The pattern of food consumption has a profound influence on metabolic hormone secretion, but until recently only crude manipulations of feeding events have been possible in rodents. Using a CLAMS-based system to overcome this problem, we have investigated the effect of 3 weeks of grazing (consumption of 1/24th of the total daily food intake of ad libitum-fed controls every 30 min during the dark phase (18.0006.00 h)) and meal feeding (three 1-h periods of ad libitum food access at 18.00, 23.30 and 05.00 h) on skeletal growth and femoral strength in 6-week-old male SpragueDawley rats.
Grazing and meal-fed rats showed a 15% reduction in cumulative food intake, but only meal-fed animals exhibited less weight gain than ad libitum-fed controls. Similarly, although body length was reduced by 3% in both grazing and meal-fed rats (P<0.05), tibial and femoral length was only reduced in meal-fed animals (3% lower; P<0.05). Overall cortical strength (as assessed by three-point bending) was unaffected with either feeding pattern, but grazing rats showed a 24% increase in the geometric component of strength (2nd moment of area; P<0.05), due largely to a 35% increase in the thickness of the posterior cortex (P<0.05 vs meal-fed).
Profiles of circulating total ghrelin (as assessed by automated blood sampling) were identical in grazing and meal-fed rats, both feeding patterns eliciting the expected anticipatory rise in ghrelin prior to the commencement of the dark (feeding) phase. Overall GH secretion (area under curve), baseline levels, pulse height and pulse frequency were unaffected in grazing rats, but the daily nadir in peak heights was shifted into the early dark phase.
Given the short period of exposure to patterned feeding, the subtle effects observed in the growth and biomechanical performance of bone are remarkable, suggesting that the pattern of daily food consumption in adolescence may influence the three-dimensional shape of bone during the growth phase, potentially resulting in longer-term consequences for adult bone health.