The miracle tax diet (warning: results may vary)

Losing weight, and keeping it off, is a difficult and complex process. Yet there’s no shortage of phoney miracle diets promising quick (and unrealistic) results with minimal effort.

The latest entry to this quackery list; the miracle soda tax diet.

It’s become popular among public health advocates and lobby groups to claim we can tax ourselves thin by making sugary drinks more expensive.

Mexico recently introduced a 10 per cent soda tax to fight obesity. France, Hungary and the U.S. cities of Berkeley, Calif. and Philadelphia have done likewise.

While Canada has so far avoided this craze, earlier this month the Heart and Stroke Foundation commissioned a lengthy report from the University of Waterloo’s School of Public Health and Health Sciences to promote the soda tax diet idea.

The headline numbers were crafted to be attention grabbers. A 20 per cent tax on all sugary drinks “will result in more than 13,000 lives saved and prevent up to 200,000 cases of Type 2 diabetes, more than 60,000 cases of ischemic heart disease, more than 20,000 cases of cancer and more than 8,000 strokes,” reads the press release. Make pop a bit more expensive and we all live longer.

“Relatively modest changes at the population level can accrue into some pretty meaningful health outcomes,” agrees David Hammond, the report’s co-author and a professor at University of Waterloo, as he repeats these figures.

To reinforce its aura of scientific precision, the study includes more than 30 pages of appendices with some very specific predictions. Over the next 25 years, for example, the tax will spare 675 women from thyroid cancer, save 1,928 men from dying of chronic kidney disease and prevent 3,463 Canadians from suffering from lower back pain.

The study further claims national body mass index (BMI), a measure of Canada’s collective tubbiness, will drop by about 0.38 points. This would be a significant achievement, given BMI’s upward trajectory in recent decades.

Finally, it projects a $1.7 billion a year windfall for the federal government in new tax revenue.

The entire project is achingly precise. And the resulting media attention assumed it was all as reliable as the periodic table. But it’s a false precision. These claims are about as believable as the miracle cookie diet.

A soda tax faces many obstacles, primarily related to the human condition.

While the report claims that beverage sales will decline by a percentage greater than the tax, evidence from Mexico suggests the opposite.

After two years, Mexico’s 10 per cent tax has caused sales to drop just seven per cent. This suggests consumers resist efforts at changing their diet via tax.

Other studies have shown that when faced with a tax on soft drinks, consumers switch to fruit juice, milk or beer. The end result being no change in total calories consumed.

The Heart and Stroke Foundation tries to avoid substitution problems by taxing fruit juice and chocolate milk as well as soft drinks. While this might be appealing in theory, I suspect levying punitive taxes on “all-natural” juice, cider and dairy producers will be politically more difficult than attacking “evil” pop corporations.

Soda taxes are also regressive, since they hit lower income groups hardest. And athletes drinking Gatorade would have to pay the tax, which seems equally unfair.

But aside from all these practical and ethical issues, let’s consider whether the report’s own predictions are internally consistent.

To recap: Hammond’s computer model claims a 20 per cent tax on sugary drinks will cause Canadians to consume 25 fewer calories per day, which will lead to huge reduction in death and disease over the next 25 years. Most significantly, Canada’s collective BMI will drop 0.38 points.

Curiously enough, his report also notes that due to changing tastes, Canadians — of their own free will — have already reduced their per capita consumption of soft drinks, fruit juice and other sugary drinks by about 13 per cent since 2004.

This works out to a decline of about 28 calories per day. In other words, we’ve just lived through a bigger drop in daily beverage calorie consumption than what a tax is supposed to deliver over the next 25 years.

And if reducing sugary drinks leads inevitably to greater health, we should be able to see the proof right now.

But while sugary beverage consumption is down, national BMI is actually up 0.34 for Canadian men and 0.47 for Canadian women between 2004 and 2014.

We’re already drinking less soda, and still getting fatter. So why would a new tax make any difference?

Clearly there’s much more to our collective weight gain than controlling soda and juice consumption.

Pushed on this point, Hammond seems to distance himself from earlier claims that taxing soda will inexorably lead to a massive, and exceedingly precise, improvement in health, lives lost and disease. What began as a simple, miraculous story about beverages suddenly becomes a very complicated issue involving exercise, food and countless other issues.

“No one should tell you that sugary drink intake is the dominant factor in our diet and that however sugary drinks go, so too will obesity and diabetes and cancer,” he admits. “That is just not the way it works.” Quite true. There’s no such thing as a miracle diet. And no good reason to tax what Canadians drink.