Mechanism of Regulation of Food Intake

Mechanism of Regulation of Food Intake

Under normal physiological conditions, appetite and food intake are well balanced and continues in a

cyclic manner. Feeding center and satiety center of hypothalamus are responsible for the regulation of

appetite and food intake. These centers are regulated by the following mechanisms:

i. Glucostatic mechanism

ii. Lipostatic mechanism

iii. Peptide mechanism

iv. Hormonal mechanism

v. Thermostatic mechanism.

Glucostatic Mechanism

Cells of satiety center function as glucostats or glucose receptors, which are stimulated by increased blood glucose level.

While taking food, blood glucose level increases. Slowly the glucostats are stimulated and satiety center is activated. At one stage, it develops the feeling of ‘fullness’. Now, the satiety center inhibits the feeding

center and stops the food intake. After few hours of food intake, the blood glucose level decreases and satiety center becomes inactive. So, the feeding center is no longer inhibited. Now it becomes active and increases the appetite and induces food intake. After taking food, once again blood glucose level increases and the cycle is repeated. However, glucostats do not give response to very high level of glucose in blood (hyperglycemia). So, in conditions like diabetes, hyperglycemia fails to stimulate the satiety center. The satiety center does not inhibit the feeding center, so the frequency of food intake increases (polyphagia).

Lipostatic Mechanism

Leptin is a peptide secreted by adipocytes (cells of adipose tissue). It plays an important role in controlling the food intake and adipose tissue volume. When the volume of adipose tissues increases,

adipocytes secrete and release a large quantity of leptin into the blood. While circulating through brain,

leptin crosses the blood-brain barrier and enters hypothalamus. In hypothalamus, leptin inhibits the feeding center, resulting in loss of appetite and stoppage of food intake. It is suggested that the cells present in bloodbrain barrier contain many receptor-like proteins, which are responsible for the transport of leptin across the barrier.

Mode of action of leptin

Leptin acts through some specific neuropeptides inhypothalamus, such as:

a. Neuropeptide Y: It is secreted in small intestine, medulla and hypothalamus. Normally, this peptide

stimulates the food intake. But, leptin inhibits neuropeptide Y, leading to stoppage of food intake.

b. Pro-opiomelanocortin (POMC): It is secreted from anterior pituitary. It is also secreted from

hypothalamus, lungs, GI tract and placenta. Normally, it inhibits food intake. Leptin stimulates

the secretion of POMC.

Leptin receptor

Many leptin receptors are identified. However, leptin acts via ‘LepRb’, which is the only active receptor present in many nuclei of hypothalamus.

Peptide Mechanism

Some peptides regulate the food intake either by stimulating or inhibiting the feeding center, directly or

indirectly. The important one among the peptides is ghrelin.

Ghrelin is secreted in stomach during fasting. It directly stimulates the feeding center and increases the appetite and food intake. Besides ghrelin, several other peptides are involved in the regulation of

food intake.

Peptides, which increase the food intake:

a. Ghrelin

b. Neuropeptide Y.

Peptides, which decrease the food intake:

a. Leptin

b. Peptide YY.

Hormonal Mechanism

Some endocrine hormones and GI hormones inhibit the food intake by acting through hypothalamus.

Hormones which inhibit the food intake:

a. Somatostatin

b. Oxytocin

c. Glucagon

d. Pancreatic polypeptide

e. Cholecystokinin.

Thermostatic Mechanism

Food intake is inversely proportional to body temperature. So in fever, the food intake is decreased. Exact

mechanism of this fact is not known. It is suggested that the preoptic thermoreceptors (see above) may act via feeding center. The cytokines are also suggested to play a role in decreasing the appetite during fever.