What is Intermittent Fasting?
Intermittent Fasting (also known as time restricted eating), is a new trend that has become very popular recently mostly from the promise of weight loss from celebrities and improved body composition from athletes. However, Intermittent Fasting really is not new at all and actually has been used for thousands of years and for various reasons such as improved memory and psychological effects, autophagy (metabolic cleanup of damaged cells), and the regulation of diabetes.
First off, what is Intermittent Fasting? Well technically it really is not a diet per-se, but rather an extended window of time that you are not eating based on the data that humans need to be in a fasted state to burn fat, hence extending the fast would result in greater fat loss. There are a wide variety of approaches such as the 12-hour approach (fasting for 12h every day), 16-hour approach (fasting for 16h every day), the alternate day fast, the Warrior (a 20h fast where you only eat one large meal at night), the 5:2 (eat normally for 5 days and fast 2 days per week).
Can it improve your health?
The claim that Intermittent Fasting can improve insulin and glucose control, especially in those at high risk for type II diabetes, seems to be most promising in males. Even though there was an improvement in both male and female mice, when taking a deeper dive into humans, the fasting seemed to only positively affect the males’ regulation of glucose and tolerance of insulin to increase their insulin sensitivity.
Looking at the claim that it enhances ones psychological response was also shown to only benefit males. Even though the cognition itself was not affected, the nervous system was. When in a fasted (stressed) state, the men exhibited a Parasympathetic (rest and digest) neurological response in turn improving mental clarity. However, women showed a Sympathetic response (fight or flight) making them feel more foggy, anxious, depressed, and even increasing their heart rate. This is likely due to the fact that women release a protein from their brain called kisspeptin that stimulates their gonadotropin-releasing hormone (GnRH). It is the body’s response to puberty and the endocrine system. This hypothalamic response allows for the menstrual cycle to happen and is more sensitive to a lack of calories when fasting, in turn having a different nervous system response than men.
So what about autophagy? Sorry women, but yet again men seem to only be reaping the rewards. The idea behind autophagy is that it will increase one’s longevity by cleaning up the damaged cells and repairing and lengthening the mitochondria and telomeres. Yet, when looking at the neurons in a fasted state, men’s went through autophagy while women resisted autophagy.
Last up, probably the most trendy reason many are choosing to try Intermittent Fasting, weight loss and improved body composition (leading to increased performance). It is important to first look at the basic components that are arguably universal to weight loss no matter what diet you prescribe to; you need to one be in a caloric deficit and you need to be able adhere to the diet (it is sustainable). Ironically, this approach showed to be no more beneficial in both men and women for both fat loss and performance when comparing other diet trends. In men there was no extra benefit when comparing to diets like a low carbohydrate approach so basically a wash, but women actually showed that being in a large catabolic (fasted) state decreased muscle synthesis, led to a higher percentage of body fat vs. lean mass, and decreased aerobic adaptation.
So, what can we take away?
In conclusion, when looking at men, we can argue that for the health scope part of the equation, Intermittent Fasting can be beneficial to improve longevity, blood sugar control, insulin responses, and even fat loss with muscle gain if this diet fits into one’s lifestyle. However, I see no real reason for women to do extended periods of fasting as women have a lower tipping point of negative effects when catabolic. I would argue that it could be beneficial for both males and females to give their still digestive systems a break with shorter fasting periods overnight, and perhaps focusing on less snacking during the day. But when it comes down to over the 12 hour period of fasting, there is an evolutionary mismatch between males and females and would only suggest it for males that are able to adhere to the protocols and have more health focused vs. aesthetic and performance goals. At the end of the day, the only diet that really works, no matter what the data says, is one that you can be consistent with while still leading a full and happy life.
No matter what type of diet you choose to try, be sure that you are following the 80/20 rule of eating mostly real, whole food options 80% of the time. The other 20% can be reserved for your favorite treats!
If you’re struggling to find delicious whole food meals, check out our 4 Week Real Food, Real Quick Meal Plan!
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- Effect of Alternate-Day Fasting on Weight Loss, Weight Maintenance, and Cardioprotection Among Metabolically Healthy Obese Adults: A Randomized Clinical Trial. JAMA Internal Medicine, May 2017.
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- The Obesity Code, by Jason Fung, MD (Greystone Books, 2016).
- Intermittent fasting interventions for treatment of overweight and obesity in adults: a systematic review and meta-analysis. JBI Database of Systematic Reviews and Implementation Reports, February 2018.
- Metabolic Effects of Intermittent Fasting. Annual Review of Nutrition, August 2017.
- Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes. Cell Metabolism, May 2018.
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- Heilbronn, L. K., Civitarese, A. E., Bogacka, I., Smith, S. R., Hulver, M., & Ravussin, E. (2005, March). Glucose tolerance and skeletal muscle gene expression in response to alternate day fasting. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/15833943?dopt=Abstract