*1.2. Reward Sensitivity*

When comparing ED patients to healthy controls on reward sensitivity, we need to differentiate between the studies that use the SPSRQ and those that use the BISBAS scales to assess reward sensitivity. As mentioned before, the SPSRQ assesses specific types of rewarding situations (i.e., physical attractiveness, or social approval), whereas the BISBAS scales assess more general reward sensitivity [24]. Studies using the BAS scale to assess reward sensitivity [8,23] have shown that AN-R patients score significantly lower on reward sensitivity compared to healthy controls, whereas AN-BP and BN do not differ significantly from healthy controls. When studies combine AN-R and AN-BP in one group, the difference between them and the healthy controls disappears. Studies using the SR scale show that AN-R, AN-BP, and BN patients score significantly higher on reward sensitivity compared to healthy controls [8,24,26]. However, Glashouwer et al. [24] showed that the differences between EDs and healthy controls disappeared when items that assessed appearance/social reward were removed from the SR scale. When comparing different subtypes of EDs on the BAS scale, most studies did not find significant differences between AN-R and AN-BP [26,27,31] or AN-R, AN-BP, and BN [23,29]. Studies that found significant differences between ED subtypes showed that binge eating/purging patients (AN-BP, BN) scored significantly higher on BAS fun seeking compared to restrictive AN patients [8,23,30]. Comparing ED subtypes utilizing the SR scale showed that patients with AN-R and AN-BP did not differ significantly from each other on the SR scale, whereas BN patients scored significantly higher compared to AN-R patients.

When comparing patients with obesity to healthy controls on reward sensitivity, patients with Class I obesity without BED did not differ from healthy controls on reward sensitivity [32], whereas patients with Class I obesity with BED scored significantly higher on sensitivity to reward when compared to healthy controls [33]. Patients with Class II obesity with and without BED also scored significantly higher on reward sensitivity (both BAS/SR scales) as compared to healthy controls [34]. No study compared patients with Class III obesity with and without BED to healthy controls on sensitivity to reward.

When comparing obese patients, obese patients (Class II/III) with and without BED did not differ significantly from each other on reward sensitivity [6,34]; no studies were performed in Class I obese patients. The higher reward sensitivity in moderate/extreme obese patients makes them possibly more vulnerable to rewarding (fatty/sugary) food in our obesogenic society, which may partially explain the overconsumption of food and their subsequently becoming overweight [7,39]. Several studies have shown positive associations between sensitivity to reward and emotional overeating, preference for high fat food, binge eating, and food cravings [39].
