Is ad libitum energy intake in overweight subjects reproducible in laboratory studies using the preload paradigm?

We assessed the reproducibility of ad libitum energy intake (EI) in overweight/obese subjects. A total of six men and two women, with a body mass index 27-32 kg/m(2), aged 18-45 years, not currently dieting and weight stable during the past 3 months were studied. Participants' EI before the study was standardized. A 1047 kJ (250 kcal) liquid preload containing 40% energy from whey protein (that is, 25 g of whey protein isolate) or a non-energy control preload were consumed randomly 90 min before an ad libitum lunch meal. Participants completed visual analogue scales for subjective appetite after preloads, and reported food intake during the remainder of the day. Treatments were repeated twice to assess reproducibility of ad libitum EI. Mean ad libitum EI was 3811+/-979 kJ and 3334+/-719 kJ after control- and whey protein-containing preloads, respectively. Analysis of repeated treatments showed within-treatment mean differences (+/- s.d.; day 1 minus day 2) of -50+/-251 kJ (-12+/-60 kcal), within coefficient of variation (CV) of 4.5% and intraclass correlation of 0.97 for control preloads. These results were -142+/-544 kJ ( 34+/-130 kcal), within-subject CVs of 11.2% and intraclass correlations of 0.72 for whey protein-containing preloads. In conclusion, ad libitum EI in a laboratory study using the preload paradigm in overweight and obese subjects was highly reproducible.