As many of you know, I am a very big proponent of the lean gains style of Intermittent Fasting. For those of you that do not know, let me give you a brief rundown of the style, and why from a scientific standpoint, it may be beneficial for fat loss and moderating body composition.
While I've always been one to fast every single day, I've been doing a lot of research on the subject (specifically AMPK) and I've began to consider that while I think that it is is an amazing protocol for fat loss as well as longevity, it may not be (entirely) optimal for maximum hypertrophy of skeletal muscle. Also, let me preface that the next couple arguments I make are more based towards those that are of an advanced training status. If you are obese and untrained, it may be more beneficial for you to follow this protocol every day if it is something you chose to employ. Further, there are other forms of intermittent fasting that you could always consider (cheat mode, alternate day fasting, carb backloading, etc.)
If you're a trained individual, you know how hard it can be to pack on muscle. Further, if you are lean, you also know that it can be increasingly more difficult to shed those last couple of pounds of fat, while maintaining lean mass. If so, this may apply to you.
When you are untrained, the protein synthetic response for skeletal muscle post workout is very long. Possibly with a duration of up to 48 hours!. However, as you become more trained, that synthetic response becomes drastically shortened. Potentially to as little as 8 hours. As with anything in training, your body responds to insult (training stimulus) in order to adapt the stress. That's why you get stronger and build muscle in short. You train --> that is an insult to your body --> your body grows or gets stronger in order to adapt, so that the next time it happens, you'll be better prepared. Well the same thing happens with the protein synthetic response. As you become more trained, your body becomes desensitized to the stimulus and then doesn't respond as strongly (as in the "need" for an increased protein synthetic response is lessened, in the eyes of your body).
For the trained individual, considering the last paragraph, it becomes increasingly more important for you to maximize the time of elevated protein synthesis. Now, if your fasting throughout the morning and training in the late afternoon, this elevated protein synthesis may transcend into the next day. (See where I'm going with this?). If you go right into the next day and begin fasting, you may be wasting precious time that your body is in a protein synthetic state, further decreasing the time that you are actually "building muscle."
So what's a bro to do then? Well, if I'm not mistaken, Sean over at buildingaleanbody.com already considered this. It may be a better idea to train and fast in a cyclic nature. This would be especially beneficial while actually in a dieting phase. By having a cyclic IF/Training cycle, you not only can reduce the training frequency (which is prudent when on a caloric deficit, since you have less calories to fuel growth and recovery), but you can maximize the times of protein synthetic elevation, as well as the times that you would want to have increased AMPK activation, lipolysis and fat oxidaiton (16 hours prior to training).
Here is an example of what I mean:
You get the picture. This cyclic style may allow those who are trained to reap the benefits of Intermittent Fasting, while maximizing the times of decreased protein synthetic response. This will not only allow you to effectively lose some body fat, but you could at least take advantage of the training stimulus in an optimal fashion, and potentially put on some muscle (that is not guaranteed).
Further, this schedule may be manipulated based on when you train. If you train around noon, it may not be necessary to follow this cyclic style. If you are well trained, it may be the case that by the time you wake up the next morning (<16 hours post training), the protein synthetic response could be decreased. Unless you have access to regular biopsies and blood testing, you'll have to decide for yourself. Further, this style is simply a suggestion and a hypothesis. Always remember that most effective diet is one that you'll actually stick to. If you are more concerned with maximizing fat loss in the quickest amount of time, then it may be more optimal for you to IF every day. You'll have to make that decision on your own.