The Different Types Of Hunger
Article by Namrata Ashok
There’s always space for dessert, right? A 2016 study reported a 24% increase in whole brain metabolism when shown appetising images of food while lying in a brain scanner in hungry participants (Wang et al., 2004). This study shows that the sight of food changes brain activity and indicates that hunger may be influenced by our senses. Does that mean there is more than one type of hunger?
What is hunger?
We understand the perceptual nature of hunger because of several studies which shows that even after the removal of the stomach that hunger still persists. This finding ruled out the stomach contraction theory by Cannon and Washburn (1995) which suggested that contraction of the stomach muscles determined hunger (Hara, 1997). Nowadays, we understand that any attention and thoughts around food or interpretation from our 5 senses initiates the process of digestion and informs appetite. This relationship between our senses and appetite relates to reward pathways in the brain, which motivated humans long ago to be vulnerable, seek food, and prevent starvation (E. Tory Higgins, 2006).
Hunger, as we know it, typically relates to a strong perception and urge to eat. In a physical sense, it is an innate response for blood sugar, fat, and electrolyte levels to return to a state of internal balance. This process is coordinated by the hypothalamus in the brain and hormones produced in the stomach, one of which is Ghrelin that signals to the brain to stimulate appetite when the stomach is empty. Simultaneously, the perception of hunger has a psychological component that is dictated by satiation. Satiation is the process that leads to eating termination and “fullness” as a result of meal quality and quantity. Meal quality and quantity is influenced by learned and anticipated emotions associated with the 5 senses of the body - sight, smell, taste, hearing, and touch- as well as the nutrition profile of the meal (Amin and Mercer, 2016).
Physical Hunger
Stomach hunger is the hunger derived from internal cues, which are described in the following four theories, to maintain energy homeostasis and prevent starvation:
The glucose theory suggests that hunger is triggered to increase blood glucose levels to physiologically normal levels.
The fatty acid theory highlights that hunger is triggered when fatty acid receptors detect an increase in free fatty acid levels.
The heat production theory suggests that hunger occurs when body temperature decreases (Hara, 1997).
The distension (swelling) of the stomach, response to fluid movement, and nutrient composition of food passing through the digestive tract regulates the production of hormones responsible for hunger and satiety and informs appetite (Amin and Mercer, 2016).
Emotional Hunger
The psychological component of hunger is regulated by messenger-like substances in the brain, including dopamine, endocannabinoids, and serotonin, which contribute to the reward pathway. The regulation of energy balance by the brain can be overridden by eating to obtain pleasure in the absence of energy deficiency. Although energy balance is tightly regulated with precision, the body tends to be more tolerant to excess energy intake and body fat storage as the protective mechanism that allowed humans to cope with famine during the hunter-gatherer times (Amin and Mercer, 2016).
With this capacity of tolerance, emotional hunger tends to occur as a consequence of stress, a need for security, or is associated with an intense emotion. To our brain, the stress experienced in work is the same stress as trying to make it in time for the train when you’re late and the stress of escaping an unexpected and sudden chase. Long-term states of perceived threat by the brain, such as work stress, continuously stimulates the release of the stress hormone cortisol. This long-term elevation of cortisol upregulates appetite, especially for highly palatable and energy dense foods. Researchers activated the neurons in the brain responsible for stimulating appetite in mice and found a greater preference for sweetness and a decreased sensitivity to aversive bitter and sour tastes. Essentially, sweet foods were sweeter and more attractive, and bitter foods were palatable and less difficult to eat. Thus, stress increases the sensitivity of tongue receptors or the perception of taste stimuli to prevent starvation and ensure the body has sufficient fuel to combat the source of stress, which ancestrally were life-threatening situations where energy availability dictated our chances of survival (Fu, Minokoshi and Nakajima, 2021).
Taste Hunger
Taste Hunger is the hunger associated with a particular experience. Interestingly, the boundary theory of hunger suggests that individuals perceive how much they think they should eat based on remembering the good times associated with the taste, typically leading to overconsumption of food to meet true satisfaction (Hara, 1997). Several studies have highlighted the role of short-term memory on feeding behaviour. In fact, impaired short-term memory has been shown to contribute to feelings of uncertainty surrounding food availability and lack of control over future eating behaviours. Interestingly, paying more attention while eating has been shown to facilitate memory encoding, satiate faster, and reduce future overeating (Higgs and Asperger, 2018).
Also related to taste hunger is the effect variety has on hunger. A study that offered obese women the same bland meal on 5 consecutive days found reduced food intake on the 5th day compared to the control condition where the bland meal was offered once a week (Epstein et al., 2011). This idea is explained by the concept of “quality can replace quantity,” whereby the action and continuation of eating is driven by pleasure associated with food. The more palatable and sensory activating the food is, the more we experience pleasure. This process promotes satiation faster. On the contrary, obese individuals tend to have deficiencies in these reward pathways, perpetuating continuous eating patterns to achieve the same level of pleasure as a healthy individual (Møller, 2015).
Practical Hunger:
Finally, the literature on practical hunger is less clear (Barraclough et al., 2019) but describes hunger derived from habit and routine. This type of hunger is a reflection of learned behaviour based on time, which consists of consuming food in response to anticipated physical hunger that may not be satisfied due to external constraints. For example, practical hunger may look like feeling peckish at the same time every day regardless of the meal consumed or eating before a long meeting that runs over our habitual eating windows, knowing we are likely to get hungry during that period but may not have access to food. Practical hunger becomes apparent when jet lagged and entering a new time zone when we experience those untimely and odd moments of hunger, even if food was consumed shortly prior.
Summary
Feeding behaviour occurs in three steps (Fu et al, Minokoshi and Nakajima. 2021)
Recognition and processing of a relevant stimulus from sensory information.
Choice based on either ‘liking’, ‘wanting’, or ‘learning,’ which include the hedonic impact, motivational processing of an incentive, and learned associations with a consequence of actions within particular contextual or cultural cues respectively. However, these learned behaviours are replaced by mappings of possible outcomes and expected values in unfamiliar situations.
Termination of feeding is typically mediated physically by factors of satiation.
There are 4 types of hunger:
Physical
Emotional
Taste
Practical
This blog post was written by Namrata Ashok, a Sports Science and Nutrition BSc student at the University of Glasgow. Currently involved in two internships, work experience, podcasts, and further reading, alongside her studies, Namrata is enthusiastic about helping individuals heal and restore from the inside out, honing in on approaching the root cause. She is determined to explore the world of health, nutrition, and movement by combining research, theory, and practical experience.
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