kg in five months. Stephen Murray, London, UK
A lot of people who overeat do not do so because they are hungry but for other
reasons. A person can feel full to the point of sickness but will still eat
more. However, if you're going to overeat, then low calorie foods are better,
such as soup. But that still does not address the core issue which is the need
to eat in the first place. Jacquie, Yorkshire