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 apparent 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 DVDs, 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 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 want to ensure you control for factors such as 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 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 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 has 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. DM
"If a man seeks from the good life anything beyond itself, it is not the good life he is seeking" ~ Plotinus