Fasting promotes autophagy, a vital recycling process, and stimulates the growth factor BDNF. Autophagy is impaired in neurodegenerative conditions such as Alzheimer’s and Parkinson’s. BDNF is crucial for brain health, and low levels are associated with depression. Hence, fasting improves brain health by multiple mechanisms.
While fasting has been performed in one form or another throughout history, the main objectives for this practice seem to center around religious or weight management objectives. More recently however, interest is growing in regards to how fasting affects cognitive function. Indeed, it has been proposed that the brain and body seem to perform better during fasting periods.
In relation to the brain, fasting increases learning, memory, and alertness. Fasting also improves cognition, delays age-related cognitive decline, can help slow down neurodegeneration, may reduce brain damage and even enhances functional recovery after a stroke. In addition, it can reduce the effects of epilepsy and multiple sclerosis; although this has so far only been scientifically demonstrated using animal models.
So far few studies have investigated the cognitive benefits of fasting in humans in a rigorous scientific setting, although the cognitive benefits of various forms of fasting have been known and praised by traditional medicine across various populations around the world.
In studies done on animal models, fasting stimulates the production of a growth factor in the nerve cells called brain-derived neurotrophic factor (BDNF) (1). This protein plays a key role in learning, memory, and the generation of new nerve cells. BDNF also increases the stress resistance of neurons.
Fasting also triggers autophagy, a recycling process during which cells remove old, dysfunctional molecules (2). This in turn stimulates the body to produce new, fresh and well-functioning cells. It is basically a cell makeover, new and improved!
Autophagy and BDNF synthesis both stimulate proper brain function. They do this by promoting cell repair and by contributing to the creation of new brain cells as well as connections between them. BDNF facilitates communication within the brain. BDNF contributes to this building process, and deficits in this growth factor are associated with cognitive problems during aging such as dementia (3).
Depression is strongly associated with lower BDNF levels (4). While these low levels of BDNF have been used as a prognostic tool for depression, only recently have researchers considered the possibility that low BDNF and depression could be directly related. Indeed, many antidepressants work by increasing BDNF signaling and synthesis in the brain (5).
After a period of prolonged fasting (starving), the brain changes its fuel requirements. Sugar reserves get used up, and the body is forced to rely on fats for energy, so metabolism moves from using sugars to fats for energy. The increased use of fats for energy during fasting periods and the switch back to use sugars once eating again is known as “metabolic switching” (6). This process is called “switching” because the body switches back and forth between sugar and fat and then back to sugar for its energy.
Being able to switch back between sugar and fat metabolism easily is known as metabolic flexibility. Metabolic flexibility is vital for good health. In many conditions, this flexibility is lost. Over many decades without regular eating breaks, the brain and body mainly rely on sugars for energy and “forgot” to effectively use fats.
Metabolic switching sets off a series of processes in the body that can improve the brain’s resilience and productivity and promots its support system (7). This is one of the ways in which fasting may benefit the brain and overall cognitive function.
From an evolutionary perspective, humans are used to going without food for extended periods of time. While fasting has been part of the process of human evolution, its potential applications to modern day’s most common, disabling neurological conditions have not been extensively explored. Research has shown that fasting induces an altered metabolic state that optimizes the creation of neurons, improves the functioning of existing brain cells (referred to as plasticity), and strengthens resilience in a way that may help prevent or at least delay a wide spectrum of neurological disorders (7).
Fasting can also protect the brain against physical trauma (8). Fasting doesn’t physically repel physical damage to the brain by creating a magical ketone-powered force field (cool, but no); but fasting reduces mitochondrial dysfunction, oxidative stress, and cognitive decline that is often caused by brain trauma. In other words, it creates optimal conditions for the brain to get well.
Researchers are just starting to make sense of the complex mechanisms by which the brain relates to what we feed our bodies. Fasting carries numerous benefits which are still being explored, the key is to find a model that is sustainable for your specific lifestyle.
1. Mattson MP. Energy intake, meal frequency, and health: a neurobiological perspective. Annu Rev Nutr. 2005;25:237-60. doi:10.1146/annurev.nutr.25.050304.092526
2. Alirezaei M, Kemball CC, Flynn CT, Wood MR, Whitton JL, Kiosses WB. Short-term fasting induces profound neuronal autophagy. Autophagy. Aug 2010;6(6):702-10. doi:10.4161/auto.6.6.12376
3. Ng TKS, Ho CSH, Tam WWS, Kua EH, Ho RC. Decreased Serum Brain-Derived Neurotrophic Factor (BDNF) Levels in Patients with Alzheimer's Disease (AD): A Systematic Review and Meta-Analysis. Int J Mol Sci. Jan 10 2019;20(2)doi:10.3390/ijms20020257
4. Dwivedi Y. Brain-derived neurotrophic factor: role in depression and suicide. Neuropsychiatr Dis Treat. 2009;5:433-49. doi:10.2147/ndt.s5700
5. Zhou C, Zhong J, Zou B, et al. Meta-analyses of comparative efficacy of antidepressant medications on peripheral BDNF concentration in patients with depression. PLoS One. 2017;12(2):e0172270. doi:10.1371/journal.pone.0172270
6. Anton SD, Moehl K, Donahoo WT, et al. Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting. Obesity (Silver Spring). Feb 2018;26(2):254-268. doi:10.1002/oby.22065
7. Mattson MP, Moehl K, Ghena N, Schmaedick M, Cheng A. Intermittent metabolic switching, neuroplasticity and brain health. Nat Rev Neurosci. Feb 2018;19(2):63-80. doi:10.1038/nrn.2017.156
8. Davis LM, Pauly JR, Readnower RD, Rho JM, Sullivan PG. Fasting is neuroprotective following traumatic brain injury. J Neurosci Res. Jun 2008;86(8):1812-22. doi:10.1002/jnr.21628
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