The science of nutrition and healthy eating
The science of nutrition and healthy eating

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The science of nutrition and healthy eating

4.8 A drastic solution: bariatric surgery

There are numerous reasons for the ‘obesity epidemic’ that have all come together at a similar time. In countries where incomes have risen, there has been a marked shift from a diet based on cereals and tubers (mostly carbohydrate) to one based on fats and sugars and the inclusion of more meat.

In higher-income countries, there is a much wider range of food than ever before to tempt consumers into eating more. There are many more places to eat or to buy ready-made meals, and portion sizes are larger. In addition, people have become less active and therefore need fewer calories to maintain a steady weight. The entertainment provided by electronic devices has contributed to this. So, when you have finished studying this week, leave your computer for a while and go for a walk or do some exercise!

When we eat, normally our stomach expands from about the size of a small apple to about two litres – that is a 40-fold increase. When the stomach is empty, the hormone ghrelin is released into the blood, making you feel hungry. When the stomach is full, ghrelin secretion stops (see Ghrelin [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] ). The resulting fall in ghrelin level in the blood is detected by the brain. This may be one of the factors that make us feel full after a meal. In obese people this, and other means of appetite suppression, do not seem to work in the normal way. So they tend to eat more than thinner people.

Once people have become obese, getting their weight back down to within the normal limits is incredibly difficult, despite the enormous range of diets and dietary advice. The drastic solution for some people, when all else fails, is a gastric bypass operation.

This reduces the size of the stomach to about one-tenth of its normal size, so that it has a volume of only a few tablespoons. You can see the operation being carried out in the following video.

Download this video clip.Video player: snhe_1_week_6_vid_5.mp4
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Transcript

MICHAEL MOSLEY (VOICEOVER)
I’m here at Charing Cross Hospital to watch Bob’s surgery.
[MONITORS BEEPING] His surgeon is leading bariatric consultant Mr Ahmed Ahmed.
AHMED AHMED
So I’ve gone through the skin, and the yellow stuff there is fat. We’ll go through the fat and then through the abdominal wall muscle there. First quick peek inside, we’re going to see – all the yellow stuff here you see is fat.
MICHAEL MOSLEY (VOICEOVER)
The first stage of the operation is to shrink the size of the stomach.
AHMED AHMED
That little pale pink organ coming up, that’s your stomach right there.
MICHAEL MOSLEY
And you’re essentially going to reduce the size of that, are you?
AHMED AHMED
Yes, absolutely.
MICHAEL MOSLEY
By what sort of amount?
AHMED AHMED
We’ll probably make it about a tenth of its normal size.
MICHAEL MOSLEY
Ten per cent of what it is at the moment. Wow, that’s quite radical, isn’t it?
AHMED AHMED
Yes. The total volume’s going to be about 20 mls, which is about three or four tablespoons.
MICHAEL MOSLEY
So 90 per cent of the stomach will just be kind of left there inactive.
AHMED AHMED
Exactly. It’s still going to have its blood supply, and it’s still going to make gastric juices, but it’ll never see food again.
MICHAEL MOSLEY (VOICEOVER)
And, surprisingly enough, it’s not just Bob’s stomach they’re affecting.
MICHAEL MOSLEY
Now, you might think that just by reducing the size of his stomach, that’s how he’s going to sort out Bob’s problems, because smaller stomach, you eat less – it’s sort of straightforward. But actually, the mechanism by which it works is completely different. And it’s only relatively recently that they’ve discovered why doing gastric bypass is so effective.
AHMED AHMED
The modern thinking actually is that by making a smaller stomach, you’re actually inducing the changes in various chemical messengers, which in turn affect hunger levels and fullness levels, which in turn cause the weight loss.
INSTRUCTOR
Mm.
MICHAEL MOSLEY (VOICEOVER)
So as well as reducing the size of Bob’s stomach, the point of the operation is to change the levels of certain gut hormones. These chemical messengers are released by the gut in response to food and tell the brain when to eat or stop eating. One of the hormones, ghrelin, makes you feel hungry.
AHMED AHMED
We think that ghrelin is actually being produced from this part of the stomach, up here, this fundus. This is called the fundus of the stomach. And this is where all the cells that produce ghrelin are sort of based. Now, what we think we’re doing is we’re actually separating that part of the stomach completely from ever seeing food. So the food will never touch those cells that make the ghrelin.
MICHAEL MOSLEY (VOICEOVER)
Once they’re isolated, the ghrelin cells no longer function normally.
Hormone production will be reduced, and Bob should feel less hungry.
MICHAEL MOSLEY
Extraordinary, isn’t it? That little area of the stomach could be responsible for how hungry you feel.
MICHAEL MOSLEY (VOICEOVER):
The next stage of the operation is to reattach Bob’s smaller stomach back to his intestine.
AHMED AHMED
Good. There you go, thanks.
MICHAEL MOSLEY (VOICEOVER)
From now on, it will be right next to the part of his intestine that produces the gut hormone PYY that makes him feel full.
MICHAEL MOSLEY
How long does food normally take to get there?
AHMED AHMED
At this point, only about 20, 30 minutes, I would imagine.
MICHAEL MOSLEY
Right. So instead of taking, say, 20 minutes for your brain to get the message ‘You’re full; stop eating’, it might take what, five minutes?
AHMED AHMED
Yeah, about five minutes.
End transcript
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Weight loss after a gastric bypass operation appears to be caused not only by the small size of the stomach, which physically reduces the amount that can be eaten. It is also caused by changes in the amounts of some of the gut hormones. The cells of the stomach that produce ghrelin are completely cut off from the food and so do not function normally.

The new small stomach is attached next to some of the cells that produce PYY, which is a polypeptide produced in the small intestine which reduces the feeling of hunger. Its production conveys the information to the brain that food has been eaten. This process normally takes about 20 minutes. But, after a gastric bypass operation, it occurs within about 5 minutes of eating, causing the patient to feel full much more quickly.

Bob, whose operation is shown in the video, lost nearly 20 kg in the first six weeks after the operation. However, gastric bypass surgery is a major operation and must never be the first option for an obese person.

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