EXAMINING THE REINFORCING EFFECT OF CARBOHYDRATE-FAT COMBINATIONS AND PROCESSING LEVELS OF MODERN FOODS IN HUMANS

Modern diets increasingly blend fats and carbohydrates (F+C) in processed foods, creating combinations that may overactivate the brain’s reward systems. Yet how these nutrients and processing effects translate to food valuation—and whether this varies by body weight—remains underexplored. We investigated this question in a Finnish adult sample (N=32), combining behavioral willingness-to-pay (WTP) measures with a novel standardized image set. WTP was analyzed using linear mixed-effects models controlling for portion, liking, estimated energy density, calories, and price. Preliminary results showed an effect of F+C (β= .10, t(1081)= 2.69, p= .007), driven by the normal-weight (NW) group (β= .08, p= .12) with no effect on the overweight (OW)(β= -.05, p= 1.00) and obesity (OB) group (β= .02, p = 1.00). Post-hoc analysis revealed no F+C reward effects within all weight groups. However, the OW/OB groups bid higher overall than NW (β= -0.51, p < .001), with NW undervaluing all categories. Notably, OW participants valued fats more than carbohydrates and F+C (β= .26, p= .001), while the OB group showed no macronutrient preferences. Ultra-processed foods also did not elicit stronger reward valuation than minimally processed foods (β= -.04, p = .19), and OW/OB placed higher bids than NW (β= -.6, p < .001). Contrary to studies predicting higher reward from F+C combinations, our overall analysis showed no additive effect. Excess weight, not nutrient pairing or processing, robustly elevated food valuation. These interim findings tentatively challenge prior work, highlighting instead that adiposity can shape motivational responses to food.