Читать книгу Breakfast is a Dangerous Meal: Why You Should Ditch Your Morning Meal For Health and Wellbeing - Terence Kealey, Terence Kealey - Страница 20
ОглавлениеThere is another explanation for the apparent paradox of breakfast skippers being large: they may be leading chaotic lives. So a Finnish study of some 5,500 16-year-old girls and boys and their parents found that breakfast skippers tend to come from families that self-harm by:
smoking
failing to take sufficient exercise
neglecting education
consuming higher intakes of high-sugar, high-carbohydrate, high-fat snacks
drinking too much
being overweight.1
Extending those Finnish findings, a study from Rhode Island of nearly 10,000 adolescents showed a significant correlation between:
breakfast skipping
fast food eating
weight gain.2
But correlation is not causation, so we need to ask, is it the breakfast skipping or the fast food eating that is causing the weight gain in these adolescents? Dr Mark Pereira of the University of Minnesota has answered that question. Dr Pereira followed 3,000 young adults over fifteen years, showing that those who ate at fast food restaurants more than twice a week gained an extra 10 pounds (4.5 kg), and had a twofold greater increase in insulin-resistance than those who ate there less than once a week.3 Dr Pereira therefore confirmed that fast food is dangerous food, if only because it is so high in calories: ‘a single meal from one of these restaurants often contains enough calories to satisfy a person’s caloric requirements for an entire day.’4
And who eats fast food? People who lead chaotic lives. Dr Pereira divided his subjects into blacks and whites, and because – for shameful historical reasons – black Americans are disadvantaged, Dr Pereira thus also provided a link between social class and fast food. And Dr Pereira found that, fifteen years into the study:
black people were visiting fast food restaurants 2.15 times a week against 1.60 times for white people
the black people in Dr Pereira’s study had nearly two years’ less education than white people
black people took three-quarters of the exercise of white people
black people watched nearly twice as much television as white people
black people ate some 400 calories more per day than white people
black people drank 50 per cent more soft drinks than white people
black people ate 50 per cent more meat than white people
black people ate significantly less fibre than white people.
So the Rhode Island study on nearly 10,000 adolescents may have shown a significant correlation between breakfast skipping, fast food eating and weight gain, but from Dr Pereira’s research we know it’s not the breakfast skipping that is causing the weight gain, it’s the fast food. And the fast food eating and the breakfast skipping have a common root in a chaotic lifestyle, so we can begin to see how breakfast skipping and overweight are not causally linked but, rather, reflect the actions of a separate, third, cause: domestic chaos leading to unhealthy life choices:
So we can see how breakfast skipping may be associated with, but not causative of, weight gain. Breakfast skipping per se, in isolation, will promote weight loss, but if it is linked with a package of weight-gaining activities, it will then be associated with weight gain, thus leading unsuspecting epidemiologists to suppose that eating breakfast causes weight loss.
We might make a comparison with smoking and teenage pregnancy. Teenagers who smoke are more likely to become pregnant but no one has suggested that smoking causes pregnancy.5 Rather, dysfunctional teenagers are more likely both to smoke and to become pregnant, but the causative agent is the dysfunction. Here is a model that captures that story:
The model is not:
dysfunctional teenagers → smoke → get pregnant
And to confirm that model of association, not causation, there has even been a report that Japanese girls who skip breakfast also start to have sex two years before their breakfast-eating sisters (at 17.5 rather than 19.4 years of age). The report has not got into an English-language peer-reviewed journal, but it came from the Japan Family Planning Association, which is credible.6 Here is a model that captures that story:
The model is not:
dysfunctional teenagers → skip breakfast → have premature sex
Daniel, the lions’ den and the earliest clinical trial
Epidemiology (from the Greek epidamia, the prevalence of disease) is the science of populations, but it’s too easy in epidemiology to confuse cause and correlation. So here is a claim of cause:
eat breakfast → eat more → yet lose weight, paradoxically
(or alternatively)
skip breakfast → eat less → yet gain weight, paradoxically
and here is a claim of correlation:
Epidemiological studies that look only at breakfast and weight can easily confuse correlation with cause – except that the science of epidemiology has long generated a ‘hierarchy of evidence’ by which to distinguish them, and it is a theme of this book that epidemiologists have not always been sufficiently rigorous in applying that hierarchy.
The hierarchy of evidence: Conflicts over diet are age-old, and some can be sourced to the Bible. Daniel was a Jew who had been captured by Nebuchadnezzar, the King of Babylon, and who was consequently condemned to various vicissitudes including the lions’ den (from which, happily, he was rescued). Daniel was also instructed to eat the food of the royal court, to which he objected on grounds of observance. Let Daniel I: 12–16 take up the story of how he asked that he and his fellow captives be given:
nothing but vegetables to eat and water to drink. Then [Daniel said] compare our appearance with that of the young men who eat the royal food, and treat your servants in accordance with what you see. So he [the chief official] agreed to this and tested them for ten days. At the end of the ten days they looked healthier and better nourished than any of the young men who ate the royal food. So the guard took away their choice food and the wine they were to drink and gave them vegetables instead [New International Version].
This was a clinical trial! The first to have been recorded. But though it wasn’t too badly controlled, we think we can do better now, and today we understand that some methodologies are more powerful than others and that they can be ranked in a hierarchy of evidence:
Systematic reviews and meta-analyses
Randomised blinded controlled trials
Randomised controlled trials
Cohort studies
Case-control studies
Cross-sectional surveys
Case reports.
Let me briefly look at these, starting with the weakest methodologies.7
7. Case reports: In such a report, the medical history of a patient is told as a story. ‘Mr Joe Blogs has always smoked and he has just celebrated his eightieth birthday, therefore smoking potentiates longevity.’ It doesn’t require genius to understand why case reports provide only weak evidence of cause and effect.
6. Cross-sectional surveys: These are ‘snapshots’. In such studies, people are asked two questions, which might be: what do you eat for breakfast and what is your weight? As I’ve shown above, many breakfast studies fall into this category, which is unfortunate because this sort of snapshot study can be very misleading, i.e. at any one time people may be large and thus skip breakfast while, later, those people may be slim and thus eat it, but it is not the eating of breakfast that makes you slim (and, vice versa, not the skipping of breakfast that makes you fat); rather, it’s being large that encourages people to skip breakfast, and being slim that encourages people to eat it. So cross-sectional or snapshot studies can lead to conclusions that are 100 per cent wrong.
5. Case-control studies: These are not used frequently in breakfast research, so I’ll not describe them here.
4. Cohort studies: These are an attempt at avoiding the problems of a ‘snapshot’. In a cohort study, two groups of people are selected because they either do or do not eat breakfast (say) and then some years later their outcomes are determined. During the 1940s, 1950s and 1960s Bradford Hill and Richard Doll performed their famous cohort study on doctors who either did or did not smoke, discovering that smoking causes lung cancer.fn1
3. Randomised controlled trials: Now we are moving from observations to experiments, where participants are given a drug or some other intervention (such as skipping breakfast or not eating the royal food) and scientists then determine the effect.
Experiments, though, are only as good as their controls: if you give a drug to a group of people and then get an effect, you need to know that those people were not going to produce that effect anyway, so in clinical medicine we do controlled trials, where the responses of subjects to a drug are compared to the responses of subjects who do not receive the drug. But the experimenter mustn’t pick the control subjects, because that might bias the results, so in clinical medicine we do randomised controlled trials, where the two groups of subjects are selected to be as similar as possible, with individuals being distributed between the two groups randomly.
2. Randomised blinded controlled trials: Ideally, to avoid subconscious bias, neither the experimenters nor the subjects of a trial should know who is part of the intervention group and who is part of the control group, but unfortunately I need not explain this any further as we can’t do blinded trials in breakfast: blinding requires that we provide control subjects with placebos, yet we can’t provide placebos for breakfast. Breakfast studies have therefore been deprived of the most robust experimental protocols, but as the science of astronomy illustrates, knowledge can progress without the full panoply of experimental protocols: if we are careful in our observations, we can – in the absence of experiments – show that the earth moves round the sun rather than vice versa, but we do have to view the observations carefully, without preconceptions.
1. Systematic reviews and meta-analyses: These are sophisticated words that describe the sophisticated methods by which the results of many different trials can be pooled, to provide more secure conclusions than any one trial can provide.
Conclusion: Clinical medicine has created a hierarchy of evidence, and in this book I try to show where breakfast epidemiologists have, unfortunately, ignored the hierarchy, to thus confuse correlation with cause.
