Submitted by Amy Sercel MS RD CD
Edited by Marcia Bristow MS RDN CSSD CD
Intermittent Fasting has recently become popular as a method to lose weight and reduce the risk of diseases like diabetes, heart disease, and cancer. While there are very few studies examining Intermittent Fasting’s effectiveness in humans,1 many studies in mice and rats suggest that it does lead to health benefits. One explanation for this is Intermittent Fasting’s impact on autophagy.
Autophagy, or “self-eating,”2 describes the process in which your cells break down proteins or other structures and recycle them into new cellular components. This process is an essential defense mechanism for your cells and naturally occurs in all healthy people. Your cells trigger autophagy to prevent tumor growth in some cancers, destroy damaged cellular materials, and eliminate infectious bacteria or viruses.1–4 Studies show that autophagy increases in response to stress, such as the stress that occurs when you're deprived of energy. This makes sense, since low energy intake means that your cells aren’t consistently given the building blocks they need to make new molecules for survival. Instead, they’re forced to recycle old, damaged, or unusable materials to create the components that keep them functioning.2
Both fasting (going 24-48 hours without eating) and calorie restriction (eating 10-40% fewer calories than usual while making sure to meet your vitamin and mineral needs) have been shown to increase autophagy throughout the body.2,3 Researchers are currently working to determine how this may translate into actionable advice, especially when it comes to preventing and treating diseases. Some studies in mice suggest that chemotherapy may become more effective against cancer cells during Intermittent Fasting; however, it’s still unclear which types of chemotherapy work best when combined with Intermittent Fasting.3 Similarly, it’s thought that neurodegenerative diseases like Alzheimer’s and Parkinson’s are partially caused by a disruption of autophagy in the brain. While one study showed that fasting did improve autophagy in the brains of mice with these diseases, it was unclear whether this was enough to show any improvement in symptoms.2
Lastly, since Intermittent Fasting is still relatively new, more research is needed to determine what degree is even safe. Some studies have shown that just one 24-hour fast per month may protect against heart disease and diabetes,1 but many online articles, blogs, and social media posts suggest fasting as frequently as two or three days per week. Fasting too often will push your body into starvation mode, causing slowed metabolism, decreased immune system, difficulty thinking straight, and many other health problems. A study in rats also showed that chronic starvation actually prevents autophagy and damages brain cells,4 which is completely counterproductive if your goal is to boost autophagy.
Until more research is done in humans, it is best to err on the side of caution. Choose a balanced diet that meets your needs for vitamins and minerals without providing excessive calories. Eat when you're hungry, and stop when you are comfortably full, not stuffed. Many studies support the health benefits of a meal pattern rich in unprocessed foods, whole grains, lean protein, fruits, and vegetables; eating this way will keep you as healthy as possible while still allowing you to enjoy your meals every day.
1. Horne BD, Muhlestein JB, Anderson JL. Health effects of intermittent fasting: hormesis or harm? A systematic review. Am J Clin Nutr. 2015;102(2):464-470. doi:10.3945/ajcn.115.109553
2. The effect of fasting or calorie restriction on autophagy induction: A review of the literature - ScienceDirect. https://www-sciencedirect-com.ezproxy.uvm.edu/science/article/pii/S1568163718301478. Accessed March 11, 2019.
3. Antunes F, Erustes AG, Costa AJ, et al. Autophagy and intermittent fasting: the connection for cancer therapy? Clinics. 2018;73. doi:10.6061/clinics/2018/e814s
4. Alirezaei M, Kemball CC, Flynn CT, Wood MR, Whitton JL, Kiosses WB. Short-term fasting induces profound neuronal autophagy. Autophagy. 2010;6(6):702-710. doi:10.4161/auto.6.6.12376