A couple of interesting stories have come to my attention lately. Despite my efforts to get them across on Twitter, they are still not quite getting the attention I think they deserve, so I’m going to recite them here.
These stories are on the role of sugar and the role of antibiotics in human health. First I’ll start with the one that is more solid, the case of sugar. It’s essentially accepted doctrine that sugar is harmful to health. This ranges from any sugar at all to “excessive” consumption of sugar. Indeed, it’s accepted in many circles that sugar is behind the rise in obesity rates. There’s only one problem: there isn’t actually any good evidence for this.
Let me repeat a point, a point I will keep repeating until it sinks in: uncontrolled correlational studies do not count as evidence.
With that out of the way, let review an interesting post by Anne Buchanan. (Yes, that one. Before anyone makes the accusation, yes, I am well aware of Buchanan’s and crew’s heredity denial. But the expression “even a broken clock…” is a key bit of wisdom to keep in mind. I judge arguments, not people, and so should you.)
The search for magic health bullets, or the Single Evil goes on unabated, despite a steady record of essential failure. Is that fair? Well, we’ve got decades of very extensive, expensive, and expansively technical studies of some questions of major public health relevance — and little to show for it.
As a new example, after a two-year effort to connect the dots between between sugar and disease, the World Health Organization, whose large professional research staff should know how to do that, believes it has done so, and now recommends we all reduce our sugar intake to 10% of our diet, or better yet, 5%. That’s 12 or fewer tablespoons of sugar a day.
To answer that question, the WHO commissioned a meta-analysis, that is, a single combined analysis of all pertinent previous cohort studies of the effects of sugar on obesity, which was published last month in the British Medical Journal by Morenga et al.
That is, people in these studies were either asked to add or subtract sugary foods and drinks from their diet, but change nothing else, or they were asked to subtract sugar and substitute it with a different carbohydrate. Presumably the latter was to control for the effect of simply adding or subtracting calories of any sort, though this isn’t clear in the paper.
From these 30 trials and 38 prospective cohort studies, what do they conclude? Well, of the 30 trials, five studies measured the effect of reducing dietary sugars. To quote the authors of the WHO commissioned BMJ paper, “Reduction in dietary sugars intake was associated with significantly reduced weight (-0.80 kg (95% confidence interval -1.21 to -0.39); P lt 0.001) at the end of the intervention period by comparison with no reduction or an increase in sugars intake.”
So, five studies report statistically ‘significant’ weight loss with reduction in sugar intake. But what are we talking about here? Well, an average decrease of less than 2 pounds, or at most 2 1/2 pounds, with variation around that. This may be ‘statistically significant’, but all I can say is that if I lost 2 pounds I wouldn’t think it important enough to tell my mother about, never mind publish it. And, only one of the studies, participants were asked to substitute low sugar foods for the high sugar foods they were eliminating. So, one study tried to test the effect of eliminating sugar, but not changing caloric intake, but the others did not.
So, after all of this effort, on a subject that has been widely trumpeted as well-known, is sugar bad for us? Maybe, but we don’t know it from this study. All the studies included in the meta-analysis are based on methods of assessing food intake that are themselves questionable. Dietary recall, the method used in the trials, and food frequency questionnaires used in the cohort studies, or indeed just about any other method of dietary assessment, are notoriously inaccurate measures of what we eat. And, the amount of weight gain reported to be due to sugar consumption is perhaps statistically significant, but with respect to the dangers associated with obesity, it’s trivial.
All of this is predicated on the assumption that weight gain is unhealthy. Or leads to ill health. The WHO paper didn’t address the strength of the evidence for this. Nor did they show any evidence to suggest that sugar contributes to ill health, or even weight gain, any more than any other food. When speculating on how sugar could be associated with weight gain, the authors write, “The most obvious mechanism by which increasing sugars might promote weight gain is by increasing energy consumption to an extent that exceeds energy output and distorts energy balance.” That is, people who gain weight consume more of anything than they burn, as the isoenergetic studies suggest. By this logic, eliminating milk or eggs or meat and not replacing them would cause weight loss, too.
Sugar consumption is much less unambiguously associated with tooth decay. Or at least I thought so, and it seemed something ‘everybody knows’…..until I read the review commissioned by the WHO, a paper in the Journal of Dental Research, the foundation for the WHO recommendation that sugar consumption should be less than 5% of our diet.
From 5,990 papers identified, 55 studies were eligible – 3 intervention, 8 cohort, 20 population, and 24 cross-sectional. Data variability limited meta-analysis. Of the studies, 42 out of 50 of those in children and 5 out of 5 in adults reported at least one positive association between sugars and caries. There is evidence of moderate quality showing that caries is lower when free-sugars intake is < 10% E. With the < 5% E cut-off, a significant relationship was observed, but the evidence was judged to be of very low quality. The findings are relevant to minimizing caries risk throughout the life course.
The evidence for an association is judged to be ‘moderate’ or ‘of very low quality.’ This largely reflects the fact that most studies didn’t ask the question the WHO was interested in — is there a threshold amount of sugar that is highly associated with cavities? Still, the studies do show an association, even if confounders like socioeconomic status might be problems.
Buchanan seems to be channeling many criticisms I have made, as I did in a Twitter discussion I once had with John Durant. The commonly held belief that sugar per se leads to ill-health – even the most basic (and commonly accepted) link in the case of tooth decay – isn’t based on any good evidence. That sugar is the cause of the rise in obesity is also commonly believed, but is not substantiated.
Notice that sugar is notoriously absent from Greg Cochran’s discussion of health problems stemming from poor adaptation to evolutionary novel foodstuffs (Death by Chocolate | West Hunter). Odds are people looking at sugar are looking in the wrong place.
What should they be looking at? This brings me to antibiotics. Apparently, antibiotics reliably leads to weight gain in animals:
IF you walk into a farm-supply store today, you’re likely to find a bag of antibiotic powder that claims to boost the growth of poultry and livestock. That’s because decades of agricultural research has shown that antibiotics seem to flip a switch in young animals’ bodies, helping them pack on pounds. Manufacturers brag about the miraculous effects of feeding antibiotics to chicks and nursing calves. Dusty agricultural journals attest to the ways in which the drugs can act like a kind of superfood to produce cheap meat.
Now, of course, I am a huge critic of generalizing from animals to humans. However, the article does mention that at least one human trial was conducted:
Researchers also tried this out in a study of Navy recruits. “Nutritional effects of antibiotics have been noted for some time” in farm animals, the authors of the 1954 study wrote. But “to date there have been few studies of the nutritional effects in humans, and what little evidence is available is largely concerned with young children. The present report seems of interest, therefore, because of the results obtained in a controlled observation of several hundred young American males.” The Navy men who took a dose of antibiotics every morning for seven weeks gained more weight, on average, than the control group.
Unfortunately, time is often lacking for me. I suppose if I dug more deeply (which I may still do at some point), I could turn up evidence that could more definitively establish, yay or nay, on the role of antibiotics in human obesity. However, for now, I will put this out there as an idea that needs further attention. Attempts to nail down the cause of the rise in obesity have been infamously unsuccessful. Part of the investigation has been handicapped by the fact that diet and exercise are assumed to be the ultimate causes. This is far from clear at the moment. I don’t know if antibiotics will hold up as a potential cause either. I am not claiming to know the method that antibiotics plays this role (whether they, for example, alter the composition of the gut microbiome). However, I do believe this is worth closer attention.
For sugar and antibiotics, an interesting irony exists. One is commonly believed to be behind poor health and obesity, and in fact may not be. The other an agent that has legitimately been instrumental in improving human health, but may have the side effect of fattening us up. The laser-like focus on lifestyle has served to make us more paranoid about health, but what do we have to show for it? Not much, as previously discussed in my posts on the matter (Trans Fat Hysteria and the Mystery of Heart Disease and Even George W. Bush Has Heart Disease). Of course, we are likely to run into trouble with antibiotics soon anyway (see Imagining the Post-Antibiotics Future)…
EDIT: As an example of a worthless correlational study, I present this meta analysis published in the journal PLOS ONE of observational studies looking at birth by Cesarian section versus vaginal delivery and later obesity. It found that babies delivered by C-section were more likely to be obese as adults. It’s an example of the best and baddest of correlational studies. Did even one of those studies control for parental obesity? Doesn’t look that way. Did any of them try to look at differences between siblings where one was delivered vaginally and the other by C-section? Nope. It is a completely worthless study; all it shows is that obese people may be more prone to give birth via C-section – with no idea of the true causes or best correlates at least. Yet, it is being circulated as if it was definitive proof. Give me a break.