Episode 146 – Is Intermittent Fasting Bad for Muscle Growth?

Key Topics Covered

Clock on plate representing intermittent fasting.

  • We will largely be referring to 16:8 type approaches, although other options can exist.
  • There are two ways of looking at this:
  1. The theoretical approach e.g. if total food and exercise were matched, what would happen?
  2. The practical approach e.g. what typically happens?

Protein Distribution – Part 1

  • The main reason most people would propose that intermittent fasting would be bad for muscle growth is because of protein distribution being limited.
  • A great paper from 2018 titled “How much protein can the body use in a single meal for muscle-building? Implications for daily protein distribution” concluded that if you want to maximize muscle growth, you should aim for 1.6-2.2g/kg of body weight protein per day, split over 4-6 meals that are evenly distributed
  • This is a great paper for many reasons. One is that although it provided that recommendation, it also explored a LOT of areas of protein research. It looked at higher vs lower frequencies and different intakes. It explored things from both an acute MPS standpoint and a longitudinal muscle growth perspective. 
  • It also touched on how larger amounts of protein in one go likely keeps MPS elevated for longer.
  • Reading through all the references, it did stand out how few longitudinal muscle growth studies were included though, which is really interesting, since that’s what we care about.

Protein Distribution – Part 2

  • From another angle – research looking at intermittent fasting approaches involving appropriate total calories and protein typically finds that people retain similar amounts of muscle to those distributing their protein intake.
  • Another recent study titled  “The anabolic response to protein ingestion during recovery from exercise has no upper limit in magnitude and duration in vivo in humans”  involved 100g of protein ingested post-workout vs 25g. It found that the anabolic response to the higher amount of protein was more significant and of greater duration than the 25g amount. 
  • Many people have viewed that as groundbreaking information -when you look deeper into it, this is surprising for a few reasons
  • 1) Previous studies have touched on the idea that larger amounts would likely keep MPS elevated for longer due to digestion time.
  • 2) Total protein intake has always been the priority. Arbitrary limits like 30g in a single sitting could mean certain people would miss their total protein target
  • 3) The intermittent fasting research has long shown muscle retention seems fine – which wouldn’t make sense if the distribution was the be-all and end all.

Protein Distribution – Part 3

  • That 100g protein distribution study has often been overinterpreted.
    • Some people have insinuated that it means that 100g in one go would work as well as 100g split 4 times across the day. 
    • But that wasn’t what was studied. It was 100g vs 25g. Who’s to say 35g wouldn’t have been better than 25g, and results happened to cap out after that amount.
    • It would also not be wise to base every decision and completely change your perspective off that study.
  • Even though based on the research, intermittent fasting has worked well for muscle retention assuming total intake is equated for, I probably wouldn’t risk it with a competitive bodybuilder for example, where risk of muscle loss late in prep is a lot higher.

Logistical Difficulties

  • The biggest logistical difficulty when interpreting the research is that it’s actually rare for intermittent fasting studies to involve muscle growth. 
  • Usually the participants end up in a calorie deficit.
  • Example: “Time-restricted feeding in young men performing resistance training: A randomized controlled trial” from 2016. 8 weeks resistance training. The non-TRF group gained 2.3kg of lean mass. The TRF group gained 0kg lean mass – partly because their reported intake decreased by 650kcal per day.

Other Research

  • A 2020 systematic review found 8 studies looking at intermittent fasting and resistance training. 
  • 7 of the 8 showed no significant muscle gain or loss
  • Only one of them found muscle gain.
    • In that study, they gained 1.2kg lean mass over 8 weeks, which was impressive, and also the same result as the non-time restricted eating group.
    • It’s important to note that this is only one study.
  • We also care more about longitudinal muscle growth than acute MPS information. A lot of studies use acute MPS as a main data point. 
  • This is difficult too since sample sizes skew that due to aspects such as genetics. Adherence of participants also adds in a whole other new variable.

Practical Concerns

Multiple meal examples.

  • From a practical perspective, it can be tougher to consume sufficient total calories and protein if intermittent fasting.
  • Anectodaly and in practice, plenty of people in the real world have been able to gain muscle with this approach.
  • Often they are people who initially got leaner, then maintained for a while, then gained some size intentionally.
  • This is important to note as it’s clearly not impossible to consume enough food with intermittent fasting approaches. 

Other Thoughts and Considerations

Training Performance

  • Training timing can become more relevant. 
  • Some individuals prefer training fasted, and that’s fine. BUT If you are looking to optimise performance for hard sessions, it makes sense to eat beforehand at some stage – particularly if it is a glycogen depleting session.

Protein Timing

  • The anabolic window also matters to an extent. Although it isn’t this very short period of time that we once thought it to be, it is still beneficial to have protein within 3-5 hours.
  • One option here is ‘modified fasting; where you could consume 30g of protein upon waking and then don’t eat anything else until your eating window starts. This will really depend on WHY you are fasting.

Summary

  • Fasting has some logistical challenges and some theoretical reasons why it might not be as effective for muscle growth.
  • But from another perspective, we also don’t have anywhere near enough research to compare for sure about how much, if any, difference there is if all other factors are equal.
  • Personally, if I was obsessed with muscle growth, I wouldn’t do intermittent fasting. But at the other extreme, I also wouldn’t be scared that it is impossible to gain muscle with that approach either. 

Relevant Blogs / Resources

Blog Posts:

Relevant Studies: