Hunger: between fasting and eating disorders

By Selin Ilgaz

Humans, for a long time, have been through inconsistencies in their access to food, shifting between periods of prosperity and periods of famine [1]. Today, there is a general stabilization in our society; and furthermore, we even have access to more food than what we need. Indeed, portions keep getting bigger, people’s weights keep expanding and we increasingly consume more calories than what our bodies can burn. For this theme of the Allotment Project, I am going to focus on the aspects of fasting, looking at its benefits on health and mood as well as its possible complications. This will lead to the subject of eating disorders such as anorexia and bulimia.

Fasting periods are rituals practiced throughout humanity and across all cultures and religions. It is believed that fasting procures a sense of spirituality, helping the individuals to reach their spiritual self. Aside from spiritual ends, fasting has also been considered a treatment for acute and chronic diseases from the existence of early medicine, improving mood and increasing mental alertness [1]. But what does empirical research say about that? Is therapeutic fasting effective and does it really help us feel better?

Although fasting is a common phenomenon across all religions with a primary objective of spirituality, medical fasting can be very different in its practice, aiming at different goals. I am only going to discuss the latter type of fasting that is extensively designed and studied, and usually practiced in chronic pain cases. There are two principal ways to practice therapeutic fasting, one being a restricted calorie diet (eating up to 800 kcal per day) and the other being intermittent fasting (24-hour fasting followed by a 24-hour non-fasting period); of course, both of them being practiced for a suggested limited amount of time.

Medical fasting has been proven to increase life expectancy of animals [2] and to facilitate a healthy ageing among humans [3].  It has also been established that fasting has an effect in the prevention of cardiovascular diseases [4], degenerative diseases such as Alzheimer’s or Parkinson’s [5], cancer [6], and diabetes [7]. Moreover, its efficacy in the treatment of chronic pain and migraine syndromes has been confirmed [8]. Aside from an improvement of clinical symptoms, fasting is also beneficial in mood alleviation. Subjectively, participants recorded a significant amelioration of their mood and their sleep quality which could be linked to an increase of endorphin release observed in the first days of fasting [9] – and this, independently of other factors (i.e. weight loss). Also, studies on rats have showed an increase in serotonin levels during fasting, thus proposing an explanation to the improvement of migraine symptoms [10] and to the antidepressant like effects of fasting [11]. Finally, a study among chronic pain patients showed a rapid amelioration of depressive and anxiety symptoms, along with a significant weight loss and a normalisation of blood pressure [12].

Even though fasting has showed to have potentially positive effects on mood, it is still unclear whether the improvement is maintained over time [1]. One thing for sure is that medical fasting is mostly a safe practice when the procedure is being carried out under control. Furthermore, it can be interesting to use it as an additional or an alternative treatment for drug resistant psychiatric disorders. It has a low cost and it is easier to practice compared to other alternative treatments like electro-convulsive therapy [1].

This sense of calm and mood improvement resulting from a period of fasting is positively reinforcing the intentional choice of abandoning external rewards and it is ultimately argued that mood alleviation linked to fasting is actually an adaptive mechanism coming from the struggle for survival while searching for food. Therefore, as Fond (2013) says, “The human body may be programmed to cope with famine, but not with over-feeding” [1].

However, there are inconsistencies as to the effects of fasting on cognition. Indeed, you can think that deprivation of food may alter our cognitive functions [13]. For instance, an eating disorder characterised with a restricted diet, anorexia, showed an impaired profile of executive functions [13]. A review gathered 10 articles on the subject and results are contradictory: half of the studies showed no effect of fasting on cognition and the other half showed deficits of cognition (short-term memory, encoding, attention, reaction time and/or vigilance). Hence, there is an incomplete profile of the effects of fasting on cognition, probably due to differences between studies in the tasks used, the type and duration of fasting, the variety of individuals gathered in the studies [13]. As to the impairments of the executive functions in anorexia, this may be linked to a certain cognitive profile predisposing individuals to develop the psychopathology and furthermore, the deficits linked with anorexia are reduced once the patient has recovered [13].

Thus, coming back to the example of anorexia, such patients have a specific premorbid profile: individuals with anorexia have anxious, obsessional and inflexible characteristics, related to the dysregulations of the serotoninergic and dopaminergic systems in the brain [14]. As food restriction provides the individual with an improved positive mood, it is argued that patients with anorexia could easily fall into the vicious circle of reducing food intake in order to lower levels of anxiety, leading to the chronic aspect of the disorder [14].

As we talk about restricting diets, there is also the opposite facet to it: overeating. Overeating is usually linked with bulimia or binge eating disorders. Although anorexia and bulimia sound like two oppositional pathologies, they actually share a lot of mechanisms and moreover transitions occur between the two [15]. They share specific personality traits such as anxiety, harm avoidance, perfectionism and obsessionality [15]. They however differ in self-control behaviours. On the one hand, purely restrictive type anorectic individuals are inclined to be overcontrolled and over concerned about consequences, they are being able to delay any kind of rewards and can maintain self-denial of pleasures in life (i.e. food). Whereas on the other hand, bulimic patients are much more impulsive, involved in novelty seeking behaviours and are less worried about the future. These differences in inhibition also translate in their brain circuits. Indeed, functional MRI studies show that both pathologies display altered activity in the executive/cognitive circuitry situated on the dorsal part of the brain but this altered activity go in different ways for both disorders. Namely, anorectic individuals have an exaggerated dorsal cognitive circuit function leading to an ability of inhibition of the drive to consume. In contrast, bulimic patients have a reduced activity in this circuit, which leads to a difficulty in controlling their impulses [15].

It is important to note that despite the stereotypical views that eating disorders are linked with the will to be socially desired, they actually have an account of genetic heritability. Also, if anorexia was only coming from a diet gone out-of-control or a side-effect of fasting, the rate of anorectic individuals would be much higher in the society [15]: today, anorexia affects only 0.7% of the females in the general population [16].


[1] Fond, G., Macgregor, A., Leboyer, M. and Michalsen, A. Fasting in mood disorders: neurobiology and effectiveness. A review of the literature. Psychiatry Res., 2013, DOI: 10.1016/j.psychres. 2012.12.018

[2] Omodei, D., Fontana, L., 2011. Calorie restriction and prevention of age-associated chronic disease. FEBS Lett 585, 1537-1542.

[3] Martin B, Mattson MP, Maudsley S (2006) Caloric restriction and intermittent fasting: two potential diets for successful brain aging.Ageing Res. Rev. 5, 332–353.

[4] Ahmadi, N., Eshaghian, S., Huizenga, R., Sosnin, K., Ebrahimi, R., Siegel, R., 2011. Effects of intense exercise and moderate caloric restriction on cardiovascular risk factors and inflammation. Am J Med 124, 978-982.

[5] Jadiya, P., Chatterjee, M., Sammi, S.R., Kaur, S., Palit, G., Nazir, A., 2011. Sir-2.1 modulates ‘calorie-restriction-mediated’ prevention of neurodegeneration in Caenorhabditis elegans: implications for Parkinson’s disease. Biochem Biophys Res Commun 413, 306-310.

[6] Buschemeyer, W.C., 3rd, Klink, J.C., Mavropoulos, J.C., Poulton, S.H., Demark-Wahnefried, W., Hursting, S.D., Cohen, P., Hwang, D., Johnson, T.L., Freedland, S.J., 2010. Effect of intermittent fasting with or without caloric restriction on prostate cancer growth and survival in SCID mice. Prostate 70, 1037-1043.

[7] Hammer, S., Snel, M., Lamb, H.J., Jazet, I.M., van der Meer, R.W., Pijl, H., Meinders, E.A., Romijn, J.A., de Roos, A., Smit, J.W., 2008. Prolonged caloric restriction in obese patients with type 2 diabetes mellitus decreases myocardial triglyceride content and improves myocardial function. J Am Coll Cardiol 52, 1006-1012.

[8] Michalsen, A., 2010. Prolonged fasting as a method of mood enhancement in chronic pain syndromes: a review of clinical evidence and mechanisms. Curr Pain Headache Rep 14, 80- 87.

[9] Molina, P.E., Hashiguchi, Y., Meijerink, W.J., Naukam, R.J., Boxer, R., Abumrad, N.N., 1995. Modulation of endogenous opiate production: effect of fasting. Biochem Biophys Res Commun 207, 312-317.

[10] Ishida, A., Nakajima, W., Takada, G., 1997. Short-term fasting alters neonatal rat striatal dopamine levels and serotonin metabolism: an in vivo microdialysis study. Brain Res Dev Brain Res 104, 131-136.

[11] Li B, Zhao J, Lv J, Tang F, Liu L, Sun Z, et al. Additive antidepressant–‐like effects of fasting with imipramine via modulation of 5–‐HT2 receptors in the mice. Prog Neuropsychopharmacol Bol Psychiatry. 2014 Jan 3;48:199–‐206. PubMed PMID: 24036107. Epub 2013/09/17. eng.

[12] Michalsen, A., Weidenhammer, W., Melchart, D., Langhorst, J., Saha, J., Dobos, G., 2002. [Short-term therapeutic fasting in the treatment of chronic pain and fatigue syndromes—wellbeing and side effects with and without mineral supplements]. Forsch Komplementarmed Klass Naturheilkd 9, 221-227.

[13] Erik M. Benau, Natalia C. Orloff, E. Amy Janke, Lucy Serpell, C. Alix Timko, A Systematic Review of the Effects of Experimental Fasting on Cognition, Appetite (2014),

[14] Kaye WH, Wierenga CE, Bailer UF, Simmons AN, Bischoff-Grethe A. Nothing tastes as good as skinny feels: the neurobiology of anorexia nervosa. Trends Neurosci. 2013;36(2):110–120. doi: 10.1016/j.tins.2013.01.003

[15] Kaye WH, Wierenga CE, Bailer UF, et al. Does a shared neurobiology for foods and drugs of abuse contribute to extremes of food ingestion in anorexia and bulimia nervosa?Biol Psychiatry. 2013 Feb 1.

[16] Kaye W: Neurobiology of anorexia and bulimia nervosa. Physiol Behav 2008; 94:121–135


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