We all know that all too familiar feeling of hunger that sets in after skipping a meal, perhaps if you were in a rush to leave home to get to work on time! It’s uncomfortable and can lead to some rather loud grumbles, which can be distracting mid-meeting!
What exactly causes it and how does our body recognise that we’re hungry?
How does the brain know you’re hungry?
As humans, we require a certain amount of energy from food to sustain us. This amount varies a great deal from person to person and changes throughout the life course.
Striking the balance between the amount of food we consume, with the amount we expend is complex and involves coordinated regulation by the central nervous system (CNS). This process is governed by hormones and can be referred to as homeostasis. The CNS receives signals from the Gastrointestinal tract (stomach and intestines), pancreas and body fat.
These systems are all interlinked by hormones, nerves and other cell signalling molecules that impact whether we feel hungry or full by activating specific areas of the brain.
What causes the feeling of hunger?
What drives appetite and food intake is extremely complex, but we’ve rounded up a handful of the factors involved:
- Ghrelin is a hormone produced in the gut which stimulates food intake and makes you feel hungry. It’s highest when we fast, and production drops almost immediately after we start eating. Protein and carbohydrates have a stronger effect than fat on ghrelin suppression.
- Leptin is a hormone primarily produced by fat cells; the more fat you have, the more leptin you produce. Leptin signals to your brain, more precisely the hypothalamus, how much energy there is in store should food become scarce. Based on that signal, the brain can impact how hungry you feel and how much you eat. It is secreted as a signal that we’ve had enough to eat for the meantime.
- Stress has been found to both increase and decrease hunger and impact our eating behaviour. This is largely thought to be due to fluctuations in cortisol levels but also linked to the duration of stress (2). The hypothalamic-pituitary-adrenal axis (HPA axis), is a term used to show the interaction between the hypothalamus, pituitary gland, and adrenal glands and plays a vital role in the body’s response to stress. The pathway of the axis results in the production of cortisol (stress hormone). When it comes to acute stress that requires a physical response, the HPA axis regulation of food intake allows the stressful event to be dealt with and the energy used to be replaced afterwards (so a short-term decrease in appetite). In the case of ongoing psychological stress, however, chronically elevated cortisol can lead to chronically stimulated eating behaviour and excessive weight (3). Further, those experiencing chronic stress have been found to show an increased preference for and consumption of hyper-palatable, energy-dense foods high in sugar and fat (4).
- Food aroma and taste, aka the sight and smell of food, can have an effect on how much you feel like consuming. Research has shown that your sense of smell improves when fasting and declines when you are full (2). Research has also shown that how long food is in your mouth can contribute to satiety (feeling of fullness) through nutrient sensing systems (5).
- Food components such as protein, carbohydrates and fat are broken down into amino acids, glucose and fatty acids during the digestion process. These components each have specific roles within the body and provide us with energy. However, they also send signals to the brain to change the amount of food we eat via different mechanisms. When the neurons observe increased levels of the three components mentioned, the hypothalamus signals a reduction in short-term food intake (6).
How much should you listen to your hunger cues?
When you are in a deficit, it is not uncommon to feel more hungry, especially if you have drastically cut your calorie intake (we usually recommend a more gradual, sustainable approach to counteract this).
A little hunger here and there can occur as you are consuming less than your body requires for the activity it is carrying out.
However, if this persists or begins to impact your day-to-day life, you should not ignore your hunger cues. At this stage, reevaluating your calorie intake (and macronutrient breakdown) will likely be beneficial.
It is important to be aware that equations used to calculate calorie requirements provide an estimation of your needs but do not take into account all individual variations. This means they won’t always be spot-on from the get-go and can need tweaking over time.
For many, it is also normal to feel like you just can’t get satiated on a day when you have completed an intense workout. If you know this is a common occurrence for you, it can be helpful to revisit your meal timings and layout of your intake – for example, aim to incorporate some extra snacks into your total intake to ensure you are not leaving large gaps between your meals.
As noted, hunger and eating behaviour are very complex and can be impacted by an array of factors. If you have any questions on this or would like to discuss your FFF plan with one of our Nutritionists, book in for a call here!
References
- Chao AM, Fogelman N, Hart R, Grilo CM, Sinha R. A Laboratory-Based Study of the Priming Effects of Food Cues and Stress on Hunger and Food Intake in Individuals with Obesity. Obesity. 2020;28(11):2090-7.
- Ulusoy, S., Dinc, M., Dalgic, A., Topak, M., Dizdar, D. and İs, A., 2017. Are people who have a better smell sense, more affected from satiation?. Brazilian Journal of Otorhinolaryngology, 83(6), pp.640-645.
- Sominsky, L. and Spencer, S., 2014. Eating behaviour and stress: a pathway to obesity. Frontiers in Psychology, 5.
- Torres, S. and Nowson, C., 2007. Relationship between stress, eating behaviour, and obesity. Nutrition, 23(11-12), pp.887-894.
- Boesveldt, S. and de Graaf, K., 2017. The Differential Role of Smell and Taste For Eating Behavior. Perception, 46(3-4), pp.307-319.
- Chen, Y. and Knight, Z., 2016. Making sense of the sensory regulation of hunger neurons. BioEssays, 38(4), pp.316-324.
