No magic bullet

There has been a lot of fuss recently in the West Island around a paper by Dr Alan Barclay on trends in sugar consumption and obesity.  When read as a reaction to a rather extreme US paper in the prominent journal Nature claiming ‘sugar is as toxic as alcohol‘ it is a reasonable piece of analysis, but it is being overinterpreted.

The New Zealand Science Media Centre (who are typically sensible and well-informed*) and their Australian counterparts have commentary on the ‘evil sugar’ paper from three experts, who agree that specific effects of sugar beyond its calorie content are not that strong, and, of course, that excess sugar consumption doesn’t directly hurt anyone but you: it doesn’t make you get into fights or crash cars.  On the other hand, there is the calorie content.

Backing up to what we do know:

• average weight is increasing in many countries
• to a very good approximation, weight increase depends only on calories consumed in food and expended in exercise
• in overweight people, weight loss, even on diets that are far from ideal, such as the Atkins Diet, improves cholesterol, insulin resistance, and blood pressure

Secondary to all of that, we know with less confidence a lot of details about specific nutrients: saturated fats, trans-polyunsaturated fats, fructose, omega-6 polyunsaturated fats, isothiocyanates, polyphenols, sodium, potassium, calcium, beta-carotene,….  We also have reasonably good evidence that certain broad diets are not too bad.  For example, as Michael Pollan puts it “Eat food. Not too much. Mostly plants”.

Since the increase in average weight is basically due to social changes (more driving, less physical effort at work, more prepared food, etc), public health professionals want to find society-level interventions to reverse it.  That’s why there’s interest in food labelling, selective taxes, walkable neighbourhoods, `food deserts’, and so on, rather than just in advocating dieting.   Specific taxes on sugar, corn syrup, etc, are attractive because they would be easy to implement. Restrictions on sale would be harder, but not as hard as, say, reducing driving.  So it’s an attractive possibility.

On the other hand, you can (and people do) advocate any diet you want with no evidence whatsoever, but for major changes in food policy you’d like some evidence.  Dr Barclay’s analysis shows that while average weight in Australia has increased at a similar rate to the US, consumption of sugars has gone down in Australia and up in the US.  That’s true whether you measure sugar consumption from self-reported diet or from total sales of the raw materials.  A reasonable conclusion is that if you regulated sugar and did nothing else, it probably wouldn’t be enough to have much impact on obesity.

In some ways, that’s a mirror image of what did happen in the US.  There were strong efforts made to reduce % calories from fat, and specifically saturated fat, consumption, and these were somewhat effective. The reduction in % fat was partly due to a fall in consumption of animal fat, but mostly due to an increase in sugars (from corn syrup) and refined starch.  And, of course, obesity increased (although heart disease did fall). This USDA publication shows estimates based on sales, and this CDC report and paper use self-reported diet data from the NHANES surveys.  Dr Barclay’s paper even mirrors (I assume deliberately) a 2001 paper  “Divergent trends in obesity and fat intake patterns: The american paradox”.

Targetting sugar alone might well not work, but targetting sugar together with other interventions may well be effective.  I’d also want to design an intervention in a way that let you find out if it worked, something that’s worryingly rare in public health, though not as rare as it is in education.

* I’m one of their external scientific advisors, but not on this topic.