The importance of taste and palatability in carbohydrate-induced overeating in rats

Rats offered a carbohydrate solution (sugar or polysaccharide) in addition to chow typically overeat and gain excessive weight. The present study sought to determine if the palatable taste of these solutions contributes to the overeating response. Adult female rats were fitted with chronic intragastric catheters and given ad libitum access to chow and a drinking fluid that was paired with intragastric infusions. For one group (P + S), the flavored solution was a highly preferred mixture of 2% Polycose and 0.2% saccharin paired with intragastric infusions of 30% Polycose. For a second group (SOA), the flavored solution (0.03% sucrose octaacetate) had unpreferred bitter taste and was paired with intragastric infusions of 32% Polycose. Thus both groups were effectively exposed to the postingestive effects of 32% Polycose but paired with a palatable (P + S) or unpalatable (SOA) flavor. A control group had water to drink paired with intragastric water infusions. During the 4-wk experimental period, the P + S group consumed 34% more total energy (chow + Polycose) and gained more weight than did the SOA and control groups. The P + S group also consumed substantially more flavored solution and more energy as Polycose compared with the SOA group. The SOA group did not gain reliably more weight than the control group, although their total energy intake was 13% higher than that of the controls. In a choice test conducted at the end of the experiment, the P + S group displayed a strong preference (98%) for the Polycose + saccharin solution over water. In contrast to the control group, which avoided the SOA solution relative to water, the SOA group preferred the SOA solution (71%) confirming prior reports of Polycose-conditioned SOA preferences. These results demonstrate that palatability has a major effect on the overeating and obesity produced by carbohydrate solutions. In the absence of a highly preferred taste, the postingestive actions of Polycose produce only a small hyperphagic effect and no excess weight gain.