The Doctor and I recently watched “Obesity: The Post-Mortem”, a BBC3 recording of the autopsy of a 17 stone (108kg) woman. Unless you have access to BBC’s iPlayer, you’ll not be able to watch it (legally), and I imagine many of you wouldn’t want to in any event.
But even if you can’t watch it, you can nevertheless engage with the point made in her post on the show, where the Doctor says that there’s a difference between something being uncomfortable or unpleasant, and it being offensive. I agree, and want to expand on that point here.
As Africa Check reports in Daily Maverick, it’s not yet clear what the effects of the proposed sugar tax in South Africa will be. But it is clear that South Africa has a serious obesity problem – and that sugar is a clear causal factor for obesity.
A Mail&Guardian journalist recently approached me for comment on this (I’ll update this post with a link to the piece when it’s published), but because the M&G article will likely only quote snippets, here’s a fuller response to a few sugar tax issues.
In one of my first columns on Daily Maverick, Michael Pollan and his food rules (“the whiter the bread, the sooner you will be dead”) were used to illustrate the modern obsession with eating “healthy” food, or orthorexia. Pollan is an example of a celebrity nutritionist, who – while not necessarily offering harmful advice – could be accused of simplifying things to such an extent that what starts as sound advice mostly ends up being accepted on faith or as dogma.
Recently, South Africa’s sports-science guru Tim Noakes has been receiving plenty of media coverage following his about-turn on matters dietary. Many of you will recall Noakes as an advocate of carbo-loading, especially for athletes. But even those of us who aspired to complete a 10km shuffle had little to fear from the carbohydrate. Until now, where for many of us our fondness for carbohydrates “is an addiction that is at least as powerful as those associated with cigarette consumption and some recreational drugs like heroin”.
In general it’s a good thing to see scientists change their minds, because it’s evidence of the scientific method at work. When the evidence changes, so should our views. But such is the current fear of food, manifested in daily articles about epidemics of obesity and the various ways we’re killing ourselves through what we eat, that it’s sometimes a little easy to join the next dietary fashion without thinking enough about whether we’re convinced by the evidence rather than by the hysteria.
A form of cultural amnesia is apparent in most dietary programmes – they spawn books and instructional DVD’s, but are quite often simple revisions of advice we’ve heard before, packaged under a different name with a different guru’s face on the cover. But if the advice is good and presented in a way that doesn’t encourage mindless obedience, us non-specialists could certainly benefit from knowing about what – in this instance at least – appears to be somewhat of a breakthrough moment for dietary knowledge.
The breakthrough is not Noakes’s and he’s the first to admit that, citing William Harvey and William Banting, and more recently Robert Atkins and Gary Taubes as those who introduced him to the concept that most of us would apparently lose weight and live healthier lives on low-carbohydrate diets. I say “apparently” not only because I haven’t tried it myself, but also because the evidence for Noakes’s claim doesn’t seem nearly as convincing as he’d like us to believe.
While some philosophers of science (like Nancy Cartwright [pdf], for one) disagree, the gold-standard in science is generally held to be the RCT, or randomised controlled trial. In an RCT, subjects are randomly allocated to receive one or another of the different drugs or interventions being tested, and those subjects are then treated differently only in respect of differences that are intrinsic to the different treatments under comparison.
In the case of an RCT evaluating different diets, you’d therefore want to ensure that you control for factors like how much exercise subjects in each cohort do, and your randomised selection of subjects into those cohorts should have ensured a balance between other factors that could influence the outcome of the treatments being compared (whether you know about those factors or not).
For diet – and specifically, comparing diets with varying proportions of carbohydrates – two recent RCT’s are relevant here. In 2009, The New England Journal of Medicine (360,9) published a study by Frank Sacks (pdf) and others, in which four diets were tested on 811 overweight adults. The subjects were randomly assigned to one of four diets, where “the targeted percentages of energy derived from fat, protein, and carbohydrates in the four diets were 20, 15, and 65%; 20, 25, and 55%; 40, 15, and 45%; and 40, 25, and 35%”. The subjects were then monitored for two years to determine the short- and longer-term effect of these four diets.
Their results? “Any type of diet, when taught for the purpose of weight loss with enthusiasm and persistence, can be effective.” To put it more simply, “reduced-calorie diets result in clinically meaningful weight loss regardless of which macronutrients they emphasize”. So, if Sacks and his research collaborators are to be believed, eating less is the important thing rather than what you eat – at least when it comes to weight-loss.
Russell de Souza’s research (published this year in The American Journal of Clinical Nutrition) involved 424 subjects randomly allocated to diets involving 25% or 15% protein; 40% or 20% fat; and 65% or 35% carbohydrates. Again, the authors note that the subjects “lost more fat than lean mass after consumption of all diets, with no differences in changes in body composition, abdominal fat, or hepatic fat between assigned macronutrient amounts”.
Of course, Noakes might be different, and he’d know as well as anyone that a diet that works for one person might not work for all. He in fact claims that he is different (and suggests that many of us might be) in being “carbohydrate resistant”, which brings with it a predisposition to developing adult-onset diabetes. And again, this might be true – but we haven’t yet seen an RCT which compares the effects of various diets on only people who are carbohydrate resistant.
It therefore seems premature – even unjustified – to speak of this diet in such unequivocally positive terms, not to mention introducing the language of moral panics in the form of our hypothetical “addiction” to carbohydrates. As Ben Goldacre (and others, I’m sure) have pointed out, anecdotes are not data, and the bulk of the data available right now suggest that the main problem is simply that we eat too darn much.
Speaking of which, another concern with diets such as this presents itself. Much as you’ll usually find anti-vaccination idiocy represented in the middle-class but rarely by the poor, a diet like this seems quite out of reach to anyone struggling to find money to feed themselves and their families. We’re told to avoid bread, rice, pasta and potatoes in favour of eggs, fish, meat, dairy products and nuts (only some nuts – peanuts and cashews, among others, are evil nuts).
So, above and beyond wondering whether the Noakes diet is evidentially justified, rather than being yet another example of a celebrity-led fad, it’s also somewhat discomfiting on a political level. The increasingly obese poor might after all end up inheriting the earth, simply because there’s no space left on it for anyone else.
See the Daily Maverick link at the top for a range of comments on this column. One particularly worth highlighting, and pasted below, is a response from Prof. Noakes.
By focusing on the evidence or lack thereof that a low carbohydrate diet is an effective means of losing weight you miss a couple of important points. These points are more fully described in the most recent edition of my book, Challenging Beliefs. First, my personal interest in the low carbohydrate diet relates to my predisposition to develop diabetes; my substantial weight loss on this eating plan is an unexpected bonus but it is not the reason why I have committed to this eating plan. The scientific evidence is absolutely clear – it is the persistent consumption of a high carbohydrate diet by person like myself with a genetic predisposition to develop diabetes because we are carbohydrate-resistant that ultimately causes us to develop that disease. The prevention and correct treatment of the condition is also blindingly obvious and proven in the literature – it is a diet that restricts the total carbohydrate intake to as few grams a day as possible, preferably less than about 50 grams per day. Yet sadly this is not the advice that predisposed people like myself or indeed those who already have the disease are likely to receive. I wish someone had told me this 20 years ago. I do not want others not to know this information if it can save them from the disastrous consequences of this awful disease.
Thus my interest in publicizing this eating plan is not to be just another “celebrity fad diet”.
Second, for 33 years I ate the so-called heart healthy, low fat, high carbohydrate “prudent” diet – the same diet that did not prevent the development of all the complications of diabetes in my father. Yet in retrospect, all that diet did for me was to make me fat, lazy, increasingly closer to developing full blown diabetes whilst all the time destroying my running ability. When I finally discovered that these unpleasant symptoms were not caused by aging but by my high carbohydrate “healthy” diet, I was naturally somewhat surprised. Thus in advocating this alternate eating plan, I have been careful to stress that the key benefit is a dramatic increase in the quality of life – something that the scientists have not measured. So I am now able again to run as I did 20 years ago and for me this is very important. I also have a level of energy that I remember having 40 years ago. In addition I have delayed the progress of my pre-diabetes. Those are the benefits that I have enjoyed by restricting my carbohydrate intake. Whatismore, daily I receive a wad of emails from grateful South Africans indicating how much better they feel and how their quality of life and often their sporting performances have improved simply by reducing their carbohydrate intakes as have I. So you see, it is not just about weight loss.
Third you glibly say that “we simply eat too much”. I agree – but why? Lions don’t eat too much; nor do any other free-living mammal that I know (other than our cats and dogs whose health is unfortunately also being undermined by the provision of a so-called “science diets” that forces these carnivores to eat high carbohydrate diets – diets for which their evolution has not prepared them). Why is it then that lions know exactly how much too eat so that they do not become fat and lethargic and unable to hunt? Could it be because they have a perfect appetite control – something that humans have always had but have suddenly lost in the past 30-40 years as the global diabetes and obesity epidemic has increased exponentially?
You see what I have learned, as confirmed by all those who successfully adapt to this low carbohydrate eating plan, is that we rapidly lose our hunger and feel satiated all the time (since fat and protein satiate whereas carbohydrates drive hunger in many people). No longer do we spend our days hunting for addictive high carbohydrate meals that fail to satisfy hunger for more than a few hours. As a result we reduce our energy intakes by at least a third without ever feeling hungry. So we lose weight and return our body masses into the safe and healthy range without any effort. Nor do we need to exercise to maintain that weight loss (although because we now again have the energy we enjoyed at a younger age, we also become more active). The reality is that for many of us the only way to bring our appetites under control is completely to avoid carbohydrates and to return to our former evolutionary state as predatory carnivores.
Also not considered in your analysis are the health benefits of simply eating less – there is a large body of evidence showing that eating less increases life expectancy in a range of mammals. Thus eating too much of anything carries health consequences with it.
So as you personally assess whether or not you should be eating fewer or more carbohydrates, you can see that it is not simply a question of whether or not you want to lose weight. It is about quality of life and for how long you want to live. If those issues are important to you then you need to question whether or not you can improve what you eat, perhaps by eating a diet that is not as full of carbohydrates.
But if these issues are of no consequence to you – if you personally are happy to spend your life “shuffling through a 10km” – then be my guest. But don’t condemn your readers to what nearly happened to me simply because you failed to research the topic as exhaustively as this complex topic requires.