A close friend approached Nick and I last week with a dilemma, which is certainly a common one. He is looking to put on weight—ideally in the form of muscle—but also wants to get the metabolic, energy, and mental benefits of fasting or time-restricted eating (TRE). Wondering if this would be possible given data that suggest it is tougher to gain muscle on a TRE schedule, he asked what we knew on this topic or might suggest.
This question is complicated, so first it’s important to clarify each aspect of it. To begin, it’s very much possible to build muscle while fasting intermittently. Current evidence shows that yes, it may be much more difficult than it otherwise would be with frequent, sufficient protein intake throughout the day, but it clearly can be done. In that sense, this is a bit of a false dilemma; fasting and building muscle do not have to be mutually exclusive. However, if one does choose to adopt a fasting regimen while keeping muscle synthesis or weight gain/maintenance as a priority, there are a few important considerations that could go a long way.
The greatest threat to weight gain from TRE or fasting is likely just the accompanying decrease in total caloric intake. One way to ensure maintenance of caloric intake with TRE or fasting is to consume more calorically dense foods or fluids. It can be difficult to consume the same amount of calories in a limited window of time just due to feeling full, but studies show that this satiety and decline in energy may be due to the physical volume consumed just as much if not more than the caloric value. A great example of a healthy, calorically dense addition to one’s diet would be extra virgin olive oil. Additionally, exercise timing in relation to food intake is a significant factor to maximize muscle protein synthesis when fasting. Ideally, one should engage in their strength training shortly after breaking their fast to maximize assimilation of protein into the muscle. Of course, when consuming in this specific window, one would still want to prioritize protein for healthy muscle growth. A great way to do this in a calorically-dense, less-satiating way would be to liberally utilize protein shakes, but as always, minimize sugar in these drinks to prevent blood glucose spikes.
At the end of the day, it comes down to individuals’ priorities, which rarely remain constant. In my own life, I am currently prioritizing muscle protein synthesis in these months following our grueling, catabolic Ironman training. In the months leading up to the triathlon, I lost a good deal of lean body mass from the required exercise regimen, where the focus was understandably aimed heavily towards cardiorespiratory fitness and less towards strength. I also regularly engaged in fasting during that period, as I have personally found it to help me efficiently metabolize and lose fat, as well as aid in more long-term, aerobic efforts like a distance triathlon. At the time, this regimen served its purpose: I was optimizing almost entirely for that specific endurance performance. Now, focusing once again on my overall health and longevity, I am looking to regain what I lost. My exercise routine has equilibrated back to my usual balance of strength and cardio training, and I am basically not time-restricting with my nutrition at all. Rather, I am trying to maximize protein intake and muscle protein synthesis by spreading protein intake as evenly throughout the day as possible and, as a general rule, getting around one gram of protein per pound of body weight per day.
Lastly, astute readers may take issue with a regimen of maximal protein intake and virtually no time restriction, thinking that this surely leads to significant mTOR activation, minimal AMPK activation, and negative downstream effects that we have discussed. The important thing to recall is that these are pulsatile processes, not chronic. This post does not imply that I will never again fast (I likely will when I am in another period of wanting to cut down weight, prioritize fat metabolism, etc.). In my opinion, there will rarely be a long-lasting or “permanent” strategy for any one individual. There is also a difference between chronic and acute mTOR activation, even when in a period of heavy protein consumption and frequent sustenance. If we look at the actual, long-term molecular issues in metabolism, they are derived from issues like insulin resistance, dysfunctional mitochondria, and lack of muscle, not acute protein consumption or muscle synthesis. Therefore, for periods of time where it is one’s priority, I would not take any issue with zero time restriction and a high-protein diet, especially as the metabolic benefits may outweigh any downsides of transient enzymatic impacts.
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