Impulsive choice, an unwillingness to wait for a larger reward, is associated with obesity and consumption of unhealthy foods in humans. Research in rats suggests that diets high in saturated fat increase impulsive choice. The current translational study examined how diet interacted with body fat percentage and fasting glucose to predict food magnitude sensitivity in food-based impulsive choice tasks in rats and humans.
Rats (N=48) received either a control (C) or high-fat (HF) diet for 8 weeks, and humans (N=60) were split into corresponding groups based on their self-reported food intake. Both species completed an impulsive choice task, where they chose between smaller, more immediate (SS) rewards or larger, delayed (LL) rewards. A novel, experiential, real-food impulsive choice task was used in humans to improve translation between species. The SS and LL magnitudes were manipulated to determine magnitude sensitivity. Body fat percentage and fasting glucose levels were obtained, and the relationship with magnitude sensitivity was examined.
While rats fed a HF diet had greater magnitude sensitivity than the C diet (p < .001), there were no effects of diet on magnitude sensitivity in humans (p = .29). However, HF diets coupled with high body fat percentage predicted increased magnitude sensitivity in humans (ps < .05). For rats consuming a C diet (p < .001) and for humans across both dietary conditions (p < .01), higher fasting glucose levels were associated with greater magnitude sensitivity.
This translational study suggests broad similarities across species in the relationships among HF diet, body fat percentage, and magnitude sensitivity. HF diet alone increased magnitude sensitivity in rats, whereas a combination of diet, high body fat, and high fasting glucose levels best predicted impulsive choices in humans. This difference may be due to differences in control over dietary constitution and history in the two species.