Some metabolic effects on lactating rats of a low-energy diet restricted in good-quality protein.

Adult female Sprague-Dawley rats were fed ad libitum during pregnancy and lactation a control diet (CD; 16.1 kJ/g) or a low-energy diet with wheat gluten as the main protein source (LED; 13.3 kJ/g). Body weight, food intake, resting energy expenditure, respiratory quotient and substrate use by the mammary gland were measured. After the animals had been killed, the parametrial and retroperitoneal fat pads were weighed. The mean food intake (g) of the two groups of rats was similar, resulting in a lower energy intake by the LED rats, significantly different during the last 2 weeks of lactation. The mean body weight of both dams and pups in the LED group was lower, starting at day 9 of lactation. The resting energy expenditure increased gradually during lactation in the control group, whereas this increase was not seen in rats of the LED group in the last week of lactation. Rats that had fasted overnight had a respiratory quotient of 0.7 or less, whereas for rats that had been fed, the mean respiratory quotient was over 1.0. Under both conditions, rats showed ketonuria. The arteriovenous difference in 3-hydroxybutyrate level was higher and those for glucose, lactate and triacylglycerol were lower across the mammary glands of LED rats. The parametrial fat depot weighed less in LED rats. Reducing the increase in resting energy expenditure and using ketone bodies to a greater extent as fuels may represent important mechanisms in the LED dams to cover the energy cost of milk production.