The study also highlighted the need for effective strategies to counter portion size on consumption given the current eating environment.
In the study, subjects chose and ate a portion of pasta from 3 sets, each with 3 portion options. They were offered larger portions in the set but this did not affect the relative size selected. Despite these options, subjects’ meal intake was found to be higher from the set with the largest portions.
The portion size of food is an environmental factor with one of the strongest and most consistent influences on intake (portion size effect). One study believed that increasing portion size increased energy intake with visual cues like plate and package size important factors. The study also identified an increase in bite size with larger portions as another mechanism behind the portion size effect.
Another study took a different approach, by encouraging people to increase the proportion of foods low in energy density in their diets while limiting portions of high-energy-dense foods, effectively managing their body weight.
Fast food chains, major supermarkets and food manufacturers are all under pressure to moderate the energy content of portion options available in the eating environment and to implement strategies to promote choices that fall within an appropriate range for energy needs. This latest study sought to determine the sizes of the portions offered were a critical determinant of energy intake.
“Such strategies could be implemented at the level of the food provider, and include incentivising the selection of portion choices that offer a more appropriate amount of energy (e.g. through pricing) or reducing the energy density of the available portions so that larger portions do not necessarily result in overconsumption of energy,” said the study.
Researchers from Pennsylvania State University and Saint Bonaventure University began by selecting a crossover design, which invited 24 women and 26 men to eat lunch in a lab once a week for 3 weeks.
At each meal, subjects chose a portion of macaroni and cheese from a set of 3 portion options. For women the portion sets by weight (g) were 300 g/ 375 g/ 450 g/ 375 g/ 450 g/ 525 g in the first week, and 450 g/525 g/600 g; for men the portions were 33% larger.
Across all portion sets, subjects chose the smallest available portion at 59% of meals, the medium at 27%, and the largest at 15%. The size of portions offered did, however, influence meal intake. Mean intake was 16% greater when the largest set was offered than when the medium and smallest sets were offered.
Portion size effect
The researchers pointed to the robust nature of the portion size effect as a possible explanation for the results observed. They believed that while offering options allowed consumers to compare portion sizes in making a choice, the absolute size of the available portions was a critical determinant of energy intake. Thus, in an eating environment where all portion options are large, individuals are likely to overconsume.
“The failure to adjust selection of meal size in an environment of large portions might be due to habit, convenience (use of heuristics), value (more food for no additional cost), pre-meal decisions) or a lack of concern for the consequences at a single meal; this lack of adjustment could put individuals at risk for overconsumption,” concluded the study.
One study found that people were extremely adept at estimating the 'expected satiety' and 'expected satiation' of different foods. These expectations are learned over time and were strongly linked to the number of calories that ended up on a plate.
Another study found evidence for the portion size effect, conducting a series of experiments that confirmed both male and female participants tended to eat in accordance with their pre-meal intentions and a portion size effect on actual consumption was subsequently observed in males, but not in females. The portion size effect may be observed when measuring pre-meal intended consumption in males.
Available online ahead of print, Vol. 98, pp. 95–100 doi:10.1016/j.appet.2015.12.023
“Increasing the size of portion options affects intake but not portion selection at a meal.”
Authors: Faris M. Zuraikata, Liane S. Roea, Gregory J. Priviterab, Barbara J. Rollsa.