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Body weight: what causes hunger and why is it important to maintain a low body weight?

Everyone gets hungry from time to time. And some people get hungry more often than others. In this article I hope to explain why people get hungry, from a scientific point of view.

The brain is composed of lots of different areas, involved in lots of different tasks. One such area is called the hypothalamus. This area details with satiety (the feeling of having eaten enough but not too much). The exact signal from the hypothalamus will depend on a number of different natural body chemicals (discussed below) that interact with it.

Leptin is a key biological measure of hunger. Leptin is a chemical that circulates in the blood stream. The amount of leptin in the blood stream is proportional to the amount of fat the body has. Leptin acts to oppose hunger. Unhelpfully, the leptin signalling system is faulty in fat people. Hence, fat people may feel hungry even though their energy supplies (amount of fat) is high.

Interesting point: There is medical condition in which the body does not produce enough leptin. As leptin inhibits hunger, a lack of leptin will result in the feeling of hunger all the time. Although leptin deficiency can cause obesity (because the people tend to over eat) most obese people are not leptin deficient. 

Insulin is another chemical that tells the body how high the energy levels are. Insulin, unlike leptin, is a measure of sugar (carbohydrate) stores in the body. Although insulin acts to promote a feeling of fullness in healthy, normal weight individuals, its signal is defective in obese people. Hence, like leptin, insulin is not a good way of telling fat people they do not need to eat.

Ghrelin is a chemical that acts in the opposite way to insulin and leptin. Ghrelin is a chemical released by the stomach when it is empty. It acts to signal hunger. Another key chemical that acts to stimulate hunger is neuropeptide Y. This chemical is released following exercise, energy loss or fasting.

We have already explained that the biological systems are faulty in fat people. But what drives healthy people to eat when they are not hungry? A big factor to consider is social pressure. When at a party, or when having dinner with friends, there may be a tendency to eat to “fit in”. If everyone around you is eating, and you are not, it may feel uncomfortable. Another reason for eating when not hungry is the known reward from eating the food on offer. If someone offers you a lemon, for example, and you don’t like sour foods, you won’t be tempted to eat it. However, if someone offers you a piece of chocolate, and you like sweet foods, your body may tell you to eat the food, as it is a pleasurable experience.

Summary so far:

Causes hungerGhrelin, Neuropeptide Y
Inhibits hungerInsulin, Leptin


Why is it important to stay a healthy weight?

Last week we discussed why people become fat and this week we discussed the biology of hunger. Why is it so important to maintain a healthy body weight though? The answer lies in the vast array of medical conditions associated with obesity.

Obese people are

  • 3 times more likely to have a stroke
  • 2 times more likely to suffer from a heart attack
  • 2-3 times more likely to develop diabetes
  • 3 times more likely to suffer from high blood pressure
  • 12 times more likely to suffer from osteoporosis

There is also an increased risk of reduced fertility, breathing problems and several cancers.

What therapies for obesity are there?

The truth is, all diets will work if they are adhered to. BUT sticking to a diet is tough. In fact, more than 80% of people who go on a diet regain the weight they lost. Unfortunately, though, there is no magic pill. In the past, drugs have been developed which help reduce appetite (and hence hunger) but these have had an array of bad side effects such as depression, and so are no longer available.

Surgical options such as stomach stapling or gastric bands are often successful. They primarily work by reducing the amount of food the stomach can physically hold (hence, people eat less). They may also work by reducing the length of the digestive tract, thereby reducing the amount of food the body takes up. However, only certain people are eligible for free surgery on the NHS. If you are interested to know if you are eligible, it is best to speak to a professional health care advisor.


Our consultants at the London Gastroenterology centre can provide you with expert information on digestive health and body weight. They also offer endoscopy and colonoscopy services. Why not contact us to find out more?

We are available to see patients daily.

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