Body fat regulation during pregnancy and lactation: the roles of diet and insulin.

Obesity is a condition characterized by an excess of body fat, hyperphagia, hyperinsulinaemia and moderate hyperglycaemia (Bray & York, 1979). The lactating rat, despite being hyperphagic, is hypoinsulinaemic (Flint et al., 1979), moderately hypoglycaemic (Robinson et al., 1978) and may display an extensive catabolism of body fat (Steingrimsdottir et al., 1980; Rolls et al., 1984). The purpose of' the present work was t o investigate some of the physiological and metabolic changes which occur in the obese lactating rat. Previous work has shown that rats with dietary obesity, fed a cafeteria diet during pregnancy and lactation, lost considerably more weight than lean rats during lactation (Rolls & Rowe, 1982). However, it was not clear what were the relative contributions of pre-existing obesity, non-foetal weight gain in pregnancy and the diet available to the change in body weight during lactation. A net deposition of body fat occurs during pregnancy, but it is not clear whether there is an optimal level of body fat required to support lactation. The first experiment was designed t o answer these questions (see Rolls et al., 1984). Adult hooded Lister rats were made obese by offering them a variety of palatable, high-energy foods (cafeteria diet) for approx. 10 weeks. Age-niatched lean rats were fed just chow during this time. During pregnancy, obese and lean rats were offered either just chow, o r a cafeteria diet in addition to chow. Nonfoetal weight gain was greatly increased in rats fed the cafeteria diet, but was not strongly affected by pre-existing obesity (see Fig. 1). The increase in non-foetal weight gain in cafeteria-fed rats consisted predominantly of fat. It is concluded that fat deposition during pregnancy is very variable and that it is not regulated at an optimal level to sup pu r t lactation . In the second part of the experiment, half of the rats, which had been fed just chow during pregnancy, were switched to the cafeteria diet during lactation, and tlie remainder continued t o receive just chow. Similarly, half o f the rats, which had been fed the cafeteria diet during pregnancy, were fed just chow during lactation, and the remainder continued to receive the cafeteria diet. The change in body weight during lactation was inversely related to the body weight a t parturition and t o the nonfoetal weight gain during pregnancy. Therefore, the change i n body weight during lactation compensated for the prcexisting obesity and for the enhanced non-foetal weight gain in pregnancy caused by cafeteria feeding. Furthermore, the type of diet available during lactation had little effect on body weight changes in lean lactating rats. Obese rats lost considerable amounts of weight during lactation, and this occurred even when the obese rats were fed a cafeteria diet (see Fig. 1). The results show that the consumption of a palatable, high-energy diet need not invariably lead to an increase in body weight. Obese rats, provided with a cafeteria diet before parturition, showed an increased loss of body weight and a striking degree of hypophagia when they were given just chow during lactation. This decrease in energy intake P R E G N A N C Y L A C T A T I O N