All About Hunger

Why is Hunger Important?

There are 3 reasons why hunger is important. Firstly, eating gives us the energy for activities. Secondly, eating provides fuel to maintain body temperature. Thirdly, eating provides materials needed for growth and repair of tissues.

Set Point Theory

Set point varies among individuals. The set point tries to keep weight constant, and at the same time, I can pressurize our minds to change behaviour to feel hungry or full. When one’s weight rises above the set point, he/she loses appetite or uses up more energy, thus having the feeling of not wanting to eat. After which, one’s weight will then return to set point. On the other hand, when one’s weight drops below the set point, he/she has an increase appetite and use up less energy. After which, one’s weight will then returns to set point. Only when one’s weight is at the set point, he/she is in a stable and optimistic mood.

Sensory-specific satiety

The sensory-specific satiety theory is when one no longer finds a food as appealing and delicious as the first time they eat it after repeatedly consuming the food.

The sensory-specific satiety takes place at the nucleus of the solitary tract (NST), which is located in the medulla. In the picture below, the area mark in red is where the medulla is located.

Learned Taste Aversion

Learned taste aversion is “the avoidance of a particular food that is related to illness or poor nutrition” (Garrett, 2003, p. 132).

Learned Taste Preference

Learned taste preference refers to “a preference not for the nutrient itself but for the flavour of a food that contains the nutrient” (Garrett, 2003, p. 133).

Feeding Cycle

The feeding cycle is divided into 2 phases, the absorptive phase and fasting phase.

For a period of time after the meal, our body will stay at absorptive phase whereby it lives off the nutrients from the digestive system. During this time, the glucose level in our blood rises and the brain will detect it, hence, activating the parasympathetic activity. Because of this our pancreas will start to secrete a substance called the insulin. Cells that are out of the nervous system contain insulin receptors which will activate transporters to carry glucose into the bloodstream.

During this phase the body will also stock up some nutrients to prepare for the fasting. Some of these glucose will be converted into glycogen and are stored in the liver and muscles. As for the remaining glucose, it is converted into fats and stored in the adipose tissue which is also known as fat cells.

When the body is at the fasting phase, glucose level will decrease and once the brain detects it, the sympathetic activity will be activated to stop the pancreas from secreting insulin and instead start secreting the hormone glucagon which will convert stored glycogen back into glucose. The reason for this action is that now the glucose level is low and the body will have to rely on the stored glucose. The fatty acids are used by muscles and organs while the liver converts glycerol to more glucose for the brain.

Hence, from these two phases we can understand how the concept of hunger works. When we are full, we are actually at the absorptive phase, however, when we are hungry we are at fasting phase. It is actually a repetitive cycle of the two phases.

Helping words

Insulin- A hormone that enables body cells to take up glucose for energy and certain cells to store excess nutrients.

Glycogen- Storage form of glucose in animals and humans which is analogous to the starch in plants .

Brain mechanisms for hunger

The two main parts of brain that are related to hunger are hypothalamus and medulla. Hypothalamus is located near the base of the brain, beneath thalamus. It is regarded as the ‘master area’ for control of appetite (Mendieta-Zéron, López, & Diéguez, 2008). It “conveys messages to the pituitary gland, altering its release of hormones” (Kalat, 2009, p.93). Two specific regions of the hypothalamus that are actively involved in regulating ingestive behaviours are the lateral area and ventromedial area, controlling hunger and satiety respectively. Lateral hypothalamus acts as the ‘accelerator’ to ingestive behaviour while ventromedial hypothalamus acts as the ‘brake’. Findings have shown that: Animals stop eating or drinking after lateral hypothalamus was destroyed (Anand & Brobeck, 1951; Teitelbaum & Stellar, 1954) and on the other hand, animal eat endlessly when ventromedial hypothalamus is damaged (Hetherington & Ranson, 1942). Electrical stimulation to the region(s) will produces organic functioning. Next, medulla is located just above the spinal cord. It receives taste information from the tongue and a variety of sensory information from the internal organs such as signals from detectors in the stomach. Medulla contains glucoreceptors which are sensitive to glucose within body. It detects nutrient levels and initiates feeding behaviour. Research has shown that there is an increase in activity in medulla when hunger is felt (Kalat, 2009).

Hormones and hunger

Three significant hormones that are related to hunger are namely, leptin, ghrelin and orexin. Leptin is an ‘anti-obesity’ hormone that is produced by fat cells and is receptor in hypothalamus. It has profound effects on metabolism and eating, such as decreasing food intake and increasing metabolism rate. Low leptin levels initiates feeding behavior by stimulating parasympathetic nervous system.

Effects of level of leptin

In contrary to leptin which decrease food intake, ghrelin stimulates hunger and enforce feeding behavior. “Ghrelin is the only known hunger hormone” (Kalat, 2009, p. 306). It is produced in stomach, specifically in pancreas. Ghrelin is released during a period of food deprivation, where it triggers stomach contractions (Kalat, 2009), and is decreased following a meal.

Ghrelin concentration in the blood fluctuates throughout the day, rising before a meal and then decreasing upon consumption.

Ghrelin secretion and the feedback mechanism

Moving on, orexin is a neurotransmitter found in lateral hypothalamus which stimulates hunger and appetite (similar to ghrelin) and decrease metabolism rate (Carlson, 2008). This in turn increase and preserve the body’s energy stores. Studies have shown that if there is food deprivation, production of orexin will increase (Qu et al., 1996; Sakurai et al., 1998; Dube, Kalra, & Kalra, 1999). Production of orexin is also influenced by leptin and ghrelin levels. For instance, orexin cells are inhibited and feeding is reduced when there is high level of fats stored and high leptin level.

Lateral and ventromedial hypothalamus

Immediate and short-term consequences of hunger

Hunger can have various effects on individual. Firstly, there may be emotional changes such as increased anxiety, irritability and aggression (Kleinman et al., 1998; The Food Research and Action Center, 2009; DeRose, Messer, & Millman, 1998). When an individual misses his lunch, the hunger pangs come along to signal the need to have a meal. Hunger, the bodily reaction, may be intolerable to individuals and may result in frustration. Kleinman and fellow researchers (1998) state that aggression is linked to subclinical hunger in both human and animal studies. When there is no satiety in stomach, human are similar to animal and may turn aggressive or desperate.

Next, under Maslow’s hierarchy of needs, the basic/physiological needs such as food and water must be met in order for people to seek other higher needs such as love and belonging needs (e.g. acceptance in a community). With basic/physiological needs not fulfilled, behavioural problems may appear as consequences of hunger. Individual may show symptoms of social withdrawal or decreased concentration (DeRose, Messer, & Millman, 1998) as they may no longer care for the acceptance they have/not. Work performance and productivity may also be seriously affected. The goal and positive attitude to achieve, to be competent and to gain work recognition may dissolve when hunger pangs disrupt the thoughts and cognition. There may be physiological consequences of hunger, including unwanted weight loss, fatigue, headaches and frequent colds (The Food Research and Action Center, 2009; Calorie Count, About, 2010). Severe anaemia may also occur when there is protein deficiency.

Maslow's hierarchy of needs

Long Term Consequences of Hunger

Firstly, malnutrition is a long term consequence of hunger. Due to malnutrition, one may experience reduced strength, fatigue, deterioration in several body functions, and negative emotions. In children, it may affect their puberty growth.

Secondly, chronic hunger may cause high infant mortality rates, as malnourished women have a high chance of falling sick, thus having smaller babies who die earlier. When there is high infant mortality rates, birth rates are high too, thus these people will always be stuck in the vicious cycle of malnutrition and death.

Thirdly, chronic hunger may cause people to be vulnerable to common illnesses such as diarrhoea, which they lack the strength to survive through.

Lastly, chronic hunger may cause one to have a weakened immune system, which puts one in a position where he/she is more vulnerable to infection and future cases of it.