What are hunger pangs?
Hunger pains or hunger pains are intense gastric contractions that occur when the stomach is empty for many hours. It eases once the stomach is distended with food although the feeling of hunger may persist.
The stomach is a muscular hollow organ which can hold up to 1.5 liters of food. Muscles in the wall of the stomach mix food with gastric secretions and assist with breaking food down into smaller particles. These are normal peristaltic contractions that are weak higher up in the stomach (body) and become stronger lower down in the stomach (near the pylorus). These contractions are rhythmical and continue throughout the gut to ensure that food is in constant transit as it is digested.
What causes hunger pangs?
Hunger contractions occur in the stomach and are strong and successive. It may occur so quickly that it meshes into a prolonged contraction or cramp which is referred to as hunger pangs and can last for 2 to 3 minutes at a time. Over time, the pangs increase in intensity, anywhere between 12 to 24 hours after the last meal. It has been noted in cases of starvation, that after 3 to 4 days, the contractions become weaker and hunger pains reduce in intensity. In cases of stomach disorders like gastritis or peptic ulcers, hunger pangs can be quite painful. The pain associated with these conditions may also be mistaken for hunger pains.
While hunger pangs and the feeling of hunger are related, the pangs may subside after eating food yet the feeling of hunger may continue to linger. This is also associated with appetite, the desire to eat and cravings for certain foods, compared to hunger which is the need to eat.
Hunger and appetite control are linked by both the hunger and satiety centers located in the hypothalamus and is due to a complex play of :
- hormones from the stomach, fat cells (adipose tissue) and within the brain
- neural signals between the stomach and brain
- blood glucose levels
Control of Appetite by Feeding Centers in the Brain
The hunger center is also known as the lateral nuclei because of its location in the hypothalamus, while the satiety center is known as the venteromedial nuceli.
Regulation of food intake is not isolated to just these areas. There are three other areas in the brain that influence feeding and this includes :
- Paraventricular nuclei
- Dorsomedial nuclei
- Arcuate nuclei
These feeding centers do not just drive a person to eat or stop eating. It also influences blood sugar levels, energy storage in fat cells and energy utilization in terms of the body’s metabolism.
The feeding centers can be affected by :
- nerve signals through the vagus nerve as the stomach fills (distends) or when it is empty.
- chemicals released from the stomach (ghrelin) and small intestine (CCK) – refer to Digestive Hormones
- chemicals in the blood particularly from food breakdown like glucose (carbohydrate), amino acids (protein) and fatty acids (fats)
- chemicals from the fat cells (leptin)
- cerebral nerve signals as a result of sight, smell and taste
The arcuate nuclei plays an important role in the coordination of all these signals (chemical and nerve) and influencing appetite by the different types of neurotransmitters that it produces :
- orexigenic neurotransmitters that increase feeding
- anorexigenic neurotransmitters that decrease feeding
Any substance that increases appetite, even chemicals not produced by the arcuate nuclei, are referred to as orexigenic substances, like cortisol produced by the adrenal gland. Similarly, any substance that decreases appetite is known as anorexigenic substances, like insulin produced by the pancreas.
However, these substances do not just increase or decrease appetite, they also influence energy expenditure – the body’s metabolism. Many weight loss drugs act as anorexigenic substances by decreasing appetite and increasing energy expenditure.
Short Term Appetite Control
These factors can increase or decrease appetite within seconds or minutes but have a short term effect on regulating appetite.
- Food in the Mouth
- Oral monitoring of ingested food decreases appetite, possibly as a result of chewing, salivation and swallowing.
- The sense of taste also act on the satiety center which inhibits the hunger center. This explains why certain foods which are being craved for will appease hunger even in moderate amounts.
- Stretching of the Stomach
- Stretching of the stomach and first part of the small intestine (duodenum), sends nerve signals to the brain through the vagus nerve. This decreases appetite.
- The presence of fats from food in the duodenum causes the release of CCK (cholecystokinin).
- This acts on the feeding centers to decrease appetite.
- Local nerve reflexes as a result of stomach distension also stimulate the duodenum to release CCK – refer to Stomach Nerves.
- Ghrelin is secreted by the stomach after a period of not eating (fasting) and it increases appetite.
- There are other areas in the body that also secret this hormone but the stomach is one of the main sources.
- It is not known what exactly increases the secretion of ghrelin but a low blood sugar level and an empty stomach may be some of the contributing factors. Leptin secreted by fat cells may reduce ghrelin secretion.
- Peptide YY (PYY) and Glucagon-like peptide
- These two hormones are secreted by the entire gastrointestinal tract in response to all foods, especially fats.
- It decreases appetite.
- Glucagon-like peptide also causes the secretion of insulin which acts on the feeding centers to decrease appetite.
Long Term Appetite Control
These factors can increase or decrease the appetite but influence it after hours or days.
- Nutritional Status
- The body is able to assess the nutritional status and increase or decrease appetite accordingly.
- Cravings of certain foods may be a result a lack of certain nutrients and the satiety center only inhibits the feeding center once these nutrients are acquired through food.
- Nutrients in the Blood
- Low blood levels of glucose, amino acids or certain fatty acids increases appetite as these nutrient levels are constantly monitored by the hypothalamus.
- Conversely, high levels of these nutrients will decrease appetite.
- Fat Cells(adipocytes)
- Adipose tissue (fat tissue) secretes leptin which decreases appetite
- Leptin has become a major focus of weight loss in recent years because it also increases the body metabolic rate and reduce insulin secretion which promotes fat storage.
- However, leptin alone seems to be ineffective in long term weight management and treating obesity.
- Environmental Temperature
- The thermoregulatory center in the hypothalamus influences the feeding centers that are responsible for appetite control.
- Prolonged exposure to cold increases appetite as the body needs more energy to increase metabolism in order to generate heat and maintain the body temperature within a normal range.
- Similarly, the increased appetite is intended to increase in fat stores as subcutaneous fat serves to insulate the body from heat loss. This explains the reason for ‘winter fat’.
- Higher temperatures or hot weather has the opposite effect in that it decreases appetite.