I was recently approached about my opinions on Intermittent Fasting. I decided that I should take some time, look into this diet trend and put together my opinion. Intermittent Fasting has gained lots of traction recently with lots of celebrities and high-profile executives jumping on this band wagon. As with any diet trend, it is hard to argue with people's personal experiences. If someone is telling me that they felt "so much better" or "it changed their ______." Who am I are argue with those experiences?! I wanted to share with you some evidence-based information on intermittent fasting in the hopes that would help you make an informed decision.
Intermittent Fasting can mean a variety of things, but in a nutshell it is restricting the time during the day that you eat or not eating for a set period of time. The goal is normally to achieve weight loss through calorie restriction. Often people talk about feeling better, less headaches, no more pain, etc. There are three main categories to intermittent fasting 1) Alternating day fasting, 2) Whole day fasting, and 3) Time restricted fasting.
1) Alternating day fasting - This involves eat one day, fasting for the next day and then resuming eating again the next day.
2) Whole day fasting - This is normally done one a 5:2 day ratio. You would eat normally for 5 days and then for 2 days you would decrease your caloric intake to ~500 calories/day.
3) Time restricted fasting - This is limiting your eating window during the day to only 8 hours during the day and then fasting the over 16 hours.
Now that we have an idea of the definitions for Intermittent Fasting let's take a look at what this means for your body. The main goal of intermittent fasting is to help optimize your body to metabolize nutrients appropriately and decrease your risk of various diseases. How does that potentially work? Our bodies are very complex and metabolic regulation is tied to our hormones, microbiota and lifestyle factors. This graphic below is from a research article (cited below) and I thought is accurately showed how all of these factors affect our risk for chronic diseases.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4516560/figure/F1/
There are limited studies done in humans with intermittent fasting. Some of the ones that have been done are small and didn't necessarily show significant weight loss changes in those that practiced intermittent fasting compared with more conventional weight loss methods. I think that out of the different types of intermittent fasting I prefer the Time Restricted Fasting. I think that limiting the window during the day that you eat has been proven to make a positive difference in weight loss. Lots of times when we eat late at night we are reaching for unhealthy food items and that is adding to our weight struggles. The idea of restricting calories all the way to only 500 calories in one day could have some negative side effects. You could feel tired, very hungry and that might not be an "enjoyable" feeling for that day. That may not be sustainable long term. When you alternate fasting days that can be tough because your body needs that food for fuel and not having that energy available can be tough. I always ask myself that question when looking into a fad diet trend ... is that practice sustainable? If I make that change, will I be able to continue that practice as the days and weeks go by?
For more information there was a great article published in the Journal of the Academy in Nutrition and Dietetics in 2015 about Intermittent Fasting.
Professional Opinion/Conclusion: If you are wanting to practice intermittent fasting make sure that you work closely with a health professional. Make sure that your doctor feels comfortable with you limiting your calorie intake. If you are wanting to work towards losing weight, get in touch with a Registered Dietitian to help craft a successful meal plan that works for you.