"You are what you eat." (from “Der Mensch ist, was er iβt” by German philosopher Ludwig Feuerbach in 'Concerning Spiritualism and Materialism', 1863).
Nutrition is important for many bodily processes essential for good health and development. These processes include healthy gastro-intestinal, immune, and brain functioning. The aim of many diets is to adapt food intake and eating habits for weight management, reduction of cardiovascular and/or metabolic risk, among others.
One of these diets is Intermittent Fasting (IF), a type of diet in which one refrains from eating for periods of time. It is known that IF has positive effects on metabolic health, but what is the effect of this diet on brain health and cognitive performance? Moreover, does IF protect against developing brain related disorders and, if yes, for which ones is it effective? Experimental evidence on this topic was reviewed by Jip Gudden, Alejandro Arias Vasquez and Mirjam Bloemendaal from the Departments of Human Genetics and Psychiatry and published in the journal Nutrients on September 10th 2021.
IF is about fasting. In short, individuals following IF fast for fixed periods of time. The fasting periods range between 12 and 48 hours with periods of unrestricted eating between them. During these fasting periods a metabolic switch occurs where the energy source for bodily cells (muscles but also neurons) are lipids freed from bodily fat (lipolysis) rather than glucose obtained from food (glycogenolysis). These lipids are subsequently transformed into ketones, which have positive effects on brain health. Specifically, the ketones and the lower glucose levels initiate “cleaning processes” in the brain, including the recycling of dysfunctional proteins (called autophagy). Also DNA repair and the expression of Brain Derived Neurotropic Factor (BDNF) is promoted, strengthening the resistance of neurons against oxidative stress.
The current review shows that for clinical studies in humans IF shows benefits for epilepsy, Alzheimer’s disease, and multiple sclerosis on disease symptoms and progress. Animal studies show that IF exerts benefits on traits related to human brain-related diseases such as Parkinson’s disease, ischemic stroke, autism spectrum disorder, and mood and anxiety disorders, which supports the need to carry out studies investigating the role of IF in humans diagnosed or at risk of any of these diseases. For healthy individuals, the review shows that there is no clear evidence of a positive short-term effect of IF on cognitive performance.
Future research should disentangle whether positive effects of IF depend on at what age one starts the fasting regime and whether it depends on metabolic status, such as being obese or overweight. Longitudinal studies and randomized clinical trials (RCTs) will provide a window into the long-term effects of IF on the prevention and progress of brain-related diseases. Moreover, variations in fasting patterns, total caloric intake, and intake of specific nutrients may be relevant determinants of IF success.