Sweetness is a highly liked and extensively researched sensory attribute, significantly contributing to calorie intake worldwide. A recent scoping review identified over 35,000 papers on sweetness and health. Several health organizations recommend lowering the consumption of sweet-tasting foods, arguing that lowering dietary sweetness lowers preferences, which would in turn lower sugar, energy intake and body weight. However, empirical sensory data supporting this narrative are lacking. In fact, whether sweetness preferences (and perceptions) are modifiable remains unclear. To investigate this, a randomized trial has been ongoing since 2020, aiming to evaluate the long-term effects of low, regular, and high sweetness exposure on preferences. A total of 180 adults will be randomly allocated to either low (10-15% energy from sweet foods), regular (25-30% energy from sweet foods), or high dietary sweetness exposure (40-45% energy from sweet foods) for six months. The Ethics Board of Wageningen University approved the study (NL72134.081.19), and it is registered on ClinicalTrials.gov (NCT04497974). The detailed protocol has been published in BMC Public Health (https://doi.org/10.1186/s12889-022-14946-4). The primary outcome is the change in sweetness preference from baseline to six months. To assess preferences and liking, six series of sweet stimuli (familiar, unfamiliar, liquid, semi-solid, and solid) were constructed, in four consecutive experiments, each with five levels of sweetness intensity ranging from low to high, with an optimal liking level in the middle. As a control, two series of stimuli varying in saltiness (familiar, liquid, solid) were developed. Ranking on a Scale was used to assess preferences and liking, while perceptual ratings of intensity were collected using VAS. Results showed an effect of familiarity on liking across experiments, while psychohedonic and psychophysical functions had similar shapes across familiar and unfamiliar foods.