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Weighing scales

The Truth About Obesity

Chris Bavin discovers what science can tell us about why 2/3 of us are overweight - and how we can fight it.

About the programme

BBC One looks at the latest scientific research on obesity with The Truth About Obesity. While a fast food culture and our own genes have led to our expanding waistlines, small changes can help us all maximize the chances of keeping trim. The programme reveals how a simple piece of string can tell you how healthy you are, when the best time to eat is, and how our gut bacteria may keep us skinny - and we meet cutting edge researchers who hope to solve obesity with a simple injection.

Read more about the series on the BBC's programmes pages  

Discover the range of qualifications and modules from the OU related to this programme:

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Copyright: BBC

The challenge of obesity

Obesity is an increasingly common problem because, for many people, modern living involves eating excessive amounts of low cost, high-calorie food and spending a lot of time sitting down at desks, on sofas or in cars.


The Challenge of Obesity

Obesity is an increasingly common problem because, for many people, modern living involves eating excessive amounts of low cost, high-calorie food and spending a lot of time sitting down.

A diagram describing the causes of obesity.

There are many reasons why the rate of obesity and overweight individuals has increased (as outlined in the diagram below from the Nuffield Trust), one of which is our environment, and in particular how we get from A to B. In the last 20 years the cost of buying a car has reduced in relative terms, and the number of cars in Britain has increased by 10 million. During this same time period the rate of obesity in adults increased by 10%. In 2014 62% of adults in England were classified as overweight or obese, compared to 53% 20 years earlier. More than two-thirds of men and almost six in 10 women are overweight or obese.


Being overweight or obese can negatively impact your physical health, by leading to diabetes, heart disease, some types of cancer or even stroke. It can also impact on your mental health leading to low self-esteem, lack of confidence and depression. There are many ways in which a person's health in relation to their weight can be classified, but the most widely used method in the NHS is body mass index (BMI). BMI is a measure of whether you're a healthy weight for your height. You can use the BMI healthy weight calculator  to work out your score.

For most adults, a BMI of:

  • 18.5 to 24.9 means you're a healthy weight
  • 25 to 29.9 means you're overweight
  • 30 to 39.9 means you're obese
  • 40 or above means you're severely obese

Tip: Do you have a length of string?

Currently, most doctors use BMI, which measures weight against height, to calculate whether a patient is at risk of disease due to obesity, but focusing solely on BMI measures can lead to  missing ‘apple shaped’ people who are carrying worrying levels of excess weight around their middle. A recent UK study suggests that a piece of string is a more accurate measure of dangerous weight gain than the Body Mass Index (BMI). To do the string test, get a length of string and measure your height with the string, then fold it in half and check that it can fit comfortably round your waist. If the string doesn’t meet in the middle this is an indication that you are carrying too much body fat.

Generally, men with a waist circumference of 94cm (37in) or more and women with a waist circumference of 80cm (about 31.5in) or more are more likely to develop obesity-related health problems.

So what can you do?

If it's been a long time since you did any exercise, you should check out the NHS Choices Couch to 5K running plan . It consists of podcasts delivered over the course of nine weeks and has been specifically designed for absolute beginners. To begin with, you start running for short periods of time, and as the plan progresses, gradually increase the amount. At the end of the nine weeks, you should be able to run for 30 minutes non-stop, which for most people is around five kilometres (3.1 miles).

Meet the expert

A photograph of Doctor Joan Simons
Joan SimonsAssociate Dean, Faculty of Wellbeing, Education and Language StudiesVIEW FULL PROFILE
A photograph of Doctor Joan Simons
Joan SimonsAssociate Dean, Faculty of Wellbeing, Education and Language Studies

Dr Joan Simons is Associate Dean Teaching Excellence in the Faculty of Wellbeing, Education and Language Studies and one of the Directors of the Centre for Children's Wellbeing (CCW), based at The Open University.

Her background is in Child Health, adult education, management, leadership and coaching as well as adult and children's nursing, burns nursing, community health and pain management research.  Joan has held a number of posts in nurse education and worked as a research fellow at the Institute of Child Health.

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