We're fatter than ever, but is it our fault?

Kate Roach

January 2003

What makes one person fat and another thin? Since we all eat, most of us have an opinion on the subject. For many, obesity is simply a matter of poor self-control, a personal failing, one that the cash-hungry diet industry makes great play of. But, another explanation altogether is gaining ground in the scientific community. Obesity is a complex disorder of appetite regulation and energy metabolism that is controlled by biological factors. In recent years the application of genetics to understand and treat the causes of body-weight regulation has made great progress.

Small is beautiful and life is large

In our media culture, small is beautiful. Watch TV or browse a couple of popular mags and it's hard to find anyone who is heavier than the average beanpole. Many fashion models have long been considered clinically underweight, and a new study finds the same is true for centrefold models appearing in Playboy magazine, a setting in which you might expect to find a little more flesh. It turns out that seven out of ten centrefold models appearing over the last 20 years are clinically underweight. And that, it seems, is our ideal. Even so, there has been a huge surge in the numbers of people who are overweight in recent years.

In England and Wales the prevalence of obesity in adults increased from 6% in men and 8% in women in 1980 to 17% in men and 20% in women in 1997. All other Western states show similar increases, and the trend is also beginning to affect the whole of South East Asia, the United Arab Emirates and certain Pacific regions. Worldwide there are now as many people who are obese as there are people suffering from hunger. Obesity has become a global public health problem – or 'globesity' as the World Health Organisation have called it. In the World Health Report of 2002, obesity is listed as one of the top 10 human health risks.

What is obesity and why does it matter?

In clinical practice, obesity is calculated by a formula called the body mass index (BMI). To work out your BMI divide your weight in kilograms by the square of your height in metres (the square is a number multiplied by itself). If the answer is 30 or above you are obese, above 25 and you're merely overweight. The healthiest range lies between 18.5-24.9 and if you fall under 18.5 then you are considered underweight (along with most models).

So, what does a of bit extra flab matter anyway? Obesity can cause or exacerbate a range of health problems. For reasons that are not fully understood, it is associated with the development of diabetes, heart disease, increased blood pressure, sleep disturbance, certain forms of cancer and arthritis. The side effects of being obese are not restricted solely to health risks either; those who suffer are often stigmatised both socially and in the workplace. The modern Western premium on leanness binds too many individuals into a lifelong, often fruitless struggle to achieve that dream physique.

What makes some people fat and some thin?

One view has it that obesity is just a sign of a weak will. This view is undoubtedly advanced by the diet industry, who have a financial interest in promoting the idea that a few simple remedies are the only things that separate us from our ideal bodies. The remedies can be obtained from an author or company for a fee. although losing weight does improve the health of overweight or obese people, what the diet industry neglects to say is that diets have a very poor success rate. More than 90% of individuals who lose weight by dieting eventually return to their original weight.

The alternative view emerging from the laboratory is that body weight (or more precisely, body fat) is under powerful physiological control. Changes in weight in either direction generate a counter-response in the body that resists the change and re-sets the appetite to return the body to its original weight. Implicit in this view is the notion that biological factors determine the state of our bodies, be they lean or be they fat, and that this state is then maintained. Compelling evidence for this view comes from the fact that our bodies are hugely effective at maintaining a set weight over a lifetime.

Over the course of a decade, the average person gains a small amount of weight. Everyone does: from your teens to your 50s or 60s, body size is always on the up. In one decade an adult will consume about 10 million kilocalories. To account for the small change of weight that is usually observed, food intake must match energy output to within 0.17% per decade. This is an extraordinary level of precision when you think about the way most of us eat. We have different food at different times every day and most of us don't stick to a set number of calories per day. This suggests a potent physiological system is at work.

In recent years, weight regulation has received considerable interest from a growing number of scientists. The picture of obesity that emerges is not of a single disorder, but several that have different causes. Body weight is controlled by a fascinating and complex system of hormones that convey information about fat stores to brain pathways that control eating and energy output. Individual variability in the efficiency of these systems partly explains why some of us only have to look at a cream cake to gain pounds while others can stuff them down all day long with no effect.

Fat genes?

Fatness runs in families, it's in the blood. But, before you jump for joy and blame it all on your genes, scientists are careful to point out that genetic influences on bodyweight operate through susceptibility genes. In other words, there are genes that can increase the risk of obesity, but are not essential for the condition and can't cause it on their own. Nonetheless, recent studies do indicate that genetic factors account for quite a substantial proportion of the individual variation in fatness. Family pedigrees and twin studies show that our genes account for 50-90% of our body fat profiles.

These results are hard to reconcile with the fact that there are marked differences in the incidence of obesity that correspond to socio-economic groups. Obesity is largely a disorder of wealthy post-industrial societies, in which energy rich foods are readily available while the need for physical activity is reduced. An observation that, at first glance, supports a cultural, rather than a biological, cause for fatness. But, lifestyle or 'nurture' operates on an underlying pool of genes or 'nature'. Much research now works on this premise. Genes put some people more at risk of obesity than others when rich foods and little exercise are added into the equation. The hope is to identify the genes so that clinical efforts to prevent obesity can be focussed on recognition and counselling of susceptible individuals.

Can't we exercise the flab away?

A few years ago, it seemed that all we needed to do was get down to the gym and work off the flab. Indeed, the percentage of energy we burn in physical activity is a substantial amount of the whole, varying from 20% to 50%. It is a logical step to suppose that upping exercise will bite into the reserves of energy that are stored as fat and keep us trim. But, what is the evidence?

In developed countries there is a relationship between low levels of physical activity and obesity. One American study found that television viewing patterns were closely related to obesity levels in children. The relative risk of obesity is 5.3 times higher for children who watch television for 5 hours or more each day compared with those children who watch 2 hours or less. Similarly, in the UK, there is a close relationship between measures of physical activity, like car usage and television viewing, and the incidence of obesity. What these studies show us is that very low levels of physical exertion make us fatter. But, can high levels of exercise make us thinner?

Yes, exercise certainly can help keep the weight down, but only to some extent. For many of us, one of the most desirable effects of regular workouts doesn't involve weight loss at all. Muscle toning can change body shape and most of us prefer to have a pert bum and tight thighs whatever size we are. There are, of course, other health benefits to the physically active, like a healthy heart and a strong, supple body. An added bonus is the feel good factor from hormones called endorphins released in the brain during heavy physical exertion.

The big 'but' comes when you lay off the workouts. Sure as eggs is eggs, your body will slowly creep back to its original state. This is a real trap that worries health professionals and locks some of us into unhealthy patterns of exercise. The fact that we all gain weight as we age makes the situation worse still. Much like running on the spot, an obsession with the skinny ideal leads some people to tackle ever more intense exercise regimes just to maintain the way they already are. Exercise addiction is one obvious side effect of such a trap. In reality, the kind of exercise that does most good for body (and mind) is a far gentler affair. Regular daily walks of half an hour or more are recommended for a healthy heart. And, if you don't have the time, it's OK: two or three 10-minute walks will still help.

While it seems that a lack of exercise can make us fat, lots of exercise is not so effective at keeping us skinny. This is the paradox that scientists are beginning to unpick by looking at the intricate systems that regulate weight in the body. What emerges is the realisation that weight is only partly set by lifestyle.

The body's own weight regulator

The hormone systems that regulate bodyweight are genetically determined and are the focus of intense scientific scrutiny. Six years ago a hormone called leptin was identified as a key element of this system. Leptin is produced in fat tissue and feeds back information about the nutritional status of the body to areas of the brain that control food desire and energy expenditure. A decrease in body fat leads to a decrease in leptin levels and the brain responds by upping food intake. Conversely, an increase in body fat increases leptin concentrations and the brain shrinks the appetite.

The degree of leptin sensitivity, it turns out, varies from person to person. And, studies so far seem to point to the fact that some obese people are relatively insensitive to the hormone. In this situation the brain doesn't recognise rising leptin levels and is fooled into thinking that the body is in a state of constant starvation. This situation leads to a continuous niggling background hunger that is impossible to satisfy. Physicians and dieticians who warn of health risks and assume that patients can just change their habits and get slim should take note.

The discovery of leptin has spurred an explosion of on-going research on related hormones and genes. The identity of several of these genes is now known and in these instances the evidence that obesity is not straightforward gluttony is overwhelming. In years to come, it's almost inevitable that research will throw up an anti-fat pill – the pharmaceuticals industry is already falling over itself to do so. But, any drug designed to interact with the hormone systems that control body weight is likely to have much more wide-ranging effects on the body than just weight loss.

It's likely that there won't be one, but several, drug therapies for obesity in the future. As the biological systems that control our fat load come into focus, scientists are likely to find a whole string of hormones like leptin that interact with each other to keep body weight within narrow limits. Different drugs will be needed to treat malfunction in different parts of the system. But drugs are a last ditch solution and are only appropriate where there is a definite or extreme health risk. For those of us who just feel a little bit flabby it's back to the old tried and tested healthy eating and exercise. But, don't expect to change your shape dramatically – your body probably won't let you.

You might like to check out other features on our food site, including fat virus, breaking the obesity spiral and fat suckers – going for liposuction.

Find out more

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Organisations

Eating Disorders Association
Provides information, advice and publications on all aspects of eating disorders including anorexia nervosa, bulimia nervosa, binge eating and related eating disorders.

Keep Fit Association
Teachers from the Keep Fit Association teach safe and effective movement, exercise and dance classes for people of all ages and abilities.

Overeaters Anonymous
Fellowship aimed at men and women whose lives have been affected by compulsive behaviour around food, such as overeating, anorexia and bulimia.

Websites

The Association for the Study of Obesity
www.aso.org.uk
Dedicated to the understanding and treatment of obesity, providing a focus for obesity research and treatment in the UK. The website contains various factsheets on obesity.

British Nutrition Foundation
www.nutrition.org.uk
Provides information on current nutrition issues, nutritional advice and information for all stages of life – from pregnancy to pre-school children and adolescence to older adults.

Channel 4 Health
www.channel4.com/health/microsites/F/
fat_season/index.html
Check out this site for discussions on fat and whether you can catch it in a virus. Also offers advice on losing weight and help if you just hate your body.

The Fit Map
www.thefitmap.com
UK health, fitness and exercise portal with articles about healthy living, interactive tools, and details of health clubs and gyms throughout the UK.

Hormone Breakthrough in Obesity
http://news.bbc.co.uk/1/hi/health/2175739.stm
BBC News article describing how some severely obese people have benefited from being treated with injections of leptin.

Obesity-Online
www.obesity-online.com
A multi-disciplinary forum for research and treatment of massive obesity, including plastics, psychiatry, endocrinology, nutrition, nursing, dietetics and allied health. Contains information about obesity, and the health risks.

Sport England (UK)
www.sportengland.org
Aims to get more people involved in sport, provide more places to play sport and encourage higher standards of performance. Features a sports gateway database of local sporting contacts and sports facilities.

Weight Watchers
www.weightwatchers.co.uk
One of the most sensible dieting organisations. The site gives information to those seeking weight loss advice as well as explaining the weight loss services that the company provides.

The World Health Organisation
www.who.int/en/
This site gives details of the global incidence of obesity and starvation and outlines strategies for prevention. Search on 'obesity' or 'nutrition' to find in-depth reports.

Books

The Exercise Bible by Joanna Hall (Kyle Cathie, 2002) £19.99
A guide to exercise and physical activity with information on all types of exercise for a range of fitness levels and body shapes.

Just the Weigh You Are: How to be fit and healthy, whatever your size by Steven Jonas and Linda Konner (Houghton Mifflin, 2001) $22.95
Provides a plan for a healthy lifestyle, regardless of weight. Outlines areas such as self-acceptance, nutrition, exercise and stress management.

The Optimum Nutrition Bible by Patrick Holford (Piatkus Books, 1998) £12.99
The author describes how a well-balanced diet can result in a healthy body, with increased energy and fitness.

If you have any questions on weight problems or slimming for our trained advisors, go to just ask.

For further information about organisations, websites and reading, go to our get help directory on the food site.

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