Intermittent fasting (IF) is currently one of the world’s most popular health and wellness trends. It is an eating pattern that involves a cycle of eating and fasting for various periods throughout the day. Intermittent fasting does not put any restrictions on the type of foods you can eat, but rather on the time during which you can eat. Most people who participate in intermittent fasting eat during an 8-hour window and fast for 16 hours. This process is known as the 16/8 method. However, there are many different ways to participate in intermittent fasting. Most people already “fast” every day, while they sleep. Intermittent fasting can be as simple as not eating for 12 hours from 8pm after dinner to 8am the next morning. Other types of IF include extending that fast a little longer.
There are various processes that occur in the body when we both eat and fast. During the fed state, the blood insulin level rises and stores the glucose (sugar) in the liver and muscle as glycogen. When the storage space for glycogen is reached, the liver turns the excess glucose into fat. When fasting, our insulin levels decrease, allowing our body to use up the glycogen and fat stores more efficiently to provide energy. (1)
Many people do IF in order to lose weight, as it is an effective way to limit calories and potentially reduce fat. (2) Others do it for the metabolic health benefits, as some studies point to the reduction of metabolic risk factors such as high blood pressure and abdominal fat. (2) Some research also suggests that it can help protect against diseases, including heart disease, type 2 diabetes, cancer, Alzheimer’s disease, and more. (3) Other people simply like the convenience of IF.
Overall, intermittent fasting may be a good option for you if you find yourself eating constantly throughout the day, eating late at night, or simply have a busy schedule and like the convenience of eating during a particular time window. Yet, intermittent fasting can have detrimental effects on some individuals.
Depending on the length of the fasting period, people may experience headaches, lethargy, crankiness, and constipation. (4) To decrease some of these unwanted side effects, you may want to restrict your fasting to 12 hours. Additionally, intermittent fasting may cause you to overeat. There's a strong biological push to overeat following fasting periods because your appetite hormones and hunger center in your brain go into overdrive when you are deprived of food. (4) Additionally, a 2018 study found that two common effects of calorie-restricted diets—a slowed metabolism and increased appetite—are just as likely when people practice intermittent fasting as when they cut calories every day. (5)
When it comes to an athlete population, intermittent fasting may not be a good idea. Studies show that individuals who participate in intermittent fasting may experience mental and physical tiredness and exhaustion during training, especially during morning workouts. (6) Additionally, one of the biggest challenges athletes face is simply eating enough. Since fasting is associated with a variable calorie restriction, it could be difficult for athletes to cover their calorie intake through a 4 or 8 hours eating window (7) Finally, protein and carbohydrate consumption after training is essential for recovery. It is recommended to consume a meal within 2 hours of training in order to restore glycogen deposits and promote muscle repair and growth. (8) If an athlete were to train during a fasting window, recovery would be severely compromised.
Unfortunately, intermittent fasting can have detrimental effects on athletic women. In this population, intermittent fasting might increase the risk of irregular menstruation, and lower the chance of conception. (9) Additionally, female athletes have a high level of hepcidin, a hormone that regulates iron absorption. The best window of opportunity for peak iron absorption is in the morning when hepcidin is lowest. Unfortunately, those who practice intermittent fasting usually skip breakfast. This caloric restriction could increase the risk for anemia and have detrimental effects on the individual. (10)
At Coreperform we do not endorse long periods of fasting, especially for athletes. If you are interested in fasting, try a shorter period of 10 hours. Research shows that the benefits of fasting can occur within 10-16 hours of restricted eating, while still giving the body ample time to meet energy requirements.(11)
What we do focus on is eating enough, with a focus on plant protein.
Unfortunately, many people are not consuming enough plant protein which has beneficial effects on gut health (check out an article about it here!) and muscle protein synthesis (check out an article about it here!).
Consider using Coreperform protein powder to help meet energy needs and protein requirements. Fueling yourself is one of the most beneficial things you can do for your health!
- Hartman ML, Veldhuis JD, Johnson ML, et al. Augmented growth hormone (GH) secretory burst frequency and amplitude mediate enhanced GH secretion during a two-day fast in normal men. J Clin Endocrinol Metab. 1992;74(4):757-765. doi:10.1210/jcem.74.4.1548337
- Welton S, Minty R, O'Driscoll T, et al. Intermittent fasting and weight loss: Systematic review. Can Fam Physician. 2020;66(2):117-125.
- Halagappa VK, Guo Z, Pearson M, et al. Intermittent fasting and caloric restriction ameliorate age-related behavioral deficits in the triple-transgenic mouse model of Alzheimer's disease. Neurobiol Dis. 2007;26(1):212-220. doi:10.1016/j.nbd.2006.12.019
- Rynders CA, Thomas EA, Zaman A, Pan Z, Catenacci VA, Melanson EL. Effectiveness of Intermittent Fasting and Time-Restricted Feeding Compared to Continuous Energy Restriction for Weight Loss. Nutrients. 2019;11(10):2442. Published 2019 Oct 14. doi:10.3390/nu11102442
- Grajower MM, Horne BD. Clinical Management of Intermittent Fasting in Patients with Diabetes Mellitus. Nutrients. 2019;11(4):873. Published 2019 Apr 18. doi:10.3390/nu11040873
- Moro T, Tinsley G, Bianco A, et al. Effects of eight weeks of time-restricted feeding (16/8) on basal metabolism, maximal strength, body composition, inflammation, and cardiovascular risk factors in resistance-trained males. J Transl Med. 2016;14(1):290. Published 2016 Oct 13. doi:10.1186/s12967-016-1044-0
- Burke LM, van Loon LJC, Hawley JA. Postexercise muscle glycogen resynthesis in humans. J Appl Physiol (1985). 2017;122(5):1055-1067. doi:10.1152/japplphysiol.00860.2016
- Fahrenholtz IL, Sjödin A, Benardot D, et al. Within-day energy deficiency and reproductive function in female endurance athletes. Scand J Med Sci Sports. 2018;28(3):1139-1146. doi:10.1111/sms.13030
- Nania Mohamed Pakkir Maideen; Aََََbdurazak Jumale; Rajkapoor Balasubramaniam. "Adverse Health Effects Associated with Islamic Fasting -A literature Review". Journal of Nutrition,Fasting and Health, 5, 3, 2017, 113-118. doi: 10.22038/jfh.2017.25419.1095
- Collier R. Intermittent fasting: the science of going without. CMAJ. 2013;185(9):E363-E364. doi:10.1503/cmaj.109-4451