The Hypothalamus and the Adiposity Signal  
Key References  


What is obesity and why is it bad?

What does being obese mean and why is it so unhealthy?

Obesity is a major problem in today’s society, with over 1 billion people being classed as obese worldwide costing the British NHS alone £1 billion annually. Obesity is an increase in adipose tissue, so much so that it can cause a variety of adverse health consequences. These include many emotional and physical problems, for example, emotional problems include feelings of inferiority, low self esteem, and often in children, bullying from classmates. Physical problems include high blood pressure, heart disease, some cancers and Type 2 Diabetes Mellitus (T2DM) which is where the body no longer responds to insulin and so cannot control its blood sugar levels. By 2025 300 million people are expected to suffer from obesity related diabetes, this figure is double that of 1998.

How is obesity measured?

There are many methods of measuring body fat but the most popular method is using the Body Mass Index (BMI) which measures the relationship between your weight and height. A measure of 30 or more puts you in the category of obese. For more information about the BMI test and to measure your own BMI please click here. BMI may be the most popular method but it does have its disadvantages eg. people carrying a lot of muscle will not receive an accurate BMI measure due to muscle being heavier than fat. There are other more complicated measures of fat but BMI is still the most popular method used due to it being so simple.

What drugs have been used to combat obesity?

The first anti obesity drug was developed at the end of the 1950’s.  This was Phentermine, related to amphetamines. The drug worked by stimulating the release of catecholamines thereby inducing the ‘fight or flight’ response and a loss of appetite.  This became available on the market in the early 1970’s as phentermine hydrochloride. This drug is now a controlled substance as it has been found to be highly addictive and so can only be taken for short periods of time. This drug has also been found to affect the heart causing side effects such as valve problems and hypertension. Phentermine can also cause insomnia so can only be taken at certain times of the day.

Fenfluramine was another anti obesity drug which acted to increase central serotonin levels and caused a sensation of fullness and therefore a loss of appetite. This drug was withdrawn in 1997 after reports of hypertension and other problems concerning the valves of the heart. How exactly these drugs caused a loss of appetite is not known and is probably due to a range of factors. Fenfluramine was also used in combination with Phentermine and so called called 'Fen-Phen'. 

The other anti obesity drug available is Xenical. This drug acts peripherally where it inhibits an enzyme involved in the breakdown of fat causing fatty acids to be excreted rather than digested. Side effects of this drug include bowel movement problems and the excretion of essential vitamins. The amount of weight lost by taking Xenical varies and it can only be taken for short periods of time. For more information on how Xenical works please visit the Xenical home page by clicking here.

So there has been 50 years of research into obesity and yet very few drugs have been licensed. This highlights the complicated neural system that controls appetite. Current knowledge regarding appetite and the control of food intake all stem from pioneering experiments carried out many years ago, and without which, the research into obesity could not have happened. These experiments involved establishing the role of the hypothalamus in appetite regulation and the role of peripheral signals in signalling energy levels. Please click the link below to start the discussion into how the current understanding of appetite regulation came about.

Genetics of Obesity: genes are the bullet - but you pull the trigger

Many genes are thought to be involved in appetite and obesity but very recently, a gene called the FTO gene, on chromosome 16 was found to confer a predisposition to obesity (Frayling et al, 2007). It has been known for some time that genetics play a part in obesity but this study confirms this. It was reported that 16% of the population carry this gene and if an individual carries both copies of this gene they are 70% more likely to be 3kg heavier than average. This discovery emphasises that obesity can not just stem from a poor diet and lack of exercise, but actually, that genetics does play its part. This study does not mean that this gene is solely responsible for obesity and there are likely to be many more genes involved. What this study does do is highlight the impact that genetics can play in the development of obesity and people that are discovered to have this gene can do something about it and take responsibility for their own body, after all, you can change your lifestyle but you can't change your genes. To access the research behind this story please see the Key References.

The hypothalamus and the adiposity signal

Key References

International Obesity Taskforce. A world wide organisation that is researching obesity and devising strategies on how to prevent the problem of obesity becoming bigger. Also gives excellent information on the obesity related disorders and the increasing problem of obesity in children

Frayling et al. 2007. A common variant in the FTO gene is associated with Body Mass Index and predisposes to childhood and adult obesity. Sciencexpress. pg 1-5



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