Brain response to feeding

Hi, my name is Julia Jarosławska and I am going to tell you how our brain regulates feeding behavior. Eating provides energy substrates for metabolism, and food is an essential part of everyone’s lives. The brain communicates with the digestive system, adipose tissue and other peripheral organs to control feeding behavior and energy balance. The brain initiates responses to feeding even before the ingestion of food. Just seeing and smelling the food or even looking at images of food is enough to stimulate secretion of peptide hormones in the gut and increases gut motility. You take a bite of food. Once food enters your mouth nutrients and other food-derived chemicals stimulate taste receptor cells within taste buds.

Approximately 4000 taste buds in humans are distributed throughout the tongue and oral cavity, and each taste bud contains 30 to 100 taste cells. In school we are taught that our tongues have specific areas that are susceptible to different tastes. However, the notion that the tongue is mapped into taste areas is all wrong.

There are five basic tastes identified so far: Sweet, salty, bitter, sour, and umami, and the entire tongue can sense all of these tastes more or less equally. Whereas taste receptor cells are not neurons themselves, they do communicate with the nearby neurons and the decision on taste is actually made in the brain, not on the tongue. Food moves from your mouth down the esophagus, it enters the stomach and little by little fills the space. Nerve cells surrounding gastric wall sense the stretching. These neurons communicate with the vagus nerve that goes up to the brainstem and hypothalamus the primary centers in the brain involved in the control of appetite. But that is just one input your brain uses to sense fullness.

After all, when you fill your stomach with water, you will not feel full for long. The appearance of nutrients in your digestive system and bloodstream stimulates the release of various hormones that circulate to the brain and modulate the appetite. Several hormones released from the gut in response to food intake exert anorexigenic, appetite-suppressing response in the brain, particularly in the hypothalamus. These hormones include glucagon-like peptide-1, cholecystokinin, peptide YY, pancreatic polypeptide, and oxyntomodulin. A single orexigenic, appetite-stimulating hormone, ghrelin, is known to be released by the stomach. Once nutrients and gut hormones are present in the blood, they trigger the pancreas to secrete insulin. Insulin is the body’s main tool for sugar management.

When you eat and your blood sugar rises, insulin is secreted into the blood and it prompts your muscle and fat cells to let the glucose in, and there starts the conversion of glucose into energy. Moreover, insulin stimulates the body’s fat cells to make another hormone called leptin. Leptin reacts with the receptors on neuron population in the hypothalamus. The hypothalamus has 2 sets of neurons that are important for the control of appetite. One set produces the feeling of hunger by making and releasing certain proteins. The other set inhibits hunger through its own set of compounds. Leptin inhibits the hypothalamic neurons that drive food intake and stimulates the neurons that suppress it.

Gut hormones are secreted from the gastrointestinal tract on a meal to meal basis and signal short-term nutrient availability to the brain. Hormones and cytokines released by peripheral organs exert long-term effects on energy balance. Eating behavior is critical for the acquisition of energy substrates. However, appetite is driven by factors that are beyond physiological needs. Food provides powerful visual, smell and taste signals which can override satiety and stimulate feeding. We tend to overeat sweet and salty foods that we find highly satisfying. And it is natural to get pleasure from eating, however, we need to remember that eating that is not driven by hunger may easily result in overeating and contribute to obesity.