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Locusts Help Our Understanding Of Human Obesi -

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Locusts Help Our Understanding Of Human Obesity

Reporter: Dr Maryanne Demasi

25 October 2007

Locusts are one of the major insect pests in the world - invading vast areas of the globe at
blistering speeds, demolishing crops as they go.

Amazingly, these hungry little insects can start out as shy, harmless creatures before suddenly
forming mighty armies in search of a substance essential to life - protein.

And, as Maryanne Demasi finds out, these rabid protein seekers are teaching us a lot about human
obesity.

Transcript

Narration A single swarm of locusts can eat up to 80 thousand tonnes of vegetation a day.

Professor Stephen J. Simpson They affect something like one in ten people on the planet across
continents spanning Africa, Asia, all the way through into Australia and parts of the Americas.

Narration These sometimes placid creatures can morph into swarming predators.

In environments where food is limited they only have one mission - to find their next meal.

Understanding what controls their appetite has been the hard work of Associate Professor David
Raubenheimer and Professor Stephen Simpson.

Professor Stephen J. Simpson My research into locusts began many years ago when I was interested in
working on it as a model system for studying feeding and nutrition.

Narration And surprisingly, that research on locusts has lead to some intriguing theories as to why
so many humans may be overweight.

Professor Simpson believes that while the mechanism that controls our appetite is complex, it is
partly driven by the proportion of protein in our diet.

Professor Stephen J. Simpson It's not only an energy, as of course is carbohydrate and fat, but it
contains nitrogen and it's nitrogen that is used to build new body tissues. You can't get that
nitrogen from carbohydrate and fat, so protein really does have a very important part to play in
our nutrition.

Narration He has already tested this theory in locusts by giving them meals with different
proportions of protein.

Professor Stephen J. Simpson The one here is high in protein and low in carbohydrate, and this one
here is high in carbohydrate and low in protein.

Narration By tasting the food through their foot pads protein deprived locusts instinctively
favoured the high protein meals.

Professor Stephen J. Simpson This locust will precisely balance its intake of the two sorts of food
to achieve a particular amount and ratio of the two nutrients - protein and carbohydrate.

Narration What's even more amazing is the locusts eating high protein meals seemed to be fuller
faster than those eating low protein meals.

Professor Simpson showed locusts keep eating until they reach a certain level of protein - a
"protein target".

Professor Stephen J. Simpson Now if you take those animals and you restrict them to a diet which
contains a higher than that intake target level of carbohydrate relative to protein, then what the
locust does is it keeps eating until it gets the same amount of protein, its target level, but in
so doing has grossly over consumed carbohydrate. It leads to the animal becoming obese - sounds
peculiar but the locust is actually obese, it's fat on the inside.

Narration And it's not only locusts that exhibit this behaviour. Spiders, fish and a number of
mammal species regulate their protein intake more strongly than their carbohydrate or fat intake.

So could this theory be applied to humans? Might we also overeat if we stick to diets with a low
proportion of protein? A small study performed by Professor Simpson's group suggests this could be
true.

Professor Stephen J. Simpson What we found was that those individuals that were put on the low per
cent of protein foods continued to eat substantially more non-protein energy but maintained their
absolute protein intake very similar to what they had done previously when they were self
selecting.

If you have a lower proportion of protein in the diet, you have to eat more of it to gain the same
amount of protein.

Dr Maryanne DemasiTo replace the protein in a piece of fish like this with a food that's low in
protein and high in carbs, like potatoes, I'd have to eat this many fries. Now it doesn't look like
much but that's 1600 extra kilojoules that I don't need.

Narration Now, nutritional scientists like Alison Gosby are embarking on larger trials to confirm
these findings.

The proportion of protein compared to carbs and fat will be manipulated and put to the test.
Certain foods like carrot cake will be some of the test products in the trial.

Dr Maryanne DemasiThe key to the human trials is to make sure the subjects don't know which diet
they're on and I have three carrot cakes here each with different proportions of protein 10, 15 and
25 per cent. Now I've tasted all three of them and I can't tell the difference.

The trials, which are due to start later this year, will help clarify whether humans will also keep
eating until they reach a protein target.

Interestingly, since the 1960s, the relative proportion of protein in American diets has fallen by
1.5% - and a similar change may have occurred here.

Professor Stephen J. Simpson What's happened in recent years is that processed foods have become
much more prevalent, much more affordable and much more relied upon in the human diet and they are
typically relatively lower in their percentage of protein - they have more fat and carbohydrate in
them.

Narration But understanding what controls our appetite has far bigger implications than just being
able to control our waistlines.

Professor Stephen J. Simpson As you start to put on weight you start to suffer a series of
metabolic disturbances. You become relatively resistant to insulin. You start on the road towards
type two diabetes, metabolic syndrome, as it's called, and related disorders.

Narration Ultimately, in diseases like metabolic syndrome, the body begins to burn protein, even
when there are adequate carbohydrates.

Professor Stephen J. Simpson That's going to increase your protein needs, so if you stay on your
same diet, you now have to eat even more to get to your new increased requirement for protein which
will exacerbate the problem and it snowballs. So, what we're postulating here is, if you like, a
vicious cycle to morbid obesity.

Narration Who would have thought, research into what drives the appetite of plagues of locusts,
might one day help save western nations from an obesity epidemic.

Narration Ultimately, in diseases like metabolic syndrome, the body begins to burn protein, even
when there are adequate carbohydrates.

Professor Stephen J. Simpson That's going to increase your protein needs, so if you stay on your
same diet, you now have to eat even more to get to your new increased requirement for protein which
will exacerbate the problem and it snowballs. So, what we're postulating here is, if you like, a
vicious cycle to morbid obesity.

Narration Who would have thought, research into what drives the appetite of plagues of locusts,
might one day help save western nations from an obesity epidemic.