When is fasting a good thing and when can it be harmful?


As part of being Jewish, I do a fast for 24 hours once a year on Yom Kippur. Yom Kippur is the holiday, if you can call it that, in which you ask for atonement and forgiveness for all the wrongs that you have done over the course of the year.  From sunset to sunset, we pray and meditate on how we could be kinder, nicer, and a better person to our friends and family.  As part of this meditation period, we fast as a way to show we are focused only on our wrongs and we inflict a bit of suffering on ourselves, so we can feel guilt…….as if we don’t get enough of that on a daily basis.  Well, it turns out that we aren’t just cleansing our souls as we fast on this day, we are providing a tremendous amount of health benefits to our body.  Let me explain in more detail how to fast and the benefits of fasting.
12 - 16 HOUR FAST
This is really simple. Have your last meal by 8pm and don’t eat again until 8am to noon the next day.  Condensing the feeding window helps regulate hormones like leptin and grelin, which control satiety and hunger, respectively. If you are going to give this a try, it’s best done randomly and unplanned.  If you plan it, you typically will overeat the night before you go into your fast, thus defeating the purpose of the fast. Studies show that when we restrict our eating window, we can eat 24% to 45% less calories per day. By forcing yourself to fast during this 12-16 hour window we do 2 things.  One, we allow our hormones to actually work the way they should.  It’s good to be hungry, and that hunger drives change on a hormonal level.  Two, we are training part of our brain that we don’t need food all day long.  The modern western world has been so accustomed to being able to grab something to eat at any point in time, even when we are not hungry, that we have gotten far from the thought that we actuallyhad to go out and hunt or gather when we were hungry. This is an effective way to lose weight.  I recommend 2-4 times per week.
Every once in a while, do a 24 hour fast at a maximum of 1 x every 2-3 months.  The benefits of this include all of the above, plus for those of you who are hard charging and athletes who like to train hard and find it tough to restrict calories, a 24 hour fast has the added benefit of a cleansing effect on the body on a cellular level.  I like to recommend when doing the 24 hour fast that you take the day off of training and just recover.  The effect can be restorative for the muscles, adrenals, and digestive system.
A fair warning to women on all aspects of fasting.  It seems as if men have a better response to fasting based on studies tracking weight loss, immune system function, and metabolic health.  As women, restricting calories too much, more than a single 24 hour fast every 2-3 months or fasting intermittently every day, can lead to a myriad of hormonal dysfunctions.  In order to really be safe as you try either of these fasting techniques, it is important to consume certain foods as a regular part of your nutrition. They will help with fatty acid utilization, which, in turn, will help with things like alertness, brain function, sleep, balanced hormones, and buffered stress on a metabolic and emotion level.  These foods include medium chain triglycerides, like coconut oil, as well as branch chain amino acids which are found in meat, dairy and spirulina. 
Fasting can be an effective tool for weight loss and, when done correctly, it can be even more effective in preventing disease and increasing longevity. 
Let me know what your concerns and questions are when it comes to different forms of fasting.