The study, published in the American Journal of Clinical Nutrition, could have implications in the fight against obesity, with some in the academia calling for so-called fat taxes to increase the price of 'unhealthy' foods - a proposal that has been continuously dismissed by industry as unworkable.
Indeed, only a few months ago British academics stated that if the British government imposed a "carefully targeted fat tax" on food, over 3,000 deaths from cardiovascular disease could be prevented every year (J. of Epidem. and Comm. Health, Vol. 61, pp. 689-694).
However, an industry trade association instantly dismissed the proposals as "utter nonsense", adding that "the research doesn't prove whether taxing the foods that consumers love would lead to any changes in their buying habits."
The new research does throw some compelling evidence into the ring with the findings that increasing the price of high energy density (HED) foods will lead to people changing their buying habits and switching to low-energy-density (LED) foods.
"The results of the present study suggest that basic economic principles can be studied in the laboratory and that important individual differences may exist in how LED foods can substitute for HED foods when the cost of the HED foods increases," wrote lead author Leonard Epstein from the University of Buffalo in New York.
Epstein and co-workers investigated the effect of price changes on LED and HED food purchases by 47 mothers aged between 25 and 50 years with at least one child living at home aged between two and 15.
The researchers studied how the women spent a fixed budget on a week's groceries from a selection of 60 foods. Foods were categorized as LED (less that 2.0 kilocalories per gram) or HED (at least 2.0 kcal/g). In 50 per cent of the trials, LED foods were priced at reference levels based on current local food prices, while HED food prices were varied - 75, 100, or 125 of reference prices. The other trials used constant HED and varied LED prices.
Epstein and co-workers report that all the subjects purchased more calories from HED than LED foods. However, when HED food prices were increased, a substitution of LED for HED foods was observed for non-obese subjects, On the other hand, obese subjects did not change their purchasing patterns.
"The present study provides an initial experimental test of the influence of price changes on purchases of HED or LED foods. The utility of public policy changes for shifting consumption on the basis of taxes or subsidies may depend in part on how broadly the taxes are implemented," wrote the authors.
"This is an important factor, because one potential limitation of changing prices on select foods within energy density groupings is that persons will substitute other less healthy foods for the ones that have an increased price. For example, increasing the price of soft drinks may shift purchase to sweetened fruit juice drinks."
The researchers called for further research to determine whether such interventions would have the intended effect of reducing unhealthy food consumption in at-risk populations, and whether individual differences in response to price changes could be modified.
Commenting on the study, a spokesperson for the Food and Drink Federation told FoodNavigator.com: "Any tax levied on specific food types deemed to be high in fat would be a tax on choice and patronising to consumers. It would hit lower income families who spend a higher proportion of their income on food and drink.
"Consumers will rightly feel patronised by 'top-down' messages based on the idea that they can't think for themselves and need to be taxed and coerced into healthy eating or weight-loss. Positive, non-prescriptive messages about how to create a healthy balanced diet and a more active lifestyle is the way to help consumers change their behaviour."
The 'fat tax' idea was initially reported in The Times in February 2004. The newspaper suggested that the Prime Minister's Strategy Unit - the body which advises Tony Blair's government on potential areas for legislation - was giving serious consideration to suggesting that foods such as dairy products, pastries, chocolate, pizzas and burgers should be taxed at a higher rate than other, 'healthier' products.
With obesity levels in the UK fast approaching those of the US, where some observers are already talking of an obesity epidemic, the government was looking at ways to improve the nation's health.
But the government was quick to pour cold water on the suggestion, saying that while several ideas for tackling obesity were being discussed, a fat tax was not one of them - not least because such a system would be all but unworkable.
The FDF again vociferously opposed the suggestion.
Source: American Journal of Clinical Nutrition
October 2007, Volume 86, Pages 914-922
"Price and maternal obesity influence purchasing of low- and high-energy-dense foods"
Authors: L.H. Epstein, K.K. Dearing, R.A. Paluch, J.N. Roemmich, D. Cho