So, how can we assess the views with which we are bombarded? We have to start by separating fact from opinion, then assess the reasonableness of interpretation of the evidence against scientific probability. Fact is something that is proven, can be reproduced and is consistent with other facts; opinion relies on a belief by the person making the proposition rather than proof of the proposal. We should ignore presentational gimmicks and slogans, and look for the core message. We have to assess the credibility and bias of the messenger along with his message. This is the concept behind the current philosophy of evidence-based medicine, or EBM. This is based on evaluation of the sources of information and has much to recommend it. Unfortunately, it perpetuates the Myth that it is possible to argue from the general to the particular rather than the other way round and could, if misapplied, lead to the practice of healthcare by protocol rather than the application of knowledge and judgement. Because a particular treatment is successful in the majority of patients, it does not necessarily imply that it is the best course of action in all patients.
In the preparation of this book, we have asked the authors to present what is known or is generally accepted as factual and what they consider probable and to separate it from that which is improbable or irrational. Scientists are aware that many of the commonly accepted beliefs in healthcare are based on the misconceptions that need to be exposed to scientific scrutiny. For this purpose we have asked our panel of experts, to write ‘that which they know’.
At the end of the day, we must remember that, in the world of healthcare, things are getting better. The fact that we are living longer, healthier lives suggests that there cannot be anything terribly wrong with the air we breathe, the food we eat or the way we live. We must remember this in spite of the blandishments, threats, warnings and various campaigns by governments to make us eat this diet or that, to forgo a familiar habit or to exercise ourselves until we drop. It is a sobering thought, first expressed by John Locke in 1689 in his treatise A Letter Concerning Toleration: ‘No man can be forced to be healthful, whether he will or no.’ In a free society, individuals must judge for themselves what information they choose to heed and what they ignore. Whether they should be made to feel guilty for ignoring the evidence is a matter for debate.
BY VINCENT MARKS
‘Corpulence in America is regarded, along with narcotic addiction, as something wicked, and I shall not be surprised if soon we have a prohibition against it in the name of national security.’
ASTWOOD, 1962
THE MYTH: Obesity is caused by eating the ‘wrong kinds of food.
THE FACT: Obesity in humans is caused by eating too much.
Obesity has always been with us but, whereas in the past it was the prerogative of the rich, it is now the scourge of the poor. We are told by numerous newspapers articles, life-insurance companies’ publicity material and governmental publications that it has reached ‘epidemic proportions’. It is blamed on ‘junk food’, but the real reason for its increasing incidence is far more complicated.
Currently, obesity is labelled among the commonest causes of death worldwide and not only in the developed and affluent West – but the evidence is not there. The illnesses to which obesity predispose, such as diabetes, coronary heart disease and hypertension, are undoubtedly a major cause of death in the developed world but uncomplicated obesity is rarely so. It is nevertheless an important risk factor that can be theoretically, and in some cases practically, reduced
Obesity develops when energy intake exceeds energy expenditure. It will be maintained until this balance is reversed. The supply of food as well as the type of food is involved from the start. Until recently, food was plentiful only for the rich – the poor often lived at subsistence level, although they frequently performed more manual work over longer periods. Although now looked upon as a hazard to health, the ability to become fat in times when food was not constantly available could have had an important survival value in the past. The ability to get fat was a status symbol in deprived communities and those subject to periodic famines. It is still so in some parts of the world. People who were fat at the start of a famine would have a better chance of surviving than those who were thin.
However, being fat has become a cosmetic problem for the fashion-conscious over the past half-century or so, and it was the social desirability of being thin that produced the huge diet and weight-reduction industry – not the impact of obesity on health. This has now changed – at least in part – as the medical problems attributable to overweight and obesity have become increasing well recognised. Should we worry about getting fat? Yes, because in the long term overweight predisposes us to a variety of illnesses and a shortened life expectancy. Even though some very fat people live their full three score years and ten and more, most do not.
A lot depends on what you call overweight, fat and obese. They are not the same thing, though often loosely used as such, and definitions change. Until about twenty years or so ago the term overweight was applied to those who exceeded a hypothetical ideal weight derived from survival figures obtained by the Metropolitan Life Assurance Company, whose tables adorned most commercial weighing scales found in stations and other public places, but are now long since gone. A new way of expressing fatness that, made for ease of communication in epidemiological studies, became popular in the 1980s. Called the body-mass index, or BMI, it relates weight to height through a formula devised in the nineteenth century by a Belgian epidemiologist, Adolph Quetelet. A person’s BMI is their weight in kilograms divided by the square of their height in metres. Although it has major shortcomings – it says nothing about the proportion of bodyweight that is fat, which is the real test of obesity – the BMI has become the recognised standard of measurement for fatness, although it does not relate to morbidity as well as other indicators, such as waist-to-hip ratio or even just waist measurement.
Most healthy young adults have a BMI of 20–25. Those with a BMI less than 20 are currently classified as underweight and those with a BMI of 25–30 as overweight or plump. A BMI of over 30 is arbitrarily classified as indicating obesity. Insurance company statistics and more recently large epidemiological studies reveal that people with BMIs under 20 or over 30 are poorer life risks than those with BMIs between 20 and 30. As people get older, there is a population shift from the lower to the upper half of this range. Plumpness in late middle and old age – BMIs of 25–30, especially in women – is not the health risk that it is in young and middle-aged adults; indeed it is an advantage for longevity.
Plumpness in childhood, often called ‘puppy fat’ when it occurs in adolescents, is different and has only recently become the subject of intense media attention and public concern. Evidence linking it to adult obesity is conflicting. What is certain, though, is that the real hazard is gross obesity in childhood, which, in spite of what one reads in the media, is unusual and often due to genetic and metabolic defects, an increasingly large number of which are becoming identified.