Extremism, extremism, extremism; the wonders of the fitness industry. It never ceases to amaze me how there apparently cannot be a middle-ground when it comes to bodybuilding.
It's either high-intensity interval training (HIIT) or low-intensity, steady-state (LISS) cardio; it's either high-carb dieting or no-carb dieting; it's either over-training or under-training; last but not least, it's either 9 small meals per day or 1 gluttonous feast per day.
For now, I'd like to zone in specifically on the extreme patterns of intermittent fasting, like alternate-day fasts, and why they really aren't ideal for people looking to improve body composition, especially those looking to build muscle.
Intermittent fasting taken a bit too far
While intermittent fasting, at it's core, is certainly an intriguing feeding pattern for human health and longevity, there is a point where one can take this approach a bit too far. People will argue that meal frequency is completely "irrelevant" and believe that essentially starving their body for 24+ hours and then pigging out (e.g. alternate-day fasting) is somehow beneficial.
While acute phases (generally between 8-12 hours) of fasting do have physiological benefits, such as improved insulin sensitivity,blood glucose regulation, growth hormone output, increased adiponectin levels, and others, extreme periods of food abstinence (such as fasting one day and eating ad libitum the next day) may actually induce negative metabolic effects. [1,2,3,4]
Not to mention long-term dietary compliance and applicability don't really seem feasible for most humans on such extreme feeding patterns; who really wants to go through cycles of starving themselves for a day or two and then bingeing the next? The thing that's important to keep in mind here is that alternate-day fasting diets "work" for weight loss mainly because they inherently reduce total calorie intake.
It's not likely that an individual will be able to "make up" the extra day of not eating by pigging out on feeding days, unless they are eating some very calorie-dense foods. But again, this pattern of feeding may in fact have negative ramifications on glucose metabolism, not to mention you are greatly limiting your capacity to build muscle.
Building muscle while intermittent fasting
On that same note, the rational for alternate-day fasting while trying to build muscle seems somewhat inane given that you are essentially cutting off muscle-building pathways for an entire day and trying to make up for it the next day. This fashion of starving your body one day and then overloading it the next doesn't necessarily mean all those calories are being put to good use; in fact, your body will probably just store most of the excess energy in preparation for the next "fasting" day as opposed to using it for muscle building.
When you consider that there does indeed appear to be a "cap" to muscle protein synthesis at each feeding, it doesn't make much sense to essentially limit yourself by eating every other day.  A more pragmatic approach would be either pulsing your protein intake throughout the day and then eating somewhat larger, complete meals to finish off your calorie demand, or being more abbreviated with your fast/feed pattern.
What I would suggest, if you plan to follow a fast-the-feed eating pattern, is to consider keeping the fasting period short enough to get the benefits of fasting, around 8-12 hours, and yet not limit your capacity to build muscle. If your goal is to build muscle, it should seem rather intuitive that extreme periods of food abstinence are probably not conducive to that process.
Just because something "works" doesn't mean it's optimal
A last thought to consider before wrapping up this article is that while many things in the health and fitness industry have some sort of merit, this doesn't entail that such methods are ideal/optimal for your goal(s). This article is not making the claim that you absolutely can't build muscle by following alternate-day fasting, but rather that it's probably not as efficient as a less restrictive feeding pattern.
The body is adaptable and can make do with what you give it, but sometimes we can push it a bit too far for our own good. Also, to reiterate, extreme patterns of feeding behavior often lack long-term compliance for a myriad of reasons. So just keep in these things in mind if you plan to follow intermittent fasting eating patterns while building some appreciable muscle.
1. Varady, K. A., Bhutani, S., Church, E. C., & Klempel, M. C. (2009). Short-term modified alternate-day fasting: a novel dietary strategy for weight loss and cardioprotection in obese adults. The American journal of clinical nutrition,90(5), 1138-1143.
2. Higashida, K., Fujimoto, E., Higuchi, M., & Terada, S. (2013). Effects of alternate-day fasting on high-fat diet-induced insulin resistance in rat skeletal muscle. Life Sciences.
3. Smeets, A. J., & Westerterp-Plantenga, M. S. (2008). Acute effects on metabolism and appetite profile of one meal difference in the lower range of meal frequency. British Journal of Nutrition, 99(6), 1316.
4. Carlson, O., Martin, B., Stote, K. S., Golden, E., Maudsley, S., Najjar, S. S., ... & Mattson, M. P. (2007). Impact of reduced meal frequency without caloric restriction on glucose regulation in healthy, normal-weight middle-aged men and women. Metabolism, 56(12), 1729-1734.
5. Areta JL, Burke LM, Ross ML, Camera DM, West DW, Broad EM, Jeacocke NA, Moore DR, Stellingwerff T, Phillips SM, Hawley JA, Coffey VG. Timing and distribution of protein ingestion during prolonged recovery from resistance exercise alters myofibrillar protein synthesis. J Physiol. 2013 May 1;591(Pt 9):2319-31. doi: 10.1113/jphysiol.2012.244897. Epub 2013 Mar 4.
6. Arnal, M. A., Mosoni, L., Dardevet, D., Ribeyre, M. C., Bayle, G., Prugnaud, J., & Mirand, P. P. (2002). Pulse protein feeding pattern restores stimulation of muscle protein synthesis during the feeding period in old rats. The Journal of nutrition, 132(5), 1002-1008.