Imposing a tax on sugary soft drinks and other unhealthy foods is a common suggestion made by health advocates who want people to eat better. It's just one tool in the ongoing battle to lower the troubling rates of obesity. Hitting us in the pocketbook, the thinking goes, will curb our purchases and lower our consumption of foods that are bad for us.

The only hitch? It doesn't work, according to a review of behavioural economics studies on the topic by researchers at Cornell and Ohio State universities.

The researchers found that when consumers are faced with a tax on unhealthy food, they are likely to go ahead with their purchase.

In one of the studies researchers examined, for instance, 173 adults were asked to select their lunch from various meal choices and were told of price changes while they were making their selections.

If they were told a price increase was due to a new tax on unhealthy foods, more people chose those items. On the flip side, if people were told there was a price discount for healthy foods, more people picked those foods, according to the researchers.

Not only are we keen on discounts, the researchers suggest, but we actually have a rebellious streak that makes us buy the bad stuff policy-makers want us to avoid.

Soda taxes
These findings are particularly relevant given that taxes on sugary drinks such as soda are being contemplated in many cities and regions across North America, with the first legislation in the U.S. being passed in 2014 in Berkeley, California.

Here in Canada, a report by the Montreal Economic Institute  made the point that singling out just one food category is another reason these measures might not work.

Sure, you might pay more for a bottle of cola, but if that's too pricey, the authors pointed out, you could pick up a large double-double Tim Horton's coffee instead—which would not be taxed, although it clocks in at more calories.

Warning labels on junk food?
In some jurisdictions, labelling is seen as an alternative way to deter consumers from buying junk food. After a proposal to tax soda failed, San Francisco announced in June 2015 that it would require warning labels on advertisements for sodas that have high sugar content.

But what if we see warning labels in much the same way as we see taxes? It's worth looking at the upside of the Cornell/Ohio State academic review. Instead of dwelling on the negative, it might be better to focus on discounts and positive labelling on veggies, whole grain bread and other healthful foods.

For now, that's a sound policy to implement in your own kitchen: Promote the benefits of the salad you're serving instead of tsk-tsking the cookies you're rationing.

Read on for healthier junk food choices and foods to choose instead.