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

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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.

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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.