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Stick works better than carrot to encourage healthy food purchases

February 24, 2010 |  1:30 pm

When the rubber hits the road in addressing the nation's obesity problems, it comes down, in large measure, to what Mom (or Dad) buys and puts in the cupboard. And when it comes to nudging his or her choices toward healthier foods, there's heated debate, but not much solid evidence, on what works.

Here's some -- and let me say right here, don't shoot me, I'm just the messenger. A clever new study concludes that we should tax the junk, not cheapen the good stuff to get better stuff in the cupboard. 

It turns out that jacking up by 12.5% and 25% the price of sugary soda, processed cheese, cookies and snack chips prompts shoppers with a very limited grocery budget to leave more junk food on the shelf and opt instead for foods that give a greater nutritional bang for the buck. Reducing the price of foods that are good nutritional values by the same amounts caused shoppers to buy more of them. But they ended up using the resulting savings to buy more foods that were less healthy. 

Subsidizing healthier foods actually resulted in more calories' worth of food going into the cupboard than either the condition with sin taxes or the condition that mimics real-world current pricing, the researchers found.

The study, which appears in the journal Psychological Science online, recruited 42 moms with at least one child at home. Each woman had a budget of $22.50 per person in the household to buy a week's worth of groceries (an amount that past research has found to be the minimum amount needed weekly to provide a balanced diet). Each was told to assume that the cupboards were bare, and choices were limited to 30 foods that delivered lots of calories with little nutritional value and 30 foods that yielded high nutritional value for little money, plus a selection of healthier and less healthy beverages. The subjects were then sent forth on a series of virtual shopping trips that manipulated prices to mimic conditions in which healthier food was subsidized. At the end of each trip, the contents of each subject's shopping basket was tallied for its caloric and nutritional content.

The study's lead researcher, University of Buffalo professor of pediatrics and social and preventive medicine Leonard H. Epstein, has found in the past that obese shoppers and low-income shoppers are less likely to change their shopping habits when pricing changes. But this study didn't find that: Obese moms (who made up 45% of the subjects) and lower-income women (20 of the 42 had household incomes under $50,000 a year) responded pretty much the same to price changes as their fellow shoppers with lower BMIs and higher incomes. Obese moms did lean to slightly heavier purchases of carbohydrates in all the conditions.

The study leans in the direction that it seems a lot of public opinion is going these days -- not toward higher taxes but toward measures that tilt in the direction of punishing the overweight and obese (or at least, those that eat a lot of junk food -- not necessarily an overlapping population) rather than tempting them toward better choices with carrots. It's a dilemma we've written about a lot here at the L.A. Times' Health section lately. Check here for a story on offering carrots in the way of posting nutritional content on restaurant menus. And look here for our story on punishing the fat.

-- Melissa Healy