Tag Archives: medicine

Don’t treat obesity as physiology or physics

I have a whole bunch of draft and outline blog posts from winter and spring that I was never able to find the time to finish off. To clear them out of the way, I’ve bashed out some half-hearted conclusions, and will post them this month.

Flicking through the pile of Natures that never got read properly, ready to be rid of them, I alighted on Gary Taubes’s opinion piece: Treat obesity as physiology, not physics. Bear with me while I appear to be completely off-topic talking science for a while.

Taubes argues that:

…obesity is a hormonal, regulatory defect… it is not excess calories that cause obesity, but the quantity and quality of carbohydrates consumed. The carbohydrate content of the diet must be rectified to restore health.

Taubes set out his case that it is not useful to think of obesity as a straightforward energy in/out imbalance that causes weight gain, but that it’s in understanding that specific forms of that energy — carbohydrates, and sugars doubly so — activate our body’s own fat accumulation systems (through the well understood insulin process) where solutions lie. You’ll be familiar with it from all that “Atkins diet” and “glycaemic index” stuff: energy in the form of carbs bad; energy from dietary fat not so much.

Taubes thinks this is important stuff because:

…the overeating hypothesis has failed. In the United States, and elsewhere, obesity and diabetes rates have climbed to crisis levels… despite the ubiquity of the advice that if we want to lose fat, we have to eat less and/or move more.

There is an obvious response to this, but Taubes pre-empts it:

Yet rather than blame the advice, we have taken to blaming the individuals for not following it ‘properly’.

Suggesting that Taubes thinks that if only we change the advice from “eat less and exercise more” to his “don’t eat high glycaemic index foods”, the advice will be followed and we will then succeed in defeating obesity.

I imagine any “advice” we give will be useless, whether it’s based on physics or physiology.

Because while obesity is about physics and physiology — and psychology and genetics and half a dozen other fields of science — none of those things explain what is important: why there is more obesity now than in the past, and how to make there be less of it in the future.

The laws of physics haven’t changed in fifty years. Physiology, and the genes that underlie it, can change — but only by evolution over the course of hundreds of generations, not a few decades. Sure, our bodies have a mechanism for turning carbohydrates into fat stores. But they always have.

The focus is on the quantity of energy in and the quantity out because that is what has changed during the rise of the obesity crisis. By all means refine that to a specific focus on an excess of high-glycaemic index foodstuffs and a deficit of burning off specific sugars, but the problem that really matters remains fundamentally not one of physics or physiology but of our environment.

Taubes is right to treat those who “blame individuals for not following the advice properly” with contempt. But not because the advice is wrong. Because any “advice” — right or wrong — is going to be useless. This is not a problem that individuals have created for themselves, and it’s not a problem that individuals can be “advised” to solve for themselves. This is a problem of the environment that we live in: the types of food that are available to us, and the opportunities for an active healthy lifestyle that have been taken away from us.

Taubes later uses an analogy with smoking and lung cancer, and the analogy perfectly describes what’s wrong with the idea that obesity should be treated as a physiology problem. We know a great deal about the physiology of smoking-related lung cancer. We know how all of the many different carcinogenic chemicals within cigarette smoke flow through the lungs and pass through membranes into the cells. We know the chemical reactions that they participate in and how those reactions cause damage to the cells’ DNA. We know exactly which pieces of DNA damage result in the harmful mutations that transform them into cancer cells, driven to grow and divide. We know exactly how those mutations — to genes with names like RAS and RAF, and EGFR and a dozen others — change the shape of the proteins that those genes encode, and why that change of shape causes those proteins to misbehave. We know how these things result in the tumour evading the body’s inbuilt defences, how they hijack the blood supply to allow their expansion, and how they go on to invade and destroy neighbouring tissue and eventually escape and metastasise.

And knowing these things about physiology makes not the slightest difference to solving the smoking problem. Smoking-related lung cancer, like obesity, is a process of physiology. But it’s a problem of environment. And the most important lesson from smoking for obesity is that you can’t solve a problem environment with advice alone. Bad lifestyle choices are not an individual failing. Good lifestyle choices need an infrastructure to support them.

All those helmets posts in one place

Last year I went into some detail about why existing research into the efficacy and safety of helmets for cycling does not come close to the standard of evidence that is normally required and which we would usually demand for a medical intervention (which is what they are). Basically an application to helmets of all those things that Ben Goldacre bangs on about. But I never added an easy to link to contents page when it was complete. So here it is.

Killer Cures: a very brief introduction to why it is so important to do proper thorough research on medical interventions.

So what’s the best evidence we have on bicycle helmets?: a brief review of the research that has been performed on helmet efficacy — how it was done, what it found, and what the limitations of the methods were.

Headline figures: putting the relative risk figures reported by research papers into context of absolute risk.

What is a bicyclist?: looking at one of the major flaws in existing research on helmet efficacy — ignoring the differences between transport, leisure and sport cycling.

Would a helmet help if hit by a car?: a brief diversion into one of the side-arguments, but an important one given that most transport and leisure cycling deaths and serious injuries involve a motor vehicle.

Risk compensation and bicycle helmets: why it’s important to test for potential side-effects of interventions, some of the proposed side-effects, and why the research in this area also has too many limitations.

The BMA, the BMJ, and bicycle helmet policy: introducing the BMA’s position on helmets. Just one of several organisations with a dodgy position, but one that I think is particularly important/interesting.

How did the BMA get bicycle helmets so wrong?: a sort of conclusion piece, reiterating the importance of doing proper research on both the efficacy and the side-effects of medical interventions, and how an organisation which should know better managed to abandon this principle in favour of anecdotes for helmets.

Followed by some frivolous posts:

Prevention and cure

While organising notes, I stumbled upon this quote I bookmarked years ago, from the great Harvard cancer biologist Judah Folkman:

A pediatric surgeon in Boston just finished a difficult operation. To relax, he went to the Charles River and sat down on a bench. Suddenly, he heard cries of ‘Help! Help!’ and saw a person drowning. The surgeon jumped into the river and pulled the person to safety. He lay exhausted on the banks of the river and again heard, ‘Help! Help! ’ He glanced at the river and saw another person drowning. Despite his exhaustion, he jumped into the river and pulled the second drowning person to safety. Now, he was truly exhausted and lay on the ground huffing and puffing and again heard, ‘Help! Help! ’ He raised his head to look toward the river and saw a third person drowning, but he also noticed two basic researchers walking by the river. The surgeon shouted, ‘Colleagues, you must help! This is the third drowning person in the river in one afternoon! ’ The researchers looked at the river and then at the surgeon and said, ‘Three people drowning in one afternoon? This is very interesting! We’ll walk upstream to see who’s throwing them in!’.’’

(I think actually that it would work better if cast with public health researchers in place of basic researchers. The basic researchers would be too busy describing in obscure detail of the currents of the river, while translational researchers designed a better buoyancy aid for those currents.)

Folkman was applying the metaphor to his own field, cancer, but it works equally well for death and injury on our streets. The “road safety” approach to the problem has people studying the currents and advocating hi-viz vests and bicycle helmets, while spending billions on air ambulances and major trauma units. The “road danger reduction” approach goes upstream and asks why we are allowing large volumes of fast moving vehicles into the places where we live and work and play and learn. And it’s notable that in medicine, it’s the surgeons who think that preventing injury means bicycle helmets, and the public health researchers who think that preventing injury means calming and removing cars and trucks.

Here are a few of them: Danny Dorling talking about the open sewers of the 21st century; Harry Rutter’s Street Talk on moving towards a healthier city; and Ian Roberts, acting badly, on The Energy Glut. And you can hear Robert Davis talking about “road danger reduction” at London South Bank University on thursday next week.

During the 20th century, life expectancy lengthened by 30 years in the developed world. 25 of those years are attributable to public health intervention — to prevention rather than cure. But prevention disproportionately helps the poor and frequently hinders the rich. Guess which branch of medicine gets all the money.

Cycling abuse

I stumbled upon an article in The Lancet, volume 138, issue 3554, of the 10th October 1891, which it seems has been overlooked by the internet so far. It celebrates the rise of the bicycle, but warns against its abuse — addiction, even. It has a message that James Cracknell might like to ponder before getting too carried away with the fabulous medicinal properties of bicycle helmets: cycling isn’t dangerous, it’s those sick addicts who like to race themselves to exhaustion who are dangerous.

Those who believe in the necessity of physical exercise, and we belong to their number, have need also to remember that even so good a thing as this is in excess an evil. The use of the cycle is a form of bodily recreation in itself doubtless wholesome; none the less is it open to the mischievous effects of undue indulgence. Tempted by the ease of movement, combined as a rule with attractive scenery, everyone tries it. Everyone too, finds he can do something with it, and considerations of weather, constitution, age, and health are apt to be dismissed with summary imprudence. One fruitful source of injury is competition. In this matter not even the strongest rider can afford to ignore his limit of endurance. The record-breaker, who sinks exhausted at his journey’s end, has gone a point beyond this. The septuagenarian who tries to rival his juniors by doing and repeating his twenty or thirty miles, perhaps against time, is even less wise. Lady cyclists, too, may bear in mind that their sex is somewhat the weaker. So likewise amongst men the power of endurance varies greatly, and is is better for some to admit this and be moderate than to labour after the achievements of far more muscular neighbours. In short, whenever prostration beyond mere transient fatigue follows the exercise, or when digestion suffers and weight is markedly lessened, and a pastime which ought to exhilarate becomes an anxious labour, we may be sure that it is being overdone. He that would reap its best results must content himself with much less that this; but unless he can observe such moderation, he had better abstain from it altogether.

From here, The Lancet moves on to a fascinating case series of three patients with gastric ulcers cured by a diet of ice cream. (Perhaps the placebo effect of ice cream will turn out to be more powerful than four sugar pills.)

Won’t somebody please think of the children?

In December 2005, an article of massive importance was published in the British Medical Journal. Doctors counted up the number of children being admitted to A&E with musculoskeletal injuries (breaks and sprains — many of which would have been caused by bicycle-related incidents) on summer weekends  and discovered a startling pattern. A new preventative intervention was discovered.  They authors say:

The figure shows the weekend attendance to our emergency department in June and July between 2003 and 2005. The mean attendance rate for children aged 7-15 years during the control weekends was 67.4 (SD 10.4). For the two intervention weekends the attendance rates were 36 and 37 (mean 36.5, SD 0.7). This represents a significant decrease in attendances on the intervention weekends, as both are greater than two SD from the mean control attendance rate and an unpaired t test gives a t value of 14.2 (P < 0.0001). At no other point during the three year surveillance period was attendance that low. MetOffice data suggested no confounding effect of weather conditions.

From this data on the effect of Harry Potter books on injury rate it should be blindingly obvious that countless lives would be saved if legislation made Harry Potter books compulsory — for children at the very least (we can perhaps allow adults the freedom to choose to turn themselves into dribbling brain damaged wrecks by not reading Harry Potter).

Anybody who cycles while not reading Harry Potter clearly deserves to have their brains smeared across the road. They lack any credibility.

Gwilym, S. (2005). Harry Potter casts a spell on accident prone children. BMJ, 331:1505-1506 doi:10.1136/bmj.331.7531.1505

Further reading: ‘Tis the season, from Language Log.

Appendix: Bad Science Bingo in the BMA’s “safe cycling” pages

This is just a crude brain dump of a post that comes after the serious series — posts one, two, three, four, five, six, seven and eight.

Sorry, I just can’t get over these extraordinary pages on the BMA’s website. Here’s a very quick run through some of the Bad Science Bingo points that leaped out.

There were the canards, fallacies, and methods of misdirection:

  1. Obviously there’s the emphasis on anecdotes and cases, the lowest form of evidence, which are essentially appeals to emotion.
  2. Coupled with that the description of the “beliefs” of a few doctors, designed to nudge readers into conformity (acting as a subtle argument from authority for readers who are not doctors, and an argumentum ad populum for those who are).
  3. Specifically in a couple of the anecdotes the selective recall of serious injuries in non-helmet wearers and minor injuries in helmet wearers (creating the illusion of control).
  4. “Figures from New Zealand show that in 2006 there were 883 cyclists injured and nine killed. This corresponds to 20 people per 100,000 injured and 0.2 people per 100,000 killed. These figures are lower than those reported for 1994 when legislation was first introduced.” Fun factoids, but they don’t actually say anything about helmet efficacy. Lots of things changed between 1994 and 2006. (Post hoc, etc.) Perhaps there is evidence for NZ’s legislation improving safety but the 2006 crude injury statistics aren’t it.
  5. Incidentally, while we’re on correlation and causation, the authors even get their statements on cycle tracks subtly wrong: “During the period of 1976 to 1995 Germany almost tripled their mass of cycle networks and this led to a 64 per cent drop in cyclist deaths.” While the evidence of a causative link is much stronger here, it’s a lot more complicated that a simple one “led to” the other. The reference does indeed state that Germany tripled their cycle network and that their death rate fell, but it notes that the later is in part the result — directly and indirectly — of the former.
  6. I loved this statement, when discussing the side-effect of reduced rates of cycling: “If legislation were to reduce the rates of serious injury and promote increased public confidence in cycling, the effect might be to make cycling more popular. Clearly, there is a need for further research on this matter.” I don’t know where to begin. After dismissing all the side-effects of helmets as being based on too weak and preliminary evidence, the BMA counter it all with a speculation based on none at all — and tell us that there is a clear need for more research. Well quite.

And there were specific claims or activities that run counter to the cited evidence, or subtly misrepresented it (I did not systematically check references, these are simply things that leaped out as contradicting what I recall of the literature):

  1. On page 2 the BMA list the things they are doing in addition to promoting helmets. The first item is “publicity and education campaigns in order to raise drivers’ awareness of more vulnerable road-users, including cyclists”. We know that these don’t really work.
  2. The “risk compensation” section on the fifth page cites just one source, the Spanish study described on Monday, whose study design we know can not answer the question that they are asking it to answer.
  3. “As noted in Table 2 the Macpherson and Spinks 2007 Cochrane review found no evidence to either support or counter the possibility that legislation may lead to negative societal and health impacts such as reductions in cycling participation.” You would probably read this and think, “studies have been done and they found no evidence for X.” It actually means, “the studies didn’t bother looking at X.”

And there were fun inconsistencies:

  1. Kirsty’s story on page 5, “Doctors believe that had she not been wearing a cycle helmet at the time of her crash, she would have died,” and on page 6, “They have been shown to reduce the risk of head injury and its severity should it occur. This does not apply to fatal crashes but in such instances the force of impact is considered to be so significant that most protection would fail.”

The resource is just generally bizarre. It has a very weird set of focusses. On one page it gives a seemingly arbitrary selection of factoids from cyclist demographics (notably absent is any acknowledgement that “cycling” is not a single activity); on another it notes the diversity of cycle helmet standards — but fails to discuss any of the important consequences of this, such as how few helmets these days meet the stricter standards that applied in the past, back when most of the evidence on helmet efficacy was collected. In a table on the fifth page they mention that a study found no evidence of helmets causing or exacerbating rotational injuries — yet this is the only mention they make of the rotational injuries problem. Their inclusion and omission criteria appears to be completely random.

Anyway, enough of this. I don’t want to hog the game — your turn.

How did the BMA get bicycle helmets so wrong?

In 1958, the UK licensed a drug for treating morning sickness. It worked very well. The studies all showed that pregnant women suffering from morning sickness received much relief with the drug. Three years later it was withdrawn, but not before 2,000 babies were born with birth defects — 20,000 worldwide — three quarters of whom would die in infancy. The drug was, of course, thalidomide. It managed to get licensed because too many of the people studying it were focused on very specific aspects of its activity on the disease states that it was thought to treat, and too few were stepping back and looking at the big picture. It prevented morning sickness, therefore it worked — the logic of the day.

Joe’s anecdatum: In 2003, Joe, an 18 year old male, slipped on some wet stairs in a block of flats. His head fell eight feet onto the concrete floor. He was not wearing a bicycle helmet. He had a headache for the rest of the evening. He has never been diagnosed with any long-term ill-effects.

A disaster on the scale of Thalidomide can’t happen these days because the path to drug licensing forces researchers to comprehensively check all effects and outcomes of a new drug. Individual researchers will know in extravagant detail very narrow aspects of how a new drug achieves its desired effect. Some of them will know the exact rate at which it crosses the various barriers into the blood and into organs; others will know the exact chain of activation of molecules and genes within cells, down the individual amino acid residues that are modified and the exact number of seconds after the drug is administered; others will know the exact schedule and mechanism by which the drug is broken down or expelled from the body. They’ll be really excited and enthusiastic about their new drug. But when somebody steps back and points out that the drug causes heart failure, it won’t get anywhere.

But the BMA seems to forget everything it knows about testing interventions when it comes to bicycle helmets. There are some superficial differences between helmets and what we normally think of as “medical intervention”. They are a physical intervention rather than a drug — but medicine deals with and properly tests physical interventions all the time. And it’s supposed to prevent rather than treat injuries — but medicine deals with and properly tests preventative measures, including conventional drugs, all the time. There is no intrinsic reason why bicycle helmets can not be tested properly, in line with the rules that were designed to prevent another thalidomide disaster. We have the methods and the expertise.

Joe’s anecdatum: In 2009, Joe, a 23 year old male, slid on the gravel on the Greenwich Peninsula Thames Path, hitting his head on the concrete path and writing off an £800 camera lens. He was not wearing a cycle helmet. He was unhappy and was bored for several hours waiting for Lewisham Hospital to glue his face back together. He stayed home all next day. He has never been diagnosed with any long-term effects.

And yet the evidence that we have on bicycle helmets is currently in a worse state than the evidence that got thalidomide licensed. There is some (limited) evidence that in people who have had crashes, helmets reduce the rate of specific types of head injury — just as there is undisputed evidence that thalidomide is effective in relieving morning sickness. But there is also (equally limited and disputed) evidence of several different side effects — an increase in other types of injury* and an increased rate of crashes (particularly crashes with vehicles, which are more likely to have negative outcomes). And there is also evidence that helmets discourage many people from cycling* — an activity that adds many quality years to people’s lives by preventing or delaying cardiovascular disease, cancers, diabetes, depression, dementia, and all those other diseases of sedentary lifestyles. Helmets might be an effective intervention for the types of injuries they are claimed to prevent, but that would be irrelevant if, like thalidomide, they cause more problems than they solve.

Joe’s anecdata: In 1991, Joe, a 6 year old male, on separate occasions smashed his head open a door, some concrete steps, and a glass coffee table. On no occasion was he wearing a cycle helmet. He has a scar on his forehead that is almost identical to James Murdoch’s. Unlike James Murdoch, he has never been diagnosed with any other long-term impairment or ill-effects.

I’m not saying that they do. The issue is not that there is overwhelming evidence against helmets. The evidence that they are the cause of crashes and other injuries is no stronger than the evidence that they prevent head injuries. The issue is that the evidence either way is nowhere near good enough to make a recommendation. If helmets were a drug, they would be nowhere close to getting licensed right now.

Which is why British doctors should be embarrassed that the British Medical Association currently lobbies for helmets to be compulsory when riding a bicycle. Imagine if a pharmaceutical company developed a drug which, if administered before receiving a specific kind of traumatic injury, makes that injury easier to treat. Imagine doctors and medical scientists lobbying for it to be compulsory for everybody to take this drug daily, without anybody ever having checked for side-effects.

How has this situation arisen?  The policy decision has largely been made on the insistence of A&E consultants and trauma surgeons.  Consider the anonymous quotations that are scattered through the BMA’s cycling pages:

‘I have seen – in my practice and when working in A/E – quite a number of serious head injuries from children falling off bicycles. I have also seen a number of children who wore helmets who only suffered minor injury. I am convinced that helmets reduce injury.’ — GP

’I would certainly support cycle helmet wearing for cyclists. I have seen far too many young lives ruined by head injuries.’  — Consultant in Emergency Medicine

’I am an Emergency Department Consultant and a keen cyclist. I wholly agree…that we need to move to an environment where cycle helmet wearing is the norm, rather than the exception’  — Emergency Department Consultant

’As a regular commuting cyclist through twelve miles of heavy London traffic and as a Consultant Emergency Physician I whole-heartedly support the BMA’s stance on the introduction of legislation to make the wearing of helmets mandatory.’  — Consultant and Honorary Senior Clinical Lecturer in Emergency Medicine

’Over the [last] 16 years I have worked in A/E. I have dealt with hundreds of head and facial injuries, particularly in children, that could have been avoided had a cycle helmet been worn. I have also had the misfortune to deal with a number of fatalities that I believe would have been avoided by simply wearing a helmet. I firmly believe that legislation making cycle helmet usage mandatory is essential.’  — Emergency Medicine Consultant and Clinical Director

‘I have worked in emergency medicine for the last twelve years. Personally I cycle around two and a half thousand miles each year and my family are rapidly becoming keen cyclists also. Prior to working in emergency medicine, I did not routinely wear a cycle helmet.

I have seen numerous examples of patients sustaining severe head injuries from which they will never recover whilst cycling at low speed without a helmet. I have never seen this pattern of pathology in cyclists wearing helmets under these circumstances.

I am aware of the recent Cochrane review on the subject. I firmly believe that all cyclists should wear helmets. I also believe that the only way to ensure this happens is through legislation. I can see no justification for allowing this entirety predictable pattern of head injuries to persist. I strongly support the BMA position…’  — Consultant in Emergency Medicine

That’s five emergency medics and a GP, all reciting anecdotes from A&E. Nobody who specialises in, say, public health.

Emergency medics and trauma surgeons are obviously very enthusiastic about the potential to put an end to injuries, just as people who were very focused on the problem of morning sickness were excited by thalidomide. But ironically, most doctors and scientists are not very good with complexity. They are good with the intense detail of their own specialism, but when they have a problem to solve they fail to consider that there might be relevant things happening outside of their own field. When emergency medics want to solve the problem of head and brain injury, they look at those injuries in isolation from the rest of medicine. It’s not their job to think about the bigger the picture, or worry about things like side-effects.

Indeed, dare I suggest that for most working emergency medics and GPs, the science of evidence-based medicine is not their job or even a major part of their training: they only need to practice what the scientists amongst them tell them to practice; most working doctors don’t need to understand how we know their interventions work.

Which is fine. But that stuff is somebody‘s job, and somebody isn’t doing it right at the BMA.

This way of thinking about the issue — as an isolated problem of emergency medicine — is reflected all through the BMA’s bizarre “safe cycling” pages, which emphasise these individual anecdotes and opinions of doctors in that field (despite “expert opinion” being frequently out of line with the science and despite everything we know about the ability of anecdotes to lead readers astray), while failing to ever think of the issues around helmets in terms of effects and side-effects or the usual path of research that is demanded for medical interventions.

The authors of the Cochrane review on bicycle helmets say, in dismissing risk compensation, “the fundamental issue is whether or not when bicycle riders crash and hit their heads they are benefited by wearing a helmet.” This is exactly analogous to saying that “the fundamental issue is whether or not when a pregnant woman has morning sickness her symptoms are relieved by thalidomide.” That is not the fundamental issue at all. The fundamental issue with any medical intervention is whether it does more help than harm, whether it improves the length and quality of our lives, whether we are better with it or without. That the authors of a Cochrane review are allowed to get away with saying otherwise is a great failure for evidence-based medicine. That the BMA think there is sufficient grounds not merely to promote this intervention but to enforce it is an epic failure.

* I thought about posting separately on these sets of side-effects too, but those posts would have been much like the rest of this series: there’s a plausible hypothesis, there’s some evidence to support it, but the evidence has limitations. Ultimately the conclusions always are: the evidence base is nowhere near good enough to support helmet promotion, let alone legislation.