A new review answers what do we really know about manipulating portion sizes and what questions still remain.
Professor Benton, at Swansea University, reviewed the scientific evidence available on portion sizes and this highlights a number of the complexities surrounding the Public Health Responsibility Deal's call for reduced portion sizes, as a way of obtaining reductions in the nation's caloric intakes.
The review, to be published in Critical Reviews in Food Science and Nutrition, found that simply reducing portion sizes is not an easy solution to reducing our energy intakes. The results from laboratory investigations do not necessarily reflect what happens in the real world, where there is a free market, and consumers make their decisions based on numerous different factors - with nutrition often coming some way down the list of consumer's priorities.
To date, the evidence of consumer behaviour, outside of the controlled environment of the laboratory, is unable to determine the extent that the portion size of prepared foods and drink is a major contributor to daily energy intake. The reality of the supermarket shop, is that there are a multitude of competing issues that impact on what a person purchases, and then ultimately eats.
Factors such as packaging, labelling, advertising, size of the whole pack, cost and promotion also affect an individual's choice. Benton also highlights in the review how questions remain over consumer behaviour when presented with different foods of varying energy densities (calories per 100g), as there are every time we go food shopping.
Discussing this review, Professor Benton states: "Obesity reflects the outcome of many factors, such that concerns about portion size needs to be part of a multi-faceted approach to the topic. It is unlikely that any single change is going to have a significant impact, rather there is a need for a coordinated approach that addresses a range of factors that deal with both energy intake and energy expenditure."
As purse strings are being increasingly tightened, the impact of reducing portion sizes in a free market environment is uncertain and could be potentially counter-productive, if consumers resist smaller portion sizes and view larger portions as being better value.