Tube feeding (TF) provides a model with which to study appetite when nutrient delivery bypasses the upper gastrointestinal (GI) tract and associated cephalic phase response. Nocturnal, diurnal and 24-h TF schedules are used clinically, but their effects on satiety have not been distinguished. This study tested two hypotheses: 1) bypassing the upper GI tract with TF has little satiating effect, and 2) diurnal TF suppresses appetite and food intake more than nocturnal or 24-h schedules. Six healthy men, residing in a metabolic suite, each received three continuous TF schedules (diurnal 12-h, nocturnal 12-h and 24-h; 6.86 +/- 0.51 MJ/d) in random order for 3 d over separate 10-d periods. Two days before and after TF, a placebo feed (<0.4 MJ/d) was given. Weighed measurements of ad libitum food consumption, hourly tracking of appetite and metabolic and hormonal measurements were undertaken. Compared with placebo feeding, there was a nonsignificant reduction in oral intake (1.01-2.49 MJ reduction), little change in appetite sensations with TF and an increase in total energy intake from 14.88 to 20.42 +/- 3.25 MJ. The schedules did not differ although diurnal TF was the most satiating. Changes in a variety of mediators (including leptin, insulin, cholecystokinin, metabolites and respiratory quotient) did not relate to immediate assessments of appetite and food intake. This trial suggests that continuous TF has little effect on satiety in healthy men over a period of 3 d, irrespective of the timing of the schedule. This could not be explained by changes in a variety of metabolic and hormonal signals within the time frame studied.
