Anticipatory physiological regulation in feeding biology: cephalic phase responses

Abstract

Anticipatory physiological regulation is an adaptive strategy that enables animals to respond faster to physiologic and metabolic challenges. The cephalic phase responses are anticipatory responses that prepare animals to digest, absorb, and metabolize nutrients. They enable the sensory aspects of the food to interact with the metabolic state of the animal to influence feeding behavior. The anticipatory digestive secretions and metabolic adjustments in response to food cues are key adaptations that affect digestive and metabolic efficiency and aid in controlling the resulting elevation of metabolic fuels in the blood. Cephalic phase responses enable digestion, metabolism, and appetite to be regulated in a coordinated fashion. These responses have significant effects on meal size. For example, if the cephalic phase insulin response is blocked the result is poor glucose control and smaller meals. Cephalic phase responses also are linked to motivation to feed, and may play a more direct role in regulating meal size beyond the permissive one of ameliorating negative consequences of feeding. For example, the orexigenic peptide ghrelin appears to display a cephalic phase response, rising before expected meal times. This anticipatory ghrelin response increases appetite; interestingly it also enhances fat absorption, linking appetite with digestion and metabolism.

Figure 1

Cephalic phase insulin and pancreatic polypeptide response in humans in response to sham feeding (data from Teff, 2000).

Figure 2

Plasma insulin concentration following ingestion of a mixed nutrient sandwich (data from Teff, 2000).

Figure 3

The cephalic phase insulin response to a meal was partially blocked by the infusion of trimethaphan (filled circles) relative to saline infusion (open circles). In the saline infused women a small increase in insulin was observed at minutes 5, 7 and 10 after beginning a meal, although blood glucose did not show a significant increase until 15 minutes. Insulin levels were higher in the saline infused women compared to the trimethaphan infused women at minutes 3, 7 and 15 after beginning the meal (indicated by *). Data from Ahren and Holst, 2001.

Figure 4

Cephalic phase insulin response to the ingestion of different volumes of 0.15% sodium-saccharin solution in rats. Data from Powley and Berthoud (1985). Plasma glucose levels did not change.

Figure 5

The cephalic phase insulin response to an orally infused sugar solution was significantly attenuated in rats that had been conditioned by pairing the sugar solution with a poison that caused gastrointestinal upset. There was no consistent insulin response to a sodium chloride solution. Data from Berridge et al., 1981.

Figure 6

Infusion of atropine blocks the increased secretion of gastric acid due to sham feeding in humans. Data from Katschinski et al. (1992).

Figure 7

Mean plasma ghrelin in 10 human subjects (9 women and 1 man) over a 24 hour period consuming breakfast (B), lunch (L), and dinner (D) at set times (8:00, 12:00, and 17:30). Subjects were aware of when meals were to be provided and the time. Data from Cummings et al. (2001).