The design of a mobile portion size estimation interface for a low literacy population

Being aware of one´s portion sizes is a key component of maintaining a healthy diet, however, it is difficult for individuals especially low literacy populations to estimate their consumption. Nutritional monitoring applications can help but most of them are designed for people with high literacy and numeracy skills. In this paper, we designed and evaluated six portion size estimation interfaces through a Wizard of Oz based experiment using low-fidelity prototypes with ten varying literacy individuals. The interfaces were designed based on the cognitive strategies adults use for reporting portion sizes in diet recall studies. Participants made correct estimates with interfaces designed for liquid and amorphous foods, but had difficulties with those designed for solid foods. Based on these findings, we provide recommendations for designing accurate and low literacy-accessible portion size estimating mobile interfaces.